Wood Rollercoaster Train scale model

I designed a rollercoaster train to work an a wooden rollercoaster track.

This model was designed to function as a working scale model. Each rollercoaster car has an servo motor onboard to control the harnas. At this moment the gears don't fit, it needs to be corrected.

The wheels of the train are bearings to get the lowest friction.
Size 10mm for main wheels and 8mm for side wheels.