At larger angles of rotational skin stretch, it starts to hurt, mainly in the form of a pinching sensation. The idea was to make end effectors that would be stiff for small angles (to retain sensitivity for small deformations) and then be compliant at larger angles (to relieve pinching sensation, which would enable a greater range). We think that large angle = more than 30 degrees.

Here is the first prototype, finally assembled on 22nd July 2008.

• Lego model of torisonal spring concept:
  

• Cap off to show inside mechanism:
  

• Eploded view:
  

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KNOB EXPERIMENT To compare different types of end effector (fixed, torsional (with torsion springs), and free (freely rotating end caps)) we are running a kind of open-scale test.

• set-up:
  

• Normalized Results (5 subjects):
  

• Sample of an individual subject:
  

• Same subject's normalized results: