Restrictor Plate racing

[Randy Naylor]

Due to the higher cost and maintenance problems with the UL-1 motors, pro Boat and the other motors we should allow any motor and restrict the speed of the boat with GPS on board. We should find the fastest boat and that is the max speed. Then it would become a racers race. All boats would have to have a working GPS on board at all times. If the boat went over the speed limit it would be disqualifyed.

Then it would more fair to every one and the old motors that are sitting in the closet could be used! This is for NAMBA ONLY.

[Don Wollard]

That's an option Randy, indeed. But how the heck would you (anyone) get a spec rule changed? Realistically....plus how long such take?

[john p gross]

if you set a speed limit,how could you call that racing? once the boats are all set,everyone would be going in circles at the top speed limit.:bounce:

[raptor347]

Randy,
OK, my spec rigger hits 67mph reliably on a UL-1 motor. Everyone else can now go throw more motor in their boats to try and hit that number. In essence, throw money at it to make up for lack of tuning skills.

If my boat is the bench mark and we can run any motor, what's keeping me from swapping to a hotter motor and setting the new bench mark at 75mph?

Or do we pick a max speed and that becomes the performance wall for the class? It'll be a real challenge to get around a boat that runs right at the speed limit at every point on the course with one that only hits max at the end of the straits. The tech is there to build the ultimate constrictor plate boat right now, in fact I have everything I need in the shop.

I don't know about D-9, but up here we're required to run the rules for a season to get the bugs worked out before they even come up for a vote at the district level.


Don,
Here's the Rule Change process strait from the NAMBA rule book. It takes a bit of time and effort, but anyone can start the rule change process. Ultimately passing is up to the entire membership.

2. Racing Rule Additions, Deletions, or Changes
a. The NAMBA General Membership shall vote by ballot on proposals
regarding Racing, Racing related issues, or Competition topics.
b. Proposed rule changes must be submitted to the District Director in the district
in which the submitting member resides.
c. Upon receipt of said proposal, the District Director will put the matter to a
vote within his district. This vote can occur at any time during the year as
deemed appropriate by the Director but should be handled in a timely manner.
The exact method of said vote can be handled in whatever manner is normally
followed for voting within that particular district.
d. Upon successful passage of the proposal within the district, the district
director will forward the proposal to the NAMBA office along with a
statement by the District Director that the proposal has passed within his
district and that the district desires to have the proposal sent to the general
membership for voting.
e. Proposals may be submitted to the NAMBA office at any time during the year
as long as the previous three steps have been adhered to.
f. After receipt of a proposal by the NAMBA office, it will be sent to the
NAMBA Board of Directors. The Board will review the proposal to insure
proper wording and consistency with other already existing rules.
g. After the Board of Directors has reviewed the proposal the NAMBA office
will send out the proposal to the membership for voting. The proposal will
normally be sent out with the next regular mailing of the newsletter, but
special mailings may be utilized if deemed necessary. In addition, the
proposals and ballots may be made available to the membership by
publication on the NAMBA web page.
h. Members will be given adequate time to receive the ballot, consider the
propositions, and cast their votes. Normally a period of 45 days from the date
mailed would be considered ample time for this to take place.
i. Only members in good standing at the time of the vote will be permitted to
vote. All classifications of members will permitted to vote, including adult
members, family members, and junior members.
j. Members will be permitted to return their votes to the NAMBA office by
mail, fax, or email as long as it is able to be adequately determined that the
vote is coming from a member in good standing and as long as the vote is
received by the voting deadline.
k. The NAMBA office will receive and compile the votes. The NAMBA office
may designate another entity to receive and compile the votes should this be
deemed necessary.

[photohoward1]

No one asked. Randy, what high cost? Maintenance? It's made to eventually be thrown away. As said in a previous thread...Don't over amp it and it will last a long time. Want a reliable motor? Buy a Neu 1515 and limit it to 50 amps. It will run forever. BTW. Not a good idea. If a Ul1 motor is high cost then you might have to rethink the hobby. Sorry about the tough love Randy..

[lohring]

See this post (http://www.rumrunnerracing.com/feforums/showthread.php?t=32125) for a similar idea. People here would rather use a component as the fuse than use a real fuse like electric airplane racers.

Lohring Miller

[PropNut]

If you are destroying UL-1 and ProBoat motors, you are over amping them. With these motors, we are currently running resiticor plate racing. There is nothing wrong with current rules.

[JfromJAGs]

Not arguing about right or wrong, but as the rules are, you are not running "restrictor plate racing".

It is "limited racing", as the motors are limited to a certain selection. But that's it. The motors are not restricted as a typical restrictor plate would do it - restricting the air flow, thus possible fuel flow and in the end power output.

I think what Randy was asking for is a solution that limits the power of these motors per rules to an amount that's safe for them - without the risk or even possibility to over amp and destroy them.

Technologically similar to a restrictor plate would be a current limiter, a device that would measure the current and then automatically throttles down if you are over the limit. Some (expensive) car ESCs got this feature. It's used as a torque limiter, to prevent wheel spin, but basically its a power restrictor.

When certain KVs are given, then another rather simple way is to limit props to certain types. Thats how we do in Germany for these type of classes. With the prop types (and sizes) we can control the current to reasonable values for the motors. Per rules, not per your ability to slow yourself down to currents that is safe for the motor.

Joerg

[Darin Jordan]

When certain KVs are given, then another rather simple way is to limit props to certain types. Thats how we do in Germany for these type of classes. With the prop types (and sizes) we can control the current to reasonable values for the motors. Per rules, not per your ability to slow yourself down to currents that is safe for the motor.

Joerg

How do you tech these props??

[JfromJAGs]

Well, in our case that was very simple: we only allowed Graupner carbon props of the K series up to 42mm size for mono and up to 43.5mm for hydro.

For your limited classes a selection of Aquacraft (Grimracer) or Proboat props could do the trick. Just sharpened and balanced, but not modified. Or maybe even better, a limited selection of Octura props - or whatever you think is a good selection for the classes.

You could tech the props with a mold/ a print of the pressure side, made out of epoxy plasticine to check shape and pitch.

Joerg

[lohring]

Our club did that with the "stock" UL-1 class. At first only the plastic prop that came with the boat was allowed. Then that was upgraded to sharpened and balanced Grim racer props that were drawn from a hat at the start of the race day. Currently, one scale club is trying to run electric boats with nitro boats by limiting prop diameter on the electrics. All are workable solutions.

I still believe that current limiters are a good solution if their characteristics are suitable and the costs are reasonable. FAI limiters from Neu cost $50, but they may not be exactly what we need. The advantage of limiters is that they encourage better hull and prop designs along with good setups while allowing a wide equipment selection.

Lohring Miller

[JfromJAGs]

I prefer an indirect power limitation for the restricted/limited classes. We do this by limiting the rpm and the props. From an experienced rule maker point of view we can choose the equipment to operate at its best efficiency, thus with minimal stress. That makes a very good school for the drivers too, you learn to understand boats and setups instead of pushing equipment. You learn how to drive in a very equal competition, nobody feels he can't win because of the equipment - or money.

Joerg

[lohring]

I agree with the "stock" class concept. It does make for very equal racing and even experienced drivers have fun racing each other. I believe limited classes are the next step up. There there is more freedom in design and setup, but costs are kept reasonable by limiting equipment.

The advantage of specifying particular motors and maybe speed controls is that that choices are restricted, simplifying the path for new racers. The disadvantage is relatively expensive components are the fuse and the rules need to be continuously updated as manufacturers change equipment. A current limiter coupled with the number of cells is one simple way to manage power in a restricted class.

Lohring Miller

[Darin Jordan]

The disadvantage is relatively expensive components are the fuse ... A current limiter coupled with the number of cells is one simple way to manage power in a restricted class.

Lohring Miller

I don't disagree that this would work, but the math doesn't...

People would have to spend an additional $50.00+ PER BOAT because a motor MIGHT burn up IF they weren't getting the help they needed or pushed the setup too far...

It sounds more expensive to me.

The P-Ltd formula is working now. Participation has increased, racing is close, racers are enjoying themselves, racers have options and choices, and racers aren't spending an unreasonable amount of money to do it.

People burned stuff up with LSH and drill motors... people burned stuff up with brushed motors.... people burned/burn stuff up with expensive brushless motors... people burn stuff up with cheap brushless motors... People burn stuff up in Spec SV-27 (as "Stock" class as it gets)...

There are "fuses" in Gas and Nitro as well, but they aren't putting artificial restrictions on those classes... And there, it would be much easier (exhaust restrictions, etc.)

What problem are we really trying to solve here?

[Darin Jordan]

... and the rules need to be continuously updated as manufacturers change equipment.

The rules were written in a way to adapt to this situation, however.

28.D.1.d.

iii) In addition, the CD has the discretion to allow the following:

(a) An aftermarket motor that is a re-labeled and exact copy of any
approved motor.
(b) Any generational change of an approved motor, or a motor that
is used in a Ready To Run (RTR) offering from a manufacturer
that produces over 100 units of said offering, as long as there is
no more than a 5% increase in any of the following
manufacturers specifications as compared to any single
approved motor: Kv, maximum constant amperage rating,
mass, and MSRP.
(c) The race flyer shall list additional allowed motors for the event

[JfromJAGs]

I agree with the "stock" class concept. ... I believe limited classes are the next step up. There there is more freedom in design and setup, but costs are kept reasonable by limiting equipment.

Lohring Miller

"Stock" classes are the most restricted classes, yes. But they are not only very restricted, they are also usually "designed" by the rules makers to not stress the equipment. The last is the most important factor for the success of such classes.

"Limited" classes are not as much restricted, yes, but why is it not possible to follow the basic idea to design the rules in a way that the equipment is not stressed to or even beyond its limits? Actually it's a bit absurd to me to limit something and don't think the story to the end. In a way that this - whatever you limit by the rules - shall not acts as an expensive fuse. I mean, why have such fuses when it's possible to design rules for limited classes without such?

Joerg

[JfromJAGs]

There are "fuses" in Gas and Nitro as well, but they aren't putting artificial restrictions on those classes... And there, it would be much easier (exhaust restrictions, etc.)

What problem are we really trying to solve here?

Beginning with the last question: Why does this thread exists? Why do similar threads exist? Maybe because not everyone is as happy as you with the rules?

Concerning the fuses and restrictions for Gas and Nitro. There are well thought and artificial restrictions in gas and nitro classes, like max. octane number or "no nitro" in gas fuel and so on. You could put nitro into gas fuel and increase the power output - but that would decrease the lifetime of the motors drastically.

Electric motors are similar to super charged combustion engines. You can crank up the power until they break within seconds - just put more load on an electric motor and it will consume the amps - and overheat. Gas and nitro motors for model boats are not super charged. So the problem does not exist for them as much as it does exist for FE. So it is difficult to compare the necessary restrictions to achieve similar results. But when you step back and take a unbiased view it is possible - in a different way, but possible.

