Proof that everything works:
I started yesterday trying to make a throttle. I could have used one of those handlebar hall effect throttles, like what’s on picoFahrrad, but the steering wheel on this one would make mounting such a throttle messy. Also, its just nice to make things yourself.
I dug through some bins of spare parts and found a constant force spring and a linear pot. I would use the spring as the basis of a mechanical spring return slide, and simple couple the pot to it. My first idea was to just use two pins that slide in the slots of the aluminum channel. It worked a few times, but then the rod dug in slightly in some parts of the slot, and it was over. It just took too much force to slide, and often got stuck.
The next idea was a little bulkier, but much less likely to have a sticking problem. It used 2 ball bearings that ride on the inside of a square tube. Also, I decided to reduce the spring force by cutting the spring in half. Don’t ever resort to this unless you absolutely have to. It takes a long time, you have to deburr everything, and who knows what awful un-tempering things you do to the spring.
Next came the battery packs, which Charles was nice enough to pretty much build for me. The kart runs off of two 4s6P for a total of 8S6P. With these LiFe cells, that’s a nominal 26V and 13.8Ah. Safe to say, this will have a much longer run time than picofahrrad.
Its nice to pad the cells with something, and I knew this would be important for me, because right now, the rider pretty much rests their feet on the packs. We were out of foam, so the leg of an old wetsuit did the job. Finally, everything was wrapped in extra wide Kapton tape.
Next I installed sensors on the motor. A while ago, Charles made this nifty ring that just presses gently onto the motor stator, and has slots that hold digital hall sensors.
The sensor ring is aligned initially by aligning the middle sensor with a space between two stator teeth. The idea behind this was explored a bit in my recent hubmotor build. The positioning of this ring is really quite sensitive. We found it extremely hard to adjust it finely enough so that the motor would run without skipping through the entire throttle range.
I am using a Kelly Controller KBS36051,20A,24-36V, so it has a reverse switch, and can take the analog input from the slide pot.
I would have placed the sensors on the other side of the motor, closer to the controller so that the wires are shorter (less noise), but the seat post is in the way.