Large pink wheel receives motion from brown motor.
Large blue wheel and small red wheel are idly mounted.
Green antenna has longitudinal revolution joint with the chassis. Violet pin is for restricting the antenna rotation.
When the antenna is on the plane surface, the beetle contacts with the desk via 2 points of the antenna and 2 points of the large wheels. The beetle does not go straight on because only one wheel is driven.
Once a point of the antenna is out of the desk, the small wheel contacts with the desk, becomes a guide wheel, and the beetle turns urgently to bring the antenna out point back to the desk. So the beetle never falls down.
This toy of spring motor was seen in Slovakia, in 1982.