Carrier Roller/Top Rollers/Upper Rollers are used to hold the track shoe up, so that the crawler has a certain tension.

The tracks are driven by hydraulic motors through closed planetary gear units running in oil bath.

It is used to connect with the walking speed reducer, transmit the power to the crawler, and drive the whole chassis forward.

Bottom Rollers/Lower Rollers/Track Rollers are used to support the crane weight and let the track shoe move along the wheel.

It is used to connect with the walking speed reducer,transmit the power to the crawler,and drive the whole chassis forward.