An electroactive supercoiled polymer artificial muscle, which is made from a conductive sewing thread using self-coiling caused by inserting a twist with a hanged appropriate weight, is 1/4-1/3 of the thread in length. Therefore, it is necessary to move the weight vertically about two or three times as long as the desired electroactive supercoiled polymer artificial muscle, resulting in a large vertical dimension of the fabrication equipment. This study has attempted to solve this problem by using constant-load springs that enable horizontal table-top fabrication equipment. It has been also demonstrated that inserting a twist into the bundled threads results in a strong electroactive supercoiled polymer artificial muscle.

It is found that the electrical resistance-length characteristic in an electroactive supercoiled polymer artificial muscle strongly depends on the temperature. This may come from the thermal expansion of coils in the artificial muscle, which increases the contact area of neighboring coils and results in a lower electrical resistance at a higher temperature. On the other hand, the electrical resistance-length characteristic collected during electrical driving seriously deviates from those collected at constant temperatures. Inhomogeneous heating during electrical driving seems to be a key for the deviation.

S-shaped nonlinearity is found in the electrical resistance-length relationship in an electroactive supercoiled polymer artificial muscle. The modulation of the electrical resistance is mainly caused by the change in the contact condition of coils in the artificial muscle upon deformation. A mathematical model based on logistic function fairly reproduces the experimental data of electrical resistance-length relationship.