-- MattSpenko? - 14 Nov 2005

This page is set up in chronological order starting with the most recent work at the top of the page.

Polypropylene

3/9/06 - This past week I looked into integrating the polypropylene pieces into a substrate of 72DC to create a structure that used the polypropylene as a cantilever beam. Rick orginally proposed this idea sometime late last year. The original results were not that good, but I learned some things from it.

Procedure - I cut the mold, placed strips of polypropylene into the proper slots in the mold, and then attempted to block the flow of polyurethane from interfering with the polypropylene strips with clay. There were several problems. First, the clay did block the flow of polyurethane; however, it also prevented the polypropylene strips from properly being anchored in the 72DC. Second, the clay is difficult to remove.

Another thing I learned is that the polypropylene hairs vary too much in thickness. I picked one sample from random (approximately 800 um thick) and found that they are too thick to be used as the lamellar pads because they are too stiff. I then measured the thickness of each one of the polypropylene patches that I received. The results are given below:

The patches that Rick gave me before he left on his interview were the best (see my discussion below).

Next step is to try some other methods of blocking off the polypropylene hairs including using glue, sorbothane, or silicone dams. Details and pictures to follow.

2/27/06 - I started experimenting with the thermoplastic (polypropylene) hairs that Rick sent me last Friday. Rick sent me two types of samples. The first was fabricated using the small (1.3 cm diameter) filters. He cut up the resulting patches into shapes that he thought had good results (Rick, did you look at these under a microscope, or can you just tell by the opaqueness?). Most of the patches were around 250 um thick, although some were as much as 490 um thick. Mostly due to the thickness, but also due to the non-uniform size and shape of the patches, I believe that these micro hairs will be difficult to work with. I think that we will end up with feet similar to those that I brought to November SWRI (see bottom of this page). By that I mean that we will get non-uniform patches in both thickness and in shape.

Rick also sent me a one thin polyproplene patch fabricated using the larger (~3 cm diamter) filters. This one is 100 um thick and looks much more promising. Along with the sample you see in the picture below, he sent another piece that didn't have any hairs on it. I used this piece as my first test piece. I placed it on one of Stickybot's toes (attached with thin tape). There is a slight difference between the compliance of the two with the polypropylene and that without.

• Use quicktime 7.x with H.264 compressor to view GeckoFootwithThermoplastic.mov.

This could be remedied by removing the polypropylene around the toe joints or by using a softer toe material. I am concerned with the manufacturing process. It requires a good bit of handling to get the polyporpylene onto the foot. Next step is to look under a microscope to see the hairs on the polyporpylene patch. Confirm they are there. Attach it to the foot, and see if there is any damage to the hairs afterward.

I looked at the hairs under a microscope before attaching it to the foot. There seemed to be some good parts to the hair patch. The clear parts definitely had no hairs on them. There was enough of a patch to cover about 80% of one toe. You can see the results below.

The patch is attached with Scotch 467 Hi Performance adhesive which is a very thin tape. I like the tape much better than glue. Those of you who saw the hairs brought down to SWRI can see the difficulties of working with glue (It overflows into the hairs easily).

Next Steps

• Receive next batch of hairs from Berkeley, integrate into foot - got them!
• Manufacture 4 more feet (Should take about 5-6 days) - Finished.
• Send feet to Berkeley for testing - still working on it...

Nickel Masters

This is my first prototype of lamellar structures with microhair patches on it. I used the procedured outlined in ... to fabricate the patches.

There are a few shortcomings of this design.

1. The microhairs are not dense enough
2. The lamellar substrate interferes with the rear of the toes
3. The top part of the hard material located at the ends of the suspension structure will interfere with the ankle flexure. This can probably be taken care of by simply removing the top part of that structure
4. The attachment process is messy and leads to glue being placed in positions I don't want it.

I should be able to take care of points 1, 2, and 3 in the next design iteration. Point 4 will need to be addressed as I experiment with other manufacturing techniques. Perhaps I could use a syringe to dispense the glue?

After thinking about it some more, I don't think the glue is going to cut it. Glue has the possibility of running too much.