Whats comperable to an Astro 25/5

[JimClark]

I have a question. of all the brushed motors available now what would be comparable to a Astro flight 25/5. Here are the spec's for what we run in Classic thunder
1/10th scale boats
5.5 to 6 lbs
Octura 447 prop
aprox 30 tp 35 mph on 12 cells

the problem Astro 25/5's aree getting harder to come by and Astroflight has really been dragging their heals as far as making new motors or even parts. We have one member who has had a 5 turn Arm on order for 5 months and they keep giving him the runaround.
Jim Clark

[Bill Sellers]

Jim,

Based on my analysis of motor parameters and performance, I think that the Graupner S700BB, 9.6V Neo (id #6306) is the best match. It could be dropped in as a direct replacement and the performance (run time, amps, efficiency) would be almost exactly the same. It is a less robust motor than the Astro 25/5, but it should do the job as well while it lasts.

Bill

[eddieh]

Bill, just curious are you picking the 9.6 for the torque? I thought the hot set up was the 8.4? I am running the non ss-1 fine design 775 and it is a very good motor with a 642 in my taifun but I am not sure you could run a 447 right off it, these motors do not allow you to adjust the timing, and i believe the hydro guys must tune them to run opposite of the way we do, as they go counter clockwise, but another thought is if enough guys wanted them Chris could order a batch tuned that way, and this would open up the twin motor doors for other applications, so it could be doable, I have a 9.6 bb in my Cesa, I think on 12 cells the 775 gets up a little faster, but I am always looking to learn,,, whatta ya think??
cheers eddie

[Bill Sellers]

Eddie,

My reasons for recommending the S700BB, 9.6V Neo is that it had almost the same characteristics as the Astro 25/5 in that the RPM/volt, winding resistance and no load current were matched. If the Kv (rpm/volt) is the same, then the torque produced per amp will be the same.

The 8.4V S700 motor is a hotter setup because it has a higher rpm/volt rating than the ferrite 9.6V. I assume that what people mean by "hotter" is that the motor will turn faster on xx cells and thus drive the boat faster given the same prop is used. Of course there are other consideration in choosing a motor, but rpm/volt is a big one.

In case you are interested, the mathematical relationship between rpm and torque is rpm/volt X torque/amp = constant for all DC motors. That is from page one of chapter one of Bob Boucher's Electric Motor Handbook.

I am not real sure of the degree of similarity between Graupner motors and Fine Design motors. It appears to me that the FDM 775 Neo is the same motor as the Graupner S700BB, 9.6V Neo.

Hope that helps.

Bill

[eddieh]

Thanx Bill , interesting, It is sort of wild the way everybody can have different ideas, I guess you have to just keep experimenting and find out what works there is only basic recipes, I was a bit bummed out after I picked up the mega s-4 and s-5 when I was relatively new and stupid, (i'm not that new anymore lol) but after a few chats I think given the right application they could do well, the rpm isn't great but the torque is, couple guys say overdrive them good approach, and I guess a surface drive would preclude a larger prop,Prop steer) anyway the more I learn, the less I know, anyway I liked the formula and appreciate the info thank you
cheers eddie

[Paul]

Hello Guys,

The 9.6 Neo won't do the job, although 700 neo is a good motor it wont push the boat past 30 mph and it surely won't like the 447 on that big boat. The SS1 is a much more powerful motor that could swing the 447 no problem but I doubt it would keep up with the 25/5.

Paul.

[Bill Sellers]

Originally posted by Paul
Hello Guys,

The 9.6 Neo won't do the job, although 700 neo is a good motor it wont push the boat past 30 mph and it surely won't like the 447 on that big boat. The SS1 is a much more powerful motor that could swing the 447 no problem but I doubt it would keep up with the 25/5.

Paul.

Just to make sure we are talking about comparing apples to apples, the published motor parameters for the 9.6 Neo and Astro 25/5 show them to be equivalent motors that should give equivalent performance in the same boat under the same conditions. That is my answer to the question that was asked.

In case some are skeptical about using theory to predict absolute performance, that is not what I am talking about. I am using the manufacturers published information about his product to compare relative performance between motors. The disparity in the observed performance to the predicted performance can either be attributed to incorrectly measured motor parameters (particularly Kv) or some other outside difference.

