Loose rotor to shaft grub/set screw problem.
Have anyone’s motors had the set/grub screws come loose that hold the rotor on the motor shaft? When I would accelerate under a heavy load, like quickly taking off from a slow speed, my Tacon Bigfoot 160 motor would momentarily over rev and sound like something was slipping. Initially, I thought my motor pulley was loose and slipping on the shaft, but ruled that after closer inspection. For the record, I have ground a huge flat spot on the motor shaft, and use plenty of thread locker on everything. After a closer look, I noticed that there were two set screws at the end of the rotor, holding it onto the shaft. One was loose and one had backed out so far, that it was almost ready to fall out. There was no trace of any threadlocker on the screws, which I assume to be an assembly defect. So, after applying a bit of thread lock and cranking down the set screws, it seems to have fixed the slipping problem.
Now, it seems to be happening a little bit on my SK3 motor. At least this one had threadlock on the set screws, but I added more and cranked them down.
I had a hard time finding any information or posts about this problem, so hopefully this will help someone who may be experiencing some unidentified slippage. And from now on, I’m checking these little buggers first thing when I get a new motor. Who knew Bigfoot had a screw loose? 
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Yep…seems to happen if you crank on the breaks a lot … In your case crank the throttle…had issue with a wiggly motor mount … When I tightened them up and reduced my the times I break hard… The problem went away… Nothing moved …
What might help is switching out the grub screws with something more beefy to crank down on…
Good looking out @Mobutusan! Thanks for sharing the fix with everyone. I know that others have, as @Michaelinvegas notes, replaced the default set screw with more robust option; M4 I think?
this happened to me on an NTM 5060 270kv. Its how i discovered these grub screws. I tightened mine back down and they were fine for a while, but i added it to my checklist to look at before riding.
@Michaelinvegas & @treenutter, the M4 bolts are a great idea. I was gonna upgrade those on the motor pulley, but it didn’t even dawn on me to use them for this application. My only concern would be the balance of the rotor, since the screw holes aren’t exactly 180 degrees from each other. On a motor pulley, we can use two bolts 180 degrees from each other to maintain balance. Maybe it’s too small to make a difference, but on the Tacon, the screw holes are inside 2 of the 5-spokes on the rotor, but kind of across the shaft from each other. On the SK3, it’s a little worse, since the screw holes are inside adjacent “spokes.” Hopeully, it’s a non-issue though since the bolts are so small and so close to the shaft.
On my own motors, I switch the M3 threading to an M4 threading. I use actual M4 bolts vs set screws to apply more clamping force.
This was a common issue with RC motors. I would have the motor casing shift.
I’d like to do one better and build in a retainer on the motor shaft + keyway and M4 bolt on my next batch of motors.
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Would you suggest this with the 6355 motors and drive system you sell? This is good info to know. Thank you!
@Mobutusan Thanks for posting this thread!
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Yeah, it was always an issue with RC motors but switching out to a bolt vs set screw definitely helps. Once I switched it out, it wouldn’t shift as much.
What length bolts do you use in place of the rotor/shaft set screws? And also, what length bolts do you use on your motor pulleys?
Took a trip to Lowes with the wife & kids in tow…and like 5 minutes…and now I feel better
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Noice! Gonna have to get my screw on soon. I tightened and threadlocked the crap out of my set screws and they still slightly slip under heavy load. My 20/36 gearing probably doesn’t help though.
20 huh? Lol is that so you have enough speed for the on ramp?
Only if the speed limit is 25mph. 
It’s my attempt at hitting the 25mph mark with my 6s, single 245kv setup. I thought my 16/36 setup would get me there, but only made it to around 22mph, which isn’t quite scary enough for me. For some reason, I want to know that my board can go fast enough to terrify and mame me, but then back off to a comfortable, realistic riding speed. I guess I just don’t want to feel limited by anything other than myself. I’ll be jumping up to 9s with all of the 3s batteries I have, as soon as I get my hands on a capable ESC, and this whole speed thing will be a non-issue.
Also, I accidentally found out that with 20/36, I can get my 6364 SK3 up to about 200*F by doing 4000mah worth of speed runs up and down the court I live on. 
I’m quickly learning what NOT to do. It’s a lot of fun! 
Hahah just go 12s and call it a day…
I would go 12s, but I already have two 245kv motors, and I don’t wanna die…
Lol don’t trust yourself?
Well for your board’s sake at least move up to 10s lol…
Did a test ride …cranked on them hard… Harder than I ever did before…didn’t budget … Hope it works for you
Awesome work guys! I have a similar build and this info is super helpful. Cheers!
Fine, I’ll do 12s. For the board’s sake. I thought anything over 200kv on 12s would cause magic smoke fairies to appear, but maybe that’s just for VESC’s?
@Mobutusan - That’s just for VESC. More so it will spit out errors. I don’t think it will smoke.
