Chalo
100 TW
This is a bike I built over the course of about a year for a friend of mine. He badly injured his leg, and his capabilities after recovery were uncertain. So I put together a bike with a few different requirements that what I've done before.
1) I wanted him to be able to set his feet down securely on the ground, from a seated position, while also having full leg extension for pedaling.
2) For simplicity, I wanted to give him a single gear that would be low enough to work without motor help, but high enough to pedal along meaningfully with the motor.
3) The bike needed enough power to climb any necessary hill without contribution at the pedals.
4) Target cruising speed was 18-20mph.
5) As much as possible, the build was to be undertaken using parts and materials I already had available, or that I could salvage or buy very cheaply.
Of the few motors I had in my possession, the best candidate was a BMC geared rear hub motor laced into a 700C wheel, with a 48V 50A controller. When I tested it, the motor demonstrated 700rpm on a 13S lithium ion battery-- which was way too fast for the application. So I went looking for a workable 24V controller, and I found one on eBay from Unite Motor that was rated 24V 25A.
I had a difficult time finding a 24V e-bike battery that was rated to deliver 25A continuously. One of my other bandmates took up a collection of about $300, so I found a 24V 10Ah bottle pack offered for $170 including shipping. She made the seller an offer of $300 for two batteries, and the seller accepted. I made a 10ga Y harness to join the two packs in parallel.
I selected from among my bikes a Dyno Glide Deluxe, which had very long 21 inch chainstays and slack frame angles, both of which worked in favor of feet-forward layout. While I was disassembling and prepping the frame for conversion, a previously unrecognized crack in the seat tube, right above the top tube, parted completely and broke off. So I made the decision to mount the new seat with an expander wedge, like a stem quill, so I wouldn't have to reattach the severed part of the frame.
The kickstand mount of the frame was also cracked, so I welded it back in place.
The forks I had used previously were a poor match to the bike's relaxed head angle, and gave the bike excessive steering trail and a tendency to flop the wheel to the side at low speeds. So I found a triple clamp fork that was left over from a pedicab project, which had much greater offset to complement the frame's slack head angle.
I made a subframe to mount a seatpost 7 inches rearward from the original location, with welded bosses to attach the battery rails, and another boss to attach support struts at the rear. One of the struts received crossbars to attach the controller.
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The new rear-set seating position meant that the handlebars were too far from the seat, so I got bars with more rearward sweep and I reversed the (very short) stem to extend rearward.
I unlaced the 700C hub motor wheel and relaced it into a wide 24" rim I salvaged from the junk pile at the bike shop. The rim came with a 24 x 3" street tire that was appropriate for the job. The front wheel was a 26" salvaged item that came with a disc rotor.
For the rear brake, I used an extra-long reach rear caliper from my treasure hoard. It was designed to do what I wanted to do-- adapt 24" wheels to a 26" cruiser frame. Unfortunately, with the addition of good Kool Stop pads, applying the brakes in earnest caused them to bend forward. So I made angle aluminum stops to mimic those used on stamped sheet metal brakes from horrible old American department store bikes.
That successfully addressed the brake flex, but braking power was unimpressive. So I decided to upgrade the brake's stiffness and mechanical advantage by lowering it with a drop bolt. This moved the brake closer to the tire by 18mm to shorten its length from pivot to pads.
Since there was a disc brake mount on the fork and a disc rotor already on the front wheel, I bought a very cheap ($22 full retail) disc caliper to provide front braking. Surprisingly, it's more than adequate.
The bike's top speed on flat ground with a mostly charged battery is 24mph. A little faster than I had in mind, but thoroughly acceptable. It handles great, tracking better with hands off the bars than anything I've ridden lately. My friend loves it and is already using it to commute to work.
The farthest he's gone on it at one time is 17 miles, after which it charged back up in about two hours. Since they're 10Ah batteries and 2A chargers, that suggests a range of over 40 miles.
although the long wheelbase makes the front of the nice well behaved, and the fat tire on the back helps with the back bumps, no?
