[MechEng83]

There are technical and strategic challenges to implement a mecanum drive effectively. I will attempt to briefly address both.

Technical - We've done mecanum for the last 2 years in 1 form or another. Our gearbox of choice is the AndyMark Toughbox Nano - 1 per wheel. I definitely recommend driving the wheel directly out of the gearbox rather than through a chain. We use quadrature encoders on each wheel and have PID tuning to make certain we control each wheel's speed, rather than just input voltage. We use a gyro on the robot to allow field oriented drive, while having an alternate robot oriented drive. Make sure that your frame is not too rigid. The robot can drive eratically if all 4 wheels are not on the ground. Our 2012 robot had what is sometimes called octocanum drive, where we switched between mecanum and traditional wheels. We designed the shifting pistons to support the robot weight on more than 3 wheels. This level of active suspension is not required, but was a side benefit in our 2012 design. Test with the robot weighed down to final competition weight - drives function differently with varying amounts of load.

Stategic - Mecanum is not better or worse than a more traditional drive. It is different. Teams who do not make strategic changes will be ineffective in using a more versatile, albiet, less pushy drive. Almost everyone understands that in a pure pushing match, mecanums will lose. What many people don't realize is that you can maneuver around a robot much more easily to avoid them or get out of a sticky situation. Driver practice is key, as the extra degree of freedom means the driver has an additonal drive component to control. Practice avoidance maneuvers around pushing robots. Practice lining up in the positions you need on the field. It pained me to see teams with mecanum drives this year driving them as a tank robot to get into a specific location, when they just needed to move sideways 6 inches.