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Sunday, November 1, 2009

Chain Reactions

As stated a couple of posts back, I needed a way to tension the motor chain so it won't come off, or mount the motor onto a separate plate with only fixed bolt holes instead of slots for tension adjustments, then bolt that plate to the existing plate. It's significantly more work to do the mounting plate, for various reasons, so I pondered some chain tensioner ideas first.

After a while of thinking, I decided to just try my other chain tensioner I'd previously used for the pedal chain, which was going to be my throttle control (that I haven't built the electronics for).

I found a "good" position for it that would also help wrap more chain around the smaller motor sprocket, as well as keep it tensioned and in-line for passing to the receiver sprocket, used some vise-grips to hold it in place while I spot-welded it to part of the unused dropout tab on this side.

Then I hooked a stiff spring thru the ex-brake-pad-mounting slot, and over the top of the dropout tab, and pinched it between the cargo pod rail and the dropout just to be sure it couldn't pop off.

There is a slight problem with it, though, as I found while on-road during a medium-length several-mile trip.

If you follow the pivot curve, you'll see that if for any reason the chain pops off the tensioner's wheel to the "inside", the entire arm will be pulled up by the spring and get jammed in the motor sprocket.

Yeah, that happened about 4 miles in, although I still can't see how it *could* come off the tensioner's wheel, as it is perfectly aligned, no wiggle or slop, and the spring is quite strong and should pull the chain tight even against bigger bumps (of which there were none).

But since the wheel is a narrow little thing, then whatever causes any misalignment sufficient to let the chain ride up on the teeth is going to be enough to also let the chain come down the other side, probably. Needs to be much wider, but with teeth in there it won't fit.

So I need to do two things:

--Move the pivot point farther back enough that the wheel and/or arm can't come in contact with the motor sprocket no matter what happens. May need to weld this to a plate that gets bolted to the dropout. Should have done that to start with, instead of directly to the dropout, but didn't think of it.

--Change the jockey wheel out for a wider pulley-style roller with raised edges to "channel" the chain between them, so it can't come off.
Started to do that before, when using it as a tensioner for the pedal chain, but did not actually make the roller. It would be a rollerblade wheel, notched on the lathe for a bit wider than the chain, then bolted into the brake arm on a hole drilled into it a little closer to the pivot. That's so I can keep the smaller threaded hole already in the end of it in case I need the arm for something else later, *and* to shorten the "length" required for the whole assembly, since the rollerblade wheel is at least three times the diameter of the jockey wheel, perhaps a bit more.

This is beginning to be close to the amount of work needed for the mounting plate redo, now, but I need to be able to make better chain tensioners anyway, since this type of arm will be used for my throttle at some point, and THAT has to be reliable, too. Might as well work it out now.

Speaking of throttle, I have to be pretty careful about how much power I give to this 4-pole motor. If I have the bike in a higher gear, say, 4th from top (of 21) or higher, and I'm at a dead stop or going fairly slow (9-10MPH), then if I push the throttle past maybe halfway, there's so much torque that it actually pops the chain over the teeth of the rear cassette sprockets! That's not good for the chain or the teeth, so I need to watch out and make *sure* I shift to lower gears before I slow down, even more than I did before.

The old motor, even with me cranking as hard as I can, could not do that--I never anticipated that as a possible problem.

I shortened the chain a few links to make it very tight on the largest front ring and the middle rear ring, just to see if it would help, but it doesn't. It still pops. Lots of torque!

I know the chain and the sprockets are both old. I'm probably going to borrow the newer chain and cassette off my regular bike (the DayGlo Avenger) to help alleviate some of this, as I suspect part of it is caused by wear, though much is simply the amount of torque available.

