An Inverted Compass Model for Passive Dynamic Brachiation

Paper in proceeding, 2027

Brachiation is a swinging motion used by apes to traverse between branches. This paper introduces an inverted compass model as a minimal template to analyze passive dynamic brachiation. The mechanism consists of two rigid links namely swing and stance legs connected by a passive hinge with its stance leg anchored to a fixed support. Using simulations, the existence of stable limit cycles for passive brachiation is demonstrated. The results show that the inverted compass model naturally balances gravitational potential energy with discrete impact losses, achieving continuous, self-stabilizing periodic motion without actuation. This model provides a straightforward framework for understanding brachiation as the inverted analogue of passive bipedal walking.