I wish i had an old wagon around. I am ging to try and find a wagon.. and on the waggon set a battery.. maybe a 24 volt marine battery. and then im going to find a small motor.. and conect a belt to one the back wheels.. maybe weld a small sproket to a metal dowl to make a sorta back axel on the wagon... this would liknk my little motor to the wagon.. i think will put a alternato from one of the old trucks around here conencted to the front wheel.. maybe just weld the damn turning part that normal uses a belt to turn it straight to a front wheel. maybe even to both sides.. then link them to the battery that is controling the electric motor.
and just see what happens.. I know the battery power will start the wheels turning... and once the wheels start turning the two alternators will be producing power back to the battery.. a long as its not to heavy the engie should turn fast enough for the speed to make the alternators produce enought o keep the battery charging.
Probly have to use a capacitor to keep everything in check.