Originally Posted by
ScrawnyKayaker
TwoShort, that's a handsome bike! I like that idler pulley. It looks really clean with the spring parallel to the bight of chain. Did you abandon that system due to the mentioned failure mode, or lack of replacement parts? Did the wheel survive??
That idler looked really nice, ran smooth and was easy to get set up right. In addition to the spring, there is a swivel so the pulley can twist. If you get the attachment point in the right plane, everything just floats to where it should be. But...
The pulley always moved around quite a bit; it would ding off the chain stay every time I dropped off a curb. Finally, in the midst of a hard sprint it swung (or maybe I kicked it) into the rear wheel. The spring got completely ripped apart; the wheel lost a couple spokes, and locked up completely with the chain wrapped around the hub. Maybe because I was so far out of the saddle, this produced a very long, easily controllable skid; I didn't even fall over.
I couldn't figure out how to build a spring system with this ones advantages that wouldn't run this risk (or not within the confines of my engineering ability). Moreover, my internal vision of the perfect retro-direct has no spring, or something like that. Note that this was the 4th repetition of the cycle: get this bike working, use it for 2-8 months until it breaks, and hang it on the wall for 1-4 months until I feel like taking another wack.
For repetition number 5 I returned to the rigid bracket I had learned a lot about in cycles 1-3, filled in the holes in the frame from previous experiments, gave the whole thing a nice paint job, solved the pedal-unthreading problem once and for all (epoxy), and generally spiffed up the bike a lot. This edition was great for 6 months; no problems except once that the chain derailed from the big freewheel with no great consequences. Then it derailed again, fell off the rest of the drive chain until it was dragging from the bottom bracket, and got under the rear wheel for a skid that tossed me hard into the pavement.
So now I'm actually in the hang-on-the-wall phase awaiting cycle number 6... which probably just means putting a plastic disk alongside the big freewheel to prevent it's derailing. Which will be ugly in both a visual and mechanical-purity sense; but road-rash is good motivation to compromise.
Have I convinced you you need a retro-direct yet?