Joerg

[Darin Jordan]

Concerning the fuses and restrictions for Gas and Nitro. There are well thought and artificial restrictions in gas and nitro classes, like max. octane number or "no nitro" in gas fuel and so on. You could put nitro into gas fuel and increase the power output - but that would decrease the lifetime of the motors drastically.

Regardless... none of that is keeping guys from doing things light lightening parts to an absolute minimum, cranking compression, etc... Unless you expressly limit this stuff item by item, someone, somewhere, is going to do whatever it takes to gain an advantage.

In fact, my experience with all forms of racing is that, the more restricted the class, the more this is the case. The more it HAS to be the case in order to gain an advantage, which is, after all, the point... Unless all we are measuring is ones driving ability.

I'm not trying to argue about all these options... they are all viable, legit, etc...

But, I'll ask again... WHAT is the problem this thread is trying to solve??

[Darin Jordan]

Maybe because not everyone is as happy as you with the rules?

Further... When has ANY set of rules made "everyone" happy?? :shrug:

[JfromJAGs]

Further... When has ANY set of rules made "everyone" happy?? :shrug:
Although desirable, it's probably impossible to make everyone happy - I agree (in your words: I don't disagree) - but rules should be at least acceptable for everyone who wants to race. And if I understand the complaints correctly, then this might not be the case.

So it's appropriate to think about possible improvements - some solutions have been sketched. Just because there might not be the perfect solution, thinking should not be abandoned in general. At least this is what I was taught...

[Darin Jordan]

Just because there might not be the perfect solution, thinking should not be abandoned in general. At least this is what I was taught...

I think we were all generally taught that...

In addition, however, I believe it's important to start from a definable issue, before you start trying to solve a "problem"...

From the original post:
"Due to the higher cost and maintenance problems with the UL-1 motors, pro Boat and the other motors"

I think the reason that many of us are questioning all of this is because the premise, in our experience, and from what one can generally discern from surveying the vast majority of races and racers out there, is a false one.

Perhaps we should break this down:

"Due to the higher cost..."
1) The motors on the list are NO "higher cost"... they are actually pretty reasonable. A UL-1 Motor is $79.99 (no water jacket). A Pro Boat motor is now $98.99, but includes the water jacket. Not out of line with any number of other BL motor offerings out there.

"Due to the higher .... maintenance..."
2) These are NO maintenance motors, and, in fact, must remain sealed "as provided by the manufacturer. They either work, or they don't.

I believe there may be provision in one of the gray areas of the rules to replace the bearings, but this doesn't seem to be an issue with these motors.

There have been batches of both AQ and PB motors that have had strings of failures, but, at least on the PB side, which I can speak to directly since I was the one that identified and got the problem fixed, these were incidental manufacturing issues that could have happened with ANY Chinese derived motor source. For the vast majority out there (likely the more silent majority... why would you post if you AREN'T having problems... ;) ), the motors and equipment are NOT working as fuses... they are just working!

My point with this is that there is not a lot of evidence out there that people are "burning up motors" on a regular basis. Surely, some have, but in the vast majority of those cases, it was people finding the limits. They found it, and backed off, and are having success with solid, reliable, equipment, just like with any other motor package.


The suggested solution was to allow ANY motor, and somehow artificially restrict the speeds, whether by an "on-board GPS", or otherwise. Both of which seem to be solving a problem OTHER than the supposed problem that was stated.

I'm sorry, but that doesn't sound like an issue with the rules. It sounds like a desire to "run what you brung", and still have a competitive shot. You bring your M8, I'll bring my M3, but you need to put a block under your gas pedal. Doesn't sound like much fun to me, but I know that's not the point.

The playing field with the rules exactly as they are, is incredibly EVEN. Everyone has the same shot, the same limits, and a balanced opportunity to be competitive. There isn't anyone that has a competitive advantage, or disadvantage, due to equipment, or the rules under which the equipment must be used.

I don't think anyone here has an issue with a club doing WHATEVER they want in their local district or club level... I think that's been stated clearly by several here, and, frankly, is how NAMBA generally works anyhow. Doing this, one can adjust their club to the competitive nature of the participants.

I do, however, reject the notion that our rules are somehow skewed, or unfair, or poorly written, or provide some a competitive advantage over others. There is no evidence of that, on the water, or in theory. Having a solid, stable, set of National rules, that are simple to understand and clearly written, provides EVERYONE the same opportunity to compete at a National event. How they take advantage of that is up to them. Not everyone, regardless of how the rules are written, is going to be able to compete at the same level. That's what makes it racing, and not just an exercise in lapping.

[Doby]

But, I'll ask again... WHAT is the problem this thread is trying to solve??

None;).........

[Darin Jordan]

I forgot to mention one more factor in all of this...

The original idea for the P-Ltd power specification was to make a place for any number of the RTR offerings to be purchased off the shelf, and with little or no modifications, have a place to come and be competitive. The idea to open it up to any hull actually came a bit later, in an effort to be more inclusive. That is, in part, why the motor selection was limited to the list that currently exists.

[Coug90]

This thread caught my eye. I'm with Darin on this one. I must admit I was also wondering what the real problem to be solved was here. I'm glad someone has tried to break it down a little. I think that the changes that were being proposed would simply gut the enthusiasm from any class you impose them on. If the classes are popular, something must be working right. I guess it comes down to why you like this hobby and decided to join in. You join because you like enough of what's going on. Life's too short to continue doing something you don't like. I like to tinker with stuff, learn and see what I can create within the rules that I've been given. I like to challenge my skills, learn new ones and test them against others with the same desire. It's why I compete and hang out with others who like to compete and have fun. Nothing's perfect, but I figure it's "fair" if we all have the same set of rules to work within. There will always be different skill levels and there will always be cost of equipment that fails or ages. Things wear out. Instead of castrating competition because it doesn't seem "fair", maybe it's time to donate that old gear to someone who would be happy to have it. Recycle it. Clean out the closet. Take an old boat, put that old gear in it and give it to a kid or someone to run for fun. Maybe that's where the future of our hobby will come from. Better yet, maybe that's where a new hobby will come from.

[JfromJAGs]

Darin, you can dissect every single word or you can just leave it - it won't change anything. The title of the thread - the idea behind the arguments - is "restrictor plate racing".

Someone said what you got IS exactly this - all I'm saying is, no, it's not. I'm not arguing about right or wrong concerning what you got - if you ALL like it - well, why should I care?

Obviously there are at least some thoughts to improve the concept. I'm just picking up the idea of a restrictor plate, I'm trying to explain why your current rules don't have such a restrictor (even though you might think you got it) and finally how it could be done for FE - with an example of how we did it.

Now, you can decide what to do: ignore the problem and postulate there is none - or think about a solution.

Happy Eastern,
Joerg

[Darin Jordan]

Now, you can decide what to do: ignore the problem and postulate there is none - or think about a solution.

Happy Eastern,
Joerg

OK, so you've broken it down to only two choices... either we are ignoring "the problem" and simply talking it away, or we must come up with a solution to it... even though many/most don't believe there actually is one??

Seems like you've simply accepted that there IS a problem, regardless of any rational, or evidence, being mentioned, that suggests otherwise.

I'd suggest that there is a THIRD possibility: that the majority HAVE recognized the risks associated with the rules as NAMBA has them, and are simply willing to take responsibility for accepting those risks?

We're putting electronics into boats, potentially exposing them to water... that's a risk right out of the box, and we all accept it.

I guess my point, or question, as it were, would be this:

Is the participation, competitive balance, affordability/expense, FUN/Excitement, FAIRNESS (for you Democrats out there... ;) ), etc. of the P-Limited NAMBA Power Specification Classes going to be improved in any way by requiring an additional piece of equipment, such as Lohring's suggestion for the F5B style airplane current limiter, or imposing artificial (and tough to manage) "speed limits"??

We spend an additional $50.00+ or whatever it would cost (boat parts are usually more expensive than plane/car/heli stuff), to save us from POTENTIALLY burning up an $80.00 motor?? Doesn't change the competitive balance. Doesn't make anything more "fair". Perhaps lowers the FUN/Excitement factor, though racing is racing, regardless of the speed. Increases the complexity. Puts even GREATER emphasis on tuning, a lack of which seems to be what is causing some to be having issues with reliability in their current motor selection.

I would suggest that this path increases the gap, although, "competitive balance" didn't seem to be the goal of this thread, based on the original statements, that I've already broken down.

OR, we could do as Randy suggested... we put on on-board GPS in the boat, race for 1-mile, and then find out when we get the boat back to shore if we've "broken out" of our speed bracket?? Somehow, in the process, working through then known glitches in GPS speed readings for "max speed"?? And, if, as suggested, the "fastest boat" sets the maximum speed for the event, and that becomes the breakout speed. With the Any Motor concept, that fastest speed could get pretty interesting.

We could limit the props that can be used, but then you narrow down the available hull/power system combination choices, and you still favor those who know how to tune, prop tweak, and setup their equipment.

If I'm reading you correctly, Joerg, you are suggesting that we would need to somehow put a limiter, or limits, in the rules, that would assure that we could never, ever, run these power systems up to enough amps/watts to risk damage to them. I think that's what you are suggesting is considered "Restrictor Plate Racing"??

I agree.

Lohrings suggestion for a current limiter... suggestions for "single hull" style classes, etc... all would be very restricted and might attain some level of equipment protection.

I think if a group wants to go try these concepts, they should do it. Nothing stopping them from doing it.

Doesn't mean there is anything inherently wrong with the rules we have in place now, however... or that any of us are somehow "ignoring the problem"... I guess we just don't all agree there is one.

Happy Easter to all of you over the pond as well. I hope your weekend involves good times with family and friends!

[JfromJAGs]

If I'm reading you correctly, Joerg, you are suggesting that we would need to somehow put a limiter, or limits, in the rules, that would assure that we could never, ever, run these power systems up to enough amps/watts to risk damage to them. I think that's what you are suggesting is considered "Restrictor Plate Racing"??

I agree.

Yep, thats the core of my suggestion: find a way to protect the equipment by rules, not by the individual capability to back off before it breaks.

And instead of giving direct limits, like suggested by Randy (GPS speed) or Lohring (current limiter), my suggestion is to use an indirect method by limiting RPM and props.

The combination of RPM and prop limits the amount of power a drive system can transfer to the water, thus with a given cell count it also limits the current. This is not a hard limit as an electrical current limiter, but still good enough if you aim for a safe current for the motor, preferable the operating point of the motors, the current of best efficiency.

I think this takes almost nothing away from the fun, the excitement and the key knowledge of racing boats in limited classes - and its available at no cost and no additional equipment.

But again, its a suggestion. You are free to consider it.

Joerg

[Darin Jordan]

my suggestion is to use an indirect method by limiting RPM and props.

But again, its a suggestion. You are free to consider it.

