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Friday, August 21, 2009

Power Levels and Motors and Noise

I found the battery specs:

Naturally, they don't list any model matching these exactly, as they show an SSP12-18, but these are SSP12-17. Close enough to base any assumptions about it's specs on, though.

On the battery that died in last post's ride, I took a look under the barely-glued-on strip covering the rubber vent caps, and I am going to try adding drops of water into it's cells to see if I can revive it. I mean, I can't hurt it any worse than it already is, right? ;-)

I'm sort of thinking about trying the bike out at 48V, since that (with 4x 12V 17Ah) would have about the same energy density as two of the larger 12V 31Ah U1s as a 24V pack, but should theoretically take a lot less current to get the same torque/speed out of it. That means the batteries would last even longer, because the Peukert effect that causes batteries to supply less total power the faster the power is sucked out of them would apply less.

The motor appears able to handle it, as I don't see any more sparking on the brushes at 36V than 24V when I watch it in the dark, so I will probably test it with one of the motors I've got pulled apart right now (the one that had the grease leak).

I wanted to use that 4pole motor on the bike but so far hadn't found any bolts in my stuff that would fit it, except for carriage bolts, which don't have a shaped head on them to turn, just a round-stud end, and a several-inch-long machine bolt with threads only on the first inch or so, which means if I cut it to make it fit without several inches of washers stacked on it, it won't have any threads. And I only had the two total, and need four--two short, even two inches would be fine, maybe less, plus two longer, perhaps 3 inches.

I found some good short machine bolts that will work for the short end of the 4pole motor mount plate. I'll weld a nut to the head end of a carriage bolt and use that to tighten down the long-bolt end of it. 3 bolts should be able to hold it at least for testing. If I find a second carriage bolt I'll use two. I'm sure I have several just like this one, in a box somewhere. I *really* want to see what this motor can do. :)

I could definitely do this higher voltage stuff with the treadmill motor, and I'm still pondering a drop-in drivetrain and motor plate that would let me put the treadmill motor on in place of the wheelchair motor without modifying that bottom plate any further, and would come off and go on as quickly and easily as the wheelchair motors do (which is one thing I really like about them).

One thing I *don't* like about them is that they're pretty noisy. I fixed a little of that by putting a rubber pad between the motor and the bike frame's mounting plate, but noise is still conducted thru the bolts, and I don't have a long enough set of them to use a pad on the bolt side, too, with fender washers and whatnot to keep things from sliding around against that chain tension. The pad itself came out of an old dead Macintosh Plus, from what looks like an optional harddisk bay I didn't have in mine back when I still had it working, a decade or two ago. At least, I don't remember it.

The treadmill motor by itself is a lot quieter, but I suspect most drivetrains I make for it are going to add significant noise, just because I'm not great at machining the parts and mounts for things, so nothing lines up exactly right.

One problem I have is that none of the crank-mounted chainring sets are perfectly round. The rings might be round but if so they're offset a little from center, so there can be as much as 1/8" or more difference in distance from center to edge from one extreme to the other, which means the chain gets tighter and looser and causes more wear and also more noise. Since the teeth aren't 1:1, it also means that as they rotate around they offset their rotation, so the tighter/looser pattern changes over time.

Not only does this cause noise, but it is going to make my tension-based throttle system impractical until I can fix it. As I watch that spring-loaded throttle arm roll over the chain, it goes up and down by almost 1/3 of it's full travel, with no load on the chain at all except this tighter/looser rotation pattern!

I'm not even sure I *can* fix it, because, for instance, the chainring on the drivetrain input is steel swaged to the aluminum crank/squaretaper socket. If the offset is there, I can do nothing about it. If the offset is due to a bent BB spindle/crankshaft (possible but highly unlikely) I can't fix that either, because I dont' have an extra.

For the front chainring, it's not only offset circumferentially, it's also bent around the entire gainring rim just a little bit here and there, so the edges appear to "wobble", making it rub more on the sides of the chain at some point than others (and possibly one day under the right conditions to even lift the chain off the ring, if the teeth ever catch an edge of the chain). It did not start out this bad, so I think the little bending it already had is being made worse by the very high tension forces on it as I pedal hard during startup from a dead stop without a motor on there. Shouldn't worsen more if that's true, now that I have the motor back on.

What I need to fix that is newer and/or better-made square-taper cranksets with the chainring sets on them. What I would *like* if I could pick and choose is a handful of the *same kind* of crank spiders, plus the chainrings that go on them in a good variation of sizes. Then I could pick and choose my ratios, and they'd be stiff enough to not have to worry about this offset and bending happening, hopefully.

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