Responsive materials^1,2,3 have been used to generate structures with built-in complex geometries^4,5,6, linear actuators^7,8,9 and microswimmers^10,11,12. These results suggest that complex, fully functional machines composed solely from shape-changing materials might be possible¹³. Nonetheless, to accomplish rotary motion in these materials still relies on the classical wheel and axle motifs. Here we explore geometric zero-energy modes to elicit rotary motion in elastic materials in the absence of a rigid wheel travelling around an axle. We show that prestrained polymer fibres closed into rings exhibit self-actuation and continuous motion when placed between two heat baths due to elastic deformations that arise from rotational-symmetry breaking around the rod's axis. Our findings illustrate a simple but robust model to create active motion in mechanically prestrained objects.

响应材料^1,2,3已用于生成具有内置复杂几何形状^4,5,6，线性致动器^7,8,9和微^游泳器^{10,11,12的结构}。这些结果表明，仅由可变形材料构成的复杂，功能齐全的机器就有可能实现¹³。尽管如此，在这些材料中完成旋转运动仍然依赖于经典的车轮和车轴图案。在这里，我们探索几何零能量模式在没有刚性轮绕轴运动的情况下引发弹性材料中的旋转运动。我们显示，封闭在环中的预应力聚合物纤维在放置在两个热浴之间时会表现出自驱动和连续运动，这是由于绕杆轴旋转对称性断裂而产生的弹性变形。我们的发现说明了一个简单但可靠的模型，可以在机械预紧的物体中产生主动运动。