[Hendog]

Once you have spent the energy of the weight descending to the bottom of the wheel you must replenish/inject energy to sustain the power. In your example you sustain your weight at the 3 o’clock position by attaching it to a pulley and hanging it from the frame of the “vehicle”: the two forces cancel each other out. If however you supply 20N of energy you should gain your acceleration (ignoring friction as you say).