Years ago, I saw an article in, I think it was Popular Mechanics, on a large flywheel mounted under a bus. It stored energy from a small motor and when it braked it was used to assistthe braking and would store energy. On acceleration,the stored energy helped the small motor to move the bus. The experimental unit worked so good, there was enough stored energy in the spinning flywheel that it could start the small engine after spinning down all night. Probably could be installed on one of the machines here.