Here are some things I did to finish up the bike. I will continue to add to this page anytime I make an improvement to the bike.
I disassembled the frame, batteries, and controller and spray painted them in military green and black.
I had many windy days to contend with, so I put up a wind screen in a bamboo hollow so I could finish the job.
I only painted the sides of the batteries and the parts of the aluminum that would show. This was just for looks; the aluminum would not have corroded.
The finished job looked pretty good, although there were places where the paint ripped off during reassembly. I probably should have prepped the surface better and let it dry for weeks, not days.
I decided to install a large cover over the terminals of the lower battery stack, which is more exposed to rain, fingers, tools, and while riding, the left leg. I got a piece of clear acrylic from Home Depot and broke a lot of it in the process of cutting, drilling, and bending. The jigsaw worked better than the scoring tool. Drilling was precarious and required much practice, using every size bit up to the largest required. I used a heat gun for the bending.
But in the end I had a piece which fit nicely to the bolts on the left side of the lower stack. I also marked, removed, and drilled small holes into the piece, so I can insert the probes of my voltmeter to check cell voltages.
It has been working well on the motorcycle, with no vibrating or cracking.
I designed the sprocket/chain guard in Sketchup (free version) with the Solid Inspector, Shape Bender, and Sketchup STL plugins loaded. I measured the area of the sprocket in order to get the dimensions right, using the motor diagram to get the precise dimensions of the four unused threaded holes (the smaller holes which were not already used for mounting the motor.
Sketchup was harder than I expected. I had to view some tutorials and practice basic techniques. And when I thought I was nearly finished I discovered I had to start all over again due to some non-manifold (non-watertight) seams. They looked OK but when inspected closely it was going to be harder to repair than to rebuild.
So I got in the habit of building a few steps at a time, checking often with the Solid Inspector function. I also periodically uploaded the design to Shapeways to verify that it could be 3D printed. It worked.
I also drew it at 1000x actual size (using meters scale instead of mm) and scaled it by 0.001 before exporting with the ‘Export STL’ function.
In the end it looked like this:
I uploaded it to Shapeways and ordered it in “Black Strong and Flexible Plastic.” It looked decent when it arrived.
I was impressed that even the sharp angles (the raised plastic that forms the letters W, M, and N) which Shapeways identified as risky had come out fine.
However, when I checked the fit it was clear that the outer part of the extended chain guard was interfering with the frame. I trimmed it using an angle grinder, round hand file and sandpaper. The grinding revealed white plastic immediately under the black surface so I had to paint it. I painted it using the same black semi-gloss which I used for the batteries. It looked OK but would have been better with a less glossy finish.
I put it in place with the bolts resting in the mounts, and tightened the bolts with an allen wrench. I also used a thin rubber washer between the bolts and the plastic mounts to create a little tension on the bolts without applying much pressure. I didn’t want to risk cracking the plastic.
The picture above is looking downward and shows where I had to trim the guard to make it fit.
In the end it looked pretty good, felt strong, and dressed up the left side of the bike nicely. More importantly, it protected against shoelaces or pantlegs entangling in the sprocket. I test rode it several times and found no striking from the chain, loosening, cracking, or any other problem.
I installed the 14-tooth front sprocket in place of the 13-tooth. My overall impression is that performance did not change as much as I expected, but noise went down more than I expected.
Acceleration is what I was most worried about. The difference was discernable but pretty small. Here is a graph of acceleration:
Efficiency appears to be about the same, but a little better above 50 mph.
I didn’t get an absolute top speed, but I got a little over 72 mph so there is probably not much change there.
I think the biggest change is that it is more pleasant to ride. It is quieter at all speeds. I didn’t expect this, but the decreased chordal effects may explain the perceptible improvement in noise with a small increase in sprocket size.
Also, I like the slow-speed handling more. It is less twitchy at very low speeds, as when doing tight figure-eights.
There was essentially no change in max current or heating of the motor. For commuting, I definitely prefer the larger front sprocket. I may try the 15-tooth just for fun, but I suspect the 14-tooth will be the best all-around.
I installed the 15-tooth sprocket and tested the bike. As expected, the low end acceleration was worse than with the 14-tooth. However, unlike the switch from the 13- to 14-tooth sprocket, the loss of performance was objectionable in my opinion. It just felt like it lost a lot of spirit.
The high end performance was decent, and actually felt and sounded smoother, hitting top speed around 76 mph. However, it drew more current (peaking over 42oA, compared with about 370A with the 14-tooth) during the ride, and overall efficiency was worse.
Clearly I had gone too tall on the gear ratio (3.33). This correlates with the rule of thumb that it is good to stay above 3.5. But I think it’s also good to experiment to find out what works best on your motorcycle.
I reinstalled the 14-tooth sprocket which gives me the best blend of low and high speed characteristics.