Connect gear to a shaft

[hotrock7]

Hey Endless-Sphere,
I came across my first problem on my new electric longboard that I cannot figure out.
At first, setup was working perfectly! I could ride around with ease. This only lasted for an hour or so though; then, my motor would stall and make awful noises as soon as I stood on it. I thought for sure it was an issue with the motor, until I kept playing with it and found out that my gear that was on the shaft that connects the belt to a timing pulley on the wheel was the issue. The wheel spins with ease when it's in the air, minor issues occur when on the ground, then it all fails when I stand on it. The gear is connected to the shaft by two tiny set screws that get screwed in with a hex key. What I am thinking is that as soon as the motor has to provide enough torque to power something heavy (like a 110 pound girl xD) it works too hard on the shaft that it forces it to slip a bit. My conclusion is that I need a better way to mount the gear to the shaft. Those tiny set screws are basically stripped at this point so I am in desperate need of solutions.

Extra info:
Motor: Turnigy Aerodrive SK3 - 5055-280kv Brushless Outrunner Motor (hobbyking)
Gear: http://sdp-si.com/eStore/Catalog/PartNumber/A%206A25M014DF0906
Batteries: http://www.ebay.com/itm/2X-ZIPPY-5000mAh-7-4v-2S1P-2S-20C-30C-LiPo-RC-FREE-EC5-Traxxas-Dean-HXT-ADAPTER-/121429145474 (in series)

Thank you so much

Amanda

 

[Punx0r]

Yep, that sounds like your problem. Grub screws aren't really up to heavy-duty applications (a keyway is the real answer) but you have a few options to beef it up depending on your mechanical skills.

Firstly, I'm guessing the set screws are pointed and the shaft is round? If so, I would consider drilling a short distance into the shaft (if it's soft enough) or grinding a flat onto it where the set screw locates and use a flat-bottomed screw. This would give you a mechanical lock. I would also consider drilling and tapping to fit a larger diameter screw and installing more than one per pulley.

 

[Kodin]

Filing flats on the shaft where the set screws sit works really well for stepper motor couplings on my milling machine. Tighten the set screws once, then remove; should have left a mark on the shaft where they sit. File that down 1-2mm so you have a nice flat, and if the screws start slipping they will "climb" up the flat like a slope and self-tighten. ...Unless they are too small and either cut into the shaft or shear. But you won't know until you try, and there's nothing to lose in adding the flats first really. Other option is weld 'em up, but welding doesn't work well with dissimilar metals. I'd also suggest checking the bearings while loaded with weight to make sure they turn easily. Could be a bearing or two have failed and work fine with zero preload, but once you get on it the bearings start binding.