The comment about the 700 Neo not pushing the boat past 30 mph is certainly possible, but neither would the Astro 25/5 under the same conditions (battery, boat weight, prop, weather, etc).

Bill

[Paul]

Hello Bill,

The speeds Jim mentioned where 30/35 MPH out of the 25/5 motors. The Astro motors and 700 Neo may have similar numbers but the Astro is a better built motor with much stronger magnets. Unfortunately the SS1 doesn't have any published numbers but from using all the 700 motors experience suggests the SS1 would be the best choice.

Paul.

[Bill Sellers]

Paul,

I totally agree with you about the differences between an Astro motor and a 700 motor. The Astro will last longer because it is built stronger and can be refurbished to extend its life. Some day soon I am going to have to buy an SS1 just to try it out.

Bill

[FrankW]

The SS1 is an awesome motor and could definitly turn a X447R prop (if it can turn an X645, it can turn a X447R). However, it might not be quite as efficient as the Astro motor.

Jim, you've seen how the PDX LSH's run with the SS1. We haven't really set up our boats for true racing conditions yet. I was using a X640, and was keeping up with Garry's Atlas (running a 9.6 Neo with a X642). And he was keeping up with your Bardahl.

While our boats are smaller and lighter than Classic Thunder, they haven't been tuned for maximum performance yet. I'm sure an SS1 could push a Classic Thunder to 30 mph and maybe a bit more. Even if it produces slightly less power, you can see it as an oportunity to design around it and try to improve your current design even farther.

One thing that you can not do with an SS1 that you can do with an Astro is adjust the timing, which can be good and bad. I acually like not having to adjust the timing, one less thing to worry about. The cost of an SS1 is about half that of an Astro, and the SS1 is readily available.

What it really boils down to is experimentation. Try an SS1 and see.

-Frank

[eddieh]

I am still not conviced about running the ss1 backwards?? if I am reading it correctly, Jims folks spin clockwise ergo the 447 prop, I think a lot of the sealed can motors are a few degrees advanced from the factory, I know the 600 is, and My 700 spins better to the left then to the right, I would think that it would be a key factor to see if it was possible to get a righty or reverse rotation motor, I posted that before, it will also help out in some different applications as well. there was an article on how to advance and change the advance for 600's I'll post it if I can find it, cheers eddie

[Andrewg]

The Mega Midi 7 has a neutral Kv of 1900 rpm so would be a little hotter but also as or more torquey

The Mega Midi S3 has a neutral Kv of 1600 rpm and so is closer to the Astro and at 3oz heavier would also offer more mass for heat dissipation

They are also readily available and in expensive the Midi should be around $120 and the S3 around $140-$150

[Andrewg]

Jim

I will sponsor you - I just love that Bardahl!!!!

[JimClark]

Andrew am i missing something here on the mega usa page it is listing these motors as 7 cells. We run 12cells.
Jim Clark

Originally posted by Andrewg
The Mega Midi 7 has a neutral Kv of 1900 rpm so would be a little hotter but also as or more torquey

The Mega Midi S3 has a neutral Kv of 1600 rpm and so is closer to the Astro and at 3oz heavier would also offer more mass for heat dissipation

They are also readily available and in expensive the Midi should be around $120 and the S3 around $140-$150

[JimClark]

Andrew thanks for the offer but I really don't need a sponsor now if you want to sponsor a race next year we could work that out. Or if you wanted to give me a reallllllllllllll killer price on a motor I might go for that. Right now I just need to work on my driving I don't need to go faster until I get better at driving and am confident in driving in traffic. I should send you some video of our races. Would you want a tape or a do you have a DVD player? I can make a SVCD that should play on a DVD player.

Jim Clark

Originally posted by Andrewg
Jim

I will sponsor you - I just love that Bardahl!!!!

[Andrewg]

Jim was that a price that will kill you or a killer price?

Re the motors the Midis are fine on 12 cells I have run my 3 turn on 16 cells in a Bladerunner of all things (that is a story which I will post soon at fastelectrics.com)

The motors have an underload limit at 25000 rpm - but they compare in cost to the Astros.

