KR-E Electric Motorcycle

 

After a Kawasaki KR-1 I had damaged (deep scoring) the cylinders I decided to make it into an electric conversion. A key goal I had was subtlety, apart from a few tells, it had to look like a normal bike.

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The specs:
Motor ME0708 brushed permanent magnet, 4.8kw continuous or 15kw for 1 min max.
Batteries 3 38Ah 12V AGM SLA
Controller alltrax AXE4844

It’s set up for 200A max, which is about half what it could do with better batteries. The rev counter has been replaced with an ammeter, and there is also a digital display with energy used and voltage/temps etc. The main electronics are in the tank, which has the bottom cut out of it. With the DC converter under the rider seat, and the charger going under the pillion with a 3 pin plug. The motor is mounted directly to the swingarm to maintain constant chain tension, it drives the wheel through a 14/62 reduction, I machined the 62 tooth sprocket to around 20% of its original weight.

The max speed so far is just over 70kmhr, range is quite low around 10km. One thing you notice real quick is the lack of engine braking (didn’t see enough benefit to pay an extra hundred bucks for a controller with regen), basically every corner feels like one you have clicked it down into neutral instead of first, which is impossible cos it’s got no gears. Which is why it’s got the big e-stop on the tank, if the controller goes awry, the most likely outcome is the bike takes off at full throttle. All in all it’s pretty entertaining to ride.

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It has custom dash with an amp-meter replacing the rev counter; which I did by putting a new decal in it then sending the right frequency signal to move the needle. It also has a simple 2-line display which shows voltage and ahrs used etc. This setup is controlled by an STM32 microcontroller.

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It was not a very complex build in the mechanical sense, with the motor mount and sprocket machining being the only precision jobs. To ensure accuracy of these tasks I drew up the bike in CAD, drawing the whole bike was not required but it was a good learning experience.

I ran the bike to uni and back for a year or two, after which point my commuting habits changed, and the batteries were getting a little tired so I removed them and they are now used as storage batteries. I plan on upgrading this to LiFePO4 type batteries when time and funds allow; which will hopefully get significantly more range, and a few more km in top speed.