Prius Motorbike Part 6: Attaching Everything!

With the housing machined, it was time to attach everything to the bike!

First up was to figure out how to transmit the torque to the wheel. I really wanted to avoid welding to the hub, as I was afraid of warping the hub bearing races. To solve this I simply connected to the rim instead. I waterjet out a big piece of aluminum which connected to the rim with a bunch of bent tabs. Each of the eight tabs had an alignment feature to a spoke and two holes for socket head cap screws. This worked pretty well but didn’t turn out quite as concentric as I’d hoped, was non-concentric to about a millimeter. Close enough.

Drilling the holes to actually attach this was funny. I wanted to drill from the inside to ensure that the holes lined up, so I made an uber drill bit extender from aluminum rod. I drilled a hole with the drill bit on the lathe and slotted it with the bandsaw. I clamped all that with a shaft collar. However this was too big (shaft collar wouldn’t fit in between the spokes) so I switched to superglue in the end. To get the drill bit out I heated the whole thing to really hot with a blowtorch and the superglue lit on fire and the drill bit came right out.

Now time to attach the motor.

Mason helped me do some MIG welding to attach the motor. I also waterjet a big sprocket.

I installed the chain and the sprockets, as well as the bike hub board and a thumb throttle (decided to ditch the brake position sensor). After that it was time to duct tape on the inverter and a dodgy 50V lipo and give it a whirl!

I encountered two problems: 1) the inverter would not turn on on my under-charged 3s lipo, solved with a quick charge, and 2), position sensor noise, which was solved by squeezing the position sensor wires. After that it rode like a dream.

First drive parameters:

  • 50v dodgy lipo for main pack
  • 30 amps d, 15 amps q, scaled linearly with throttle position

First drive thoughts:

  • On 50V, performance was good, but unfortunately poorer than expected. Base speed was only about 6-8 mph, which means that the 160V I was planning on running will only bring base speed to about 20. A full 200V will bring base speed up to 25 or 30 or so. I am not sure why this is, but it could be that I need some sort of phase offset or something to compensate for increasing speed.
  • Torque seemed to drop off incredibly fast after base speed- although this is probably because I am not using a real lookup table (oops). Real lookup table coming soon!
  • Once the throttle locked on at 10% speed- probably because it is a sketchy chinese thumb throttle. Must buy new one.
  • Really need to make a differential amplifier for the position sensor wires.

With that said it was time to attach more batteries. Bayley gave me four 10s2p drill batteries, for a total of about 150v nominal. I also found a smaller 10s 1p battery which I can put in series for speed runs at 185v (full 200 when charged!!).

I rode around for a bit on two drill batteries, and rode it home on three.

Although torque is still a lacking at high speeds, this thing is really, really, really good. 120v really makes it quite a nice ride. Its quieter than expected, the noisiest part is definitely the chain rather than the spur gears.


Second drive parameters:

  • 3x 40v 10s2p 18650 drill batteries for main pack
  • 30 amps d, 15 amps q, scaled linearly with throttle position

Second drive thoughts:

  • Holy crap this thing is good.
  • Holy crap this thing is really good. I drove it hope but didn’t want to stop so I went up and down the esplanade at 20-30mph at 3am with no headlights.
  • The inverter may not be rated for enough d current to run field weakening properly. The limiting factor is actually the shunts right now- I used 2 milliohm shunts, which generate 0.08 volts at 40 amps. This is amplified by 20 by the shunt amplifier, which gives 1.6 volts. Because the shunts are bidirectional this is actually 3.2 volts, almost at the full 3.3v of the ADC. The fix here will probably be to just use 1.5 or 1 milliohm shunts.
  • I need real footpegs. Using the front wheel pegs as footpegs is acceptable but I’m sure looks a bit weird.
  • I also need a real motor protector. Right now the position sensor wires and phase wires stick out the end of the motor, meaning that if I were to lay the bike over they would be shredded, along with part of the inverter (!not good as 200v shorts into your leg!) so yeah.

I passed some aggressive bikers on the way back to MITERS the next morning which is always a fun time. At MITERS I charged all the batteries to precisely 40.5 volts and series’ed all four for the full 160v. Man it rips.

Next up was the attachment of a motor protection thing:

I’ve been on a few more drives since this and man this vehicle is epic.

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