fine control of robot with mecanum wheels

[Ether]

I am advising a team that built a robot with mecanum wheels, and they are very unhappy with the lack of fine control of robot movements, especially at low speeds.

Each 8" mecanum wheel is powered via a chain connected to an AM toughbox gearbox with a CIM motor.

There are no encoders, so the wheels are being commanded open-loop (i.e. they are being given voltage commands).

My analysis is that the design has too much friction in the drive train, and the gear ratio is too high, to obtain fine control at low speeds with an open-loop command.

The solution I proposed is to use a lower gear ratio (sacrificing top speed for better fine control at low speeds), or to add encoders and CAN bus so the Jags can do closed-loop speed control of the wheels. Neither of these solutions can be accomplished before their next competition.

I see no other viable options. Comments or suggestions?


~