Humans have long been inspired by the incredible abilities of ants. They can go anywhere, build vast underground networks, and carry objects more than 100 times their weight. Indeed, despite their diminutive size, ants seem to be able to affect the human world quite a lot. We may be tempted to attribute this amazing capability primarily to the muscular strength of insects, which is certainly impressive, however as Archimedes adeptly pointed out over 2000 years ago, the ground reaction forces are equally important:
"Give me a place to stand and with a lever I will move the whole world'' –Archimedes.
While humans rely on gravity and friction, both of these quantities become problematic as mass reduces with volume. At small scales, insects instead exploit interaction mechanisms like adhesion that, unlike coulomb friction, scale with area and do not depend on the magnitude of a normal force. However, adhesion without a method of release is not useful; an insect or robot would become stuck and could not move. In addition, at smaller scales, legged locomotion requires higher step rates than at larger scales to maintain the same absolute velocity. Therefore, the "controllable" adhesives that ants use must engage and disengage more quickly at small scales.
The goal of this work is to build microrobots that are inspired by ants to apply forces that are large enough to appreciably affect the human scale world. We want to build microrobots that can not only explore a disaster site in a search and rescue mission, but pull the survivors to safety when they are found. We have developed the first step toward that goal: a family of "µTug" robots that use a controllable adhesive, just like ants, to move objects up to 2000 times their size, while still being able to run at 30Hz. In order to build such robots, we examine 4 core properties of the adhesives and the actuators required to use them. We also explore the interactions of microrobots working as teams to move loads well beyond the capability of a single robot. Unlike many microrobots, the µTugs are shown to achieve near perfect sharing of load so force capabilities for a team are simply linear with number of robots. Thus a team of 6 microrobots, with a total mass of 100g, was capable of exerting enough force to move the author's 1800kg automobile.
David Christensen is finishing his Ph.D. in mechanical engineering this quarter. Before coming to Stanford for the graduate degree, he served as Director of Research and Development at Valimet Inc. a manufacturer of micron sized spherical metal powders used in applications including aerospace (solid rockets and turbine blades), metallic 3d printing, automobile airbags, solar panels, and metallic pigments. David focused on Mechatronics, MEMS, Smart materials and Biomechanics in his time at Stanford. He worked on synthetic gecko adhesives, robotic sensors, and microrobotics with Prof. Mark Cutkosky as well as the design of resonant MEMS sensors with Prof. Tom Kenny. David is also an Accel Innovation Scholar: a Stanford program built to enable late stage graduate students with the tools needed to undertake entrepreneurial endeavors such as bringing their research out of lab and into the world.