Some parts are used to fix tread link into the base of the device, so that the mounting device will move together with the tread link stably. Some are used to tilt the medium motor, so that the color blocks could slide down by gravity. If you take a look at the step-by-step instruction, there are lots of small parts, connectors used in this unit. Personally, I feel that mounting device is the most complex in this model. They provide support for the whole conveyor belt structure. Other three sprocket wheels are passive wheels which are driven alone by tread link, but they are not useless.
There are four sprocket wheels distributed in a line. Connect to Tread Linkīig motor drives the knob wheels and changes the direction of transmission and drives one of the sprocket wheels. Since driving the sprocket wheels and the whole tread links and mounting device requires high torque, I would say it is more appropriate to use knob wheels, instead of other bigger but more fragile gears. Meanwhile, their advantages are that they are much stronger than gears and can handle significantly higher torque. Knob wheels are not gears, but they can mesh with other knob wheels just like bevel gears.
The axis of the big motor is connected to one of the knob wheels. It is not supposed to be used by player, but used to set the mounting device to an initial position. The touch sensor is fixed onto a proper position. This part consists of one big motor as the output power and a touch sensor.