We are using a magnepot absolute encoder from digikey. They have three terminals for soldering that we have found to be robust, and a flat on the shaft so they can’t slip, so they are good for this application.
I agree with your points about the 550, but they are only slightly lighter, and slightly cheaper, and we would have to make a separate order to buy some. We use a ton of 775s, so it was convenient by comparison.
To make getting Into the depot smoother, we cut the ramps seen in the CAD model out of 0.375" aluminum plate. One failed from a hard sideways impact, and several bent their mounting bolts over time.
The wheels held up well over all. We had one need replaced on practice bot. Its flange peeled over because the tread was only attached to the wheel on the ends. (only half the rivet holes were used)
To install tread, we started by making a template out of u channel to drill the holes and cut the tread to length. Then we stretched the tread over the wheel and used 3/16" rivets to mount it.
This was consistently painful because the tread was cut too small, so it was under a lot of tension once installed. It was made more difficult because we put backing washers on the inside of the wheel to spread the load, which were difficult to get into place.
In the future I would probably use slots for square nuts to fit into, and bolt the tread on with 8 32s.
When you right click you should be able to hit export and then use the drop down for STEP. If that’s not working I might need to change the permissions.