Never used a washer motor. A small motor that will turn a wire brush will work great. A variable bench grinder is great. You turn it down and when you apply to much pressure it will automatically stop instead of tearing up your bird.
Most upland birds can be fleshed with your finger nail and a butter knife.
Water fowl have to be degreased after fleshing. Alot of the supply catalogs have bird fleshers. Good luck with it.