you can do this by using a multi-section sweep and thicken surface functions i will explain how to make the twisted part of the belt below
The first step is to get the master geometry setup, you need a sweep of the belt around the cogs. and two lines perpendicular to the belt center line offset slightly from the center of the belt
using this geometry create 2 multi section sweep using the ends of the sweeps and the perpendicular lines as reference. the ends of the sweep must be set as tangent to the previously created sweeps. and the start and end arrows must be pointing in opposite direction this will make the belt flip.
once both multi section sweeps have been created join the bodies and create a thick surface