-- GregKatz? - 12 Aug 2008

Week 2: June 30 - July 3

It was a busy week this week with 4 main areas of focus:

• Microwedge Backing Layer
• Microwedges with Suspension and Hierarchy
• Electroadhesion
• Cleaning the Fish Tank.

Early on in the week my time was dedicated reading background papers and discussing the issues with Sanjay, Aaron and others. Later in the week, I moved to more brainstorming and early prototyping.

Microwedge Backing Layer

Ideally the Microwedges will be held on an extremely thin, highly conformable, but inextensible backing layer. This week Aaron and I were able to cast the thinnest backing layer to date. It was extremely precarious taking it out of the mold but it was successful. It was so thin it was partially see-through.

To make the backing layer inextensible we will most likely need to make a composite. The challenge is to keep the backing thin and to find a way to adhere to silicone which does not naturally stick to practically anything. We are working with mylar now because it is pretty thin and certainly inextensible. We have three plans for now. The first is to try a very thin layer of epoxy to attach a layer of mylar to the back of a very thin silicone sample. The second is to encase a layer of mylar in between two layers of uncured silicone and let the silicone form around the mylar, trapping it in place. The third is to try making Microwedges out of polyurethane instead of silicone. Polyurethane should adhere more easily to mylar and other inextensible layers, but we haven't been able to try because we polyurethane is not agreeable with the SU-8 photolithographic mold we are currently using. We will try to make a daughter mold out of wax and latex next week.

Microwedges and Suspension or Hierarchy

Though the small size of Microwedges is responsible for greater adhesion, it also makes it more difficult to get full engagement of anything but the smallest sample size. To make Microwedges practical for large scale patches, we must find a way to ensure that all or at least most of the wedges are engaged so that maximum adhesion is achieved. Though we hypothesize that electroadhesion may help with the problem and have already seen that a deeper preload does help, these solutions are not complete. Eventually, some sort of suspension must be implemented to encourage close conformation of Microwedges to a variety of surfaces, especially surfaces somewhat rougher than glass.

Since the gecko solves the problem with the use of hierarchy, this has been our main focus. This is a difficult and longterm project because the best design for suspension is unknown and manufacture of even the most basic ideas is challenging. Designs have been characterized into two main categories: stalks on stalks and stalks on flaps. Stalks on flaps is favored because it retains the thin backing layer that has been proven and is modeled on the lamalae of the gecko. We have discussed making flaps out of Microwedge samples with either epoxy or by casting. We have also discussed casting microwedges on to preformed flaps. There have been some basic prototyping attempts, but they are still preliminary. We hope that manufacture will be easier if we make the flaps out of polyurethane which is easier to adhere to other materials (or itself).

Electroadhesion

Adding an electroadhesive clamping force to the feet of sticky bot could potentially improve overall adhesion significantly. We hope that it will be helpful in improving the preload, helping to pull the feet in close to the wall for good contact of DPS stalks or Microwedges, and to simply add some extra adhesive force.

Learning the Process

This week Sanjay taught me how to mix carbon and silicone oil to make a conductive spray for the back of the silicone Microwedge samples. He also taught me how to do the spraying and to use the high voltage supply. We were able to do a very quick prototype made of aluminum foil and mylar early in the week which was very helpful for learning how the technique works. Then after mixing, spraying, and drying we were able to do a first test on a Microwedge sample.

First Prototype

The prototype did successfully show that a conductive spray on only the back of a thinly cast Microwedge sample was definitely showing electroadhesive force on glass. At 4 kV we could feel the sample being clamped down to the glass. It seemed by eye that electroadhesion was indeed helping the sample to conform fully to the glass.

What is Next

Since the best mold for making Microwedges is expensive and fragile, the first test was done on a sample from an older mold. We also aren't ready to test the electroadhesion prototype on Noe's test bed. So we don't really know how well electroadhesion is working in conjunction with the directional adhesive force of the Microwedges. We need to spray a good sample of Microwedges and set up a test on the test bed. We will have to compare the force of a sample with and without the electroadhesion turned on as well as a flat sample with electroadhesion but without any wedges.

Cleaning the Fish Tank

Smelled a little funky, but actually was kind of fun. And now the fish look way better.