permaculture

[Paul Cereghino <paul.cereghino@comcast.net>]

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 
high speeds!

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.
>
> LL
>