Tony Smith wrote:

> You'd be surprised at how well the cable setup works.  If you get slippage,
> you just wind the cable around the rod a couple more times.  Not sure of the
> efficiency or mechanical advantages, but the force is really only limited by
> the strength of the cable.  You don't really need a spring to keep tension,
> you can attach the ends of the cable to whatever it is you're moving.

Sounds like what I was planning with a belt. The problem is the tensioning,
with both approaches. Bi-directional pull/push of 1000 N... I don't
understand when you say that I don't need a spring to keep the tension. Of
course I can use a screw or something and re-tension when needed, but
something needs to be adjustable (or self-adjusting), doesn't it?

> As a complete aside on simple ideas, I recently discovered how the tracks
> are kept taut on bulldozers, not that I'd ever wondered.  On most
> motorcycles, to remove slack in the chain you loosen the rear axle,
> slide the wheel back, and re-tighten.  On a bulldozer, it's hydraulic. 
> Rather than pressure being applied by air or springs, it's by grease. 
> When the track becomes loose, you just pump in more grease.  The grease
> can't be compressed, so the tension is maintained.  Rather neat, I
> thought.  I've contemplated making this work on a bike. 

Calling a grease-driven mechanism "hydraulics" is stretching it a bit :)

On a bike, you'd probably have the problem of having to synchronize the
movement on both sides of the axle. Not a problem for bulldozers.

Gerhard

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