H.H. I always make my own crank arms out of either 1/8" thick or 1/16" thick flat aluminum stock from Lowe's. I've even used small lengths of pexiglass for small motorized props.
the hard part is figuring out how to attach them to the rotating motor shaft.

Hey, I just remembered something that might work for you.
Check out this motor:

https://www.surpluscenter.com/item.a...tname=electric