passive actuation

Wax motorwikipedia.org

Wax motors are linear actuators that turn thermal energy into mechanical motion via wax phase change. They consist of a wax chamber, a plunger, a heat source (electric, solar, combustion, ambient) and a heat sink. Wax expands 5‑20% on melting, delivering forces up to ~4000 N, with a bias spring providing 20‑30% of that force for retraction. Advantages include high force density, smooth actuation,…