Feet for StickyBot II

Currently, StickyBot II does not climb as well as the original StickyBot. Also, neither robot has managed to climb using microwedges. New feet are being designed in order to improve the climbing ability of StickyBot II using DPS stalks, or microwedges with electrostatic adhesion.

New feet are being designed for StickyBot II. These feet feature ball joint-like structures to allow the adhesive on the foot to align with the climbing surface. Ideally, these feet will work with microwedges as well as DPS stalks.

Version 1 Foot Design

ankle.jpg foot.jpg sbfoot.jpg

SolidWorks files of this design may be found on Yoda: \\Yoda\Users\laurelf\SB_II\Feet\V1_SWfiles

This design features a single ball joint-like structure (ankle) located towards the back of the footplate. The structure in the middle of the ankle screws into the leg of StickyBot II while the outer ring glues into the footplate. The flexures in between allow the footplate to rotate and displace relative to the ankle. The white areas were made with Task 9 while the yellow areas were made with Vytaflex 20. The footplate features an outer ring to constrain the ankle and a recess below it allows the middle of the ankle to rotate. The footplate was built out of Task 9.

New DPS stalks were made for the feet. Tap Blue silicone was used with the following recipe: 50 grams part A, 5 grams part B, 4 grams thinner. The stalks were allowed to cure for ~6 hours beneath 3 cinderblocks.

Preliminary Results

The first problem with the Version 1 feet was that the back corner of the footpad hit the robotís leg. This problem was alleviated by removing the bottom corners of the feet with a Dremmel tool. It was also noticed that stalks further away from the ball joint did not engage nearly as well as stalks near the ball joint. Stalks at the ball joint would be pressed completely flat while stalks at the top of the foot would not even be in contact with the wall. Because of this, adhesive patches are currently centered on the ball joint of the ankle.

Version 2 Foot Design

v2_foot.jpg

SolidWorks files of this design may be found on Yoda: \\Yoda\Users\laurelf\SB_II\Feet\V2_SWfiles

Since Version 1 indicated that only stalks near the ball joint conformed well to the surface, this design has multiple small surfaces each with their own ball joint (similar idea to StickyToes). The robotís leg attaches to a ball joint which connects to the three toes with other ball joints. I do not intend to start building this design until I get a bit more information on how the robot behaves with the Version 1 feet. Hopefully some of that information will help me improve the design.

Version 3 Feet Designs

After much modification of the Version 1 design it was found that in order for the robot to stick, the adhesive patch needs to be located further from the ball joint. Also, the Vytaflex in the ball joints of the version 1 feet ripped out. Because of this, new designs have been drawn up. These designs are much thinner and longer than the original feet and have solid Vytaflex flexures rather than four thin flexures. Thin spurs will be made to attach to the bottom of the foot below the ball joint. This will help the patch come into contact with the wall.

solid_foot.jpg

Solid foot design: This design is essentially the same as the original foot except that it is thinner and longer. It features one large area where DPS stalks or microwedges may be attached.

toed_foot.jpg

Toed foot design: This design is essentially a modified version 2 design. It features three long toes that individually conform to the wall.

frame_foot.jpg

Frame foot design: This design was made with electrostatic adhesion in mind. In this version a thin film such as mylar would be stretched across the frame. Conductive microwedges would then be attached to the mylar. When the electrostatic adhesion is activated, the wedges will be attracted to the wall and pull the film into close contact.
-- LaurelFullerton - 20 Aug 2008

Prototypes of all three versions of the foot were built but the first batch was unsuccessful. The fabric embedded in the ball joint did not bond with the vytaflex at all. A second batch has been started, this one will not have any fabric in the flexures.
-- LaurelFullerton - 28 Aug 2008

Future Work

Once the second batch of feet cure I will mount DPS stalks and microwedges on them and try to make StickyBot climb. The frame feet will have electrostatics while the other designs will use normal adhesives.
-- LaurelFullerton - 28 Aug 2008

 
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