Method of making large spring index artificial muscles

A method comprising making a high-spring-index coiled fiber or yarn, wherein the method makes the high-spring-index coiled fiber or yarn without using a sacrificial core material whose diameter approximately defines the inner-coil diameter, and wherein the method to make the high-spring-index coiled fiber or yarn comprises:

• (a) inserting twist separately into two or more individual fibers and/or yarns, wherein the amount of the twist insert is below a level of twist that results in the coiling of the two or more individual fibers and/or yarns;
• (b) plying the two or more individual fibers and/or yarns by inserting plying twist to form a multi-ply structure, wherein the amount of plying twist inserted creates coils in the two or more individual fibers and/or yarns of the multi-ply structure;
• (c) performing a first setting process upon the multi-ply structure to set the coils in the two or more individual fibers and/or yarns of the multi-ply structure without permanently binding together the two or more individual fibers and/or yarns in the multi-ply structure so that the multi-ply structure is substantially stable against untwist when torsionally untethered;
• (d) after the step of setting, unplying the two or more individual fibers and/or yarns in the multi-ply structure to obtain the high-spring-index coiled fiber or yarn;
• and
• (e) after the step of unplying, performing a second setting process in which the high-spring-index coiled fiber or yarn is set when not torsionally or positionally tethered.