Study of 20,000 jumps shows how a hopping robot could conserve its energy

October 29, 2012 by John Toon
Georgia Tech Assistant Professor Daniel Goldman (left) and Graduate Student Jeffrey Aguilar examine a simple robot built to the dynamics of jumping. The research could lead to reduced power consumption by hopping robots. Credit: Gary Meek

A new study shows that jumping can be much more complicated than it might seem. In research that could extend the range of future rescue and exploration robots, scientists have found that hopping robots could dramatically reduce the amount of energy they use by adopting a unique two-part "stutter jump."

Taking a short hop before a big jump could allow spring-based "pogo-stick" robots to reduce their as much as ten-fold. The formula for the two-part jump was discovered by analyzing nearly 20,000 jumps made by a simple laboratory robot under a wide range of conditions.

"If we time things right, the robot can jump with a tenth of the power required to jump to the same height under other conditions," said Daniel Goldman, an assistant professor in the School of Physics at the Georgia Institute of Technology. "In the stutter jumps, we can move the mass at a lower frequency to get off the ground. We achieve the same takeoff velocity as a conventional jump, but it is developed over a longer period of time with much less power."

The research was reported October 26 in the journal . The work was supported by the Army Research Laboratory's MAST program, the Army Research Office, the National Science Foundation, the Burroughs Wellcome Fund and the GEM Fellowship.

is an important means of locomotion for animals, and could be important to future generations of robots. Jumping has been extensively studied in , which use stretched tendons to store energy.

The Georgia Tech research into robot jumping began with a goal of learning how hopping robots would interact with complicated surfaces – such as sand, granular materials or debris from a disaster. Goldman quickly realized he'd need to know more about the physics of jumping to separate the surface issues from the factors controlled by the dynamics of jumping.

Inspired by student-directed experiments on the dynamics of hopping in his and chaos class, Goldman asked Jeffrey Aguilar, a graduate student in the George W. Woodruff School of Mechanical Engineering, to construct the simplest jumping robot. Aguilar built a one-kilogram robot that is composed of a spring beneath a mass capable of moving up and down on a thrust rod. Aguilar used computer controls to vary the starting position of the mass on the rod, the amplitude of the motion, the pattern of movement and the frequency of movement applied by an actuator built into the robot's mass. A high-speed camera and a contact sensor measured and recorded the height of each jump.

Aguilar and Goldman then collaborated with theorists Professor Kurt Wiesenfeld and Alex Lesov, from the Georgia Tech School of Physics, to explain the results of the experiments.

The researchers expected to find that the optimal jumping frequency would be related to the resonant frequency of the spring and mass system, but that turned out not to be true. Detailed evaluation of the jumps showed that frequencies above and below the resonance provided optimal jumping – and additional analysis revealed what the researchers called the "stutter jump."

"The preparatory hop allows the robot to time things such that it can use a lower energy to get to the same jump height," Goldman explained. "You really don't have to move the mass rapidly to get a good jump."

The amount of energy that can be stored in batteries can limit the range and duration of robotic missions, so the stutter jump could be helpful for small robots that have limited power. Optimizing the efficiency of jumping could therefore allow the robots to complete longer and more complex missions.

But because it requires longer to perform than a simple jump, the two-step jump may not be suitable for all conditions.

"If you're a small robot and you want to jump over an obstacle, you could save energy by using the stutter jump even though that would take longer," said Goldman. "But if a hazard is threatening, you may need to expend the additional energy to make a quick jump to get out of the way."

For the future, Goldman and his research team plan to study how complicated surfaces affect jumping. They are currently studying the effects of sand, and will turn to other substrates to develop a better understanding of how exploration or rescue robots can hop through them.

Goldman's past work has focused on the lessons learned from the locomotion of biological systems, so the team is also interested in what the robot can teach them about how animals jump. "What we have learned here can function as a hypothesis for biological systems, but it may not explain everything," he said.

The simple jumping turned out to be a useful system to study, not only because of the interesting behaviors that turned up, but also because the results were counter to what the researchers had expected.

"In physics, we often study the steady-state solution," Goldman noted. "If we wait enough time for the transient phenomena to die off, then we can study what's left. It turns out that in this system, we really care about the transients."

Explore further: Researcher designs robot that jumps like a grasshopper

More information: Control a demonstration of the jumping studied in this project

Aguilar, Jeffrey et al., "Lift-off dynamics in a simple jumping robot," Physical Review Letters (2012): prl.aps.org/abstract/PRL/v109/i17/e174301

Related Stories

Frogs' amazing leaps due to springy tendons

November 16, 2011

Some species of frogs and many other animals are able to jump far beyond what appear to be their capabilities. The trained contestants in the frog-jumping competition in Calaveras County, Calif., come to mind, but even ordinary ...

Recommended for you

How to curb emissions? Put a price on carbon

September 3, 2015

Literally putting a price on carbon pollution and other greenhouse gasses is the best approach for nurturing the rapid growth of renewable energy and reducing emissions.

Customizing 3-D printing

September 3, 2015

The technology behind 3-D printing is growing more and more common, but the ability to create designs for it is not. Any but the simplest designs require expertise with computer-aided design (CAD) applications, and even for ...

Magnetic fields provide a new way to communicate wirelessly

September 1, 2015

Electrical engineers at the University of California, San Diego demonstrated a new wireless communication technique that works by sending magnetic signals through the human body. The new technology could offer a lower power ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.