This joint is unpowered (passive). It hangs freely from a fixed pivot point, much like a gymnast's hands on a bar.

Modern robots like Boston Dynamics' Atlas use similar principles of momentum and balance to perform flips and navigate rough terrain.

In the field of robotics, the Acrobot is a benchmark for testing and nonlinear control algorithms. Developers use it to answer a critical question: How can a machine learn to perform a task when it doesn't have direct control over its primary pivot point?