MIT researchers have demonstrated diminutive drones that can zip around with bug-like agility and resilience, which could eventually perform tasks such as pollinating a field of crops or searching for survivors amid the rubble of a collapsed building. The soft actuators that propel these micro-robots are very durable, but they require much higher voltages than similarly sized rigid actuators. The featherweight robots can’t carry the necessary power electronics that would allow them fly on their own.
Now, these researchers have pioneered a fabrication technique that enables them to build soft actuators that operate with 75 percent lower voltage than current versions while carrying 80 percent more payload. These soft actuators are like artificial muscles that rapidly flap the robot’s wings.
This new fabrication technique produces artificial muscles with fewer defects, which dramatically extends the lifespan of the components and increases the robot’s performance and payload.
The rectangular micro-robot, which weighs less than one-fourth of a penny, has four sets of wings that are each driven by a soft actuator. These muscle-like actuators are made from layers of elastomer that are sandwiched between two very thin electrodes and then rolled into a squishy cylinder. When voltage is applied to the actuator, the electrodes squeeze the elastomer, and that mechanical strain is used to flap the wing.
The more surface area the actuator has, the less voltage is required. So, the research team build these artificial muscles by alternating between as many ultrathin layers of elastomer and electrode as they can. As elastomer layers get thinner, they become more unstable.
For the first time, the researchers were able to create an actuator with 20 layers, each of which is 10 micrometers in thickness. After they created a 20-layer artificial muscle, they tested it against their previous six-layer version and state-of-the-art, rigid actuators.
During liftoff experiments, the 20-layer actuator, which requires less than 500 volts to operate, exerted enough power to give the robot a lift-to-weight ratio of 3.7 to 1, so it could carry items that are nearly three times its weight.
They also demonstrated a 20-second hovering flight, the longest ever recorded by a sub-gram robot, according to the researchers. The 20-layer actuator was still working smoothly after being driven for more than 2 million cycles, far outpacing the lifespan of other actuators.
Now, the team is limited to how thin they can make the layers and aims to reduce the thickness to only 1 micrometer, which would open the door to many applications for these insect-sized robots.