Ebike week 2: Drive

A slightly less productive week this week, as I'm limited in what I have the ability to make. I did some more CAD modelling and took measurements of the bike frame to try to figure out how the entire drive unit is going to fit in the 12cm space between the cranks, and had a go at making an adapter to mount the sprocket to the back wheel.

mo cad

The back wheel hub has a small tapered section on the left hand side which I figured I could use to locate a hub on, and mount the sprocket to that using its preexisting bolt holes. The hub could then be fixed to the wheel with zip ties around enough spokes to hold it reasonably securely and let it transfer torque. I'm not imagining this as a long term solution, just a test setup.

hub

hub and sprocket on wheel

From my mockup and measurements it looks like everything can just about squeeze into the space, but it's going to be very tight.

I'm probably going to have to mount the motor/reduction/jackshaft stuff on the seat tube, with a combination of the water bottle cage mounting screws and a clamp at the top end. I'm still not quite sure how well it will resist torque from the chain turning it leftwards - possibly torque arms to the seat stays will be needed. Now the sprocket is on the wheel and I should have some 12mm studding turning up as a standin jackshaft, the next job will be mocking up a 3d printed mount for all the motor gubbins to see if it can actually fit. Good thing my 2kg of PLA turned up!

-PKM