Our SCP actuators are composed of conductive Nylon 6,6
sewing thread. The conductive coating allows for electric
heating. Multiple conductive nylon threads were tried, and
the Shieldex Conductive Yarn (117/17, Denier: 240/34f,
weight: 0.238g/m, coil diameter: 720um) was found to be
the best in terms of strain and force production. To construct
a SCP actuator, a length of the conductive thread is twisted
with a motor while a 50g weight hangs off the end to keep the
thread taut. As twists are inserted into the thread, the thread
shortens; beyond a critical number of twists, coils begin
to form along the twisted thread. When the thread is fully
coiled, a voltage potential is applied across the thread and
adjusted to supply approximately 0.2 W/cm length, which
heats the coils to above 150C. This heat-treatment causes
the resting length of the coiled thread to plastically elongate
and the coils to set.