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Hop to it: Sandia hoppers leapfrog conventional wisdom about robot mobility

DARPA work leads to unique combustion jumper inspired during observant designer’s fishing trip

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SPRINGING OVER THE HEAD of co-developer Gary Fischer is a new hopping robot developed at Sandia’s Intelligent Systems and Robotics Center. This one, shown going through its paces in a multiple-exposure photograph, jumps about three feet high on each jump and could travel as far as five miles on a tank of gas. (Photo by Randy Montoya)
Download 300dpi JPEG image, ‘hop_pix.jpg’, 1 Mb

A hopping machine inspired by the clumsy jumping of grasshoppers may soon give robots unprecedented mobility for exploring other planets, gathering war-fighting intelligence, and assisting police during standoffs or surveillance operations.

The unique robot, developed at Sandia’s Intelligent Systems and Robotics Center 15200, uses a combustion-driven piston to make leaps as high as 20 feet. The work is funded by the Defense Advanced Research Projects Agency (DARPA).

Other mobile robots use wheels, treads like those on tanks, or insect-like legs to get over and around obstacles. Some are operated remotely by a person who can steer the robot clear of impediments. But reliable, autonomous mobility in difficult environments has eluded robot engineers and complicated planned planetary exploration missions.

Rush Robinett of Intelligent Systems Sensors and Controls Dept. 15211 conceived the idea of a hopping robot as he was catching grasshoppers to use for trout fishing.

"I noticed they jump around in a random fashion, hit the ground in an arbitrary orientation, right themselves, and jump again," he says. "I said to myself: ‘I can make a robot do that.'"

But making the idea work wasn’t easy. Others had tried jumpers using electrically actuated springs and other methods, but the energy required for a leap that could at least clear the robot’s own height was too great, and batteries wouldn’t last long enough for long-range missions.

Senior Scientist Barry Spletzer (15211) suggested that because hydrocarbon fuels provide much greater energy densities (energy per unit of volume) than batteries, a small combustion-powered hopper theoretically could travel greater distances and clear larger obstacles.

In 1997 DARPA asked Sandia to create a hopping robotic platform for military reconnaissance applications.

"Most mobile robots are designed to steer directly to a spot very efficiently," says Barry. "But over long distances you don’t need that kind of precision. With a hopper you have time to make corrections after each jump, so it doesn’t need to steer while it’s in the air. Once we determined that semi-random mobility was OK, we knew a hopper was possible." The hopping robot is contained inside a grapefruit-sized plastic shell shaped something like the children’s toy Weeble, so the hopper rights itself after each jump — piston toward the ground but slightly askew.

A pre-programmed microprocessor inside the hopper reads an internal compass, and a gimbal mechanism rotates the offset-weighted internal workings so that the hopper rolls around until it is pointed in the desired direction. The combustion chamber fires, the piston punches the ground, and the hopper leaps.

Achieving ‘topple’

One hopper jumps about 3 feet in the air and 6 feet from its starting point on each jump and can last about 4,000 hops — roughly five miles — on a single tank of gas, which is about 20 grams of fuel. Each hopping cycle is about 5 seconds. Another hopper developed by Sandia for DARPA as an experimental mobile landmine platform jumps 10 to 20 feet in the air and can go about 100 hops on a tank of fuel. The researchers are working to create a self-healing minefield, with hopping mines that sense an adversary’s mine-clearing operations and cooperate with each other to fill any gaps. The hoppers have been tested in a variety of conditions, and they performed reliably against obstacles, mud, sand, and rough terrain, says Barry.

Several patents are pending on the invention.

"We spent a long time getting here," says Gary Fischer (15211), who developed the robot’s unique internal combustion engine that makes it hop. "It wasn’t easy."

Recalling his youthful experience launching tennis balls out of a tube using lighter fluid, Gary first suggested that evaporated fuels might provide power needed for high hops. At one point the research team had set a goal of simply achieving atmospheric combustion in a small piston chamber. The first "jumps" did nothing more than topple the robot.

"Our first jumps were weak because we were looking for the correct fuel mixtures and spark energies to achieve ignition," he says. "When we finally made it fall over, we were happy."

Later the team tried maximizing the power of the piston, ultimately achieving hops higher than 30 feet. "When we did that we knew we were on to something," he says.

The research team now is working on a hopper that can be controlled remotely using a joystick, as well as hoppers with shock-absorbing rubber shells that can land on concrete.

Because the hopper is lightweight and could be inexpensive to produce, Barry foresees a variety of worldly uses for hoppers.

"You’d like a robot that Marines or SWAT teams could toss into a second story window, then hop it around for a look inside," he says. "That could save lives."

"But where we want to go is Mars and the moon," he says. "With a hopper, you could go much farther from the lander. You could throw out a dozen of these to search in all directions."

Last modified: Oct. 23, 2000