Whether they use wheels, treads, or even legs, robots often have trouble extricating themselves from situations they may encounter on a space mission. Their design can also prevent them from easily navigating around certain obstacles. The chances of hitting a roadblock only increase when human control is removed, as in the case of autonomous robots. Hopping robots inspired by the clumsy jumping of grasshoppers could prove to be the answer to giving robots unprecedented mobility for exploring other planets, gathering battlefield intelligence, and assisting police during standoffs or surveillance operations.
The hopping robots, developed by researchers at the Department of Energy’s Sandia National Laboratories, use combustion-driven pistons to make leaps as high as 20ft. When the combustion chamber fires, a piston punches the ground, propelling the hopper into the air.
One of the Sandia hopping robots is contained inside a grapefruit-sized plastic shell shaped like an egg so that the hopper rights itself after each jump with the piston facing towards 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 tiny hopper jumps about 3ft in the air and 6ft from its starting point on each jump and, theoretically, could last about 4,000 hops on a single tank of gas, which is about 20g of fuel. Each hopping cycle is about five seconds. Another hopper, about the size of a coffee can, is able to jump 10-20ft in the air and theoretically could achieve 100 hops on a tank of fuel.
Rush Robinett of Sandia’s Intelligent Systems and Robotics Center (ISRC) 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.’”
“Most mobile robots are designed to steer directly to a spot very efficiently,” says ISRC senior scientist Barry Spletzer. “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 the air. Once we determined that semi-random mobility was OK, we knew a hopper was possible.”
The researchers opted for a combustion-powered hopper because hydrocarbon fuels provide much greater energy densities than batteries and allow the hopper to travel greater distances and clear larger obstacles. Others had tried jumpers using electrically-actuated springs and different 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.
The team’s first attempts at developing the combustion engine did nothing more than topple the robot, but by perfecting the fuel mixtures and spark energies to achieve ignition, and by maximizing the power of the piston they were ultimately able to achieve hops higher than 30ft.
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, Spletzer 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,” says Spletzer. “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.”
To see what the hopping robot is capable when set on wheels, check out the video below of the robot propelling itself over a fence before continuing on its merry way.
