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Tuesday, November 10, 2009

Taco Hell: Sprocket With A Side Of Chain

I broke the bike today. :(

Everything was very happy yesterday, for the most part, and I had successfully ridden over a dozen miles on the new 4-pole motor and redone drivetrain, testing it for strength and whatnot in the next to highest gear for almost all of the trip, including startups, with essentially no problems I didn't reasonably expect.

Then today I leave for work, and not 1/8 mile into the trip, I get cut off by a truck making an unsignalled right turn around me (without stopping or slowing) at a 4-way stop I was just coming up to. I braked easily without any danger, but I ended up stopped in the highest gear. I'd used that from a complete stop yesterday without problems, but today I guess the strain was just too much, and the front chainring, the largest one, FOLDED like I was trying to make a taco.

At first I didn't see the problem, looking at it from the side.

Then I started trying to put the chain back on, and it was REALLY obvious what was wrong.

Here's a couple more pics of it, after I removed it.

It also bent the middle ring, by pulling it with the bolts holding the large ring onto the set.

Yeah, it's toast. Maybe I can unbolt them all and hammer them flat again, but that's never worked well so far on the warped ones I've pulled off of kids' bikes.

The chain is on the granny ring in all these pics.

Almost looks normal above, doesn't it?
Then you look at it edge-on again, and...

It almost looks like i hit a curb with it, but I didn't. It was the force of the chain. My guess is that the ring was already weak in that one area, and the chain tension as I started up under load at high gear just PULLED it like that. I don't really know for sure.

Fortunately it didn't damage the granny ring, which is the one actually swaged to the crank, so I was able to run the bike to and from work on that ring and the next-to-highest rear ring.

Because both rings are so small, there was so much extra chain I had to actually take links out so it wouldn't pop off the rings from the torque. :roll: I never had a reason to try this combination before, so didn't realize that would ever be a problem. I think I need a different derailer to take up the slack better.

To get around 11MPH max speed, which sucked in traffic but it was better than not getting to work at all. I even still made it with almost 20 minutes to spare.

But whatever torque all this put on the bike must be twisting the frame slightly, because it causes the chain to pop off the motor drivetrain a LOT, due to the misalignment, so I definitely have to fix the alignment problems (see the blog for mentions and discussions about that part).

Since I don't think it will flatten out well enough I just went ahead and pulled the triple off my DayGlo Avenger, but the crank on it is long and forced me to move several parts of the bike. I cannot cut the crank off because this is the only crank I have left for the DGA bike, which is my emergency bike in case this one breaks unfixably and I have to go places.

I had to move the 3rd (rear) battery to the left, and block it with some wood so the clamps don't pull it into the path of the crank.

I also had to space the front end of the lower right cargo pod rail out by nearly a couple of inches, so that the resulting angle would let the crank clear (with extra room) the rail at it's back portion.

Here's the closeness of the crank to the ex-dropout the rail is bolted to in front.

I had to lightly file the tip of the crank to clear. It still brushes it under load as the frame twists some. Needs more filing.

This is the new clearance to the rail. Prior to moving the rail, the crank lined up directly under the rail, completely.

The controller was even in the way:

I had to take it out of that spot, and for now it is tied to the side of the batteries, just clearing the pedals.
This is how it looks where it used to be now

The good news is that all this work made the bike work better, at least in theory. It was cold and dark by the time I was done, and I was so hungry my hands were shaking, so I called it a night and will road test it tomorrow. So far all I did was do a quick ride a few dozen feet around the yard.

The "new" rings are 28-38-48, where the old were 24-34-42, and I generally ran on that 42 ring unless I was going up hills.

Now I will probably run it on the 38 most of the time, which will not get as fast a speed but will be a little better chain alignment for most gears shifting thru the range, once I fix the derailer issues.

The front derailer has had problems for a while, and does not properly shift upwards into the third gear; I need to see if I have a replacement derailer that will fit here. Some don't have the cable coming from the right direction, or are only for two gears instead of three, etc.

