This robot hand features internal ligaments that torsionally link successive sections of the fingers to allow the efficient use of a single tension element - i.e. you only need one tendon per three jointed finger. Reducing the finger to a single degree of freedom greatly improves its ability to firmly grasp cylindrical objects.
View the video instructions here: https://youtu.be/CfB8Mrh1dSI
Simply press in 6x10x3mm bearings (available from Technobots website, part no: 4255-130) between the finger sections and add the torsional ligaments by threading nylon fishing line (100daN approx. diameter 1.1mm) through the finger sections to link the top of one joint to the bottom of the section two along i.e. the top of the knuckle is linked to the underside of the middle section and the top of the first section is linked to the bottom of the tip section and vice versa. Attach dyneema tendons by spreading the ends of a dyneema kiteline and embedding the fibres in polymorph. A single spring made from 3mm polyurethane tubing is attached to the top of the knuckle to extend the fingers.