flywheel hub arrangement as seen best in fig5 the first side of differential 118 i e the side of the differential positioned adjacent to first flywheel 112 includes a first planetary gear 146 positioned to mesh with and engage first input output gear 142 a so that turning either of the gears causes the other to likewise turn planetary gear 146 is further positioned to mesh with and engage reversing gear 148 which drives a shaft extending through the differential to another planetary gear 150 shown in fig6 located on the opposite side of the differential that planetary gear 150 in engagement with second input output gear 142 b it should be understood that reversing gear 148 is not engaged with first input output gear 142 but only with planetary gear 146 and thus serves only to transfer and reverse rotation from one side of the differential to the other as seen in fig5 and 6 an identical second planetary gear reversing gear arrangement is positioned on the opposite side of approximately one hundred eighty degrees around the input output gears with the differential configured as just described it can be seen that rotation of first input output 142 a turns planetary gear 146 and reversing gear 148 that rotation is carried to planetary gear 150 on the opposite side of the differential and to second input output gear 142 b thus flywheel rotation on one side of the differential is transferred to rotation in the opposite direction on the other side of the differential preferably the gear ratio between the first and second sides of the differential is approximately 1 1 although variations from that ratio are accommodated by the present invention further other configurations and arrangements of the gearing may be employed.