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Sunday, April 12, 2009

Absolute Power...

Today was a nice surprise: one of the anonymous commenters on this blog brought over a much needed power source: two used U1 deep cycle batteries and a charger for them.

The batteries didn't have nuts on the bolts, but the very first nuts I pulled out of a bag of salvaged ones from some closed-down store's trashed fixtures fit them. I suppose it was a lucky night, and some other disaster will befall me later to make up for it. Or perhaps this luck is making up for the disaster that has damaged my lighting battery. (Or possibly the lighting battery damage was pre-payment for this luck?)

Along with that was a powerchair wheel (for it's hub plate) and matching 24V/3.6A motor with right-angle gearbox.

At first I was more excited about the batteries, but the motor with right-angle gearbox could make adding the motor to this (or any) bike much simpler than with the treadmill motor I already have. The treadmill motor requires some sort of external reduction from speed to torque, which I had planned on by 3:1 belt reduction followed by 10:1 chain reduction. The first-stage belt would be quieter than chain at the moderately-high speeds the treadmill motor would run at for 24 to 36 volts, but would suffer power loss from stretching, loss of friction when wet, etc. Having two stages meant I didn't need as big a receiver chainring, or as long/heavy a chain, etc.

However, with the gearbox ready to reduce the speed to torque already on the new motor, I don't need any of that--just a small receiver chainring on the drivetrain input that's the same size as the one to be placed on the motor itself, if I need 1:1 transfer (probably).

Additionally, a right-angle gearbox (not really possible using belts or chains) means the longish motor can go parallel to the bike frame, instead of transverse to it, and it won't be sticking out the side like the treadmill motor has to.

Even better, the gearbox has a place to clamp it to the powerchair frame tubing, and that will let me clamp directly to the bike's frame tubing, either top or down tube just below the seat. It appears that it might even align the chainring-bearing axle hub close enough to the plane of the receiver chainring, when mounted that way, to work perfectly. Additionally, clamping to the tubing in this manner will allow simply moving it forward or backward along the tubing to adjust the chain tension.

Now, there *is* one problem: With the treadmill motor I had a freewheel setup in the pulley-to-chain transfer axle, so that pedalling wouldn't drive the motor, if the motor was unpowered for any reason. Since that device won't be in the drivetrain for this new motor, any pedalling will be transferred not only to the drivetrain, but also back into the motor's gearbox.

Since the new motor appears from the sound it makes while running to use a worm gear to drive the gearbox, it would be physically impossible to drive it when unpowered, but fortunately being from a powerchair it's designers already thought of that, and provided a clutch lever on the gearbox to allow the motor itself to be disengaged from the gearing. Unfortunately even disenganged the gearing has significant friction in it for reasons I haven't yet opened the gearbox to determine, which hopefully is a fixable problem rather than part of it's design, but I suspect the latter is actually true.

If so, then to pedal any significant amount without power for the motor, I'll need to loosen the tension and remove the chain to the motor, until I can insert an actual freewheel into this drivetrain, which will probably have to be done at the receiver end, where the rear crankshaft has been adapted to transfer power from both pedal chain and motor chain into the actual gearshifting drivetrain. I already have a freewheel there, but it is non-functional (was broken when I got it; the palls are damaged and won't latch) and will have to be replaced with a functional one as soon as I can get it off of the wheel it's on. I would also like to replace the freewheel that failed that I have on the pedal chain (to prevent the motor from driving the pedals) at some point, but I only have one working freewheel that will fit and do this job (one of the built-in chainring styles used on fixed-gear bikes).

Either way, to operate the clutch I can either setup a cable linkage to an ex-shifter lever on the handlebars, or I can just reach down and manually turn it when I am stuck without power (which is bound to happen sooner or later). The latter is simpler and lighter, and almost certainly what I'll go with.

The charger's separate external plate has a regular computer-type AC input jack, and (not connected to anything) a 25-amp push-to-reset thermal breaker, as well as a 6-amp-scale analog magnetic-deflection current meter.

That meter could be used to monitor either motor current *or* battery charge current, if I wire up the charger and meter so that it'd be between the battery positive and the charger's positive output, as well as the motor controller V+. That way any current flow to *or* from the battery would be monitored. Since it doesn't have it's own shunt or electronics, I'd have to build that. For now, I'll probably forego the entire plate, and instead use a power-input jack I have from a PC power supply on the side or bottom of the cargo box, wired to the cable from this plate.

I need to dig up some connectors to either match or replace the ones already on the charger and the motor, so I can easily plug/unplug them from the rest of the system when needed. I didn't have that ability with the frictiondrive system on the upright bike, except that I'd used an ATX powersupply motherboard connector to get all power and control signals to and from the motor/controller plate I had bolted to the side of teh bike. The motors were directly wired to the controller board.

The hub from the powerchair wheel

has a core almost exactly the same size as some of the freewheel cassettes from various bikes I have, making it easy to choose what kind of chainring to go on there.

I plopped an assortment of salvaged chainrings down

and the first one I tried, on the lower right, fits the bill perfectly. It's six holes (there for making it lighter, rather than mounting it) line up perfectly with the four mounting holes in the hub, not only for diameter but also for radial spacing.

I grabbed the first four bolts that were about the right diameter that also had nuts with them, and temporarily secured the chainring to the hub. It's not yet perfectly centered, as these bolts are a bit smaller than the holes, but I should have something exactly the right size either in a salvaged item not yet taken apart, or in a box of hardware already salvaged. The chainring's teeth all clear the hub's outer edge sufficiently so that the chain should not rub on the hub itself, and only contact the chainring.

You can see here approximately where it might mount, though I'm just holding it next to the bike, and it'd actually get mounted between the Magna frame's two seat stays and the Schwinn frame's down tube. In order to get it in there, I'll have to unbolt the frames from each other and move them apart a bit, then back together once the motor is in place. Good thing I never welded them together! :-)

I did a quick motor test just to see what it might look like in operation with the sprocket, just directly attached to the two U1 batteries:

Not much else to say yet, except that later this coming week I ought to be able to get it all mounted up for a test.

For the test, I'll probably just put both batteries in the leftside cargo pod, as I don't yet have the rightside pod modified to clear the derailer and such. If I get a third U1 (which might be needed for sufficient power with this motor, but even if not would be helpful for extra range on long trips), it might get mounted directly behind the seat, in front of the rear axle but above the wheel, on the rack, or it might get mounted in the space the lighting battery(ies) is in currently, since I should not need a separate battery for lighting if there is a third U1.

So in case I haven't said it yet, Thank you, Anonymous! I couldn't have bought any of these things, even used, with the economic situation the way it is, anytime within the last or next year, possibly more! If you'd rather be acknowledged by name, just say so, and I'll replace the references to Anonymous here with the name you specify in our email conversations.

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