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E-Bike Conversion

Reprogamming the Controller

Electronics

Luckily, the stock DC/DC converter has an input range of 36-100v which makes our maximum of 84v completely in range (middle/2nd photo). That supplies the 12v for the accessories,  so we only need 48v for the display. Since a step down converter from the battery voltage to 48v is much more expensive than a step up from 12v to 48v I used the latter. The display isn't using a large amount of power so we aren't too worried about efficiency here and it's much less than the rated output of 70 Watts from the step up.

The 12v step down has an ENABLE input which has the same input voltage as VIN from the data sheet. So we can use a switch there as an on/off for our 12v system since we no longer can use the enable from the display. That requires the 48v input which requires the 12v from the DC/DC which requires the enable, which means nothing will happen.

The schematic on the left is an updated version of the one on the wiki for CAKE bikes which you can see here. (Click on wiring schematic on the menu or scroll down)

Fit and Finish

After getting all the parts for my system, I wired everything up and made sure that it worked.  I was a little nervous since I had no way to verify everything was working when I purchased the bike, but everything worked fine as seen in the video. So the next step is to fit everything into the bike and ride away into the sunset. 

On the right is the battery in the bike initially, I will go into the battery box and it's creation after the controller box.

Initially I had crudely mounted the components by drilling into the controller box and cutting out a slot for the wires. It worked but I needed a more permanent solution.
So, I used a Creality Ferret 3D Scanner to scan the complex shape of the controller box and model around it as seen in the GIF on the left (first). In my version I changed the position of the step down converter, added mounting holes for the step up converter and on/off switch. I also made the box taller since my wiring took up a bit more space than the stock wiring and I didn't want anything to be under stress inside the box. 

 The bike was now fully working, however the battery badly needed an enclosure. So, I modeled a box in CAD based on measurements of the battery and then 3D scanned the battery to triple check everything would fit. The outer dimensions of the box were also taken into account of course. I also 3D printed some test parts to make sure the lid would fit the XT-60 connector (charge port) and Bluetooth BMS module. I put the BT module in a plastic box since it is Low-Energy BT and the signal is easily dampened by the metal walls of the battery box.

I created some technical drawings for the box and sent it over to PCBWay to get it manufactured it using sheet metal and welding. Everything fit as intended and the final product is shown in the rightmost (last) photo.

After finishing the electronics and riding the bike around in the summer, the motor started overheating. This happened since I was outputting way more power to the motor than the stock bike.  From the real-time heat sensor stats in the Kilowatt app I could see the motor was constantly at the temperature limit to reduce power (80 C). This leads to the bike feeling sluggish and slow and causes extra wear on the motor.  I did some research and decided the easiest way to cool it down would be to open it up and put in Statorade by Grin Technologies. Statorade is a ferro fluid which sticks to the magnets on the outside of the motor, bridging the air gap (gap seen in leftmost photo). This allows the heat which is generated in the coils of the motor to dissipate much faster since the ferrofluid conducts heat better than air. Grin has a video explaining the idea here.
Opening the motor was quite a pain which involved a heat gun, a bunch of hammering and a very large screwdriver. I closed it up with some silicon sealant and have not had any heat related issues with the motor since. 

Its all finished! Time to ride off into the sunset.
Big thanks to the CAKE Riders community on discord whose information aided this project.