Flex shaft issues..impulse 32

[Dan.L]

I recently bought a new proboat impulse 32, I am having issues with breaking flex shafts. I ran approximately 17 battery packs with the stock shaft before it snapped mostly run at 75% throttle and I'm running 2x 3s battery packs. It is breaking where the flex shaft meets the solid shaft. I replaced the stock shaft and it snapped in the same spot immediately upon taking the boat out. I replaced it again and managed to run 2 packs and it started to break in the same area. I am just getting into the hobby of rc boats, have owned planes and drones so this is all kinda of new to me. I do grease after each run as well with marine grease. Can anyone give me any suggestions as I am tired of losing props and shafts, starting to get discouraged. 😒

[alvinm]

I've had mine for while now and never had any issues. I admit that I don't dog it out, just smooth accelerations to top end runs. The flex shaft is pretty beefy so I'm a little surprised that it's breaking the way your describing. Did you ever balance the props? Any weird vibrations when you throttle the boat up out of the water?

[eehess81]

Are you leaving a gap between drive dog and strut? The flex shaft shrinks when throttle is applied..if you don't have a gap it can break. Leave a gap the width of the flex shaft

[alvinm]

Good point. I stick the Flex shaft all the way in and then back it out a millimeter or two. Nothing precise, just enough to allow the shaft to shorten up.

[Panther6834]

Good point. I stick the Flex shaft all the way in and then back it out a millimeter or two. Nothing precise, just enough to allow the shaft to shorten up.

1-2mm isn't enough...at least, for a boat that size. I know I'm still learning when it comes to FE boats, but, at the same time, I'm not exactly in 'agreement' with the "Leave a gap the width of the flex shaft" comment. It's a good 'starting point', but not a definitive answer. I say that is, if the overall length of the cable is short, you could actually leave less than the "width of the flex shaft"...and, if the overall length of the cable is long, you should leave more than the "width of the flex shaft" (say, approx 1.5 times the width). The advise I just gave you was given to me by someone who's been racing for over 20 years. While I might not yet know a huge amount where FE boats are concerned, he certainly does...so, I trust his advise.

As Jim described it to me, the reason is that a short cable isn't going to 'shrink' as much, whereas a longer cable would 'shrink' more. As an example, I have three boats of approximately the same length (33-36"), all using flex cables of the same thickness...but having different flex cable lengths. The longest is 240mm, the shortest is approx 100mm, and then other two (for a twin-powered cat) are in-between at 175mm (these are just the lengths of the flexible portion). With the cat, the gap is approximately equal to the cable width. With the longer cable, I typically set the gap 1.5-2x the cable diameter. And, with my TFL Pursuit w/ Integrated Drive (the 100mm cable), the gap is approx 0.5-0.75x the cable width. Jim is the one who originally helped me set them to "proper" distance...and, again, I trust his judgement.


~ More peace, love, and kindness would make the world a much better place

[eehess81]

Sorry to generalize with the gap length. Yes.. a shorter cable will not shrink as much. Better to leave a little wider gap than needed.

[alvinm]

I haven't had an issue just eyeballing the gap and I have just about every boat Pro boat makes with no issues. The Impulse doesn't need that much. The BJ 42 definitely needs more.

[Dan.L]

Thank you everyone I have always left a gap and greased the shaft i will try to leave less of a gap when I get home. I have to go buy another shaft and hopefully this is my last one. I will keep everyone updated if the gap is the issue.

[eehess81]

You mean more of a gap?? Really couldn't think of another reason to break driveshafts at that spot.

[Dan.L]

Yes sorry I meant more of a gap..ill try it when I get home I'm out of town at work right now. Horizon hobbies is sending me a new shaft so I'll try to leave more of a gap

[Panther6834]

Yes sorry I meant more of a gap..ill try it when I get home I'm out of town at work right now. Horizon hobbies is sending me a new shaft so I'll try to leave more of a gap

Do, or do not. There is no try.


~ More peace, love, and kindness would make the world a much better place

[eehess81]

Wise you are

[paulejr]

What if it is a two piece shaft , would it shrink out of the strut section? seems so one would leave more or less spacing ??

[Notoriousone]

Two things, a HD flexshaft from OSE will be much stronger than a stock proboat shaft and will probably fix the issue. Second, have you changed the motor position, that could affect the angle of the cable and cause it to break

[CJPB32]

I own an Impulse 32 for 2 summers now- -stock Spektrum ESC, motor, on 6s smart batteries. I broke the OEM flex shaft the second time out. Bought OSE's flex shafts and have not had a problem since.

I also meticulously aligned the shaft to motor collet; nearly perfect. I run 3 blade CNC's.

[paulejr]

Gap? I thought they went out of business....