One of the biggest challenges facing researchers who are working on small robots is how to power them. The problem is that most batteries add significantly to the weight and take up lots of space inside small robots, making them impractical. Scientists have come up with a robot called the RoBeetle that doesn’t use a battery, instead relying on liquid methanol for power.
The body of the RoBeetle is a fuel tank filled with methanol. It has four legs with the rear legs fixed and the front legs attached to a transmission. The transmission is connected to a leaf spring-tensioned in a way that pulls the legs backwards. Its design allows the robot to stand upright when still.
The actuator used inside the robot is a nickel-titanium shape-memory (SMA) alloy. It’s a wire that gets longer when it heats up and shrinks when it cools down. That wire is coated “messily” in platinum. The mechanical design of the system is able to modulate the flow of fuel using a purely mechanical system.
The actuation cycle that causes the robot to walk begins with a full fuel tank and a cold SMA wire. The platinum coating of the wire facilitates a reaction with the methanol and oxygen in the air to generate a couple of water molecules and carbon dioxide along with heat. The messy platinum coating is important as it allows a lot of surface area for the platinum to interact with as much methanol as possible.
In a second or two, the SMA wire can increase in temperature from 50 to 100 degrees Celsius thanks to the reaction. With each punctuation, the robot moves forward by 1.2 millimeters. The top speed for the robot is 0.76 millimeters per second.