Joerg

In considering this... we already have a limited RPM... The motors are 1500KV, 1800KV, and 2030KV... They are all the same basic dimensions, weight, and overall Wattage. They have similar wire sizes and the same number of poles (6). The stator stacks are the same length, and the rotor lengths are the same, even though the AQ Gold motors have a tad longer can length and are listed as 36-56-#### motors, compared to the PB motors being 36-50-####. The rotors all measure ~30mm. The AQ Gold cans are 56mm and the PB cans are 50mm, but again, the stator lengths and rotor lengths are the same. Rotor diameter on the PB motors is a tad larger than the rotor diameter on the AQ Gold motors.

Basically, these motors are all in the same general design family.

So I can understand your premise better for consideration... Are you suggesting that, as Randy suggested, we allow ANY motor at a given KV, and then limit the prop size??

Considering limiting the props... Can you detail exactly what this means? Are you spec'ing a SPECIFIC prop, or just limiting blades, diameter, etc.??

[JfromJAGs]

My suggestion is to stick to the motors you got (maybe even narrow the selection down a bit) and then ADD prop restrictions to that.

With different KVs you will need different props: a certain prop for a certain KV number. A lower KV will need a bigger prop and/or more pitch to get to the same speed. So the less motors you allow and the more they are similar in design and KV, the easier it gets to achieve a leveled field.

ANY motor of a certain KV would be possible as well, but it would favor the bigger, the more effective and the more expensive types - which is not necessary as long as you use the cheaper motors within their limits and as long as you are happy with the speeds you get out of this.

Basically you probably got a pretty good understanding of what props to use with each given motor, right? So considering that these props stress the motors right to their limits, I would go down 1 or 2 sizes to bring the currents down to a more reasonable range. It will probably need some tests in real boats with data loggers installed to narrow this down, but with the experience you already got, it shouldn't be a big deal.

For the motor types you mentioned I think 50-60A should be the limit. Optimal would probably be less than that. 100A, as Lohring mentioned in another thread, is for sure too much for them. If you need the power of 100A then you should use bigger motors.

My suggestion would be to allow only one, maybe 2 certain props for each motor or KV number. As I said, the more KVs you allow, the more complex it gets. Maybe you can narrow this down to 1500&1800 KV for mono and 1800&2030 KV for hydro?

I would suggest to allow only sharpening and balancing, no bending. The problem with bending (or allowing any prop of a given size) is that you can increase the pitch. This will give more speed, but also uses more power and thus needs more current.

The process is very similar to the restrictor plates in NASCAR racing. To level the playing field on a healthy power level, each motor manufacturer gets his own restrictor plate. Here every motor KV gets his own prop - keeping in mind similar speeds and reasonable currents.

Joerg

[jantagg]

I think you are all going about this in the wrong direction. It has been my observation over years of racing the the slower boats finish the race and thus are the ones taking home the trophies and I don't think that is fair. My suggestion would be to make all boats competing obtain and run at a speed EQUAL to the fastest boat.

Just my thoughts.

[JfromJAGs]

Tom, I have read your post several times now and as English is not my mother language, I still don't get it if your post is meant ironically or not. Sorry, thats my fault.

Concerning your message, the debate about "Restrictor Plate Racing" is about racing with (reasonably priced) equipment, but WITHOUT using this equipment as a fuse. The idea is to find rules to race with this equipment within healthy limits, to prevent that racers over amp their equipment. If you - the NAMBA races - want this for "Limited Racing" is another question. I'm just presenting a way how it could be done.

With the above sketched solution "Stator Friendly Racing" would be possible by the rules. One of the side effects would indeed be a more leveled field. So unless you don't throttle back or have a serious bug in your setup, all boats should be capable of running at similar speed as the fastest boat.

But still, the boats won't be as slow as that you can't screw up the setup and end up upside down - thats not the intention of the suggestion. So the old racing rule still applies: to finsh first, you need to finish first.

Joerg

[lohring]

Facts are always useful in these debates. Below is a snip of the data my ICE 100 logger recorded during a tune up race with Jerry Dunlap. I would consider this to be representative of what the fast P Limited outboards are doing in my area. Jerry was running a Top Speed 3 with a Turnigy 120 speed control and a Grim Racer 42 x 55 prop. I ran a Leecraft XTR-21 based wood prototype with a water cooled Castle ICE 100 ESC and the same prop. We ran both Turnigy Nanotech 5000 mah and Gens Ace 5300 mah packs. The speeds of both boats were similar.

Both the motor and ESC are operating above their rated currents. Even so, I expect the ESC to last indefinitely when water cooled. The motor should also last a long time because water cooling and short run times will prevent insulation breakdown. However, there is no way to find these limits without testing under actual race conditions. I bet the motor will fail before the ESC, therefore, it's a one time "fuse". A true limiter can be used over and over preserving both itself and the equipment.

Lohring Miller

[jantagg]

Joerg,

I don't know about your English speaking skills but, your English writing skills would put a lot of us Yanks to shame.

Now for my post. It was written with a bit of tongue-in-cheek but, with some logic in that I have witness many not so fast boats win the prize.

I don't think restricters would work because there are too many variables involved with racing even if you discount the ability of the drivers. In the Unlimited class of full-size race boats they use resticters on the turbine engines to reduce damage to the motors. That has helped save engines but has done nothing to change the outcome of the fastest boats. The Oh Boy! Oberto and Spirit of Qatar still dominate qualification speeds even though all boats use the same engines and quite the same design boats. The propellers all come from the same vendor.

B-T-W when are you going to up your speed record.

Bragging rights from your accomplishment is something that gives us great pleasure to hold over the heads of our friendly gas guys.

Tom

[JfromJAGs]

Tom, then I think I understood your post correctly - I was just not sure. Your observation has definitely some truth, especially the faster the classes are: you need to find a balance between speed and arrival. But isn't that, what racing is about?

You are also correct that any form of restriction will not change the outcome of a race completely. But nobody was asking for this. The better driver and the more fine tuned setup can - and shall - win. Again, this is racing.

Randys initial post and also some other posts made by Lohring (and others) were aiming at something else. They were asking for rules to protect the equipment. Very similar to what is done in almost all "real" racing classes: Unlimited hydros, NASCAR, F1 - all installed restrictions to keep the costs on a "reasonable" level and to prevent "single-use&dispose" for the key parts.

Concerning the record - well, its still standing. But I think it will be broken this year, there are some contenders and there is plenty of technology available to do it. Chris was very close last year, I will give it a shot with an old boat in August and there are others as well. I have been the figurehead for some years now and I have taken my share of shit for it - so I wouldn't mind if someone else would step up.

Lohring, do I read this correctly: 100A on the straight, 120A around the corners? This is a UL-1 motor? Do you have the IR and idle current of this motor? This motor at 212g is rated at 50A cont., so you are running it at twice the load is was designed for?

Before we argue about what type of restrictor should be used, do you want to keep that motor size or do you want to keep that power and speed level?

Joerg

[lohring]

My only record of the UL-1 motor characteristics is on my spreadsheet of motor performance. I have measured the resistance of a UL-1 motor, but I'm not sure where those figures came from. In any case the IR was 15 mOhm and the idle current was 3.71 amps. You read the graph correctly. I was pulling over 120 amps in the corners.

Everyone is sure the motors will instantly melt if the rated currents are exceeded. As I keep pointing out, electric motors can be seriously overloaded. Heat is the enemy, and we cool our motors very well. In addition, I suspect Tower Hobbies doesn't want to hear stories about the poor quality of their motors so they rate them conservatively for air cooled operation. Commercial electric motors have THERMAL overload protection. Our full size electric boat motor probably was rated at about 15 hp as a hydraulic pump motor. We developed close to 110 hp for the record runs.

I think classes could be set by both voltage (number of cells) and current limitations. Something in the 100 to 150 amp range allows relatively low cost equipment with a wide selection these days. Power and performance will depend on voltage if the current is limited. It's really what we do now, but the current is limited by the equipment. I think a direct approach is feasible at a fairly low cost.

Lohring Miller

[JfromJAGs]

Everyone is sure the motors will instantly melt if the rated currents are exceeded. As I keep pointing out, electric motors can be seriously overloaded. Heat is the enemy, and we cool our motors very well.

To explain this, attached are 2 pictures. Both are based on basic motor calculations, showing the output power (P_Out), power loss as heat (P_Loss) and the efficiency (Eta) of each motor. Picture 1 is the UL1 motor (IR 15mOhm, 3.71A idle, 212g). Picture 2 is a LBP 4074/2Y motor (IR 6.2mOhm, estimated 2.7A idle at 4s and 375g).

The UL1 motor works best in a range of 50-75A, max. efficiency is at about 88% at 60A. In the 50-75A range the power loss is 100-120W - an amount that can be cooled without a big problem. At 100A the losses reach 200W and at 125A its even 300W - an amount you might just barely be able to cool. At 150A and 400W its gone, especially as in reality the losses are even a bit higher, because the IR increases with temperature. This makes it completely clear, that you are running this motor on the very sharp edge of thermal death.

If you want to run at these power and speed levels, then I would suggest a bigger (and heavier) motor, a motor appropriate for these power levels. A similar priced motor could be a LBP4074/2Y, shown in the second picture. With the much lower IR and the relatively low idle current the peak efficiency is 93% and the usable range is much wider. You can run it from 50A to at least 150A. For comparison, the power loss at 100A is 100W and thus only half of the lighter UL1 motor, even at 150A its below 200W. Considering the higher mass of this motor this would be healthy usage of the equipment.

So there are 3 possible solutions:

1. if you want to keep the speed, my suggestion would be a bigger motor with similar KV and the same 4255 prop.
2. If you want to keep the RTR motors you should go down to a 1800 KV motor and also keep the prop - boats will be slower.
3. If you want to keep the UL1 motor, go down in prop size - this will make the boats slower and this brings the currents down. But I'm not sure if that is a good idea for the boats you are running.

If you keep the UL1 motor and the 4255 prop and just install a 60-80A current limiter, then thinks will be worse, as the limiter must throttle the ESC down. So you will be running at partial throttle, which will overheat the ESC and most likely also the motor.

Joerg

[JfromJAGs]

BTW, a LBP4074/2.5Y with 2000 KV should be the better replacement - I just don't find reliable technical information about it to make a similar graph.

Joerg

[lohring]

Thanks for the data, but that's my point. Restricting currents would allow intelligent equipment selection. Restricting equipment means the equipment will be pushed to the limit. Tower carefully picked a low cost motor and speed control to operate at rated currents of 50 amps with 80 amp bursts. It will run for years at those levels. We are seriously abusing the motor and its life will be limited. If the ESC was limited to the Tower one, it would be abused as well.

The 1/10 scale clubs do run a selection of 1800 KV motors like you suggest. They also limit prop selection by racing counter clockwise. This means right hand props, and only a few are available in close to the right size. The combination inadvertently makes a good spec class until people like Brian Buaas start thinking outside the box. It was argued that "stock" meant the motor's connectors couldn't be changed. Softening solder on the connectors was actually a reasonable fuse, but aftermarket connectors were allowed.

