· By Chimera BMX

2020 - Prototyping the Electric BMX at 42v w/ freewheel cranks

Just a moment ago Austin's Google Photos reminded him that on this day in 2020, he was tinkering with the first iteration of the Chimera Electric BMX prototype on his living room table. Specifically, he was trying out a 100 amp Castle Controller.

At that time, the bike that we now call the "V1" was a little lighter, but a lot clunkier. Austin hadn't yet received the prototype parts for our High-Drive clutch mechanism, which allows the motor to spin the back wheel without also spinning the chainwheel. Instead, he had to make use of trials-bike cranks with a modified White Industries freewheel, and a chunky cog from Misumi. Here are a few photos: 

Chimera Electric BMX V1 during prototype phase 2020

Chimera Electric BMX prototype phase 2020

Chimera Electric BMX half-finished High-Drive mechanism 2020

Chimera Electric BMX V1 during product development 2020

The bike was a lot more dangerous to ride at this time. For one, whenever the motor spun, the large chainwheel would also spin right next to the rider's leg. As any mid-drive owner can attest, this runs the danger of pant-legs being eaten. Also, Austin hadn't yet installed rear brakes, and the front brakes were mechanical rather than hydraulic. So the bike didn't stop very quickly.

Keen observers will also notice that the bike had a smaller battery pack. It's a 44v 12s pack out of Molicel P42a in an end-to-end arrangement. This pack still runs! This is impressive considering how much we abused it. But the pack wasn't the right fit. In order to achieve the desired 35+mph top speed, we had to use a lot more field weakening. When we would hit steep hills at top speed, the field weakening would generate an amount of heat in both the motor and the battery pack that was a little too close to the limit. The heat limit never actually got exceeded. But a steeper hill or a rider heavier than Austin would have been able to overheat the system. That's one of the reasons we went with the higher 52v packs we use now.

Still, the bike was a blast to ride. It was only 33lbs due to the lack of rear brakes and the smaller battery pack. And the freewheel at the crank made an additional whizzing sound that turned heads whenever Austin would blast through neighborhoods. 

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