Part Sorting

The parts (in yellow, orange and pink) are sorted based on their lengths. They move on blue runway thanks to green belt (external teeth) of a belt drive (its two pulleys are not shown) and fall down into three boxes.
The first box receives shortest parts (in yellow), the last box receives longest ones (in pink).
The hole on the blue runway is of wedge shape.
The parts always contact the runway right wall due to the gravity.
This sorting way has not been verified in practice.