I'm playing with Scorpion motors in moderate cost replacement systems for 7.5 and 11 cc nitro motors. I still try to keep currents around 100 to 150 amps with power determined by the cell count; 6S for the 7.5 cc replacement and 8S for the 11 cc replacement. I bet the same current limiter could be used over a range of voltages to accomplish this.

A scale club is testing the above 11 cc nitro replacement electric system against nitro boats. They are also restricting the maximum propeller diameter. It seems like a good start, but the electric boats still win because of reliability and better power characteristics. I can't imagine fair, high level racing between nitro and electric boats even though our club does that in some "open" classes.

Lohring Miller

[Darin Jordan]

Lohring... you know I'm your buddy and I have a lot of respect for you. You are one of the most intelligent people I know...

But now that the buttering up is complete... ;)...

You guys are forgetting the ORIGINAL INTENT of the P-Ltd classes...

The class is NOT designed around the idea of taking Limited motors and making crazy combos out of them. It's designed around the idea of making a competitive place for READY-TO-RUN offerings to be purchased and raced pretty much off the shelf.

By opening this concept up to ANY hull, and leaving only the Power System (Motors) spec'd, allowed the class to be inclusive to everyone.

The option of allowing OTHER-than-RTR motor offerings was ruled out, and has not been an acceptable idea, at least not to those that voted or discussed the rules for these classes.

That's not to say there aren't those that would like to see Ammo, and other motor manufacturers included, but the majority seem to understand the level of complication that this would be to incorporate, especially given the relatively primitive nature of our teching and the small size of our organization. It would also render the off-the-shelf power systems from these RTRs obsolete and uncompetitive. And, regardless of what some might think, a person CAN still be very competitive, under the existing rules, with a RTR hull in the Mono, Sport Hydro, OPC, and Offshore competition parts of the P-Ltd specification.

The class you guys are discussing is a DIFFERENT CLASS concept all together. That's fine, but I think we need to clearly separate the two.

[JfromJAGs]

I think quite some thoughts are being mixed now:

a. I just came across a similar thread on OSE. Randys initial idea was only about his own club. Having a lot of different boats on different power&speed levels and the wish to race together, it sounds reasonable to bring them all to a similar speed. Anyways, this has not much to do with the P-Limited rules and reading this thread brought back some really bad memories - personal attacks and so on. I don't need this.

b. Using the ESC as a fuse for P-limited, as Andy suggested, would work very similar to limiting the motors only. Then either the motor or the ESC is a fuse - so? If you would want a direct current limitation, then a current limiter device would be a much better solution. But still, such devices need some more thoughts: How precise are they? How to make them cheat-proof? How much do they cost? Where to get them? What happens if a device fails?

c. As explained, RPM restrictions together with prop limits are another and effective way to limit power and current. A simply way to limit the currents to healthy levels both for ESC and motor (and batteries). Running just electrics it would work well. But running electrics mixed with nitro? I think, no matter what you try, this will not work well. Because the power characteristics of nitro and electric motors are significantly different. On the other hand, its probably as good as it gets running them together.

=> But what really puzzles me is that almost nobody of those who were in the rule committee got at least a basic understanding of electric motors, their characteristics and limitations.

Brian (sorry, just an example), how does it come that you are surprised that from similar sized and constructed motors, running them all on 4s, the one with the higher KV is the faster motor? I mean, isn't that clear? Given the same size, the motor with higher KV got less winds, correct? Less winds mean less internal resistance (because shorter and thicker wire), correct? The internal resistance controls how much you can load a motor, as the IR creates the heat according to the ohmic laws: heat = current^2 * IR. So, lower IR = more current possible = more power = more speed. As long as your props don't get too small, which is not the case at the RPMs we are talking about, it is impossible to race similar sized motors from 1500 to 2000 KV on the same level - at least without further restrictions.

Joerg

[JfromJAGs]

You guys are forgetting the ORIGINAL INTENT of the P-Ltd classes...

Or maybe you don't know it?

There has been "P-Limited" many years before you started racing. It was raced with 700 sized brushed motors on 12 NiXX cells. Boats and so on were open. I think for most of those, who are racing FE for many years, the RTR motors were just a modern replacement for the 700 sizes brushed motors - at least this is what it should have been.

So looking at P-Limited from this side, what you got now is not as good as it used to be. With a 2000 KV BL motor its now much faster, not as beginner friendly and you are risking the equipment more then ever.

But, yes, maybe this is the basic misunderstanding in the debate?

Joerg

[Darin Jordan]

Or maybe you don't know it?

REALLY, Joerg?? Do you REALLY want to go there?? Seriously... I'm pretty sure that I, of all people, have a pretty good idea... I've taken enough abuse on the issue by now to deserve a little credit in having SOMETHING to do with the class specification being implemented in the first place... I'm pretty sure I KNOW what the original intent was.

Yes, 700 motors were going by the wayside... but we also had a desire to 1) have more options 2) provide a place for RTR boats to run competitively 3) create a cost-effective class structure. There may be other desires, but these were pretty prominent.


There has been "P-Limited" many years before you started racing. It was raced with 700 sized brushed motors on 12 NiXX cells. Boats and so on were open. I think for most of those, who are racing FE for many years, the RTR motors were just a modern replacement for the 700 sizes brushed motors - at least this is what it should have been.

Close... but not exactly right....

The SV27 power system was originally being looked at as a replacement for LSH/LSO power systems... As the discussion evolved, we ended up where we are now, and developed a new power specification system that would be more inclusive, and would be based around the current RTR offerings, not some obscure drill-motor.

It's certainly one opinion to say it's "not as good as it was before"... but the numbers participating, and the number of Nitro converts, etc., would suggest otherwise.

You guys are still operating off the premise that people are "burning up" equipment... The numbers would suggest this is the exception, not the rule...

[JfromJAGs]

I do belief that you got a pretty good idea about what you wanted from these classes, and probably what your club wanted from them. But I'm also pretty sure that others had slightly different ideas - but we don't need to argue about this.

It's certainly one opinion to say it's "not as good as it was before"... but the numbers participating, and the number of Nitro converts, etc., would suggest otherwise.
I think this is very difficult to judge and one could argue in an opposite way. My impression is that with the 2p rules the regular classes have been virtually killed and that many FE racers either quit or are converting to limited classes. To me the number of entries of the last 2-3 Nationals indicate this. Considering the possibilities of LiPo and BL technology and how much the prices went down, there could have already been quite more new people or people converting from nitro - if they would not fear to burn up their equipment with the given rules. I don't know if this is true or not - as you don't know if your arguments are true or not - both impossible to prove. But honestly, wouldn't it make sense to have rules which protect the equipment (better)?

As I pointed out, this is possible at no additional cost. By either keeping the speeds and using similar priced, but more appropriate motors or be keeping the motors and slowing a bit down - in both cases, by giving prop limits.

You guys are still operating off the premise that people are "burning up" equipment... The numbers would suggest this is the exception, not the rule...

Well, it's good that it's only the exception. But even if it's the exception, it did happen and it will happen again. I know this by looking at the eagle tree data Lohring has posted. Again, why do not get rid of the exceptions if it's possible at no cost? I have not read a single technical argument against this simple solution. Except the proclamation that the problem doesn't exist - which is obviously not the case, as even you just admitted that there are exceptions.

Joerg

P.S. You might recognize, I'm having fun with this debate... so please don't get annoyed.

[Darin Jordan]

P.S. You might recognize, I'm having fun with this debate... so please don't get annoyed.

:bounce:

It's all good... I'm well beyond the "getting annoyed" stage with any of this... In the big scheme of things... it's really not that important. With the incredibly SMALL number of racers that it actually affects, it's not really worth getting riled up over... ;)

[JfromJAGs]

Well, this doesn't take away anything from the truth of the arguments...

[lohring]

I think what this discussion has turned into is what would be a good rules system or systems to race under. To summarize some existing rule elements:

1. Set classes by cell count (voltage) Result - power is restricted by how high you can push the current

2. Restrict cell weight Result - total energy is restricted so careful balancing with quality engineering for particular race conditions is needed (I suspect this would be Joerg's favorite)

3. Restrict equipment ("spec" classes) Result - easy entry for new racers, but experienced racers push the equipment to win. also depends on manufacturer's offerings which will change

4. Restrict propellers Result - very equal racing depending on the restrictions, but potentially frustrates the best propeller tweekers.

Combinations of the above are also used like NAMBA P limited where cell count and motors are restricted.

It comes down to what we are trying to do. My favorite beginners rule set restricts the equipment AND propellers. This puts the emphasis on driving and setup skills while cutting the advantage experienced racers have. They still usually win, at least in my area. The 1/10 scale classes run this system (not completely intentionally) and it lets them concentrate on building scale boats without needing to engineer the power plant. The "stock" Super V 27 and UL-1 classes are also successful examples with more serious propeller restrictions.

As racers get experienced, they want more freedom to experiment. My thought is that a class system that restricts voltage and current might fit above the limited classes. The final step would be our present voltage only or cell weight only classes. There equipment development is encouraged to generate the next level of electric boats.

In my club we started in electrics with the "stock" Super V and UL-1 classes. As people got more experienced they wanted more speed so the UL-1 class evolved into the 1/12 sport scale class where any hull can be used with any manufacturer's stock power plant. Here we see things like a nitro Miss Vegas converted to run a UL-1 power plant. Some of those racers are also running P limited tunnels and riggers. It was a good evolution and a tribute to the success of the current rules at getting people into electrics. I would like to come up with ways to expand something like this into a little larger boats.

I'm also having fun with this debate and am very interested in ideas and comments. Please keep it up.

Lohring Miller

PS Darin, buttering up hasn't been needed since I met you in person. Contrary to popular opinion, you are really a nice, very intelligent guy.

[JfromJAGs]

To make it short, I prefer 2 different solutions for 2 different purposes. Behind both solutions is the idea to have rules to protect the equipment.

1. For beginner, advanced or limited classes I prefer indirect power limits by limiting the RPM and the props. Then choose motor size and ESC accordingly - so these work best at the required power. Battery capacity needs to be chosen according to runtime/race distance - or vice versa. Preferably empty the cells only by half or less.

2. For the open or expert classes I prefer energy limiters or counters. For enduro (Naviga style) racing this prevents the usage of low C rate, but high capacity cells - because these will only last for some cycles.

For US style sprint racing the limiters can simulate the extremely high C rates required for 1min races. 1min means 60C, but to get a decent lifetime 90C - 120C would be more appropriate. So take a 45C cell and allow it to be emptied only to 1/2 - and you "created" a 90C cell. I prefer this over length limits, as I think these lead to undrivable boats.

