extreme torque steer

[Bande1]

new boat ive been working on is a 42" catamaran. I took its new motor out for its maiden today and it torque steers so bad I dont know what to do. I tried +18 trim leftward. at a slow takeoff the boat veers left quite hard. maybe 45 degrees within 30 yards. under full throttle with that much leftward trim it pulls rightward even more extreme. the boat could probably do an oval all on its own.

it did NOT have this with its old motor. it had some torque steer, normal torque steer. nowhere near like this. Ive never seen a boat do this. It has a skeg removed and a 40 size rudder. I do have a 60 size I can try. would a 6" rudder help?


boat in question. its a 12s setup turning 30k rpm under load with a M447 and a Prather S230 prop. small props for this hull. COG is about 32-34%

IMG_20230728_112156.jpg

[Xrayted]

What's the KV of the new motor, and was the previous setup also 12S? If not, a 12S setup is going to have a lot more peak power/torque than a lower voltage setup will, even if the RPM is kept identical to a single 6S higher KV combo. Sort of like putting a 800HP V8 in a Mini Cooper. It might be fast, but also undrivable.

I'm just guessing here because the only time I've experienced severe torque roll like you describe is if the motor/prop combo is much too big for the size of the model and overpowering it

[Bande1]

What's the KV of the new motor, and was the previous setup also 12S? If not, a 12S setup is going to have a lot more peak power/torque than a lower voltage setup will, even if the RPM is kept identical to a single 6S higher KV combo. Sort of like putting a 800HP V8 in a Mini Cooper. It might be fast, but also undrivable.

I'm just guessing here because the only time I've experienced severe torque roll like you describe is if the motor/prop combo is much too big for the size of the model and overpowering it

its an 850kv TP 5670. it had a 1520kv 4070 on 6s. The 56mm motor seems to be what most people converted this boat with when you search the archives. I just find it really hard to believe this boat is wanting like a 42mm prop or something. its supposed to be running 55-65mm props.

[TRUCKPULL]

Back it down to 9s or 10s, then you can run the size of prop that the boat needs. (ABC 2115 -17-45-2blade) You may even be able to run a 1.9" -3 blade.

Other chouse is to take it apart and build it into a TWIN setup_ two 5670's 1170 KV. on 8s each.

Larry

[Bande1]

Back it down to 9s or 10s, then you can run the size of prop that the boat needs. (ABC 2115 -17-45-2blade) You may even be able to run a 1.9" -3 blade.

Other chouse is to take it apart and build it into a TWIN setup_ two 5670's 1170 KV. on 8s each.

Larry

I cant wrap my head around bigger props at lower RPM solving torque steer. it seems counter-intuitive. Then its almost cheaper to buy a whole new motor...again... than to buy a few sets of 10s batteries. arggg...im gonna try a 1717 or 1719 prop first. what do you think? smaller diameter higher pitch? I also twisted the 1/4 flex shaft so another parts order anyway....

all this was done with end points at 85%....I havent even begun to open it up. Hit 61mph.

[Bande1]

you know what I have a 1/4 flex shaft not turned down and a X670 prop that came off it as a gasser. should I try 8s and a huge prop? poor batteries gonna cry for mercy though....

[Peter A]

These hulls, like most tunnels, like a skeg strut, that and a bigger rudder will help with the torque steer, it is not uncommon even with the gas tunnels.
I ran one with a castle 2028 790 kv on 10s. Prop was an X452, it didn't have significant torque steer issues. It ran a speedmaster 1/4"skeg strut and inline rudder.

[Bande1]

These hulls, like most tunnels, like a skeg strut, that and a bigger rudder will help with the torque steer, it is not uncommon even with the gas tunnels.
I ran one with a castle 2028 790 kv on 10s. Prop was an X452, it didn't have significant torque steer issues. It ran a speedmaster 1/4"skeg strut and inline rudder.

thanks peter, I cut the skeg off because everyone said not to run it.

[Peter A]

thanks peter, I cut the skeg off because everyone said not to run it.

Lol, 'everyone' is an expert!

[paulejr]

would the hull not sitting level at rest effect the torque steer? my mono 32 was about 4 oz heavy on the port side and I added that amount to the stbd side to lay it flat , now only a slight right trim to make it go straight at speed ( 58.9 mph ) My Zonda (42) ran 70 mph on twin 4216's ....just saying , dont get stuck trying only one or two things to get your hull to run.. also check for tweaked framing from construction warping something ? Its a wing , so my not hurt to check hull alignment against a flat surface.

[Bande1]

would the hull not sitting level at rest effect the torque steer? my mono 32 was about 4 oz heavy on the port side and I added that amount to the stbd side to lay it flat , now only a slight right trim to make it go straight at speed ( 58.9 mph ) My Zonda (42) ran 70 mph on twin 4216's ....just saying , dont get stuck trying only one or two things to get your hull to run.. also check for tweaked framing from construction warping something ? Its a wing , so my not hurt to check hull alignment against a flat surface.

certainly something to consider Paul. It is in fact right side heavy.

[Bande1]

UPDATE: boat is doing really good this morning. Installed larger rudder (6"), some weight distribution to the left, and a .030" aluminum shim under the right side of the strut mount. its slower by a little bit but super smooth and cornering very well now. Top speed isnt mind blowing but I can hold wide open through out the entire course.

IMG_20230804_092945.jpg
IMG_20230804_094429.jpg

[paulejr]

Excellent !

[Bande1]

Got my speed back. Took 7,000w to do this.

IMG_20230805_114321.jpg

[Bande1]

Problem has NOT been fixed. It started again intermittently. I think now it is a stalling servo. I had an old futaba servo in it that was very weak. upgraded to a 20kg and it mostly went away except today coming out of a corner it veered left hard and would not steer out of it until I let off the throttle. So I put a 40kg unit on order to see if that does the final trick.

on the bright side ABC props have set my PB. Was lapping with our top members of the club today with IMPBA winning nitro hydro's and riggers.
IMG_20230812_125243.jpg