MIT’s miniature robots fly using artificial muscles

Researchers have used a new manufacturing technology to produce low-voltage, soft actuators that can lift an insect-like drone into the air.

MIT researchers had already succeeded in building working insect robots with artificial muscles less than a year ago, and while they were robust and functional, their efficiency was far below that of similarly small actuators. Researchers have since developed a method to create artificial muscles that operate at roughly 75% less tension than current versions, while being able to carry roughly 80% more payload. These have been used to build the next generation of MIT insect robots.

The soft actuators produced at MIT are made from layers of elastomer sandwiched between two very thin electrodes and then shaped into a smooth cylinder. When a voltage is applied to the actuator, the electrodes compress the elastomer and use this mechanical stress to move the wing. As MIT researchers have experimented, the larger the surface area of the actuator, the lower the voltage needed. So the researchers tried to build these artificial muscles by alternating as many layers of ultra-thin elastomer and electrode as they could.

For the first time, the researchers have succeeded in building an actuator with 20 layers, each only 10 micrometres thick, about the diameter of a red blood cell. However, this presented MIT scientists with a new challenge: the elastomers are stretched to the right thinness by centrifugation, and in many cases bubbles as small as a micrometre are formed in the process. At this micrometre size, these bubbles can cause significant inefficiencies. However, experiments have shown that it makes sense to pump out the bubbles after centrifugation, while the elastomer is still wet, and then to dry it. Removing the bubbles increased the force exerted by the actuator by almost 300% and also significantly increased its lifetime.

The researchers have also optimised the thin electrodes to be assembled with elastomers, which are made of carbon nanotubes with a diameter of about fifty thousandths of the diameter of a human hair. The higher concentration of carbon nanotubes increases the actuator’s performance, but the dense layers also contain more defects. Once the researchers had successfully created the 20-layer artificial muscle, they used it to build the next version of an insect-like robot powered by soft actuators.

In flight tests, the 20-layer elastomer actuator required less than 500 volts to operate, while the robot could lift more than three times its weight with their help. The robot has also completed a 20-second hover, which may not seem like much, but one of its creators says it is the longest flight ever achieved by a robot smaller than a gram. The artificial muscle also performed flawlessly after more than 2 million contractions.

Source: MIT