Joerg

[lohring]

That's an interesting system for beginner's classes. Rpm would need to be controlled by limiting voltage and Kv. That means motor Kv checks. The props could be closely described for very equal racing, or just limited in diameter. I think propeller diameter limits would work as an excellent current limiter. People don't appreciate that the power increases as the fifth power of propeller diameter. Diameter is easily checked and that type of limit could extend to more advanced classes.

Please spend some time describing energy limiters. I know they are used in FAI aircraft events, but I am not sure exactly how they work. Is there a straightforward design? What are the electronics involved?

Lohring Miller

[JfromJAGs]

1. Indirect power limits can span a wide range. It starts with "one design" classes (like RTR boats), a selection of certain motors with certain unmodified props and it could be as "open" as any motor with a certain RPM limit and props limited only to a certain diameter. So far I have only experience with limited numbers of motors (all with the same RPM) and only one prop per class.

2. An energy limiter or counter measures current, voltage and time, then multiplies these 3 and and sums them up - the result is the energy in Wh (Watt-hours). A counter only sums the energy up, while a limiter is connected in between the receiver and the ESC and can throttle the ESC down.

Considering
* the possibilities to cheat
* the problems when interfacing with different receivers and ESC
* how to throttle down (abruptly or slowly - if slowly how fast and how much)
* universal usability for all classes
* simplicity of usage
* ...
we came to the conclusion that we would prefer only counters and no limiters. Once you are over the limit for the class we would add penalty time or subtract laps - depending on the amount of energy you are over the limit.

A counter would consist of a precision shunt (very low IR like 0.1-0.2 mOhm, 0.5-1% precision) with a current amplifier circuit, a voltage divider, a 2 channel ADC (analog to digital converter) to measure current and voltage and a micro controller (µC) to do the calculations. The sampling rate of the ADC needs to be faster than the PWM frequency of the ESC at partial throttle, otherwise the result is not correct (actually I believe all available limiters and loggers are not correct concerning partial throttle operation). The ADC should have a resolution of at least 12 bit (4096 steps), with good linearity and low noise. Thus an external ADC is required as the internal ADC in micro controllers are not fast and/or precise enough. The micro controller needs to be feed by a precision crystal, simple oscillators are not exactly enough. The µC will either have a small 4 digit 7 segment display or - what I prefer - a communication link to connect an external display which a CD would connect to each boat after the race.

Except the high sampling rate ADC I had build a prototype using a small Arduino board and a Microchips ADC. I will need to exchange the ADC though, as the partial throttle problem came to my mind only after I had build the first prototype.

Joerg

[Darin Jordan]

Good Lord...


OR, we could just provide a list of 4 or 5 accepable motors, limit the voltage to 4S, and go racing...

[JfromJAGs]

Darin, please don't take this personal, but I think your comment is a first class example of the superficiality for which the US is known in the world. On the one hand I do admire the KISS principle, as Europeans often tend to be too technical and often think to complicated. So I try to make technical things as simple as possible - BUT not simpler.

As I pointed out, a solution for any form of limited racing is extremely simple: just indirectly limit the amount of power the motor can deliver by limiting RPM AND prop.

Designing energy limiters or counters is a bit more complicated. Its not rocket science though and I think especially you - as an Embedded Software Engineer - should speak that language fluently. I mean, nobody needs to know how a sensorless brushless ESC or 2.4GHz transmission really works - which is way more complicated than any limiter would be - as long as there is someone who builds these things and knows his stuff.

So instead of mocking I'd like to see your technical input. Lohring said you are a nice and intelligent person.

Joerg

[Darin Jordan]

Joerg,

Participation in Formula one is what it is because it's WAY too technical... Enter NASCAR... They have to fight just to make the race, and people from the most meager means can start out at the grass-roots level and build their way to competitiveness.

My point is that I don't WANT to see it get this technical. I'm pretty sure I'm not alone, but others can speak for themselves.

It's ALREADY too technical for a majority to clearly understand, or, at the very least, for them NOT to have some apprehensions about.

If you/we start adding counters and current limiters and this and that "black-box", then we won't even get people out in the first place, so what's the point?

I don't profess to have even half of the technical knowledge that you or Lohring or Brian or any number of you have. BUT, what I do have is a decent feel for the racing environment, and a bit of common sense, and have been around enough to know that if this gets any more complex, even from a "what equipment do I need to buy" standpoint, people will go find something else to do.

I also see limited power systems, similar to what we have spec'd, working just fine in cars, and other forms of racing. I'm still not convinced we need to reinvent the wheel, just because we have the technical knowledge to do so, or because a few people aren't having the success or equipment reliability that others are.

Just the way I see it, but then, I'm a very minor player, so my opinion is just that...mine...

[HTVboats]

Good Lord...


OR, we could just provide a list of 4 or 5 accepable motors, limit the voltage to 4S, and go racing...

Bingo! Give that man a cigar!:hammer:
Mic

[JfromJAGs]

Darin, I don't know what to say. I have tried to explain the differences between combustion engines and electric motors many times. You need to compare electric motors with supercharged combustion engines without any charge pressure limit. There is only a fuel limit (battery capacity), but with the existing battery capacities there's plenty of fuel available to blow the motors. So you can't compare your existing rules to any form of car racing and say this is the same. It's not. And this is why it's not working similarly well.

But, if you don't understand this and if you don't want to understand this and if you are happy with the fact that you don't understand it - so what shall I say? Look, I have pointed you guys onto a simple solution (limit rpm AND props). You can - but you don't have to consider this.

Joerg

[Darin Jordan]

So you can't compare your existing rules to any form of car racing and say this is the same.

Joerg... give me a break... My analogy had NOTHING to do with the MOTORS/ENGINES involved... it had to do with the complexities of the equipment, and the level of understanding required to make each go competitively. To simplify it so you'll understand what I'm trying to say, it's pretty simple...

The MORE complex a system is, the FEWER participants and racers you will have...

Replace "complex" with "expensive", and the statement also holds true.

This statement is "motor/engine" style and "fuel" independent...

We are constantly having to answer questions on the most BASIC bits and pieces of this FE hobby... (what does 2P mean, what's a "mAh"? How does C-Rating affect performance? and, the always classic "What is the BEST prop for my boat??") Trying to add MORE complexity to the equation is going to improve this HOW?? You think it'll bring more racers into the mix??


It's not. And this is why it's not working similarly well.

WHY do people keep saying this (a VERY few people, I might suggest)??? SHOW me how it's "not working"... Do the 2012 Nationals entries reflect this?? Are the P-Ltd classes the LEAST participated in?? Do we have people putting their boats on the shelves or moving to other classes??

Do we ACTUALLY have a pile of "burnt up" P-Ltd motors to show for our efforts??


But, if you don't understand this and if you don't want to understand this and if you are happy with the fact that you don't understand it - so what shall I say?

Joerg... first you insult my country, and now you are directly insulting me. :nono: ;) I clearly understand what you are saying. Your suggestions are solid ones, and your grasp of the technology is clear.

My argument has NOTHING to do with agreeing or disagreeing, with the merit of your solutions... They are FINE solutions that would do the technical things you aim for them to do.

In fact, I'd go one step further and say that many of them (limiters, etc) would save people from themselves. Takes the personal responsibility for your setup, tuning, etc., right out of the equation...

If that's the goal, and the members of NAMBA want to go that route, that's fine...

It's my opinion, based on actually being here and racing the class and developing production boats that fit in the class and paying attention to what people are saying/doing on the forums, etc... that there seems to be an effort here to solve a "problem" that DOES NOT REALLY EXIST!

If you had similar limits on your 140+ mph effort, it would have never happened.... Spectacular things don't happen under those kinds of restrictions. You have to fail from time to time to find out how far you can push things. That's racing, or so I thought...



Look, I have pointed you guys onto a simple solution (limit rpm AND props). You can - but you don't have to consider this.

Joerg

We have already limited the RPM... I agree, as I've said before, that the 2030KV UL-1 motors is an outlier, and, in hind-sight, probably should not have been included in the power specification... It's there, and we have to work with that.

It's not up to ME to consider limiting props... I run under the NAMBA racing rules, and I'm just a racer. Much like my original opinion that we should require the "stock" ESCs that came with the motors (remember, it's a class based on "current and future RTR offerings")... I have to go with what the organization comes up with as a collective, and no one has pushed forward with any prop limit suggestions.

Besides, it is also my opinion that this would severely restrict hull options, as all hulls don't work equally when it comes to Props...

The bottom line is this: I don't believe, and haven't seen any solid evidence, that there is a "problem" here that needs solving. Any situations that exist would be pretty easily solved by teaching people and helping them develop their packages, which ALL of us do whenever we get the opportunity.

We can add a bunch of electronic gizmos to help protect people from their own decisions, which might protect equipment to some degree, but it's not going to solve the issue and it's going to increase the complexity of the system in general, further alienating an already thin racer participant pool.

[lohring]

I think the P limited concept has done a lot to get beginners into the hobby. It is not a great way to limit the power output in a given class of boats especially while encouraging component development and intelligent equipment selection.

At the race yesterday I was very interested in the P limited hydro racing. I haven't been logging my motor, so I don't know how badly we are abusing these motors, but I promise they are being run well beyond their rated limits. We had 4 Raptor riggers at different stages of development with speed controls that varied from the original Aquacraft to an ICE 200 and batteries from low resistance Grim Racer packs to Turnigy nano-techs with twice the internal resistance. No one used stock connectors, but the fast setups are now using 6.5 mm bullets. The high end setups easily cost twice as much as the more stock setups. Everyone used the UL-1 motor. Two different props were run, the ABC S-15 and the ABC 1818 both cut for lower blade area and very close to 45 mm diameter. Cups, blade areas, and other prop details were different. The driving characteristics of the props were different, but the speeds were very similar.

The things that made the biggest difference in speed were the quality of all the components, other than the motor, and boat setup. I think exactly the same result would happen if the class only limited motor Kv and propeller diameter. The most efficient components would still win and speeds would be a little faster because the motors would be more efficient. It wouldn't be a beginner's class, but, at least in my club, it isn't a beginner's class any more than 3.5 hydro is. The beginner's classes restrict more of the equipment than just the motor. This would NOT be the same as open P class because the currents there could be over twice as high, doubling the power and requiring a different boat and propeller.

Propellers are an excellent power control, especially when the rpm is controlled. Power absorbed varies as the fifth power of the diameter and the cube of the rpm. Power varies directly with things like blade area and pitch. Both diameter and Kv are fairly easy to measure. Diameter matters by far the most and can be measured quickly with great precision using a ring gauge. Kv doesn't need to be checked with as great precision.

Lohring Miller

[Nautiboyz]

Darin, please don't take this personal, but I think your comment is a first class example of the superficiality for which the US is known in the world. On the one hand I do admire the KISS principle, as Europeans often tend to be too technical and often think to complicated. So I try to make technical things as simple as possible - BUT not simpler.

