Z-axis Belt Drive

12/28/20 Update:
A "Z" travel guide added to bed and idler pulleys removed from the bed. Improved vibration control. The guide uses 1/4" rod. The two printed parts, stl and scad, included. Needs 2020 extrusion and corners. Print bushing at 100% to prevent pinching rod. Picture included showing changes.

No lead screw core xy printer.
My experiment: Having all belt drives, the bed supported by belts.
I built this core xy Mini by MacGyver leaving out the Z-axis parts.
I stayed true to the structure of his Mini, but changed some parts, using ones that I already had.
The slotted motor mounting is great for belt tension.
I am using this printer now and it works as expected, however, reducing speed, like travel, is a big help reducing vibration, which I find is the main problem.

My plan was to create a Z-axis drive using a belt system and if it failed, add the cantilever as a bed support, still using belts.
I found the bed is subject to the vibration of the xy movement because o