pic: Omni Design Trial

[George1902]

Originally Posted by squirrel

The rollers act as "tread" when the weel is going straight ahead. To be able to roll relative to the wheel, there must be sideways motion. If there is no sideways motion, the roller in contact with the floor cannot roll, it can only "go along for the ride" as the wheel turns.

If this were correct a mecanum drivetrain couldn't produce diagonal motion. It's done by driving the corner wheels, but if what you say is correct, the robot would just drive straight anyway.

In ideal conditions a mecanum wheel will behave exactly like an omni wheel at 45*. Each system will be approximately 70% (sqrt(2)/2) efficient in forward-backward and side-to-side motion.

The confusion comes in that real life is never "ideal." 70% efficiency assumes that the rollers will have zero friction with their shafts. In an omni bot the inefficiency is universal and generally cancels itself out. In a mecanum bot however, the inefficiency causes the mecanum wheel to behave more like a regular wheel, so you end up with a little more than 70% power in forward-backward motion and a little less than 70% in side-to-side motion.

If you completely eliminate the roller-shaft friction, you get a perfect 70% efficiency, and likewise if you completely lock the rollers to their shafts you get a regular wheel. Reality lies somewhere in between.