Joerg

Wow Joerg, You come out with a comment like that and you are only concerned with offending Darin?? I'm sure it must be a heavy burden for you to represent the conscience of the entire world on its view toward the US. Almost as ridiculous and arrogant is your self described view how the world views ALL Europeans.

Everyone has their own perspective. We all try to explain our points of view the best we can. That's all you can do. Sometimes your successful, sometimes you're not. Get over it and move on. Resorting to offensive remarks only diminishes your credibility.

[Darin Jordan]

Propellers are an excellent power control, especially when the rpm is controlled. Power absorbed varies as the fifth power of the diameter and the cube of the rpm. Power varies directly with things like blade area and pitch. Both diameter and Kv are fairly easy to measure. Diameter matters by far the most and can be measured quickly with great precision using a ring gauge. Kv doesn't need to be checked with as great precision.

Lohring Miller

Lohring... I wish I could have been there... Would have been an H-10 on my boat... tweaked and twisted, appropriately....

I'm not completely clear on what you are "suggesting" here... Are you trying to say you would advocate a prop diameter limit for the P-Ltd classes??

[properchopper]

Joerg,

Participation in Formula one is what it is because it's WAY too technical... Enter NASCAR... They have to fight just to make the race, and people from the most meager means can start out at the grass-roots level and build their way to competitiveness.

My point is that I don't WANT to see it get this technical. I'm pretty sure I'm not alone, but others can speak for themselves.

It's ALREADY too technical for a majority to clearly understand, or, at the very least, for them NOT to have some apprehensions about.

If you/we start adding counters and current limiters and this and that "black-box", then we won't even get people out in the first place, so what's the point?

I don't profess to have even half of the technical knowledge that you or Lohring or Brian or any number of you have. BUT, what I do have is a decent feel for the racing environment, and a bit of common sense, and have been around enough to know that if this gets any more complex, even from a "what equipment do I need to buy" standpoint, people will go find something else to do.

I also see limited power systems, similar to what we have spec'd, working just fine in cars, and other forms of racing. I'm still not convinced we need to reinvent the wheel, just because we have the technical knowledge to do so, or because a few people aren't having the success or equipment reliability that others are.

Just the way I see it, but then, I'm a very minor player, so my opinion is just that...mine...

I'd like to speak from the perspective of a "grass roots" racer with a budding group of local guys now taking the plunge in "spec" racing who will be affected by any further changes in "da rulz". I agree with Darin that adding complexity in the form of any sort of extra gear to the mix will likely discourage these folks from wanting to set up such extras with the added need to check/inspect/monitor. Heck, I have six spec class boats for as many classes - now would I need to add another piece of gear (in the form of an electronic "limiter") to each ? Would my club guys want to do this now that they're just tentatively readying their aspirations ? Obviously not.

As far as I'm concerned (and I realize that I'm a relative junior member of the racing community and my opinions may lack the pedigree/credibility of more seasoned racers) there's plenty of good racing going on as it now exists. Sure there's always room for further improvement/regulation but such evolution will be momumentally difficult to achieve consensus and may, as has been stated, alienate a portion of an already small pool of members- witness what's already been debated on various "specing" issues and the resulting granfallooning.

[JfromJAGs]

Darin, no need to get upset. It just shows again that we are talking 2 different languages. I want to talk about the technical aspects. You are talking about something else. I don't think I ever read a technically founded reply or argument from you. That makes it really hard to exchange thoughts. Never mind.

[JfromJAGs]

Tony, this is what really makes it difficult for me to argue. Nobody seams to read or understand my posts. Or people only read what Darin makes out of them? What you have highlighted is what Darin made up. I never wrote that concerning the limited classes. Please compare my post #47 (and maybe #27 and #29).

1. My suggestion for the "Limited" classes was: leave the motors you got and just add appropriate prop limits. How difficult is that? How much does that cost? Together with the RPM limits of the given motors a prop limit will keep the currents in control and it will solve the (small?) problem of people burning their motors.

2. "Unlimited" sprint classes are different and more complicated to control. Only for them my suggested solution is a energy limiter or counter device.

Joerg

[JfromJAGs]

...the superficiality for which the US is known in the world...

Wow Joerg, You come out with a comment like that and you are only concerned with offending Darin??

Well, hmm. I thought you knew this? I mean what do you think the world thinks of the US? Sorry, I did not intend to offend anybody. I thought that was common knowledge. Not? I mean, I know what the world thinks about us "Krauts" -- and I need to admitt that most of that is even at least a bit true.

For the rest - see my avatar ;)

[Darin Jordan]

Darin, no need to get upset. It just shows again that we are talking 2 different languages. I want to talk about the technical aspects. You are talking about something else. I don't think I ever read a technically founded reply or argument from you. That makes it really hard to exchange thoughts. Never mind.

Joerg,

I don't think I was upset... I put in a winky face... ;) I like discussing this stuff with you... :D

Doesn't mean I won't be passionate when I do...


I think what you aren't getting is that I don't dispute the technical merit of what you are saying... You are right. I'm not sure what more I have to add to what has already been posted. You, and Lohring, both far out-do me in all respects to the technical side of this discussion. I'm not sure what more I could add, if anything.

My point, this entire time, has been pretty clear, and were targeted at the subject class: P-Ltd...

I think I even agreed that, on a local level, restricting props makes some sense. Go for it. We've talked about it for OUR district and were just trying to figure out which props would go with which motor sets... Limits in diameter or ?? Different ones for the 1500, 1800, and 2030KV motor packages... Hell... it might even make the 2030 less of an outlier if we could chop it off at the neck a tad and allow something reasonable for the 1800 and 1500KV motors... perhaps...

Anything beyond that, however, is adding a level of complexity that doesn't need to exist, in P-Limited, anyhow... and would appear to be solving a problem that doesn't really exist on a level that warrants the additional components or restrictions.

I did NOT think we were discussing the "Open" motored classes, because Randy never mentioned the open-motored classes... That's a whole different ball game, and frankly, they wouldn't be "open" if we started adding a bunch of restrictions to them. Would just have another "Limited" class...

[Darin Jordan]

1. My suggestion for the "Limited" classes was: leave the motors you got and just add appropriate prop limits. How difficult is that? How much does that cost? Together with the RPM limits of the given motors a prop limit will keep the currents in control and it will solve the (small?) problem of people burning their motors.

2. "Unlimited" sprint classes are different and more complicated to control. Only for them my suggested solution is a energy limiter or counter device.

Joerg

That may be why we are missing our conversational targets... I've NEVER been here discussing ANYTHING other than #1... P-Limited classes...

"Open" classes (N, P, Q, S, T) never even crossed my mind in this discussion... :doh: I didn't see that as part of the original question or posts...

;)

[JfromJAGs]

Darin, for some reason its really hard for me to understand what you are trying to say. It never came to MY mind that you agree to an arguments, when you don't disagree and still keep arguing against it. How was that when you got married? ;)

Well, yes, the title is "Restrictor Plate Racing". This can mean "limited classes", P-Limited in particular, but not necessarily. Lohring was also talking about electric equivalents for certain (stock) nitro engines. Also, Lohring and me were discussing the usage of current limiters for such equivalent or limited classes. I was explaining why I suggested the indirect limits (RPM and prop) for such classes. Especially with post #47 I said I see 2 different topics and thus 2 different solutions - one for "limited", the other for "unlimited" racing.

Concerning "unlimited" or "open", this does not mean "not limited at all". Thats not the case. The regular classes M to T are limited too. They used to be limited by energy (number of cells of a certain size). In 2007 the energy at least doubled with 2p and since 2008 they are indirectly restricted by the size of the hull. My proposal was to go back to energy limits and as appropriate 90-120C LiPos are not yet available, thus use limiters to artificially "create" these.

Joerg

[JfromJAGs]

Propellers are an excellent power control, especially when the rpm is controlled. Power absorbed varies as the fifth power of the diameter and the cube of the rpm. Power varies directly with things like blade area and pitch. Both diameter and Kv are fairly easy to measure. Diameter matters by far the most and can be measured quickly with great precision using a ring gauge. Kv doesn't need to be checked with as great precision.

Lohring Miller

I need to look this up, but I know that the thrust of the propeller comes from the mass flow within the disc area of the prop: how much the fluid increases its speed within this disc. The disc area increases with the prop diameter to the second, but both RPM and pitch increase the flow speed directly. So I would expect that pitch has a similar effect as RPM. And as I know how much the RPM changes the power consumption of a prop, I doubt pitch is negligible.

So only limiting the diameter and leaving the pitch open might not be a reasonable restriction.

Joerg

[Darin Jordan]

Also, Lohring and me were discussing the usage of current limiters for such equivalent or limited classes.

Joerg... that's fine... but Lohring and you got OFF TOPIC.... :tongue:


"Due to the higher cost and maintenance problems with the UL-1 motors, pro Boat and the other motors we should allow any motor and restrict the speed of the boat with GPS on board."

If you were here, and racing in the P-Limited Class... you would have recognized that Randy was addressing THIS CLASS in particular... or an alternative to it... I'm not sure what he's talking about with the "other motors part", because Pro Boat and Aqua Craft are currently the only two manufacturers on the list, but either way, it's clearly addressing this class.

My ENTIRE discussion has been done in the light of discussing the power systems in THIS PARTICULAR class... Randy was suggesting that we throw OUT the power specification that limits the motors to a specific list, and use some alternative form of "limit" on the class... I'm against that, as my discussion should clearly show.

Any discussion outside of the P-Limited class was extraneous... albeit, enlightening... :wave:

Either way... the P-Limited portion of this discussion seems to have run it's course...

[JfromJAGs]

Anyways, in case you would come to the conclusion that you would want to enhance the limited classes concerning a more equipment friendly usage and/or a more equally leveled field, then you know how it could be done: add a selection of unmodified (only balanced and sharpened) props to the rules.

IF you, the NAMBA racers or any club wants this - thats another question.

Joerg

[Darin Jordan]

Anyways, in case you would come to the conclusion that you would want to enhance the limited classes concerning a more equipment friendly usage and/or a more equally leveled field, then you know how it could be done: add a selection of unmodified (only balanced and sharpened) props to the rules.
Joerg

Yup... and then we could start a new thread, debating exactly how to go about tech'ing such things... ;)

[JfromJAGs]

I think this has been answered in post #10 (http://www.rumrunnerracing.com/feforums/showpost.php?p=290856&postcount=10) ;)

[Darin Jordan]

I think this has been answered in post #10 (http://www.rumrunnerracing.com/feforums/showpost.php?p=290856&postcount=10) ;)

Yup... we certainly could do that...