I'm also considering taking the front 3-ring set off the DGA to swap for the one on here, but if I do, I won't *have* a spare bike, as I have no other square-taper crank set I can put on the DGA. I could swap it out when I need to, I suppose, but I'd rather not have to do that sort of thing. The DGA set is larger diameter for all three rings, so it would give me back my 20MPH top speed (currently around 18MPH-ish max), if I calculated correctly, as well as having less wear on it than the smaller rings i'm using now. Plus, with the larger ring and more teeth, it'd have better power transfer into the chain (less strain on each tooth).

I also need to replace that damaged rear-shifter cable housing. That is preventing me from shifting properly, and sometimes doesnt' shift at all until I move it several stops over from whereever it was.

Then I need to fix the front shifter. I'm tempted to just take it off, and manually move it from ring to ring whenever I need to shift for hills, since it is so rare to need to do this. Almost always I am on the largest front ring, and shifting thru the entire range of rear rings.

Another thing I'm seriously considering is to separate the pedal and motor drivetrains, running the motor to the left side, and having just a three-speed motor sprocket selection (a three speed hub would make this very easy, as long as it has no freewheel built in).

This would simplify some things, and complicate others.

I find that typically, even before the shifting problem came up, I would use the lowest or next to lowest rear chainring, then somewhere in the middle, then the highest. If I can just use a 3-ring setup off the front of a regular one-piece BB, and it's shifter, I could make a left-side shifter for the motor drivetrain. I just have to make sure it has ratios for the right road speeds.

That takes away some of the hill-climbing ability, though, in that even this motor will heat up more unless I can shift to higher motor speeds for lower wheel speeds but more wheel torque.

It does make it easier by far for me to use the regen capability of the controller, but only if I can also make a clutch of some type to disengage the motor entirely for coasting.

It also means I will have two completely independent drivetrains, with the rear wheel being the only common point. I have an idea about that, too, using a variation of my "dualie wheel" idea, where two rims are laced onto one hub, for two tubes/tires (for less worry about having flats in back where it's really hard to deal with on the road). As long as one tire and rim is ok, then even a bent rim or blown tire won't stop me, and with two tires/rims taking the load back there, I'd have less likelihood of bending rims in the first place. :)


  1. With pedalling speed even briefly in excess of motor speed slack may have developed on the top section of chain while the lower section stayed tensioned as designed. If that's the case adding a second tensioner acting on the top portion of chain should solve the problem. This assumes the chain popped loose on the top
    of the motor sprocket- if that's not the case and the chain popped loose from the lower end of the chainring perhaps mounting the tensioner farther back close(r) to the chainring might solve the problem.

  2. So far it doesn't even matter if I have my feet on the pedals or not, to make the motor chain derail.

    When this happens, it first comes off the tensioner itself, because it rides up on the plastic jockey wheel's teeth until it hops over the edge. If I replace that with a pulley-shaped wheel instead of a sprocket-shaped wheel, it won't have that problem.

    With the tensioner, it has not actually come off the motor sprocket unless it comes off the tensioner first, and then the tensioner gets rammed against the motor sprocket and hub, which is what then causes any further derailing.

    I have to be very careful with power application for now, as almost any sudden application of power, or rapid shifting up thru the gears, will cause either the motor chain tensioner to come out of the chain path or the chain to pop on the rear wheel cassette.

    The latter is not immediately disastrous, but it's going to break something if I keep doing it.

    The former, however, forces me to stop ASAP and undo the tensioner arm, take it off, realign it, bolt it back on, and reinsert it into the chain path. That's annoying.

    If I had an actual derailer in that spot instead of the single-wheel tensioner arm, it should not have the problem due to the double wheels plus the cage around it, so I am going to try that tonite if I can, while I ponder the other solutions for a more final one.

  3. Instead of a roller blade wheel, try a skateboard wheel. They seem to work better for me in that area. Also for another version look at the way I did mine on my trike by using the back bb. (I have a rear bb also the way I build my trikes)

    That works pretty well. I've used it for 5 different electric motor setups so far and am now running a 49cc pocket bike engine on my personal trike through it.


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