The Briggs & Stratton Etek is the electric motor equivalent of a legendary Pokemon. It is renowned amongst electric vehicle and robot fighting enthusiasts for having high torque capability for its weight. Read more about this breed of motor here.
(image from robot marketplace)
I was lucky to get my paws on a real Etek while in California. It was seized – the shaft would not turn. I took it apart using the boom extension hydraulic cylinder on a big forklift and shimmed the outer casing with soda can shims.
Back in Cambridge, the Etek was attached to the thing pictured below:
…where it worked great for a while, then got exceedingly grindy and difficult to turn.
So I popped it open
The commutator-side of the rotor was touching the stator, so I inserted some shims punched with a sharpened piece of tubing.
Before zipping everything back up, I noticed that the rotor was dished. In the picture below it bends upward slightly:
Furthermore, the act of reinstalling the (iron and copper) rotor into the magnetized motor housing was enough to deform the rotor until it touched the magnets. A bad case of a flaccid rotor.
1 – Unbend the rotor and check with a straight edge
2. bathe it in high temperature epoxy
degassing shown below
3. Cure the gelled epoxy in a toaster
4. remove the extra epoxy
5. resurface the commutator
6. profit. The Etek rotor is happily stiffened and no longer suffers from the grindies.