Well, I’ve fixed the caster problem after a bit of detective work.
A few of you wrote to ask if the 3″ casters were touching the side of the foot shell, they weren’t but clearance is tight.
To simplify troubleshooting I took the center ankle/foot assemble off Artoo and was able to duplicate the locking wheel on the workbench. It even did it with the foot shell removed.
Turns out it was as simple as some crud in the casters bearing. They’d been siting in my workshop for quite some time, so who knows what had gotten in there. And no matter how careful I was, there’s a good chance I got something in there while I was trimming the caster base plate.
The symptom was when the caster did a quick turn it would freeze and drag, slow turns were fine – but anything rapid would cause the lock.
I got some degreaser and soaked the bearing. I then blasted it with air to try and knock out whatever was causing the problem. Once I was happy the bearing was turning fine I re-applied some bearing grease using a small syringe.
And here’s a short video demonstrating the new casters in action
Only time will tell if the new wheel casters perform better in the field compared to the ominballs.