Last modified: 2025-07-04 08:46:35
< 2025-06-30 2025-07-04 >Some good progress here. The axle bearings are mounted, sprocket hub is mounted, chain and motor are mounted:
There is an M6 threaded hole through the axle, that is what the sprocket hub mounts to. So the M6 bolt is taking all of the load from the motor, but the motor isn't very powerful so I think it's fine. If it ever breaks I can weld the sprocket hub to the axle.
ChatGPT reckons an M6 bolt through a 20mm steel axle will probably break if I put 135 Nm of torque through it. Also reckons that if the motor tops out at 8 mph using 350 W, then there is 19 Nm of torque at the axle, so plenty of safety margin. Unsure how accurate that is though. If it ever breaks I can weld the sprocket hub to the axle.
I then wired up all the electronics:
And it drives! ...backwards.
This may be a major blunder because the motor may be more powerful in one direction than the other, unsure. The plan is to come up with some sort of reversing switch (just a DPDT switch, I think fine to carry the motor current without switching a relay, it's about 10 amps, if it fails I can add a relay).
And then I can move on to making the "steering tower" thing, and then think about foot plates, a seat, bodywork, and a brake. And then we're done?
It very much feels like it doesn't want to steer. This may be an issue. Will find out when I can actually drive it for the first time.
Next I tried to do the cross-drilling on the steering gearbox input shaft:
I did manage, as you can see, but drilling through the pinion was very difficult. It was hardened. I blunted 2 drills and broke a third. I managed to do it eventually by annealing it with the blowtorch (though it is still very hard) and starting the hole with a grinding tool with the Dremel.
So next things are:
Steering box is back in, I also drilled out the flats from one of the rear wheels so that it will be able to slip on the axle, and it steers much better now, great success.
For the reversing switch I think I want a large-ish, maybe waterproof, momentary DPDT push button. So you hold it down to reverse and let go to go forwards. Or do I want it non-momentary and with a big lever on it so it feels more like a shift lever? Maybe keep it simple.
I tried to drive it and found that it doesn't have enough torque to get me up the slope of the driveway! Which is very very minor!
Chatting to ChatGPT I realised that in 2025-06-13 I used the diameter of the wheel as if it were a circumference, in calculating how much gearing I need. I actually need a further 3.14:1 reduction! D'oh!
So it has 3x less torque than intended, and would have 3x the expected top speed.
So now what? Probably it needs another stage of reduction. Very annoying.
< 2025-06-30 2025-07-04 >