[MrForbes]

KOP items for the control system from previous years are mostly not allowed. But there are special rules about the control system, that do not apply to other parts of the robot. There are also special rules about motors, and pneumatics, and power distribution. Wheels are not part of any of these special categories

The use of mechanical parts appears to be completely wide open, as long as the part is not hazardous, or too expensive.

The slick wheels are neither hazardous nor expensive.