Summary

https://youtu.be/AN21Toetsiw
No timing belts, no tensioners, but a threaded M8 rod. Considerably slower than a timing belt, but for most plotter applications that should not be a problem. The X and Y axis of this plotter are identical. The carriers are connected and each carrier activates the end stop of the other axis. The length of an axis is free to choose. The pen lift is operated by a mini servo. Only six different printed parts are used, some of them printed two or four times.
See also:
https://www.thingiverse.com/thing:2655181
https://www.thingiverse.com/thing:2668631