The diagram on the left shows the basic structure of the finger. When tension is applied to the cable (orange), the compliant material (blue) deforms and causes the finger to bend.

We will make the finger using a two-step molding process. Referring to the diagram on the left, in the first step we will cast the (red) structural, high-modulus material while embedding a channel for the cable. We will then use a CNC mill to cut the mold for the second step, and use this mold to cast the (blue) flexible, low-modulus material. Finally, we will add the cable.

Variation: Morphology

By varying the lengths and thicknesses of the finger links, the stiffness and corresponding bending behavior of the fingers can be altered. In the image to the right, the number and lengths of the compliant and rigid finger sections were varied. An equal load was applied to each cable and the resulting effects on bending can be seen.

Other Variations

As with all bending actuators, material selection defines the bending behavior as a lower durometer material will exhibit larger deformations, and vice versa.

One of the advantages of the SDM process is that it is possible to embed objects in the finger during fabrication. Embedding different items, such as pressure sensors at the finger tips, or structural reinforcements within the compliant sections, can change the functionality of the fingers.