Just a thought and I know there is the brushless class - BUT

An inexpensive 12 cell brushless setup $199-230 will be cheaper for new people than a 25/5 and esc. The "turbine" boats could step up to 18 cells which would give them about the right horsepower diferential at the correct scale weight.

Most importantly the brushless motors are easy to make run in reverse and dont suffer for it - and they will become cheaper and cheaper and dont wear out

Perhaps there could be a penalty system for a combined 25/5 brushless race like only using 10 cells and carrying two disconnected until the 25/5's were all gone.????


Jim I have rambled ona bit - just thinking out aloud dont mean to make you r life complicated

[JimClark]

Andrew I understand what you are saying my concern is if the MIdis will handle a 5.5 to 6 pound boat and give us the runtime.
Jim

[QUOTE]Originally posted by Andrewg
[B]Jim was that a price that will kill you or a killer price?

Re the motors the Midis are fine on 12 cells I have run my 3 turn on 16 cells in a Bladerunner of all things (that is a story which I will post soon at fastelectrics.com)

The motors have an underload limit at 25000 rpm - but they compare in cost to the Astros.

[eddieh]

Originally posted by Jim Clark
the problem Astro 25/5's aree getting harder to come by and Astroflight has really been dragging their heals as far as making new motors or even parts. We have one member who has had a 5 turn Arm on order for 5 months and they keep giving him the runaround.
Jim Clark

jim found this site they list the armature , hope it helps, cheers eddie
http://www.newcreations-rc.com/

[JimClark]

Thanks Eddie I know of New Creations they are good people. They rebuilt my motor for mr a year ago. their problem its they still have to get the parts from Astroflight and they told me they have trouble also.
Jim Clark

Originally posted by Eddieh


jim found this site they list the armature , hope it helps, cheers eddie
http://www.newcreations-rc.com/

[JimClark]

are there brushed Cordites or Plett's that would work for the classic thunder boats if so which ones for 12 cells. Pardon my ignorance on this issue but my only experience is with the astro motors.
Jim Clark

[T4r3e2y1]

Hey Jim...

A good Plett would be the 30 series 6 turn, that'd work well with the heavy hulls and large diameter props, maybe even a 7 turn. Problem with the pletts and cordites is the price, your talkin $225-250 just for the motor, and I honestly don't see them holding up any better than an astro. I really think someone needs to try the ss1 in reverse rotation, just for kicks, and see how it does.

I just went and looked at the ss1, and judging from the magnet to brush relation, it looks to have nuetral timing. I doubt that any of these motors being mass produced will have anything other than zero degrees timing.

[eddieh]

Trey/Jim, well if it turns out they are timed this article says it won't be a big deal if they are anything like the 600 have a look,cheers eddie
Graupner Speed 600 Race modifications

16 Jun 00 - Timing reversal technique added.

Timing Change For Reverse Rotation

If you want to use the Speed 600 Race motor with reversed rotation (e.g. for single stage gearbox or as a pusher) the timing needs to be reversed. The modification is actually quite simple and is as follows:

1. Release the springs holding the brushes and withdrawn the brushes.

2. Open the 2 tags that hold the backplate in position. This is much easier said than done as they are quire strong, but it can be done with a little patience. I slightly damaged the brush carriers on my 1st motor, but they were easily straightened & perfectly serviceable. This can be avoided by total removal of the brush carriers, but I haven't bothered with this so far.

3. Remove the backplate and armature from the motor and put them one side.

4. It is a good idea to back the motor with soft tissue to help stop the swarf from attaching to the magnets.

5. You will notice that the tags are cut about 6.5mm to one side of the middle of the magnets. Cut 2 new tags (with a hacksaw or slitting wheel on a drill) the equidistant the other side of the centre of the magnets.

6. Clean all traces of swarf from the motor and magnets and reassemble using the new tags.

Sounds horrible, but probably takes as long to do as it takes me to type (and I'm quite a quick typist). If you need more assistance, please e-mail me.

Fitting Ballrace Bearings

One the motor has been opened, as above, the plain bearings are very easily pressed out and ballrace bearings can be fitted in place. The bearings I have been using are 3/8" outside diameter, 1/8" inside diameter and 5/32" thick.