Design of an Egg-Shaped Roly-Poly Bumper Car Based on Centre-of-Gravity Self-Balancing

To overcome the problems of conventional bumper cars, namely fixed cockpits that cannot convey the mechanical process of a collision, passive rocking mechanisms with poor controllability, and a seat height that cannot accommodate occupants of different builds, a parent-child bumper car integrating the centre-of-gravity self-balancing principle of a roly-poly toy with omnidirectional mobility is designed. The vehicle consists of an egg-shaped cockpit, a crank-and-linkage controllable rocking mechanism, a gravity-adaptive lifting seat and a four-wheel Mecanum chassis: a low-centre-of-gravity counterweighted configuration provides a natural restoring moment; a servo motor drives a crank-and-rocker four-bar linkage to produce graded rocking according to the collision impact intensity; pressure sensors under the seat together with a screw-lifting mechanism adjust the seat height so as to constrain the centre of gravity of the whole vehicle in accordance with the occupant weight; and four independently driven Mecanum wheels achieve zero-radius spinning and lateral translation. The cockpit configuration was compared and selected, the tilt angle and the driving torque were verified, and the cross-sections of the links were sized and checked; a scaled prototype was then fabricated and functionally tested. The results show that under a collision at 2 m/s the egg-shaped cockpit reaches a maximum stress of about 0.29 MPa with a safety factor of about 69 and a fatigue life of more than one hundred million cycles, its comprehensive performance being superior to that of the square and spherical configurations; the overturning moment of the rocking mechanism at the 20-degree tilt limit is 51.3 N*m, the required torque calculated with a safety factor of 2 is 102.6 N*m, and the selected servo gear motor delivers 112.2 N*m, meeting the requirement; with a 16 mm connecting rod the buckling safety factor is 2.42 and the bending stress is 103.3 MPa, both within the allowable values. The prototype reproduces collision-graded rocking, weight-limited seat lifting and omnidirectional movement, confirming the feasibility of the scheme