A few years back, I had this great idea that I was going to home-brew an electric two-wheeled vehicle from the ground up. This turned out to be a somewhat ill-conceived project, but a great learning experience.
As far as the finished product, I ended up with a not-terribly-rigid frame that wasn’t particularly straight, and an underpowered drivetrain that was excessively complex for what it was. Further, this entire mess was powered by an all-scrap electrical system which had two speeds: on and off
Read on for a full retelling of specifications and lessons learned:
The donor parts for this project were pretty straight forward:
- Two scrap bicycles, a 20″ and a 26″
- Half a weight bench worth of square tubing
- Various SLA Batteries in states of disrepair
- One “pump-duty” 24v motor (donated by Ron)
- A few old bike chains (donated by Jason)
- Various electronics robbed from a dead UPS
My first assault on this project was building the basic frame, starting at the top and front. I determined that I wanted to use the 20″ wheels (Based on what I guesstimated the torque capabilities of the motor to be) because smaller wheels would be able to turn faster, requiring less gearing down. I also realized that the 20″ frame was too small to support all the gear required to make the bike go.
In retrospect, I’d have been better off sticking with a prebuilt frame, as literally my first cut (where I detached the green headset from it’s frame) was flawed enough to screw up handling substantially. Moreover, I had problems getting the “seat” level; This part of the project was quite a bit of work.
Compared to framebuilding, the drivetrain was relatively easy. Making it work properly was less easy. This bike was built in the pre-lathe era (before I got my 7×10″ Mini-lathe), so all the gear boring was done by hand, resulting in some wobbly gears and a lot of difficulties when assembling the chaining. Better gear-building (or just buying the right gears) would go a LONG way.
The motor was actually the shining star of the entire project. It really exceeded all expectations, not to mention all reasonable need for this project. With the tallness of my gearing setup, I was overheating the wiring on a regular basis. I ended up modifying the motor to accept nut-and-bolt wiring connections, and using 6 or 8 gauge wire internally. Even then, a pair of brand new 12ah SLAs were drawn down to just a few volts at locked rotor. I’d now estimate this motor to be in the 2HP range, where I’d initially thought it was more like 500w (.75HP).
While simple and generally a huge hack, the electrical system wasn’t too bad. It consisted of a giant transistor (Rated 200A @ 70V or something), a circuit breaker, and a microswitch. The breaker was a hard-disconnect for the motor, to make for safe testing, and the microswitch was mounted under an old brake lever on the handlebars, giving a “squeeze to go” sort of control. I’d intended to eventually build or buy a better speed control, but that proved premature.
As it turns out, I ended up chopping the bike up during a winter cleanup, and “scratching the electric itch” with a Schwinn S-500 scooter for $30 on Craigslist. It’s a blast to ride, now that it has new batteries.