Scavenging the Headset

A number of components on my future trike, such as the forks, headset, handle bars, etc, which are conveniently available at low cost in the form of a second hand BMX. After scouring forums and online auction sites for several days I stumbled across the perfect donor.

The donor bike before I got my hands on it.

The donor bike before I got my hands on it.

At the reasonable price of $30, the front end of this “BMX” would make a brilliant start. It even has stunt pegs on the front wheel that I can use as foot pegs!

Once I had the bike home I began ripping into it. The first thing to do was remove all the components which I planned on keeping, but were currently getting in the way, namely the fork, front wheel, and handle bars. I’ve grown up on bikes my entire life, a push bike was my sole form of transport until I was well into my 20’s, however I’d never owned a BMX before, so some things took me a little longer to figure out than they perhaps should have. It turns out there’s no way to remove the fork from the headset without first removing the crimp on the front break cable and pulling it through part of the sheath.

With the fork and handle bar removed, I attacked the frame. I planned to remove the headset and head tube, leaving the two intact but was a little worried the heat of the cutoff disk (way faster than a hacksaw) would ignite the paint, so I used a wire brush drill attachment to remove the paint from around the head tube first. Finally it was time to do irreparable damage to the bike, so I grabbed the angle grinder, and the cutoff disk and set to work. About now is when I thought to start taking photos, unfortunately this was after I’d removed the head tube.

The frame with the recently removed head tube

The frame with the recently removed head tube

Showing how I held the head tube while doing the bulk of the grinding

Showing how I held the head tube while doing the bulk of the grinding

A close up of the head tube after initial grinding before I cleaned it up

A close up of the head tube after initial grinding before I cleaned it up

Showing how the head tube was held for the final cleanup and polish

Showing how the head tube was held for the final cleanup and polish

The end result.

The end result.

That’s the extent of the physical build so far. I’ve decided that building my own motor controller is the way forward from an electronics point of view. While I’ve designed and built 3ph motor controllers before, they were on the order of 100W, 3kW is going to pose some interesting challenges. Why am I building my own controller you ask? I’d originally planned on using a cheap Chinese motor controller from a model aircraft, however these don’t like high torque startups. They’re designed for running props, which provide almost no torque at low speeds and typically have no current limit, so will spontaneously explode if you try doing anything too mean to them. While there are reasonably priced controllers available for vehicle use which over come these limitations, they normally assume a much higher phase inductance and resistance. Also, as reasonably priced as they may be, they still aren’t cheap. Finally, I love a challenge, and enjoy pushing my abilities, so here’s hoping I can manage that without too many lost FETs (especially since some of them approach $20 each and I need a dozen of them!).

– Mike

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