-- GregKatz? - 12 Aug 2008
It was a busy week this week with 4 main areas of focus:
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.
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).
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.
Smelled a little funky, but actually was kind of fun. And now the fish look way better.