Shear limits of thermoplastic gecko-inspired adhesive

Our work on the wear and high-cycle properties of gecko synthetic adhesives has been published in Langmuir.

Langmuir_TOC

We examined the behavior of high-density polyethylene (HDPE) and polypropylene (PP) microfiber arrays during repeated cycles of engagement on a glass surface, with a normal preload of less than 40 kPa. We found that fiber arrays maintained 54% of the original shear stress of 300 kPa after 10 000 cycles, despite showing a marked plastic deformation of fiber tips. This deformation could be due to shear-induced plastic creep of the fiber tips from high adhesion forces, adhesive wear, or thermal effects.

We hypothesize that a fundamental material limit has been reached for these fiber arrays and that future gecko synthetic adhesive designs must take into account the high adhesive forces generated to avoid damage. Although the synthetic material and natural gecko arrays have a similar elastic modulus, the synthetic material does not show the same wear-free dynamic friction as the gecko.

Fiber_Damage

Matterhorn Peak June 2011

Via the East Couloir, Nick Kohut and I made a very pleasant ascent of Matterhorn Peak (12,279′).

P1040288

Matterhorn peak on approach: Nick seen as a tiny dot in the shadow.

A little mist on the way up, gave us some great views of the sawtooth ridge poking through. I had also got Nick to agree to me bringing my skis along and skiing the descent while he down climbed – very gracious. Unfortunately, the east couloir was just burned enough to make skiing it impossible, so we skirted along the ridge to the top of the ski dreams descent. It was a bit firm, but a great descent overall. While glissading, Nick took a bit of a slide and scraped up his arms some before self-arresting. But a few gel-shots later to give him a boost, he was back on his feet.

In the gut of the E couloir

We raced out the trailhead, trying to make the lockers where we had stored some supplies (read: whiskey) before the building closed. We finished off the day with some zucchini sticks at rhino burger in Bridgeport.

Here is a link to more photos: Mine and Nicks

Microconnector for Modular Robots

Our work on low-profile microconnectors for modular robots has been published in The Journal of Micromechanics and Microengineering in October 2010.

SEM cross section

This image shows the connector fabricated on a posterboard backing, however, they can be fabricated on a wide variety of backings from silicon wafer to cloth.

robot stills

We have developed a micromolded connector for applications such as folded millirobots  here reusability, low engaged profile and rapid assembly are required. Using laser micromachining and micromolding techniques, the microconnector is formed with a manufacturing process that can be integrated with the rapid prototyping of the millirobots. The microconnector engages through shear in one direction while forming a strong connection in orthogonal directions, with an engaged thickness of 200 microns. The microconnectors have been shown to be strong in the shear and normal pull-off directions with strengths of 42 and 27 N/cm^2, respectively, as well as being robust to shear failure, maintaining over 65% of their strength after being run to failure ten times. Due to the anisotropic property of the microconnector, it can also be rapidly engaged and disengaged repeatedly in the release direction without degrading the connector strength. The microconnectors have also been successfully integrated into various millirobots for quick appendage changes, showing their applicability to millirobots.

One possible use for the microconnector: allowing modular robots to combine into larger functional units, as shown in this animation below:

PM robot assembly