[lohring]

For the diameter and rpm relation to power see: http://mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html I believe those relationships apply to all turbomachinery. More detailed data on a popular non cavitating propeller series can be found here: http://deepblue.lib.umich.edu/bitstream/2027.42/3557/5/bab2786.0001.001.pdf I have similar data for Rolla surface piercing propellers and they have the same basic characteristics. I'd be glad to send to copy to anyone who asks. I would need to work through some examples to be sure that power absorbed is directly proportional to blade area and pitch, but that's a common assertion among airplane modelers. See http://www.auroramodelaircraft.com/html/library.html Propeller Graphs (Speed vs. Pitch and RPM, etc.). NACA report 640 (http://aerade.cranfield.ac.uk/ara/1938/naca-report-640.pdf) gives a lot more comprehensive data that looks like it supports the direct relation of pitch and blade area to power over small changes. I also plan to data log a series of model propellers in some different hulls for comparison. All this will take quite a while, so be patient.

My thought is that diameter and rpm restrictions control the major power absorbing factors while allowing the kind of fooling around modelers love. It's being tried in some less restrictive forms around here. Naturally, the really experienced racers have faster boats. That will always happen.

Lohring Miller

[HTVboats]

I have been following this thread here and the locked one on OSE. I just cannot see how some of the most inteligent technical minds are going to improve and expand FE racing with more restrictions to "level the playing field" or make racing cheaper. When you mandate props which are not that expensive to start with and even buying them worked is not beyond most people, you to me cut the heart out of setup and making hulls competative. Take away tinkering to make it all even does not push the envelope forward. Face it the best guys who put the time in testing and recognize going backwards will rise to the podium. To take away their best tools and hope to run with them does not improve anyone or prove your a first class driver. I would rather run with the best wide open, take my lumps and learn.
Anyone reading all this either being new or a veteran is not going to be inclined to build more FE boats. Makes me want to get away from limited/spec and just race unrestricted boats period. The market and manufacturers will always make better equipment. Using technology to stop or limit progess just because you can doesn't make sense to me. At the end of a race day anything above a visual or lineaer measurable rule will not be enforced anyway. Race officials have their hands full getting an event off and then to tear down or measure with more than a ruler is not going to happen beyond national championships or record trials.
Mic

[Darin Jordan]

For the diameter and rpm relation to power see: http://mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html I believe those relationships apply to all turbomachinery. More detailed data on a popular non cavitating propeller series can be found here: http://deepblue.lib.umich.edu/bitstream/2027.42/3557/5/bab2786.0001.001.pdf I have similar data for Rolla surface piercing propellers and they have the same basic characteristics. I'd be glad to send to copy to anyone who asks. I would need to work through some examples to be sure that power absorbed is directly proportional to blade area and pitch, but that's a common assertion among airplane modelers. See http://www.auroramodelaircraft.com/html/library.html Propeller Graphs (Speed vs. Pitch and RPM, etc.). NACA report 640 (http://aerade.cranfield.ac.uk/ara/1938/naca-report-640.pdf) gives a lot more comprehensive data that looks like it supports the direct relation of pitch and blade area to power over small changes. I also plan to data log a series of model propellers in some different hulls for comparison. All this will take quite a while, so be patient.

My thought is that diameter and rpm restrictions control the major power absorbing factors while allowing the kind of fooling around modelers love. It's being tried in some less restrictive forms around here. Naturally, the really experienced racers have faster boats. That will always happen.

Lohring Miller

Lohring... I'm not even going to begin to take the time to try to read all of that at the moment... but just had a thought...

IF one was going to limit props... Would it not level things out a bit more by adding one additional limiting factor: Pitch Ratio??

If I'm not mistaken, this affects the "rake" on the hub of the blades... If you limited this, along with Diameter, I would think that would help to reduce the effects that bending might have on the prop, while still allowing for fine-tuning and some tweaking??

Just a passing thought. May be way off base, but I thought I'd "blurt" it out there... ;)

[lohring]

I didn't expect any people to read the articles. I looked them up to be sure I wasn't being confused. The first is from an MIT class on propellers and covers the basic relationships. A good book on marine propellers is The Propeller Handboo (http://www.amazon.com/The-Propeller-Handbook-Installing-Understanding/dp/0071381767/ref=sr_1_1?s=books&ie=UTF8&qid=1334841242&sr=1-1)k.

After thinking about electronic solutions to the basic issue of setting classes, restricting power, I thought restricting the propeller might be a simple, easy to enforce solution. Joerg pointed it out as well.

No method is going to be perfect and the P limited rules are one way to set classes. But any rule set has consequences. Restricting displacement in internal combustion engine racing classes leads to small, powerful, expensive engines. Limiting almost everything you can think of gives you NASCAR with big, crude, expensive engines with similar power. This topic is an exploration of some different ways to regulate electric classes and what might happen with a proposed rule set.

Power with electrics is very simple. Thrust is what drives the boat. Thrust power is thrust times speed. That comes from the input power, volts times amps, times the power plant and propeller efficiencies. We only control 1/2 of the input power, volts, in the open classes. That means we encourage the highest currents possible. Batteries are no longer the limitation they once were. If we control both voltage and current, we encourage the development of efficient power plants and propellers. I believe this is a lot more desirable than encouraging 500 amp speed controls like the current rules do.

Lohring Miller

[JfromJAGs]

I have been following this thread here and the locked one on OSE. I just cannot see how some of the most inteligent technical minds are going to improve and expand FE racing with more restrictions to "level the playing field" or make racing cheaper. When you mandate props which are not that expensive to start with and even buying them worked is not beyond most people, you to me cut the heart out of setup and making hulls competative. Take away tinkering to make it all even does not push the envelope forward. Face it the best guys who put the time in testing and recognize going backwards will rise to the podium. To take away their best tools and hope to run with them does not improve anyone or prove your a first class driver. I would rather run with the best wide open, take my lumps and learn.
Anyone reading all this either being new or a veteran is not going to be inclined to build more FE boats. Makes me want to get away from limited/spec and just race unrestricted boats period. The market and manufacturers will always make better equipment. Using technology to stop or limit progess just because you can doesn't make sense to me. At the end of a race day anything above a visual or lineaer measurable rule will not be enforced anyway. Race officials have their hands full getting an event off and then to tear down or measure with more than a ruler is not going to happen beyond national championships or record trials.
Mic

Mic, I see your point - and to some extent I agree - but let me explain why a prop limit might still be a good solution for "limited" classes.

1. I assume you are using a mobile phone. Millions of scientist and engineers have contributed to this technology in the last 100 years. If any such 2 scientist would discuss this technology then I'm sure this sounds like a discussion between Geordi and Data. BUT, the end product is still simple enough to use, even for kids and completely uneducated people. So if the outcome of any of such discussions is easy, why is it bad that the discussion may go deep into propulsion technology?

2. A ruler might be a little bit too simple to check everything involved in FE racing. But I guess such a prop pattern/mold would be very close.

3. We were talking about "limited" racing and "restrictor plate racing" here. This is indeed different to "open" racing. If you don't like the limits in "limited" racing, well, yes, race in the normal open classes without such limits. I mean - isn't this what the open classes are for?

4. The purpose of "restrictor plate racing" in general is to keep the cost under control. Whatever rule there is in "limited" racing, it's there to control cost and with this attract new racers. It does not mean racing is cheap or easy. It is cheaper and easier than open racing, yes, but not that it would take away anything of the fun and excitement of racing.

5. "Limiting" can be anything. You can limit the voltage, currents, motors, props, hulls or even rudder sizes. The history of racing has shown that it was usually a good idea to limit the power and then let the racers select the rest to work best and reliable. Above we have found that limiting ONLY volts and motors is not such a type of limit, because then such motor are used above their design specs and the only limit is the drivers ambition - and pocket. On the other hand limiting voltage&motors AND props would be a power limit that would let the racers use the equipment within its design limits - assuming props are selected carefully. But, you are right, this would take away - as and restriction would do. First: choice of motors and second: choice and tweaking of props. But similar to F1, where all teams have to use the same tires and motor electronics, there are plenty of other things to fine tune your boat - besides driving skills. So how much does it really take away?

6. The 3 main factors of a prop are diameter, pitch and concavity. Pitch with RPM controls the speed, while diameter and concavity adjust the thrust. The thrust thats needed to overcome the resistance of a certain boat at a certain speed. But when we talk about diameter then this is not exactly correct. What really counts is the control surface, the area where the prop pierces through the water. So with moving the prop up and down, and thus changing the control surface size, one will also be able to fine tune the propulsion system even if diameter and concavity are given. Assuming the selected prop basically fits to the job, there is are still possibilities to fine tune the setup. And honestly, I think most people should to that instead of bending props worse.

Joerg

[JfromJAGs]

I didn't expect any people to read the articles.

Well, I did read them ;). And I will even come up with an explanation why D^5 is correct for plane props, but still does not apply for what we were talking about. I'll post that later.

Joerg

[JfromJAGs]

Ok, here we go.

1. At constant speed, power is equal to thrust times speed:
P = T*v

2. According to the first document, "11.7.3 Actuator Disk Theory"
T = p * A * (ve² - v²) / 2

T = thrust
p = density of medium
A = actuator disk (the area in which a medium is accelerated)
ve = exit speed (of medium far after the disk)
v = boat speed (speed of medium before accelerated)

3. Let me define a speed factor fs between ve and v
ve = fs * v => fs = ve/v = Pt/Pl

This factor fs describes how much the propeller accelerates the medium within the actuator disk. Considering a well designed prop for the power level this is basically the relation between the trailing edge pitch (Pt) and leading edge pitch (Pl) - a function of the concavity of the prop. This considers that the boat travels approximately at the leading edge pitch speed and the water exists the prop at the trailing edge pitch speed.

4. Using 2. and 3. we get:
T = p * A * v²/2 * (fs² - 1)
or for power:
P = p * A * v³/2 * (fs² - 1)

5a. The actuator disk is a portion c of the prop area:
A = c * PI/4 * D²

D = diameter
c = working portion of prop, probably 30-60% for a surface piercing prop

5b. The boat travels at a speed determined by motor rpm multiplied by propeller pitch, minus slip. Or with a matched prop, rpm multiplied by blade entry pitch
v = n * Pe

n = rotations per second
Pe = blade entry pitch (= average pitch * slip factor)

6. Using 4, 5a and 5b we get:
P = p*c*PI/8 * D² * (n * Pe)³ * (fs² - 1)

Conclusion:
* prop diameter influences the power to the second
* prop rpm and pitch influence the power to the third
* prop concavity influences the power a little bit more than linear

So prop pitch and blade concavity influence the required power at least as much as the diameter of the prop. And I think this what everybody knows who has worked with props: changing pitch and cup can change the behavior and thrust massively. => Only specifying a certain prop size will not work as a power limitation. Limiting power will only work if also pitch and concavity are fixed too.

NB: If there wouldn't be any increase in speed within the actuator disk, then fs would become 1, thus 1-1 = 0. Thus thrust (and power to push the boat) will be zero.

