Edge of Innovation

MicroTug: This mini-robot can lift 2,000 times its own weight

Marek Hoffmann Autor, Hemd & Hoodie

What do a caterpillar and a gecko have in common? The answer: They were both the inspiration for the development of MicroTugs — arguably the strongest robots in the world.

At least, that is the case when comparing the robots’ strength relative to their “body weight”. The smallest of these robots was assembled under a microscope and weighs only 12 grams — but it can move a load of more than 24 kilograms. This corresponds to a factor of around 2,000!

Similar ratios can also be found in nature. For example, the male dung beetle—itself only a maximum of 11 mm long—can pull 1,141 times its own body weight. The mini-bots—developed by mechanical engineers at Stanford University in California—have yet another special feature: They can shift these enormous loads even on smooth and vertical surfaces.

Following in nature’s footsteps

Such a feat is made possible by imitating the mechanisms used by the two creatures previously mentioned and the way in which these mechanisms interact. To begin with, the robots have special components to provide motion.

Motion based on complex “sticky” gecko toe design

These components are based on the complex design of the “sticky” toes that geckos are famous for. They consist of hundreds of lamellae (or membranes) that are composed of millions of microscopically fine hairs, each of which is divided further into even thinner strands. These “split” ends use Van der Waals forces to interact directly with the molecules of the surface that the gecko is climbing on.

The connection between the two acts as an adhesive that can be detached in only one direction — a bit like a hook inserted into a loop. No additional force needs to be applied to break the adhesive bond. Instead, it is simply a matter of changing the direction in which the grip takes effect.

gecko feet

The researchers overcame this challenge as early as 2006, developing a first prototype—called the StickyBot—with feet made from an innovative “one-way adhesive” that consisted of microscopically small polymer hairs. The latest advancement on this development now also includes the split ends, which are only around 20 micrometers in width and which guarantee an even better grip.

Mini-bots mimic the motion of caterpillars

However, this mechanism alone would not enable the mini-robots to move weights of the magnitude mentioned above. For this to be achieved, the type of motion seen in caterpillars is required. Instead of crawling, caterpillars place their rear feet right next to their front feed, thus forming a bridge.

3d

The mini-bots imitate this style, but instead of using two pairs of feet that can be moved independently, they use two thin rubber mats. Firstly, these feet increase the surface area that the polymer hairs can grip to when under a load.

Secondly, one mat always remains firmly in place and holds the applied weight while the other mat pushes forwards. This minimizes the risk of the robot “slipping” and losing its grip.

Strong helpers in an emergency

One field of application in particular that has been identified by the researchers for these powerful devices is an industrial environment in which very heavy loads have to be moved back and forth.

Moving obstacles out of the way or transporting insertion tools

“Field work” is also feasible, for example in cases of natural disasters and accidents where obstacles have to be moved out of the way or where insertion tools need to be transported. For instance, in the event of a house fire, a ladder could be moved along the house wall to a higher floor to make it easier for people to escape.

team

Incidentally, the strongest robot in the world—based on outright lifting power—is called “Godzilla”. This robot is used in the automotive industry, has a weight of over 8.5 tons, and can lift a load of 1,350 kilograms.

Image 1: Wikipedia — Douglasy (CC BY-SA 3.0)
Image 2 & 3: Biomimetics & Dexterous Manipulation Lab, Stanford University 

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