Hacky Racers – Rear Axle

There are many choices for the rear axle. On our scratch-build we used a solid (no diff) axle, chain-driven, with ‘sack-truck’ wheels driven by splines. Here are some details

Axle Tube

We used a heavy-walled 7/8″ steel tube as the axle.

Axle Bearings

Pressed-steel pillow-blocks are cheap, easy to fit, and easy to align. We found that – eventually – we had to tack-weld the axle to the bearings, otherwise it would move sideways during races.

Driving the Wheels

Our 250mm ‘sack truck’ wheels have plastic spokes. We strengthened the wheels with epoxy filling to prevent the spokes tearing out, and we drove the wheels with tangs welded onto the axle which engage into the spokes. We also cleaned the beads and the rims with acetone and inflated to 30psi, to prevent the driven hubs spinning inside the tyres. We also drilled-out the hubs to match the axle.

Driving the Axle

We welded a 60-tooth chain sprocket onto a tube (which just fits over the axle). When we were happy with the fit and had sorted any run-out, we slid that onto the axle. This allowed us to leave the final welds – to fix the tube to the axle – until after later aligning the motor and chain correctly. See also Braking.


To hold the wheels in place, we welded M10 flange nuts (inverted) inside the ends of the axles. M10 set-screws and large ‘repair’ washers clamp the wheels tightly against the tangs.