[artdutra04]

If you are planning on using a free-spinningn tri-wheel design (all three wheels are powered, with the carrier automatically rotating over obstacles), make sure the input shaft and wheels rotate in the same direction and make sure the sun gear is significantly larger than the planetary gears (e.g. gear the wheels faster than the input shaft).

This means you will have to gear the carrier input slower (only to gear it faster at the wheels, I know it's an ugly solution), but the torque exerted on the individual wheels needs to be less than the torque needed to rotate the entire tri-wheel carrier assembly. If this is inverted (small sun, large planetary), the robot won't go anywhere with the tri-wheel carriers just rolling over themselves.