The experiment today was a partial success; I forgot to really crank down the mounts on the 2-pole and it got pulled back by the chain little by little as I rode, and about halfway thru my pre-work riding the chain slipped off because it was too loose, and got wrapped up in the chainrings and locked up the motor/drivetrain.
Unfortunately, Murphy was watching, and so an unrelated wiring issue (loose splice and tape on the throttle cable from an emergency repair I had forgotten to fix more permanently) happened to fail at the same time, in such a way that the throttle acted stuck full "on". :( Since I couldn't hear the motor turning (because it was jammed) and I'd turned the throttle lever all the way down, I didn't notice the problem until I smelled something and then saw smoke coming out of the motor housing, while I was stopped trying to unravel the chain mess.
I flipped the breaker and checked temperatures by hand, and I could not even touch the motor's cylindrical housing without burning myself, and after a couple of minutes the gearbox and output shaft and sprocket heated up to be really really uncomfortable to touch (was still trying to get the chain untangled), even though I was melting ice cubes out of my water cup on the motor housing to cool it as fast as I could, and had taken the plastic nose cap off to let air in there. The controller's heatsink was pretty hot, but I could comfortably leave even the back of my hand against it. Dunno what the inside temperature on it was like, though.
Before continuing, I let it cool till I could leave my hand on it (barely), left the cover off, and rode to work still using the motor, but at reduced speed with lots of pedalling, so I wouldn't overheat it any worse. It does still work, but it is definitely damaged--I can see the winding color is changed even without taking the armature out, the smell is pretty yucky, and there is a lot of commutator/brush noise, so I think one or more segments may have lifted a little from the heat. :(
It worked on the way home, too, still noisy, but the chain kept coming off over and over which was very annoying. I couldn't tighten it without taking the batteries out first, because the two-stack is right on top of the front motor bolts. :( SOMEbody did a crappy job of engineering this part of the bike for on-road adjustments. ::rolls eyes::
On the other hand, the radiator-hose-clamp battery straps held them in place fine, even with the potholes I ran into. I had expected them to shift around, especially the rear one.
No other problems besides the motor/chain issue, so I am going to try mounting the 4-pole motor, now that I have some bolts to fit it, and see if it runs the bike well enough without anything breaking. :)
The newly-added rear brakes worked fine, though there is almost no brake action until it is squeezed really hard. Also, I forgot to point this out in the previous post, but I decided to use the Honda scooter's brake lever that has a parking-brake latch, which physically holds the brake in squeezed position when set. I'm pretty sure that the scooter's brakes used a different amount of mechanical advantage and that's why the sensitivity is very different from the usual bike brakes, with me using the scooter brake lever to control regular bike caliper brakes.
Nice thing about the parkng brake is that unless someone messes with that, it's also not going anywhere even if somehow the motor gets turned on, since the parking brake is on the driven wheel.
Balance of the bike is definitely different, with that third battery up higher than the other two, and all of them a little higher than they were in the side trays, but centered on the bike both longitudinally and laterally.
Wednesday, September 16, 2009
Post-Diet Test Ride, First Stage
3 comments:
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Your progress is fast (to me). Your trouble with the chain popping reminds me that my chain idler is a bit lax.
ReplyDeleteMy bike has no rear brake, so I installed the other brake behind the stock front caliper brake. The stock is before the fork and the previous rear is behind. If it were on the rear, it would definitely be better.
I thought about an idler a couple of times, but it adds too much noise and isn't needed if I properly set the motor position and tighten it down. ;)
ReplyDeleteThe problem with dual-braking on a single wheel is that while it probably does provide more stopping power (effectively simply increasing the surface area of the brake pads), it does not increase the contact patch with the road.
That means that while you can more easily stop that *wheel*, it just skids easier, by breaking loose contact with the road.
Having the brakes on both wheels ensures up to twice the contact area and so up to twice the braking power (initially, until weight is transferred to front in suspended systems, less so in hardnose/tail systems.)
That's part of the reason I've been wanting to get my rear brakes installed, because I could stop the front wheel but the bike would just skid instead of stopping, because that little contact patch isn't enough for something this heavy.
I'm pretty sure that's why some places have enacted not only power and speed limits for ebikes, but also weight limits. At higher speeds a heavy bike just doesn't have enough contact patch to stop it quickly.
Plus unless you're an experienced rider at those speeds with a heavy bike, it's really really easy to lose control of an upright-style bike when stopping suddenly enough to skid it. Not so easy for a low-slung bike like mine or a fully recumbent, but still possible, especially in a turn.
Those are some good observations about stopping power. My problem is that my caliper brakes can barely stop the bike quickly even with both levers pressed against the handlebars, much less be able to lock up the front wheel in normal, dry conditions. I can't weld pivot points for modern high-force caliper brakes onto my frame since I lack the skill and the supplies. ;)
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