Sticky Toes

With large patches of adhesive, it is difficult to maintain alignment of the entire patch. When the patch is misaligned relative to the surface, the stalks/wedges do not come into close contact with the surface and adhesion cannot occur. Additionally, any sort or moment at the adhesion surface causes the adhesive patch to peel off.

Sticky Toes are intended to alleviate the problems outlined above. Rather that using one large patch, Sticky Toes use many small patches that individually conform to the surface. This should provide the adhesion force of a large patch without the difficulty of aligning a large area.

Track Design

The first Sticky Toe design used a four-bar linkage to align the patch and two tracks to provide horizontal and vertical compliance without changing alignment. The four-bar linkage seems promising, it aligns with the surface and provides some normal and shear compliance. The two tracks, however, are less useful. The long inner track tends to bend rather than slide and keeping the tracks in plane requires additional parts.

Four-Bar Linkage Design

The track idea has been scrapped, but four-bar linkages are still being investigated. A few alternate designs were developed: a less stiff four-bar linkage, a flexible cantilever, and a compliant two-element design. None of the alternatives seem to work better than the four-bar linkage on the original Sticky Toe. The new four-bar mechanism was too compliant, the cantilever conformed well to the surface but could not exert any forces on it, and the two-element design simply did not behave well.

Future Work

The geometry of the original four-bar linkage will be revised so that the instantaneous center of rotation is located exactly at the adhesive patch. Ideally, the center of rotation will travel down the length of the patch as the top bar moves. Also, the four-bar mechanism is likely to be loaded from the side rather than the top (based on how the robot leg attaches to current adhesive patches). The geometry of the mechanism should be revised to take this into consideration.

-- LaurelFullerton - 01 Aug 2008