Pulley Electric Bicycle Conversion

After quite a few revisions, the design for the pulley was set to disk brake mounts as shown above. Initially the design was spoke based but it seemed like a precarious way to put power into the wheel. When the spokes on my old wheel broke (not from the motor) I ended up ordering a wheel that has disk brake mounts on the hub so we could design the pulley like this.

The pulley teeth were generated using an online pully generator which allowed us to generate a pulley with a HTD 5mm pitch. Meaning belts and smaller keyed pulleys for the motor were widely available in this standard. 

The larger pulley is printed in PTEG with multiple walls to make sure it can withstand the force from propelling the bike.

After burning both a Turnigy SK8 and a Flipsky 4.12 under virtually no load (I wouldn't recommend them though maybe defective?) I finally settled on a MakerX HI100 which is a higher quality ESC. All of these controllers are VESC based. I really like the VESC software as it's really easy to work with and is open source. Plus we were also able to get motor control via UART with an Arduino to work to implement a pedal assist feature. 

I used the same process to set up the MakerX as the previous two controllers which confirms they were probably bad controllers, I followed all instructions given by the manufactures for both ESCs that burnt.

Another upside of using this controller is knowing that it is running well below it's limits (1000w continuous) meaning it shouldn't burn out if even I'm pinning the throttle on a hot day.

Mounting the motor was a challenge since the frame geometry is complicated and hard to model (odd angles and irregular ovals).  The idea is to use clamps with old cut up inner tubes inside to provide an even and strong grasp on the irregular frame shape.

The left photo was an earlier version with weaker tensioners and a slightly misaligned pulley. After a few revisions the setup on the right worked well.

There is some slack in the belt in that video that was fixed with a slightly shorter belt.

Here's the bike working:

As you can see in the video the electrical system is pretty simple. There's a breaker switch and an XT90 anti-spark wire key to turn on and off the bike by interrupting the battery power. Then it's just a battery, controller, motor like any other PEV. I like that I can take the wire key with me and it disables the electrical system which makes the bike slightly more annoying to steal.

The breaker switch is needed since the bike is powered from two lithium polymer batteries with no BMS. In the event of a short circuit the battery has no built in overcurrent/short protection so the breaker switch provides that resettable safety with reasonable efficiency/price.

The motor could definitely use more gearing down however there isn't really any space for a larger pulley since it would hit the frame of the bicycle. Though in it's current state it is able to go from a stop under it's own power and push the bike over 20mph.

All in all this is a great around town small PEV. There are a few items that would be nice to haves for this bike that I might add in the future: 

• Cable guard for motor/hall wires

• Guard around spinning motor (holes were provisioned for this)

• Dedicated hole in saddle bag with waterproofing

• Brake lights/headlights