I have been working on a cool electronics/motor science/electric bike project this semester and I thought I would share it here as it is quite interesting and amusing. As far as I know few people (if any?) have used IPM motors for their E-bikes, as they are quite difficult to use properly. This project has been a ton of effort and time but it’s been worth it, I’ve learned a lot and now have an extremely powerful electric bike. It has much more than wheelie torque at low speed, but it also has quite a good top speed of nearly 50mph. This project was mostly done to see if I could get good performance out of an IPM motor, but had the side effect of making a pretty cool electric vehicle.
Anyways, here goes.
The Bike of Motor Science: a BMX bike powered by the 4kw IPM motor from a Toyota Prius Air Conditioner Compressor. A work in progress.
The big components:
160v 4Ah from 4x electric leaf blower batteries
Custom built FOC motor controller using FNA25060 brick and STM32F303K8 microcontroller
AS5047P rotor position sensor
Homemade motor module built from a ‘06-’08 Toyota Prius air conditioner compressor rotor and stator and KHK module 1.5 spur gears, good for 4kw continuous and 6kw peak
Haro BMX bike
Basically I bought this from a junkyard:
And rehoused the innards into this:
And attached it to a bike. Additionally I spent many months developing a controller and a firmware to run that controller.
Why go to a junkyard, buy an air conditioner compressor, strip it down, use only the rotor and stator, and build an entire custom housing for specifically this motor? Why specifically an air conditioner compressor motor?
Several reasons I chose the air conditioner compressor motor:
- They can be had at a junkyard for cheap ($75 from my local junkyard)
- They are quite a good amount of motor per dollar (less than $20/Kw)
- They are inrunners, meaning they are easier to cool, easier to mount, easier to seal from dirt, etc, etc. Inrunners are also very power dense. They are not as torque dense as an outrunner, but who cares- that’s what gears are for.
- Motors of this size are not very common- 4kw is bigger than the RC plane market offers (at least cheaply). Possibly some electric bike motors are this powerful but I don’t know the e-bike market that well.
- Lastly, but most importantly, this air conditioner happens to be an interior permanent magnet (IPM) motor.
Additionally IPM motors have great field weakening capabilities, meaning that they, when controlled right, have virtually unlimited top speed. These benefits make them ideal motors for traction applications, where high efficiency is needed at a great range of speeds. IPM motors really deserve more than this several-sentence explanation, so I encourage you to read bayley’s great post about them. http://isopack.blogspot.com/2017/08/fun ... agnet.html
Current performance metrics of this bike:
Easily wheelie torque, probably more by a factor of 20-50% (she wheelies hard)
Currently good torque up to maybe 20mph or so, when torque drops down slowly as speed increases
Max speed ever reached: 49.2 mph (!!!!)
Some more pics:
Hopefully in the coming months I will be making additional upgrades, hopefully further boosting performance. Its the good stuff!
Additionally, you can find some more detail and build logs on my website. http://www.austin-b.com/prius-motorbike ... r-science/