7. Now considering you got a series of props of different sizes, but all have the same geometry, especially the same pitch to diameter ratio (pr = P/D), then the absolute pitch can be described in relation to the diameter and pitch ratio:
Pe = pr * D

8. Using 6. and 7. we get:
P = p*c*PI/8*pr³ * D^5 * n³ * (fs² - 1)

Conclusion: given a certain series of props, like the Octura X4 series or plane props, then the required power increases with diameter to the fifth. But, again, to the second because of the increased disk size and to the third because of the increased pitch.

Joerg

[HTVboats]

Joerg,
You and that one other guy keep designing those "cell phones" and your right the rest of us just need a dial tone.
A number of years ago when I ran full sized boats we created a production V-bottom class (mono) to use semi obsolete and inexpensive boats & motors. Good stainless props then cost about $300-400 for a blank and another $100-300 to get them cut how you wanted. To take the expense out we made a rule only aluminum production props could be used. They cost under $100 and no one would spend much time or money modifying them past a hammer and a trailer ball. Slowed the boats down and eventually killed the desire to set up things and the wonderful inexpensive class died. Seems those expensive props were what made the boats perform and the actual cheaper way to go faster over motor and hull mods.
My comment on the ruler was to make the point that technical inspections just are not going to happen unless they are pretty much linear. Voltage, size and weight are easy and how close does that blade have to fit in a mold. A few thousanths on a model prop can be a big difference. How thin is the blade at different points since sharpening and balancing are allowed. Maybe you could just mandate only production "plastic props" untouched.
If it gets too complicated it may kill what was in best intentions designed to improve racing.
Mic

[lohring]

I thought we were exploring simple to inspect ways to limit power in a given race class. The present open rules are simple to inspect, but power is limited by how much you want to spend developing high amp motors and speed controls and how hard to drive you want to make your boat. The best limited equipment power plant rule in my opinion is the 1/10 scale rule because it restricts both motors and, unintentionally, props. The prop limitation is changing as manufacturers make more right hand props.

Joerg, give me some time to consider your post. My thinking comes from the definition of the torque coefficient that's universally used and the relation of torque and power. A power coefficient may also be used giving the same result. I was most worried about the linear relation of pitch and area to power. I'll investigate that further, but it still looks true. Below are the commonly accepted relationships:

Lohring Miller

[JfromJAGs]

Mic, don't get me wrong. My suggestion is not to make the boats slow. But I suggest to use the equipment within its design limits and this obviously means for the given motors that the limited boats will need to run a bit slower than now. If you want to keep the speed then use appropriate motors - which need to be bigger than those selected now.

Lohring, as written in the last paragraphs: the coefficients are correct, I don't question them. But as shown above, they only apply under certain constraints: they assume that all props you compare got the same pitch ratio. If thats the case, yes, power increases to the fifth with size. But again, this increase is split: to the second based on diameter and to the third because of the increased absolute pitch. So pitch behaves similar to RPM - also to the third - which makes sense to me and which I had guessed in an earlier post. The above formula #6 describes pretty much my practical experience.

Joerg

[lohring]

Joerg, I'm a slow learner and my math skills are a little rusty. I'm slowly working my way through your arguments. I think I'll calculate some examples from the Rolla data for our prop sizes. I also need to get more data from some real boats. Currently I have three sizes of basically the same hull: an 1/8 and 1/10 scale Executone as well as an electric sport 40 with the 8255 design. All were designed to be limited power plant prototypes, not open class boats. The 1/8 scale boat holds the NAMBA two lap record, and I have the data from that run. Brian is running the sport 40 this weekend and I'll get data from that boat. The 1/0 scale boat is ready to test. They should make great prop test hulls.

I'll start reporting on their performance data.

Lohring Miller

[lohring]

In my area the scale racers are the most active in investigating spec rules. The latest from RCU where they are trying to get electrics to race equally with 11 cc nitro boats are:

Motor- NEU 1527 1.5Y. or equivalent. (825 Kv)
Batteries - 14.8V 4S lipo cells (2 per set for a total of 8s)
ESC – Open. (Minimum of 150 amp continuous)
Prop - up to 55MM diameter

The first race of the year results were:
R/C U's 1st race is in the books. 1st place Dave Brandt driving His E-lam, 2nd- myself (John Olson) with my Bud Light, 3rd went to David Newton driving an electric Formula boat 2.

Those specs are very close to my NAMBA two lap record holding 1/8 scale boat with a Scorpion 800 Kv motor. It looks like they are accomplishing their goal of equal racing, but the season is young. RCU has some of the best racing drivers in the country with years of experience building and driving scale boats. It should be an excellent test of propeller restrictions added to spec Kv motors.

Lohring Miller

[JfromJAGs]

What does "or equivalent" mean? At how many amps are these motors usually run in these setup?

Joerg

[lohring]

I thing "equivalent" means the Kv needs to be similar. These are trial rules, so they will be tweeked.

"In the spirit of good sportsmanship, any FE boats having a noticeable speed advantage over the nitro boats will be asked to detune their boats to ensure competitive racing. If they do not comply, they shall be disqualified from the class for the race weekend."

Some data from my 1/8 scale boat during its record run as well as a heat from Brian Buaas driving my sport 40. The Sport 40 runs:
Scorpion HK 4025 1100 KV motor
Turnigy 180 amp speed control
6S 5000 40 or 45C batteries

Below is a graph of the Mutt's data for an entire heat from the launch at 350 seconds through the mill to the start at 400 seconds to the finish around 490 seconds. Note that the rpm at around 20,000 (that's about 80% of the nominal 1100 Kv x 22.2 volts no load rpm) is a little low compared to nitro engines, the average current is around 130 to 140 amps, and current spikes go to over 190 amps, especially when you hit the throttle at the start. Not as visible on the graph is the voltage. Freshly charged it was 25.18 volts. At the start it fell to 20 volts and then held to between 20 and 23 volts for the rest of the race depending on load. The final voltage after the heat was 21.16.

The 1/8 scale boat is 20+ years old equipped with a Scorpion HK 4035 800, a Castle ICE 200 lite ESC with added water cooling, and two Gens Ace 5300 4S packs in series. Both boats were designed as "spec" class prototypes using low cost components.

Lohring Miller

[JfromJAGs]

1. You are running rather low RPMs. They are not the preferred playing field for 2 or 4 pole motors. Because of IR (12mOhm) and idle current (1.5A) the efficiency of a 1527/1.5Y at 8s maxes out at about 60A. So running this motor at 150A or more is not the preferred solution.

Higher pole motors are preferred for such low RPM applications. For example a 1912/1Y got the same RPM, only 11mOhm and the same 1.5A idle current, but weights only half. So if available, I would try to get a 1924/0.5Y. Double length and half the winds will ensure same RPM, but only half of the IR. A 1924/0.5Y weights pretty much the same as a 1527/1.5Y, but will have its maximum efficiency around 100-120A - which is more appropriate for what you are doing.

2. Are you running the same 55mm props on the nitro boats? If thats the case, then the electric motors should have an advantage concerning acceleration over the nitro boats, because of higher torque under load. If you find this to be the case and if you want to make the electric boats more equal, then I would suggest to use smaller props and higher rpm motors for the electric boats.

Besides the formulas we had above, which indicate that at speed there are many solutions to use props for a given power level, acceleration is more a question of static thrust. And static thrust is higher on bigger props - actually the efficiency of bigger props is higher at such static conditions. So going to smaller props and higher RPMs for electric boats will make them "softer" out of the corners.

Joerg

[Randy Naylor]

After coming back from the Nat's P LTD classes are doing great and was a lot of fun. I think if I get a hearing aid I could enjoy the race better. Brian and I were talking about limiting 1/8 scale and did speak about the 1527 1.5Y motor. I think I really like the 8S part that would slow the speeds down and help stop damage to hulls and for the racer that wants to go balls out leave it open in T Sport and you could run the same boat with a battery change if so inclined. I like ware you guys are going with this.

[lohring]

Brian ran the same boat in 1/8 scale and T hydro. It fits the RCU electric 1/8 scale rules including prop specs. He won both classes. The boat is a 20+ year old Dave Frank Executone originally raced by Jerry and Paul Dunlap in the late 1980s. I rebuilt it first for nitro, then for electric. Brian refined the details, drives really well, and the boat just keeps getting faster. It and the advances with the P limited boats are a lesson in how hard it is to successfully restrict a class. The best racers can take any set of rules and still go faster.

Lohring Miller

[JfromJAGs]

It and the advances with the P limited boats are a lesson in how hard it is to successfully restrict a class.
As pointed out in the above discussion, what you got now is only a small restriction. A similar feature to "restrictor plates" would need further limitations - if one wants it.

The best racers can take any set of rules and still go faster.
I doubt this has ever been a question and I doubt anyone ever wanted to change this. For restricted classes it is accepted and actually wanted that the best driver wins - not the one with the deepest pockets. So nothing wrong with this. A side effect of restrictions is usually a more leveled field - which is not bad for the moral of the drivers who do not win.

Joerg

[lohring]

how about the power sensing circuit at the bottom of this page (http://www.maxim-ic.com/app-notes/index.mvp/id/3669)?

Lohring Miller

[JfromJAGs]

1. The question is - what do you want to achieve? If you want to simulate a fuse, then this circuit together with a low IR shunt (0.1-0.2mOhm) is for sure better - kind of an electronic reusable fuse.

But would I want this behaviour of a fuse, that is, shutting everything down once I'm over a certain power limit? Me, no. First, too dangerous for the ESC. Second, too dangerous for the following boats. If one would want to have a power limited system, then I would suggest a overpower counter - a system that counts for how long you are over the limit. After 2s a first red LED comes on, and after 5s a second LED - then you are out. Change the times to whatever you like.

2. I have thought about such analog multipliers for an energy limiter. This would solve the problem of the error that happens at partial throttle when you first averaging voltage and current and then multiply them in the micro controller. But so far I have not found any of such analog multipliers with reasonable linearity and accuracy - and a reasonable price.

If one would use a 0.2mOhm shunt then 250A would equal 50mV shunt voltage. There you already have 0.8% typical inaccuracy. Going down to half throttle currents (50-100A) the inaccuracy is 2% and becomes much higher below this. The total accuracy of an energy limiter should be more in the 1% range - including all error sources.

Joerg

[lohring]

Still, the MAX4211 type circuits are close to what could work. The cost for 1 is around $4, and 1.5% accuracy is also pretty good. At the least, it could be connected to an alarm type circuit running a flasher, as an example, that would announce an over power condition. Contest supplied units could be calibrated for accuracy near the power limits. That could result in a suitable penalty during a race without affecting anything else.

Lohring Miller

[JfromJAGs]

If you want some logic behind this circuit then you need a micro controller. Then you will end up very close to an energy counter or limiter concerning hardware - the rest is just software.

Joerg

[bbr]

It,s great to see Franks boat back action.Raced with Paul & Jerry back in the 90s on the RCU circut. Hats off to Buass & Lohring.
Wild Bill U-62 RACING