Servo - January 2016

Bot Feet Aid Copter Versatility

Helicopters are pretty useful vehicles, but they come with a range of inherent problems including low speed, high complexity, rotor lift dissymmetry, gearbox and drive train vibration, and so on. Because they are essentially flying weed whackers, you can’t land one in the woods, and their skid-based landing gear requires a flat and stable surface. The latter characteristic puts serious limits on their use in natural disaster zones, on ships at sea, and in other places where they might be needed.

However, the folks at the US Defense Advanced Research Projects Agency (DARPA, www.darpa.mil) have been working with Georgia Tech ( www.gatech.edu) to improve their ability to operate from angled, irregular, and moving surfaces. The result is a novel robotic landing gear system that uses four articulated jointed legs that are equipped with force-sensitive contact sensors. In flight, the legs fold up to the fuselage. When landing, they extend and — using the sensors — automatically determine the correct angle to keep the vehicle level and prevent the rotors from striking the ground.

A test flight demonstrated: (1) a 500 percent reduction in damage resulting from hard landings; ( 2) stable takeoff and landing on slopes up to 20° and on irregular terrain; and ( 3) the ability to land on ships in violent sea conditions — all without adding much extra weight.

Is there a video, you ask? Well, sure: www.youtube.com/watch?v=OtJ3ik96PjM. DARPA’s unmanned helicopter fitted with robotic landing gear. by Jeff and Jenn Eckert

Robytes

Hedgehogs in Space

Typically, vehicles designed to move around on the moon, Mars, and other extraterrestrial locations roll around on wheels or tracks. As demonstrated by NASA’s Spirit rover, this isn’t necessarily the most effective way to travel in microgravity or over rough surfaces — particularly on smaller bodies such as comets and asteroids. Taking a completely different approach is Hedgehog: a prototype being developed along two different but parallel lines by NASA’s Jet Propulsion Lab ( www.jpl.nasa.gov), Stanford University ( www.stanford.edu), and MIT ( web.mit.edu). Specifically designed to hop and tumble on the surface instead of relying on wheels, the cube-shaped robot’s movement is created by alternately spinning and braking three internal flywheels, corresponding to X-Y-Z Cartesian axes. It also incorporates spikes on each corner to protect the vehicle and act like feet.

Future versions could incorporate various instruments in the spikes such as probes and sensors. Hedgehog can operate the same no matter which side it lands on, so tip-overs are not an issue. The standard procedure is to point itself in the desired direction (yaw), then hop long distances using one or two spikes, or just tumble short distances by rolling from one face to another. It can also perform a “tornado” maneuver in which is spins and launches itself from the surface to, e.g., escape from a sinkhole.

The prototypes weigh about 11 lb ( 5 kg) but could end up twice as heavy when equipped with cameras and instruments. A significant advantage is that a Hedgehog robot is relatively cheap by rover standards, so several could be released by the mothership, letting them spread out to explore independently.