hub motor with 12mm axle into a 14mm drop out

Hi!
I have a rear hub motor with 12mm axle.
I'm trying to install that motor on a cargo bike frame (Yuba Mundo) which have drop outs made for 14mm axles.
the frame and motor are made for disc brakes

Is there a specific lock washer I can use in that case to prevent the rotation of the axle?
Is anybody has done that and can share is experience.

thanks!

cheers

Mart

I couldn't find anything, so I made inserts out of aluminum. The fin that sticks out the inside is 2 mm to fill the gap, and they wedge against the frame so they really can't rotate, then the pinch bolts clamp the axle so it can't rotate either.
The screw into the frame mostly keeps them from falling out during wheel changes, since they're wedged against the frame so tightly to stop them moving.


I'm holding one upside down in the last two pics, the fin fits in the bottom in the dropout so the steel frame is directly in contact with the top of the axle to take the pounding loads, the pics are from when I pulled them off at about 2500 miles to inspect them, and they were just like when they got put on.

Proper term is "torque arms"

https://ebikes.ca/product-info/grin-products/torque-arms.html

https://ebikes.ca/shop/electric-bicycle-parts/torque-arms.html

It was a nice upgrade from my original prototype setup, which was some 12mm end wrenches, and a piece of 2mm shim stock shoved into the axle gap on both sides. But that ran for a couple of thousand miles too


And for John, it's not just a regular torque arm that's needed, as the Mundo has oversized dropouts, so it needs to incorporate something to fill in the gap at the axle flats.