pic: Mecanum Wheel Project - Rev. D

[Joe Johnson]

As you go forward, keep in mind the ratio of axle radius to wheel radius.

This ratio is important. It is what makes rolling better than sliding. As the ratio gets closer to 1, the advantage of rolling disappears. Yes the wheel may be turning but the reduction in friction is almost nil.

Think of it this way. If you lock the wheel and slide it across the carpet, the torque about the axle of the force from the carpet would be:

Tsliding = MUcarpet2Wheel X FonCarpet X Rwheel

If you let the wheel rotate the torque on the axle becomes:

Trolling = MUwheel2Axle X FonCarpet X Raxle

There are only two places to let Trolling << Tsliding

#1 you can MUwheel2Axle << MUcarpet2Wheel

This is possible with bearings, etc. but in a Mecanum wheel application there is not much room for bearings and you sort of want MUcarpet2Wheel to be high because it is how your robot drives around. That pretty much means you're stuck with what you get for MUwheel2Axle. The roller material probably slides better on steel than carpet, but it is not going to be like butter on a bald monkey* either ;-)

#2 you can Raxle << Rwheel
This is your best bet in a Mecanum wheel application but even this option is somewhat limited by geometry.

Bottom line: The nice radius tips of your CAD model are beautiful and will provide nice transitions from 1 roller to another, especially on somewhat uneven ground, but it when that part of the roller is in contact with the ground, it is going to act more like a faceted wheel and less like an omniwheel.

Joe J.

*from Dance of the Cucumber
...
Larry: "sus suaves movimientos"
Bob: "Oh, how smooth his motion"
Larry: "tal como mantequilla"
Bob: "like butter"
Larry: "en un chango pelon."
Bob: "on a ... bald monkey."
...