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Wednesday, December 3, 2008

Speedometer Returns, Motor Fails. :-(

Eil sent me a PDA (Palm m100) that works spectacularly well for this project, and runs on AAAs as well, which makes worries about recharging it moot. I can just carry a spare set with me (usually did for my helmet-mounted headlamp anyway).

You can see it temporarily zip-tied to the bars (actually, to the cheap multimeter I used to monitor battery power after the LED-bar-meter disintegrated from something (Vibration? Someone messing with it while I was away from it? Dunno.)). The two views I use mostly are the regular Speedometer Dial view, with just speed and odo, and the Data View that has Speed in large numbers, then Average Speed, Acceleration, Total Distance (Odometer), Max Speed, Trip Time, and Trip Distance. If you zoom in you'll see an absurd max speed of 46.9MPH, which was from when I tested the IR function with a remote.

I did not end up using the IR version of the wheel rotation counter, because this unit came with the serial Hotsync cable, which lets me simplify the whole sensor enormously. I just wired a the reed sensor directly to a male 9-pin cable cut off of an old nonfunctional monochrome monitor, per the VeloAce VAIF-1 instructions. Then I plug in the hotsync cable to that, when the PDA is on the bike.

I use FlipHack to rotate the screen, as it's easier to mount the PDA this way. One of the HackMaster variations is used to manage the hacks and make them come back automatically after any reboots. The buttons on the left, when VeloAce is running, will select which view it uses. I don't keep the stylus in the PDA so it can't fall out from vibration. Don't really need it for this purpose, anyway.

So now I have a great new way to see how fast I am going, not only to make sure I don't go over 20MPH with the motor engaged while on city streets/etc., but also because I am curious about the acceleration and average speeds, as well as to just test flat out how fast the thing can go on motors alone, now that the batteries are dying (compared to how it was when I started). But the day before I set the bike back up for using it, the top motor actually sheared it's shaft, inside the casing, just between the motor section and the bearing, so the roller end of the shaft did not fall off (and did not appear to have a problem, except that the roller didn't spin even though the motor was spinning).

The motor is probably not repairable, unless I can push the shaft out and replace it with another steel rod that's hard enough to bear the load. When I looked at the shaft's break, it appears to have had a crack in it along the slits they cut in it to insert the C-clip (jesus-clip) on the shaft to hold it between the bearings. That could have been there when it was made, or it could have happened from the side-loading placed on it by the roller against the wheel, which was not always even, such as when the tire goes over a bump and slightly expands the rest of the tire a tiny bit.

This is just some pics of the rest of the motor inside:

It's a little different than I imagined, as the magnets are to the sides of the coils (which are cast in some plastic) rather than circumferentially around them. It's a four-brush motor, with 20 coils. There do not appear to be any iron (or other) cores on the coils, which means the motor is not as efficient (or heavy) as it could be. Still, there's a surprising amount of torque for the small size at higher-than-rated voltages, and no damage to the brushes, coils, or contacts has occured from the tripled-voltage power levels I've been using all summer, and the very heavy loads placed on them.

The only problem they've had was the broken shaft, which doesn't appear to be related to the power so much as the side-loading pressure from the roller on the wheel. Pretty good for a radiator fan motor abused repurposed as a tire motor. :-)

Anyhow, it failed on the way home from work, and since the motors were wired in parallel, I got no torque on the working motor, because there was less resistance for the power to flow thru the broken motor. I had to cut a wire to the broken motor to continue home (just a moment's work, but annoying). When I got home I took that motor off and found that broken shaft after disassembling it. I just left it off the bike after that, and used the one motor left for a few days.

Since the batteries are so worn out, they're not really giving enough power for enough time to make it even worth having them on the bike at all, so day before yesterday, I decided to just remove the whole thing for now. I needed to do this anyway to add my new cargo pods, more of which there will be in the next post.

FWIW, the max speed on the single motor alone with no pedalling was about 8MPH. I could easily maintain about 15-17MPH even with just the one motor with generous but not hard pedalling. The real advantage is in accelleration, however, in that I can get to a start speed a lot easier with the motor than without it. The max speed pedalling with the motor, after the first third of my trip to work, was about 20.1MPH, and that left me straining, and the batteries more depleted than typically.

Now that the motor is off, the best I can do pedalling without straining my knees is about 11MPH, and it's more comfortable around 9.5MPH, regardless of what gear I'm in. Starting up from a standstill is harder, and I generally have to make sure I shift down to at least the lowest rear gear (of 7) and the middle front gear (of 3). If I don't, it hurts during startup, until I get to about 5MPH or so. Worse in higher gears, of course.

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