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Electrothermal carbon nanotube (CNT) yarn muscles can provide large strokes during thermal cycling. However, the slow cooling rate of thermal muscles limits their applications, since large diameter prior-art thermal muscles cannot be rapidly cycled. Herein, a fast thermally powered sheath-driven yarn muscle that uses a hybrid CNT sheath and an inexpensive polymer core, is reported. The stroke recovery rate for the hybrid muscle is much lower at all frequencies than for about the same diameter sheath-driven muscle, which means that the full cycle contractile mechanical power is much higher than for comparable prior-art hybrid muscle. More specifically, the coiled sheathdriven muscle contracts 14.3% at 1 Hz and 7.3% at 8 Hz in air when powered by a square-wave electrical voltage input, which is 2.9-and 11.4-times the stroke of the coiled hybrid muscle at these respective frequencies. An average power density of 12 kW kg −1 is obtained for a sheath-driven muscle, which is 42-times that for human skeletal muscle. These high-performance results since the heating that drives fast actuation cycles are largely restricted to the muscle sheath, and this sheath is in direct contact with ambient temperature air.

Soft robots usually have soft structures and multiple degrees of freedom, and they are capable of large deformations and safe human-machine interactions. But unlike rigid robots which can be easily assembled from multitudinous general components, the fabrications of soft robots are more difficult. This work presents a general soft robot module that can be assembled into a great variety of soft robots. This module can bend in any direction and the bending angle can be controlled easily and accurately; it has a bar-like soft body made from silicone, and the bending deformation is actuated by multiple twisted and coiled actuators (TCAs) that are uniformly distributed around the soft body. The cost of the module is very low since the silicone is very cheap and TCAs are also very cheap as that they can be easily fabricated from polymer fibers such as fishing lines and sewing threads. A prototype was made, and an angle control system was established to control the bending posture of the module precisely. To verify the versatility of the module, a two-finger soft manipulator assembled by the module was made and its grabbing ability was tested.

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