February 23, 2013
Running Cockroaches Give Robotics A Fast Track To Success
[WATCH VIDEO: From Running Roaches To Robots]
April Flowers for redOrbit — Your Universe Online
The roaches being tested were able to maintain their footing mechanically by using their momentum and the spring-like architecture of their legs, rather than neurologically by relying on impulses sent from their central nervous system to their muscles.
"The response time we observed is more than three times longer than you'd expect," said Shai Revzen, an assistant professor of electrical engineering and computer science, as well as ecology and evolutionary biology, at the University of Michigan.
"What we see is that the animals' nervous system is working at a substantial delay," he said in a statement. "It could potentially act a lot sooner, within about a thirtieth of a second, but instead, it kicks in after about a step and a half or two steps–about a tenth of a second. For some reason, the nervous system is waiting and seeing how it shapes out."
The research team sent 15 cockroaches running across a small bridge onto a placemat-sized cart on wheels. The roaches were sent one at a time, for a total of 41 trials. The cart was attached to an elastic cord, pulled tight like a loaded slingshot. This was held in place by a strong magnet on the other side. The researchers released the magnet once the roach was approximately one body length onto the cart. The force of the cart's movement is equivalent to a sumo wrestler hitting a jogger in a flying tackle. Revzen said that cockroaches are much more stable than humans.
The technique used to gather information about the roaches gait was developed by Revzen several years ago. It is called kinematic phase analysis and involves using a high-speed camera to continually measure the position of each of the insects' six feet as well as the ends of its body. The camera sends the images to a computer that merges the continuous data from all these points into an accurate estimate of the roach's position in its gait cycle at all times. This gives the research team a much more detailed picture than the common metric used to study gait — measuring the timing of footfalls.
Kinematic phase analysis converts the signals into a wave graphic, illustrating the insect's movement pattern — a pattern that only changes when the nervous system kicks in. The researchers implanted electrodes into the legs of seven cockroaches to measure nerve signals in a separate but similar experiment.
The team observed a nervous system delay that was substantially longer than they expected, running contrary to assumptions in the robotics community. In robotics, computers replace brains and movements are guided by continuous feedback to the computer from sensors on the robots' feet.
According to Revzen, the new findings might imply that the biological brain adjusts the gait only at whole-step intervals — at least in cockroaches — rather than at any point in a step. Using periodic, rather than continuous, feedback systems might lead to more stable and energy efficient walking robots.
Nature is often an inspiration for robot makers because animals have to respond to unexpected situations like rocky, uneven ground and damaged limbs as they move through the world. Revzen's team believes that studying the patterns in how they move as they adjust to these challenges could give away how their machinery and neurology work together.
"The fundamental question is, 'What can you do with a mechanical suspension versus one that requires electronic feedback?" Revzen said. "The animals obviously have much better mechanical designs than anything we know how to build. But if we could learn how they do it, we might be able to reproduce it."
Wheeled and tracked vehicles are not able to navigate more than 70 percent of Earth's land surface. Legged robots could bridge the gap for ground-based operations such as search and rescue or defense.
Revzen expects that his kinematic phase analysis could be valuable in the biomedical community for human gait analysis because of it is noninvasive and high-resolution.
"Falls are a primary cause for deterioration in the elderly," Revzen said. "Anything we can do to understand gait pathology and stabilization of gait is very valuable."