engineers build robotic bugs that can go the distance
David F. SalisburyMechanical
engineers at Vanderbilt University have designed and constructed
a small robotic "bug" that can scuttle more than half a mile on
a single battery charge.
December 1, 2000
The leader of the project, Michael Goldfarb ,
reported on the development of what may be the smallest-sized robot
capable of traveling significant distances at a special workshop
on mobile micro-robots on Friday, April 28, at the IEEE
Conference on Robotics and Automation in San Francisco.
"We set out to
determine just how small we can make viable robotic technology,
and we’ve done that," says Goldfarb.
they started out with even tinier versions, the smallest practical
robot that the researchers could produce turned out to be about
the size of one of those giant rhinoceros beetles found in thetropics.
It is about three inches long and weighs about two ounces.
two-and-a-half year program to develop the robotic bugs is part
of a larger program funded by the Defense Advanced Research Projects
Agency (DARPA) that is exploring the use of mobile micro-robots
for military reconnaissance and intelligence gathering. The basic
idea is that soldiers could carry large numbers of these lightweight,
mechanical scouts and use them to investigate the terrain ahead,
detecting enemy troops, minefields and other hazards.
To achieve a minimum size, Goldfarb and Ephrahim Garcia
took a different approach. They decided to combine batteries with
an unusual material called piezoelectric ceramic (PZT) that physically
expands when an electrical voltage is applied to it.
locomotion at this scale PZT had a number of potential advantages,
the researchers figured. "It can be made in one piece,"
says Goldfarb. "There are no significant lower limits to the
size of the actuators that you can make. They are also very energetically
conservative: They don’t throw away a lot of energy, so most of
the electrical energy comes out as mechanical energy." In this
respect PZT is 90 percent efficient, compared to about 60 percent
for DC electric motors.
years ago, when we began this project, we did not know whether this
alternative design paradigm would work," he says. In fact,
Goldfarb and his research team, which consists of research engineers
Mike Gogola and Dan Monopoli plus four graduate and undergraduate
students, went through more than 10 prototypes before achieving
an optimal design.
One of their major challenges was creating a mechanism that would
travel at a reasonable speed. "The first few designs that we
came up with had maximum speeds of about a millimeter per second,
about one three-hundredths of what we can do now," Goldfarb
final design can cover about a foot per second and carry a one-ounce
payload. That allows it to tote a battery that can keep it running
for 45 minutes, long enough to cover about a half mile. The lightest
chip video cameras available commercially weigh about half an ounce,
so the insectile robot is perfectly capable of carrying one, although
the researchers haven’t done so.
a second DARPA grant, the Vanderbilt researchers have been attempting
to apply this same approach to create flying robotic bugs, micro-ornithopters
that fly by flapping their wings. But here the engineers may have
run into a fundamental obstacle. PZT ceramics are highly efficient
but they are
heavy. The critical factor in mechanical flyers is not energy
efficiency, but energy density the amount of energy that a device
can develop per ounce.
group has designed and tested a number of different micro-ornithopters.
But so far none of them has been able to lift its own weight. For
the last few months, the researchers have been doing experiments
to determine exactly how much power PZT actuators can deliver and
to see if there are any tricks they can use to make them deliver
more. So far, none of the tricks they’ve tried have worked.
While the Vanderbilt group has concentrated on the issue of locomotion,
other research groups are looking at controllers that allow them
to navigate and give them some degree of artificial intelligence.
Still others are exploring different kinds of payloads that they
could carry such as motion sensors, video cameras, microphones and
other sensor-packs to detect land mines, toxic gases and biological
Proponents point out that robotic creepy-crawlers of this sort might
also find a number of non-military applications in law enforcement,
security, and inspection of pipes, ducts and other inaccessible
or hazardous areas.
Center for Intelligent Mechatronics:
DARPA’s Microsystems Technology Office Distributed Robotics:
Prof. Michael Goldfarb’s home page: