TWiki > Rise Web>FootDesign>RiSESpinyFeetSept08 (10 Sep 2005, MattSpenko? )
-- MattSpenko? - 09 Sep 2005

Problem A: The compliant material in the axial direction tears due to heavy loads.
Solution A: Add a hard stop to the toe to limit toe deflection. This problem was solved, but it lead to a new problem (Or it at least led us to identify another issue).

Problem B: The hard stop's limited travel does not allow other toes to make contact with a wall asperity, thus resulting in too few toes making contact with the wall. A device is needed to release the toe if and when the hard stop is reached. This would allow other spines to carry more of the load.

Proposed Solution B:

Design the shape of the hard stop cavity to promote toe detachment when the hard stop is reached.
Testing Procedure: 9/8/2005 - Use 10 toes to make a foot. One foot with the old toes and one foot with the new toes. Attach as many toes as possible to the stucco wall. The key is that each toe should be at a different height along the wall. This idea is to have one toe release when it hits the hard stop. The other toes should maintain their contact with the wall. This will ensure the foot maintains contact with the wall.

We performed 3 tests with the old toe design. Each time resulted in a foot failure, where the foot fell off of the wall. The average force on the foot at failure was about 7 Newtons. We performed 4 test with the new toe design. Two of the tests resulted in a foot failure. The other two showed that some toes would release individually, thus allowing the foot to remain in contact with the wall.

Results: They really are inconclusive. We think the idea is still good, but its not as if the toes are automatically disengaging when it reaches the hard stop. It just seems as if the toe is slightly more likely to disengage. A measurement of that likelyhood is hard to determine.

Future Directions: I think this design should continue to be incorporated into the feet, although the design does need to evolve a bit.

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