Mecanum Drive - Help

[JesseK]

Originally Posted by EricH

Roller slip is the main reason. (It's also why a mecanum is easy to push if you can get to it.) See, going full bore forwards, the rollers aren't going to want to slip very much, due to a limited amount of resistance. But going sideways, every roller wants to slip because of the resistance from the opposite wheel on its side--which, combined with the 45-degree angle, results in sideways motion.

I still don't see how the slip is different between front vs sideways if it was a 45-degree angle and the rollers were allows to roll freely. The force vectors from the wheels are the same -- half of the force "slips" with the roller, half is applied to friction. The only difference in going sideways is that the motors may turn the opposite direction (assume equal magnitude motor output), causing the force vectors to be opposite in direction but equal in magnitude. Thus the bot should have moved at the same speed sideways.

If it's "diagonal" lateral movement, the forces should STILL be roughly the same magnitude since none of the force vectors cancel each other out. The difference has to do with a divisor of sqrt(2) in a coefficient somewhere, but my notes/calculations on this are at home. I wish there was a way to compare notes publicly without just giving away answers to teams who are looking to figure things out for themselves.

I suppose the OP should gather from both of these posts that there is more behind the scenes than just building a mecanum bot.