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Tuesday, September 8, 2009

The Sound Of Silence

The bike isn't really silent, because of all the chain noise and whatnot, but it's reasonably quiet. I'm hoping to reduce a lot of the noise by freewheeling the motor and pedals separately from each other, and finding some way of keeping the bike frame itself from being an echo chamber inside the tubes (without trying to fill them with sprayfoam or something, as tempting as that would be to try, I'm sure it'd be a mistake).

I know that the frame itself is amplifying some of the noises, because it really cut down on some of the noise when I isolated the motor from the frame with that rubber pad--the chain noise on the motor's gearbox output ring was being conducted thru the gearbox body into the bike; now that noise is only conducted a little thru the rubber pad, and thru the chain itself to the receiver ring and then the rear BB via it's shaft.

I wish there was a way to isolate the shafts themselves from the bike, but the only way I can think of involves using the sealed-bearing type shafts, which I don't have, inside larger-than-usual BB shells, with something like nylon or rubber lining the shells to prevent metal-to-metal transmission of sound on the BB's and crankshafts.

Because of the even and constant way the load works on the rear BB it would probably work ok, but on the front BB with the pedals on it the load varies as the cranks rotate around via pressure from my legs, and pushes first on one side then the other. That means that the nylon or rubber would be giving way then pressing back on each side during a crank cycle, causing any pedal action to have an amount of wasted energy in recompressing the nylon/rubber each cycle, and also causing wear and cracking of the nylon/rubber over time.

So I'd have to only do it on the rear BB. Since that's where both drivetrains come together with the rear one, it's the one where the most energy turns to vibration and goes into the frame anyway, so it should help the most.

The best way to have a larger BB shell is to use one meant for the one-piece cranks, which fortunately I actually have a frame for one that's a lot like the Schwinn I'm using right now--I could pretty easily modify it to bolt right on where the Schwinn frame is, if I had both the nylon or rubber tubes and the sealed-bearing square-taper crankshaft. But I don't yet have either of the latter, so the idea is just here on the blog as a thought for later testing if I ever get those things.

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