Servo - December 2014

bots IN BRIEF

SERVO 12.2014 17

We’re all used to seeing two basic types of hovering robots. The first type is the more traditional helicopter design with a single main rotor (or two) and maybe a little tail rotor. The second type is the pervasive quadcopter (or hexacopter or octocopter or whatever). With a helicopter, you have to manage a very complex multiple-actuator linkage system for control and stability, and quadcopters have at least as many motors as they do rotors.

The Modular Robotics Laboratory at the University of Pennsylvania has been seeing what it takes to reduce both the complexity and number of actuators of rotorcraft, and they’ve come up with some very cool solutions.

To clarify what’s going on here, the rotor at the top (the bottom one is fixed) has to alter its angle of attack every single time it spins around — which is 40 times every second. It’s a complex thing to control, and if you’re trying to do it with just one motor you have to somehow manage to make it work with the only thing you do have control over: the acceleration of said motor.

By reducing the number of motors and actuators, the price of the robot drops drastically, plus, its weight goes down and endurance goes up making it much more versatile.

Part of what makes snakes so adaptable is how they can choose from a variety of gaits depending on what they’re trying to do or where they’re trying to go. Robot snakes can do this too, and in some ways they can do it even better because they can execute behaviors that real snakes don’t know how to do — like rolling longitudinally to climb up poles.

However, we still have a lot to learn about how and why snakes move the way they do. In the latest issue of Science, researchers from Georgia Tech, roboticists from Carnegie Mellon, and herpetologists from Zoo Atlanta describe how sidewinders climb up steep sandy slopes, and show how snake robots can learn from their technique.

When a sidewinder moves, the parts of its body that are in contact with the ground remain still. This helps to minimize slip — especially on loose surfaces like sand or dirt. The value of this technique increases as the slope increases, since slipping becomes more likely. The researchers want to figure out exactly how the snakes would change their gaits to better adapt to steeper slopes.

High speed footage of six adult sidewinders from Zoo Atlanta revealed that the snakes would progressively increase the length of their bodies in contact with the sand as the slopes got steeper (up to 20 degrees of incline), keeping themselves stable. Other kinds of pit vipers who didn’t use this sidewinding motion would tumble down the hill instead.

Snake robots are versatile and durable, and teaching them to climb steep slopes covered in loose granular material seems like it would come in especially handy somewhere like, say, Mars. Yep, we’re talking about snake robots in space.