how to slow a concrete mixer ??, page-58

Don't know if this helps, but an Engineering student once made me a pottery wheel using a washing machine motor turned on its side, added a centre metal table which rotated and the speed was varied using a dimmer switch. He created the rest of the 'table' with a square piece of timber which had the centre cut out for the metal rotating table. Worked a treat.
Maybe with a little imagination you can do something with that idea.

Also you can get hand operated concrete mixers. Bought one for $50.00 at an antique auction. Was beautifully balanced and would spin on its own accord for minutes once started. Wasn't rusted out - no holes and it now lives with a stonemason I knew who uses it for small batches of mortar.

Cheers,
Tangrams