Higher Strength "High Strength" VEX Gears and Axles?


My team and I have run into a bit of an issue regarding the strength of plastic (or lack thereof). We have 2 high-torque motors driving an 84:12 gear ratio, so there are considerably large amounts of torque being exerted.

Small VEX shafts twisting and breaking have been a frequent problem for us in the past, but with this new setup, the high strength 84 tooth gear itself is breaking at its center (I guess it could be described as stripping, the center of the gear essentially becomes a circle and no longer spins along with the axle).

What are some workarounds you guys have for this? I’d love an all-metal 84 tooth gear, but sadly I don’t think those exist. Size is also a bit of a constraint, so just bolting 2 of them together is probably not optimal, although if it comes to that, I suppose I’ll have to find a way.

Would using the high-strength thick shafts instead of a small shaft with inserts make a difference in the wear of the gear center? I’m assuming that once this problem is fixed, a new one to arise will simply be the axle twisting.

Any and all feedback is appreciated, I’m sure this isn’t the first time someone has wanted to make the “High Strength” parts even stronger.

Thank you all for your time,

  • William

shafts twisting is a pretty common issue, the normal shafts are pretty weak, especially if they’re under high loads spanning large distances. There are high strength shafts that exist though, High Strength Shafts & Hardware - VEX Robotics, and these are commonly used for applications like a lift to prevent that twisting.

as for your HS gears stripping, I don’t see how this can happen on low strength shafts?
The HS gears have these inserts in order to use them on the normal shafts:
you’d likely be using the square ones. those are virtually indestructible, so they can’t be stripping. Do you mean to say that the metal inserts themselves are drilling out the 1/4" hole in the gears? I’ve heard of this being an issue, but never experienced it with low strength shafts.

One pretty important thing when it comes to lifts, is to not be transferring power through your shafts when possible. If you bolt the arms of your lift directly to the 84 tooth gears that are being driven by the 12 tooth gears, the shaft that the 84t gear is on isn’t transferring any power, it’s only supporting that pivot point.

Can you post a picture of your robot? this would help us diagnose the causes of your issue, and help you fix it.


Yeah, I from the post it sounds like something similar to this:

If this is the case, one thing that can help with this is sandwiching the gears with lockbars to provide more support and stop the insert from rotating inside the gear.


If it’s possible to screw the gear directly to whatever is being powered, that would be ideal. This way no rotational force is being sent through the axle that the 84t gear is on.

(Hi, Mactar (20chars))


Hello and thanks for the input!

Yep, what I meant by stripping is the inserts themselves drilling out the center hole.

The best solution is likely the one you mentioned of eliminating torque and power transfer on the axle itself by simply making it a pivot point, I think I could definitely do this and it would likely avoid future issues if I were to strengthen the gear and then have troubles with the axle compromising.

The robot is for VRC and we’re experimenting with a mobile goal lift, with the amount of power required to overcome leverage and lift one of those goals more than a foot in the air, some pieces are getting pretty stressed.

I’ll try out what you recommended with bolting the gears directly when I have the chance, then it’ll be time to move on to transmitting rotation through an arm (chains are not working well with preliminary testing so far, maybe a large geartrain?) but that’s a discussion for another post : )

Thanks once again, I really appreciate it. Have a nice day/night! Currently past midnight where I live, but robotics > sleep (don’t worry, going to sleep right after this haha)

1 Like

High strength lockbars from robosource.net will keep the gear hubs from stripping out.