I am building a Hypercube. The existing Y idler looked to me to be a very weak part and the belt would put a lot of stress on it. I have redesigned it to make it stronger.

Designed to be bolted to the 2020 using 2 M5x10 screws. Use 2 washers for each bearing group, meaning on the inside and outside of each rectangular bearing holder. Total 4 washers. Use a single M3x40 to secure the bearings. Also I printed at 80% for strength

Source Sketchup 2017 file also included.