I’ve been toying around with an idea for a while, and I’d like to share it with the FRC community, and maybe get others to improve on it or (if they feel like a challenge ) implement it.
My idea combines some of the present implementations of 6 wheel tank drive along with the transmission in the Toyota Prius, to improve upon some of the perceived weaknesses in mecanum drives - namely motor distribution and shifting.
I’ll try to describe it as best I can here, although if it doesn’t make sense a crude paint drawing may be in order.
First, start with the standard shifting tank drive. Each side has an independent shifting transmission which directly powers two or more wheels. When driven together, the robot can move forward and backward. When driven against one another, the robot can spin clockwise and counter clockwise. This accounts for 2/3rds of the motion in mecanum drives.
Second, take the planetary gearbox used in the Prius. It takes an input from a gas motor as well as an input from an electrical motor, and combines the two into power for the wheels. Now, instead of using the shifting transmission to directly drive the wheels in the mecanum drive, use the output of the shifting transmission as the first input of a planetary gearbox. Use another motor as the second input to the planetary gearbox.
Since each wheel has an independent motor, the left/right motion of the robot can be controlled by spinning the auxillary motors against each other.
Foreseeable issues include the problem of back-driving the motor at each wheel. This will have to be designed out mechanically with a brake or worm gear. There will also be an issue mechanically with weight, complexity, as well as the number of motors required for this design. Finally, controlling this will take lots of thought and optimization.
Another observation that I’ve had while thinking about this is that each wheel doesn’t require a planetary gearbox, just one on each side. While this will allow the robot to move sideways with less complexity, it doesn’t allow all motors to push together for a higher top speed.