Thursday, August 16, 2018

Human Powered Shredder Planning


Shredder stuff begins! As part of my NAU grant I have ordered a shredder mechanism from Precious Plastic USA in Portland, Oregon. While that is being built, though, I haven't been wasting time.

In order to save money and demonstrate the shredder in off-grid places like the Flagstaff farmer's market, I've decided to power it with muscles. I picked up this early 70's Schwinn Exerciser stationary bike and will modify it to power the shredder directly. The shredder will be mounted up on what might be called the dashboard so it can be operated by the person pedaling.

I will have to reduce the gearing substantially as well. A few people have created hand-crank shredders with 5:1 gearing- that is, for every five cranks of the hand, the shredder cranks over once. I will be using leg power instead; since legs are more powerful than arms I will be able to run the shredder faster and with greater force.

Technically, this will be a bit tricky but not ridiculous. The bike came stock with a 65T (the T stands for "tooth") chainring going to a 14T cog, spinning that flywheel up to a high speed. Instead, I plan to run a 28T ring from the cranks forward onto another 28T on the flywheel. I'll stack a 14-ish tooth cog next to that 28T and run it straight up to a 65T chainring (pictured) on the input shaft of the shredder. This will reverse the stock ratio, giving it about 4.6:1 gearing. If that turns out to be too easy to pedal, or if the shredder is turning too slowly, I will be able to easily pull out the crankset, change to a larger chainring, and shred at a higher speed.

Work on this will continue as soon as I can get that flywheel to the bike shop to figure out how to stack cogs. I will also write a post soon about my "compression machine" progress!

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