You can build a compact track module including the motor. The beams on the sides are spaced in "standard grid". This makes it easy to mount the track module on your own creation. Please also see variant 2 .
The other side view:
Top view with motor dismounted:
This is what you need. Watch the colors:
If you build a mirrored module, you can make something like this:
Tip: Relax the belt while the module is not used for longer time.
Have a lot of fun.