Ebike week 3 (OK, 4): Mockups

In week 3 I had a tummy ache and spent all evening playing the Terraria 1.4 update.

In week 4: after a lot of CAD-ing and changing my mind and more CAD-ing, I finally settled on a structure for the gearbox I was happy with, that wouldn't take 8 hours to print. The removable belt cover also made mounting the motor easier.

gearbox frame

gearbox frame

I didn't even plan how closely the perspective turned out in these

It's a frame to hold the motor with a support bearing at the end of its shaft to avoid twisting the internal bearing, and a short length of 12mm jackshaft to take the larger belt pulley and mount the final drive sprocket on.

As always, this needed some post processing, which would have been a lot easier had I known about Cura's "support blocker" feature, and some "amendments" because my CAD-addled brain thought half of 32 was 18 and made the holes for the jackshaft bearings too big. Fortunately, I own a 3D printer, the solution to a lot of its own problems.

I used my last bit of filament to make some removable bosses so I could make the bearings reusable in future prints, and give them a thicker piece to press into than the 3mm cross section of the frame wall. I still haven't learned to oversize my holes, though, so some filing was needed to get the bosses to a size where I could press the bearings in (standing on it on one heel, because my vice was all the way out in the shed...)

bearing bosses

Modular design, definitely done on purpose

Having the frame all together, I needed to get the various bits mounted on the jackshaft. This required turning the end down to 8mm, tapping for M8 nuts and ten filing a D flat on it. If I'd thought about it I would have stopped tapping before the end of the M8 section to give an unthreaded bit for the sprocket to rest on, but it seems to sit square so it's OK for testing purposes. The shaft itself is M12 studding, because it's easier to mail order from DIY places than smooth shaft and fits well enough in 12mm bearings.

machined shaft

A test fit on the bike turned up a couple of issues. Firstly, mounting it straight on the bottle cage mounts puts it too close to the cranks, so the right hand pedal hits it on the way around. It'll probably have to mount higher up on a piece of flat bar that can then bolt to the cage mounts.

pedal interference

Secondly, the bottle cage mount points on the bike frame are tilted to the right so the gearbox doesn't mount parallel with the wheel. The eventual mounting solution will have to account for this twist, and ideally have some adjustability to allow fine tuning of the chain line.

Stay tuned for the part where I mangle part of a golf caddy, and possibly even get the sprocket spinning under motor power!

-PKM