Wipers are needed on this particular model because all of the wheels are insulated from the axles. In fact the wheels are fully insulated from the whole frame judging by doing a quick check with my meter. I believe this is to isolate the whole engine from the wheels for the TMCC antenna.
Not sure where the ball bearings are but I’m suspecting in the gearboxes and the motor. The outer frames have brass plain bearings for vertical travel but I can’t tell what’s at the axle end without more disassembly. Maybe someone else can check. Anyway, all the current blows through the wipers in this setup.
