Mechanum Wheel Sizes

[slijin]

Originally Posted by nxtsoccer

we should plan on using a semi-flexible frame that allows for the wheels to raise/lower a little based on terrain

In my opinion, this is a rather critical design decision that you may want to consider more thoroughly; I would avoid going with a semi-flexible frame. Although I did point out earlier that you want to make sure all wheels are always in contact with the ground, the reason I did so is to ease troubleshooting when driving becomes erratic.

A semi-flexible frame, as its name implies, has less structural rigidity, something you very rarely want to sacrifice in FRC due to head-on robot collisions.

The other problem with using a flexible frame to ensure constant 4-wheel contact is that this has the potential to similarly hinder effective driving. If the frame somehow warps such that all your wheels are touching the ground, but at different angles, your ability to drive straight will probably be seriously hindered. (If your frame flexes such that the wheels tilt out or tilt in, there will probably be minimal loss of control, given the roller design, but if your frame somehow spins your wheels with respect to the vertical, you're definitely going to lose some of your control). There's also the fact that mecanum wheels want to be mounted to a rigid frame, because they rely on that rigidity to achieve the effect that they do (the angled vectors that allow you to drive straight or strafe only do so because they have a constant angle, and the rigidity of the frame is part of what allows that angle to stay constant).