The rear derailer is having issues, probably in part because of the partly-crushed cable housing, but the derailer isn't taking up slack like it should, nor is it shifting all the way left (low gears) even though I verified the limit screws are correctly adjusted. I have a feeling it is partly my wheel spacing/alignment, leaving too large a gap between the frame and smallest sprocket, and thus unable to reach the largest sprocket farther left. The slack problem may only be an adjustment for tension, and if not I could add an external spring to pull it, but the shifting problem I might not be able to fix.

I would just use the derailer from my DGA bike, but it's the type that screws into the frame itself, rather than bolting in the dropout slot, so it won't fit. I have a few others that will, but not all of them work right.

When I was finally done with all of that, something strange happened as I flipped the breaker off for the main power on the bike. the taillights stayed on, but the headlight went off, and I wasn't sure how that could happen, and then I smelled burning electronics. It was the CCFL headlight box smoking!

I flipped the breaker without thinking , and it was already off, so I turned it back on when I did this. But it stopped the smoking before I realized the taillights were still on.

I then flipped the power switch on the headlight, and the breaker, both to off. that stopped the light and the smoke, but I don't understand why.

Another symptom is that if the breaker is off, but the light's switch is on, if I turn the throttle up the motor moves a tiny bit at a time, just creeping along. This means something is shorting thru the system to ground even around the breaker, but I have no idea where it is., and I was far too tired to deal with it right then, so I shut it all off and left it outside, came in, had dinner, and am now writing this up.

While dinner was cooking, I tested a thought I had had yesterday (?) about using CFL bulbs on DC current, since they have an internal switching power supply, just like those chargers I checked out in a previous recent post here.

Here is a 15W 900-lumen generic CFL, at 44V.

It draws about 110mA at this voltage, and is rated to draw about 240Ma at 115VAC. I'd hazard a guess that it's around half normal brightness, maybe less. It's still bright enough to light up the room pretty well, but definitely not as good as full voltage would be.

It will stay lit, but very much dimmer, as power goes down to around 22VDC. Same current reading.

It takes at least 44V to kickstart it, but after that it can be "dimmed" down to 22V. I considered using one or two as my headlights, behind a reflector and lens set out of a car, which showed promise with other lights I had tried before. This would be easy to do, relatively, but would require I add another battery to the system to get it past 44V by a safe margin.


  1. I know you are trying to save money and build everything from recycled stuff but you might want to look that the little 12v so called spotlights that harbor freight sells for about $5. The ones with the bulbs and not the led version of the same thing. They have a magnet bottom ring that can be removed and a ring bolt can be put in it's place for mounting. They make really good bike headlights and are very cheap compared to regular bike lights. I use them on both of my trikes.

  2. Nah, I don't want to use anything with the bulbs; they waste too much power for the light they give. Most of the power goes into heat and light I can't see by.

    I'm about to build an extra bright LED headlight and taillight set for a few bucks worth of parts off of DealExtreme, along with parts I already have here (celphone chargers as DC-DC converters to run them off my pack).

    I also have more than a few CCFL inverters and bulbs from various scanners and stuff, and they make the best 180-degree light I can imagine, for other people to see *me* by. It's not really for me to see *them* by, since generally there's enough streetlights and other lighting that I can see fine even with no lights at all.

    But them seeing *me*, well, a bright spotlight doesn't do nearly as much good as the CCFL with the milk-plex cover to diffuse it into a 180-degree spread, so I can be seen all the way up to directly from the side. Plus the UV in the light makes my dayglo stuff light up, nearly as visibly as in daytime. :)

    The household CFLs are just another idea, just because I thought of testing them. ;) And because it's crazy to use them on a bike, and I think they would look absolutely ridiculous, and very unique.

    Tempted to get some red "party siren" plastic light domes and use them to mount CFL bulbs in for taillights! Really really tempted!

  3. Well, if anyone ever hit you from the rear they would REALLY have a hard time saying that they didn't see you!

  4. It's tough enough as it is, since the LED marker lights I have light up the back of the cargo pods, too, so I have the entire back end of the bike already lit red. :)

    Anything that makes me more visible without blinding the rest of the traffic on the road is good enough for me.


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