[permaculture] Looking for pedalpower resources - any bicycle experts in the list?
paul.cereghino at comcast.net
Tue Jan 2 17:49:03 EST 2007
Some thoughts based just my time on bicycles:
If the tillage tools are static (being dragged through the soil), than I
bet your main issue will be the friction of the tillage tool vs. the
traction of your drive tires. This requirest that the weight above your
static tool be heavy. Since you'd be operating at low speed you'll also
have an issue with intertia, in that if you have a heavy machine with
drag due to friction in the soil, it'll take some energy just to get
moving forward, your gear ratio for low gears would need to be extreme.
On a bike at low speed with lots of drag, you can get to a point where
you need so much torque to just get going, but the second you get going
your too geared up to maintain intertia while switching gears. So how
about this as a weird idea:
If you already need to be heavy to get your traction on the drive
wheels, what about some design that uses a flywheel for the drive
impulse. The pedel crankshaft builds up intertia in the flywheel...
once intertia is built up, some kind of clutch is used to engage the
flywheel gear it down to provide a high torque/low speed rotation on the
traction tires. The weight of the flywheel doubles function to enhance
traction. The pedel power and crank shaft gearing is then used only to
build up and maintain the flywheel inertia, but is not needed to
overcome the initial and variable friction of the business end of the
tool... the potential energy of the flywheel smooths the energy
requirements while providing the weight for better traction.
The alternative approach would be to use forward momentum as your
intertia, but I was not imagining this creature would operate at foward
Since tire friction isn't an issue at low speed, consider radical tire
traction. I have seen partially submerged rice planting rigs that have
tires like paddleweels to maintain traction in mud.
Paul Cereghino, Olympia, WA
Lawrence F. London, Jr. wrote:
>I need to construct a 4 wheeled device I can ride on, steer and pedal with an 18 speed (maybe less)
>gear train. I will mount adjustable-height static tillage tooling below the frame and drive this along
>raised garden beds to scarify the soil and loosed existing weeds, prior to winter planting of spinach and a number of
>other crops. It will be too wet to get a tractor in the gardens until late Spring and I need to plant throughout January
>and February. All parts of the frame, except the tillage tool, will have to be at or above the height of the wheel
>axles. The 4 wheel bikes I have seen on the web are expensive and their frames are too low to the ground.
>Any ideas or pointers to resources will be much appreciated, especially from anyone who has done any bicycle
>modifications or built human powered devices from recycled bike parts and components.
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