Reduce setscrew clearance

We seem to be grinding down the walls of the nut trap when removing the
setscrew.
Use less clearance for motor shaft

Hopefully reduces the amount of stress on thin plastic
Add build system
Render a flattened motor shaft instead of cylindrical one

This takes some of the stress off the joint between the thinner shaft and the
collar. Also allows us to put the nut nearer to the shaft.
Reduce collar wall thickness

It doesn't need to be so far out any more.