Problems with Vex Pro mecanum wheels

[Mark Sheridan]

Originally Posted by Ether

Problem is, the rollers can appear to be free-spinning when not under load, and then bind up when they are loaded.

There is a lot of axial force on the roller under real-world operating conditions. It is prohibitively expensive to put high-quality thrust ball bearings on FRC mecanum wheel rollers. I've never seen the VEX mecanum wheels. What provision is in the design to react the high axial forces without creating excessive friction? IOW, what two materials are scrubbing against each other when the roller is axially loaded?

Yeah I was going to caution that a wheel unloaded will be different from a loaded wheel. My team never came up with a good test method for this.

I am sure you know this Ether, but so others can follow, I will be a bit more detailed. On the andy mark wheels, there is a bushing in the wheel. This rotates on a bolt. Between the wheel and hub plates are washers. If one is too zealous, one can tighten the bolts too much compressing the washers and wheels until the wont move. We had to play with this a bit because once the wheels are on the ground, the deflection of parts can create binding too. I think if its too loose, the hub plates could touch the roller. I forget how much it took to cause the failure mode, but gut tells me that situation required the bolts of be barely tighten.

I am guessing the Vex wheels are similar with a shoulder bolt or screw that supports the rollers. Thus i may be possible to over tighten the screw until the rollers bind. The roller would be compressed by the head of the screw and the hub ( plus a few washers in there).