Tiny bots can drag 2000 times their weight and climb with 100 times their weight

Microtugs are small robots created by Stanford. The small bots can apply orders of magnitude more force than it weighs. This is in stark contrast to previous small robots that have become progressively better at moving and sensing, but lacked the ability to change the world through the application of human-scale loads.

The work focuses on two major variants: a 12g ground based robot that can pull 40N in shear force, and a 9g climbing variant that can climb while carrying 10N of load. The papers discuss the controllable adhesive technology that makes these feats possible, as well as the constraints it puts on the designs and actuators. The ground based paper focuses on the concept of small robots with large loads, and the actuator work cycles necessary to enable these capabilities. The Climbing paper focuses on the anisotropic adhesion that is necessary to allow these robots to carry the continuous load present when there is no static friction in between steps.

The 9g climbing robot can carry over a kilogram vertically up glass. This is equivalent to a human climbing up a skyscraper while carrying an elephant.

A 12g micro robot uses controllable adhesive (like an Ants use) to pull 2 thousand of times its weight. This is the equivalent of a human adult dragging a blue whale around on land.

The super-strong bots – built by mechanical engineers at Stanford University in California – will be presented next month at the International Conference on Robotics and Automation in Seattle, Washington.

The secret is in the adhesives on the robots’ feet. Their design is inspired by geckos, which have climbing skills that are legendary in the animal kingdom. The adhesives are covered in minute rubber spikes that grip firmly onto the wall as the robot climbs. When pressure is applied, the spikes bend, increasing their surface area and thus their stickiness. When the robot picks its foot back up, the spikes straighten out again and detach easily.

µTugs: Enabling Microrobots to Deliver Macro Forces with Controllable Adhesives

the controllable adhesives used by insects to both carry large loads and move quickly despite their small scale inspires the µTug robot concept. These are small robots that can both move quickly and use controllable adhesion to apply interaction forces many times their body weight. The adhesives enable these autonomous robots to accomplish this feat on a variety of common surfaces without complex infrastructure. The benefits, requirements, and theoretical efficiency of the adhesive in this application are discussed as well as the practical choices of actuator and robot working surface material selection. A robot actuated by piezoelectric bimorphs demonstrates fast walking with a no-load rate of 50 Hz and a loaded rate of 10 Hz. A 12 g shape memory alloy (SMA) actuated robot demonstrates the ability to load more of the adhesive enabling it to tow 6.5 kg on glass (or 500 times its body weight). Continuous rotation actuators (electromagnetic in this case) are demonstrated on another 12 g robot give it nearly unlimited work cycles through gearing. This leads to advantages in towing capacity (up to 22 kg or over 1800 times its body weight), step size, and efficiency. This work shows that using such an adhesive system enables small robots to provide truly human scale interaction forces, despite their size and mass. This will enable future microrobots to not only sense the state of the human environment in which they operate, but apply large enough forces to modify it in response.

Vertical Dry Adhesive Climbing with a 100x Bodyweight Payload

The ability to carry large payloads could greatly increase the applications of small, low cost climbing robots. We present a linear inchworm gait that uses a single powerful actuator to climb. To make this gait possible, we leveraged two new methods of achieving controllable, anisotropic adhesion (one method produces over 200 times stronger adhesion in the preferred direction). With controllable, anisotropic adhesion, the gait is robust to missed steps. In addition, the gait provides a stance in which the robot can rest without requiring power. An autonomous 9 gram robot is able to climb a smooth vertical surface at 3 mm/s, while hoisting more than a kilogram. We also present a scaled down version of the robot, which is considerably smaller than any previous dry adhesive climbing mechanism. It is actuated by externally powered Shape Memory Alloy, weighs 20 mg, and is capable of hoisting 500 mg. These climbers show that a large hoisting ability while climbing can be achieved using dry adhesives, and the presented concepts could aid in the development of autonomous, highly functional, small robots.

Heavy lifting

All this adds up to robots with serious power. For example, one 9-gram bot can hoist more than a kilogram as it climbs. In this video it’s carrying StickyBot, the Stanford lab’s first ever robot gecko, built in 2006.

Another tiny climbing bot weighs just 20 milligrams but can carry 500 milligrams, a load about the size of a small paper clip. Engineer Elliot Hawkes built the bot under a microscope, using tweezers to put the parts together.

The most impressive feat of strength comes from a ground bot nicknamed μTug. Although it weighs just 12 grams, it can drag a weight that’s 2000 times heavier – “the same as you pulling around a blue whale”, explains David Christensen – who is in the same lab.

In future, the team thinks that machines like these could be useful for hauling heavy things in factories or on construction sites. They could also be useful in emergencies: for example, one might carry a rope ladder up to a person trapped on a high floor in a burning building.

Future work for these two robots presents many opportunities. First, adding further functionality to the 9 g climber, including robust turning and climbing downwards, is a first priority. Initial investigations in the realm show promise: two SMA actuators can pull the top pad to one side or the other for turning, and adding a simple mechanical switch actuated with SMA allows downward climbing. Adding material level anisotropy to the 9 g climber could further increase its efficiency. For the 20 mg climber, two parallel SMA actuators could allow turning. Creating an external heat source that could work over a long range, such as a laser, could power a large number of 20 mg climbers on a wall from a distance. Adding sensing is also desirable, such as line following for climbing up buildings. Another goal is to add the ability to step over obstacle, like a real inchworm does. This may involve a second small actuator or a linkage. The ability to climb rough, exterior surfaces could be added by integrating microspines [?] with the dry adhesive. With recent work on physical swarms of robots progressing rapidly, creating a large group of climbing robots with the ability to move tens of kilograms up a vertical surface is an intriguing future direction.

SOURCES- New Scientist, Youtube, Stanford

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