Effect of mass and center of gravity on vehicle speed and braking performance

(1) Troy High School, Fullerton, CA , (2) Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH

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The center of gravity (CG) of a vehicle is a key parameter that helps determine vehicle stability, braking efficiency, and safety. In a gravity vehicle, the mass of the vehicle is also an important factor in vehicle performance because it provides the sole force of propulsion. We hypothesized that if a vehicle was constructed according to mathematically-derived optimal mass and CG location, then a fast and accurate vehicle would result. To test this hypothesis, we constructed a gravity vehicle, which is a vehicle powered by its own gravity on a ramp. Mathematical calculations were used to rationalize this hypothesis. Shifting the CG rearward increased the vehicle’s effective launching height on the ramp and corresponding gravitational potential energy, resulting in greater kinetic energy and speed. However, the accuracy (m-1), defined as the reciprocal of braking distance from the target, increased initially, peaked, and then decreased as the vehicle mass increased. We performed experiments with five mass parameters and three load locations, using an unloaded vehicle as control. Speed and accuracy were then measured for 16 sets of data. Compared to front and centrally-loaded vehicles, the rear-loaded vehicles displayed the best results. As the mass increased to a medium value, both the speed and accuracy reached a maximum. The experimental results supported the hypothesis that the optimal CG position is 22 ± 1 cm rear of the front axle and the ideal mass is 867 ± 50 grams. This study highlights the significance of CG position in vehicle design.

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