Feasibility of using secondary props to generate power on an electric model aircraft
It seems to me to be somewhat pointless - your extra 2 props will create more drag, thus the main drive motor will need to work harder for the same result as without them. They're effectively cancelling each other out, and the laws of thermodynamics tell us that energy will be lost from the overall system.

It's much like connecting a solar panel to a lightbulb; physics just doesn't allow for a 100% efficient system, so it can't work.