The hands of the Robot figures are important gestural elements, and were complex projects unto themselves. The goal was never to produce a functional grasping hand - a huge undertaking - but rather to produce a sculpture that looks and moves roughly like a human hand.
The final hands (right) are 1/2 human scale. They have 4 working fingers and a fixed thumb, and are operated by 2 pull-cables per hand. This 2 cable system does not allow individual finger control, but allows a wide variety of gestures.
Early Hand Concept
The first hand design (left) was composed of 4 units of an early finger design which proved to be unsatisfactory. This finger design had torsion springs in each of the 3 finger joints which clenched the finger, and a tendon on the top side which extended the finger when pulled. The tendon was kept in place by small rings. All 4 tendons were connected to a bar, and when the bar was pulled the hand opened.
The problem was that the fingers didn't "share bending" evenly between the 3 joints. For example, joint 1 might straighten out all the way before joints 2 and 3 started straightening. It looked very awkward.
Clearly, a better finger design was needed - there was no easy way out. A design that forced equal bending at each of the 3 joints was needed.
The new finger design was developed in Lego and monofilament. It worked well. The challenge then was to execute the Lego design in durable materials at the much smaller required size.
The final finger design uses brass box tubing for the main structures, with some of each box machined away. Spring pins act as axles which hold the pivoting brass structures together. Riding on the axles are tiny Delrin disks, to which the "tendons" are affixed. Key to the design is the way the monofilament tendons criss-cross, and which disk is attached to which brass structure. Rather than giving a full description, a few detailed images have been provided for those interested. Larger versions of these can be found in the gallery section, and will print legibly.
Once a good finger design exists, it is straightforward to make 4 versions with the appropriate segment lengths (like a human hand), and mount them to a hand structure at appropriate positions and angles. Extension springs in the palm of the hand try to pull each finger to a fully clenched state. Along the back of the hand is a bar which when pulled opens the hand. This bar is pulled by 2 servos via 2 cables, so it can be straight (all fingers the same) or slanted (some fingers more open than others). The posture of the hand is thus determined by the position of these 2 servos.