doozer presented the following explanation :
Yeah, I have considered it but I'm not sure it would be up to the job. The
flywheel I am hoping to turn with it is 80cm in diameter made from three
(or more) sheets of ply. There is also the problem of expense unless
someone has one going for free...

That might work as a drive, but not as a flywheel. To provide the
flywheel action it needs weight, enough weight to keep it going once
started until your next push on the treadle.

I have seen wood turning lathes where the method of drive is a bow of
springy wood above, down to a rope around the wood being turned, then
down to a foot treadle.

You pull the bow down to tension it, loop around your wood onto the
hinged treadle. Put weight on the treadle with your foot and the wood
turns, release and it rewinds due to the tension of the bow.

If your are going along the flywheel route, then you might find parts
from a car scrap yard of some use. Brake disks for flywheel including
bearings, then two flat bits of of steel to form a crank bolted or even
better welded onto the disks.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk