1) Take the motor out, so you just have a spinny thing and a foot speed controller
2) Mount it on a piece of scrap ply, or something
3) possibly make a 'flywheel' type thing out of, say, scrap corian, mount it on the shaft (this to 'smooth out' the spin up and spin down
4) mount bobbing, start winding.
That's how I've seen it doen, anyway, and what I'm planning to do with the cheap surplus sewing machine motor I got.
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It could be great to have a foot pedal and all, but no chance my parents will let me take apart the sewing machine. Not yet atleast.