Ask most people to name a super-agile creature, and you wouldn't expect cockroaches to come high up on the list; unless you were talking to Devin Jindrich and Bob Full. Insects are extraordinary creatures because `they can go anywhere' says Full, which made him wonder how these creatures keep their balance even in the most rugged conditions. Most animals are believed to maintain balance by relying on neurally-controlled reflexes. But Full and Jindrich suspected that some of the creatures' reactions to rough terrain were simply too fast to be controlled by the creature's nervous system. They wondered whether the insect's musculoskeletal system was somehow returning the animal to the straight and narrow (p. 2803).
Full teamed up with a group of mathematicians to see if it was possible to derive a simple mechanical model to account for the insect's remarkable stability. They began modelling the insect's legs as a simple spring, attached to a solid body, with remarkable success. But could this simple model, with no nervous system, capture the way the real animal moved? The team needed to test how quickly running cockroaches reacted when suddenly knocked off balance.
Jindrich would have to deliver a jolt faster than a single cockroach step, but cockroaches are so speedy that each step lasts as little as 50 ms. Eventually, Jindrich came up with the idea of sticking a cockroach-sized cannon to an insect's back that knocked the insect off course by firing a minute projectile sideways. Jindrich built the tiny cannon from a plastic pen and fired it with gunpowder to deliver a 10 ms jolt while the insect was running. He videoed the insect's recovery with three high-speed cameras and repeated the experiment without firing the cannon so that he could see how quickly the insect recovered from being knocked sideways. After months of patiently analysing the cockroaches' perturbed trajectories, the two scientists realised that the insects successfully regained their course in the space of a single step, without even breaking their stride. They were able to self-stabilize faster than their nervous system was likely to control the recovery, just as the mathematical model predicted.
Full has since gone on to prove that his springy limb model is not only elegant, but practical too. Inspired by the cockroach, Full and a team of engineers have designed a robot propelled on six springy legs that runs over tough terrain just like a flesh-and-blood cockroach. He adds that the robot's ability to self-stabilize has liberated a huge amount of computing power that the engineers can apply to simulate other sophisticated behaviours.
- © The Company of Biologists Limited 2002