How do you make a simple spanking machine without much effort buying one and with no people?

I'd start with the pedal and back wheel part of a bicycle. Put the back axle on a stand or something and put straps on the wheel. (You might want to use a wheel with a smaller diameter so the straps can be longer!) Replace the pedals with handles of some sort so you can "pedal" with your hands. Then it's just a matter of getting everything in the right positions.

I hope you can make this work and sell the plans and make lotsa money! Have fun.