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During this investigation an existing 4 stroke-cycle gasoline engine has been modified partially without changing dynamically its mechanism for the purpose to utilize compressed air as an alternative energy source. The principle is to mechanically control the compressed air flow through the intake and exhaust valves by modifying the camshaft's lobes to operate at both sides changing the engine principle to operate from 4 strokes to 2 strokes: The compressed air in this 2 strokes mode flows in and flows out in accordance with the up and down motions of the piston every revolution of the crankshaft, which is more efficient than the 4 stroke mode. The principle was verified with a current 50 cc motorcycle modified engine to analyze the pressure behavior inside the cylinder of the compressed air engine: The intake and exhaust pressure same as the engine performance was measured.

Longitudinal equations of motion for the rider/motorcycle system are deduced. The rider's body is assumed to be composed of lower and upper leg, pelvis part, torso, head, lower and upper arms. The motorcycle is composed of front wheel with suspension, rear wheel and motorcycle frame. Equations of motion are obtained for each part. The actions and reactions working at the joints or connecting points are considered.

The dynamic behavior of the rider/motorcycle system, affected by the change of rider's posture in jumping over an obstacle, was analyzed by solving the equations of motion. The rider's behavior and motions were obtained from full scale experiments. These were combined with dynamic equations of motion for the motorcycle. The result was used to evaluate the rider's mastery of the accomplishment of the movement. To compare with the real motion obtained with a high speed camera, the computed motion was visualized as a time sequence. The comparison between the experiment and the computation showed good agreement.