View Full Version : Torque steer
09-30-2002, 03:43 PM
I have just built a motor torpedo boat (pt109) from plans out of balsa and ply.I paid special attention to making sure it was built square and true,It runs a 540 standard motor on a 7.2v 6cell pack.
A 45X prop, manouvering at slow speeds is excellent the boat sits level and sails quite nice
The problem starts at high speed when it appears to want to turn itself upside down .Looking from the back of the boat the prop spins anti clockwise and the boat wants to turn over clockwise I can only assume this is the torque of the motor
does anyone have any idea how i can stop this happening please ?
09-30-2002, 09:31 PM
First thing that comes to mind, try to get your CG as LOW in the hull as possible! Motor, batteries, on the bottom, if possible. Another note, you might want to shift the CG left to right, put a tad more on the Left side... In the manual for my Kyosho Jet Arrow, they say to put 10% of the weight towards the left to counter the prop's tendency to roll the boat...
10-01-2002, 12:56 AM
You may need to also add ballast to the hull. Does it sit high in the water? If yes that is a clear indicator that you will need some ballast.
Also as Paul said, check that the CoG is not too high up the freeboard.
10-01-2002, 10:20 AM
Thanks fo that chaps I didnt really want to add weight or put the batteries over to one side as at slow speeds it runs great.
would it wor if I put a trim tab on the side its tilting to as this would lift the hull out of the water and possibly increasespeed
excuse me if I sounds stupid but Im new to fast stuff and am learning quickly
10-02-2002, 07:33 AM
I would try the trim tab first. You can easily fabricate one out of brass sheet. Give it a try and if it works, Great. In not, then it is a simple matter to patch up the holes and try something else.
10-02-2002, 09:34 PM
Johnny, how big is this model? like a standard 1/32 scale say 30+ inches? if it is a scale model, I doubt the trim tabs would look right, I do think that a 45mm prop submerged is rather large I would think a 37mm prop would be more like it, how's the run time motor heat? octura actually makes a nice scale 0937 3 blade in a 1/8 shaft, this boat obviously is very very light I have both the dumas and the lindberg pt's and while their speed is respectable it wouldn't rotate the boat, hmm, have you considered reconfiguring to twin or triple drives, (real pt boats had triples) anyway just a few ideas, i mean 3 400's would be pretty cool...lol, cheers eddie
10-03-2002, 10:14 PM
Johnny on the other boards Nick pasch is really into torpedo boats and has built quite a few models of them, here's his email, maybe he doesn't check this side of the boards, very very knowledgeable guy maybe he can help
just a thought
10-04-2002, 02:26 PM
I'd agree with Eddieh here, that big prop is the likely problem. The larger the prop diameter, the more torque reaction by the boat. Just what is the '45X' prop used?
With a 540 motor on 6 cells I'd suggest using an Octura x431 or y534 prop if the boat uses an 1/8" prop shaft. If the boat uses a 3/16" shaft, try an Octura 1435 or x438 prop. These smaller diameter props have a lot less blade area than most 45mm props and will give longer run times along with much less torque reaction.
10-04-2002, 05:30 PM
Woh! slow down guys Im just a novice after checking the boat out again its actually got a hydrospeed 600 wich may be compounding the problem,The prop is a standard Graupner 50X
its not too bad with a 35X prop but loads slower.
I realise that a pt 109 is not the ideal boat to build as a fast boat
(it is running a lot faster than scale)
but hey Ive got two kids to impress
so Im going to try a 540 hydrospeed with some different combos of props and a pair of trim tabs I shall keep you all informed
10-04-2002, 07:08 PM
Johnny, well 50 mm is a 2 inch prop, and that to me is way too big for a submerged drive without a gear drive I run the octura x955/3 with a 3 to 1 in a scale application it performs very well but even for the motors sake, there must be some heat coming out of this thing, anyway the 600 is an excellent motor and the pt hull is the same design as most fast runabouts of the 40' and 50's I really would recommend no more then the x 40 even better with the smaller 1/8th shaft props from octura 937/3 works well, as does the 435, 632 my 2 cents, (or my 2p LOL)cheers eddie
10-05-2002, 01:57 PM
I forgot too mention that it has a 2.5 to 1 reduction gearbox and it doesnt get hot at all run times on a 1800 ma battery is about
15 mins. I have to say Im well impressed with the boat as it generally performs OK apart from the torque steer,I am however
going to try a 540 motor with a different range of props next time I go out.Also Im going to try trim tabs,Its built from the free plan that came with model boat magazine last year Im not really a scale modeller I just like it to look like something real.and the kids think its great.
Now Im going to sweetalk the wife for a traxxas villian
10-07-2002, 08:05 PM
...The prop is a standard Graupner 50X
its not too bad with a 35X prop but loads slower....so Im going to try a 540 hydrospeed with some different combos of props and a pair of trim tabs I shall keep you all informed The X50 prop you have has about 2.4 inches of pitch, so substituting an Octura x637 with your current setup should give similar speeds and run times without the torque roll problems. Graupner sells an adapter to use the X-series props on their shafts. You haven't told us how large the boat is, but if it is less than 30" the x637 should provide enough thrust. That's quite a gear reduction, most FE boats run 1.5 to 1.8:1. You could run a pretty hot 05 on that gearbox!
10-08-2002, 03:35 AM
Thanks Jay that sounds worth trying but Im going to ask another dumb question ? what is an Octura prop I assume octura is the manufacturer but I cant find anyone in the uk who sells them
I also have the Graupner catalogue and i cant find any listings or pictures of adapters you mentioned.
Also is all surface drive hardware expensive? as when I build a boat I have to build 3 one for me and one for each of my boys
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