# Scurrying Roaches Help Researchers Steady Staggering Robots

Cool Physics

The new “measure” does this by focusing on an overarching phenomenon in the walking legs, which can be seen as pendula moving back and forth. For great locomotion, they need to synch up in what is called phase-coupling oscillations.

A fun, easy experiment illustrates this physics principle. If a few, say six, metronomes – ticking rhythm pendula that piano teachers use -- are swinging out of sync, and you place them all on a platform that freely sways along with the metronomes’ swings, the swings will sync up in unison.

The phases, or directions, of their oscillations are coupling with each other by centralizing their composite mechanical impulses through the platform. This particular example of phase-coupling is mechanical, but it can also be computational or neurological -- like in the roach.

Its legs would be analogous to the swinging metronomes, and central neuromuscular activity analogous to the free-swaying platform. In the roach, not all six legs swing in the same direction.

“Their synchronization is not uniform. Three legs are synchronized in phase with each other -- the front and back legs of one side with the middle leg of the other side -- and those three are synchronized out of phase with the other three,” Neveln said. “It’s an alternating tripod gait. One tripod of three legs alternates with the other tripod of three legs.”

Useless Pogoing

And just like pendula, each leg’s swings can be graphed as a wave. All the legs’ waves can be averaged into an overall roach scurry wave and then developed into more useful math that relates centralization with decentralization and factors like entropy that can throw locomotion control off.

The resulting principles and math benefited the clunky robot, which has strong decentralized signals in its leg motors that react to leg contact with the ground, and centralized control weaker than that of the stick bug. The researchers graphed out the robot's movements, too, but they didn't result in the neatly synced group of waves that the cockroach had produced.The researchers turned with the principles and math to the clunky robot, which initially was out of sorts -- bucking or hopping uselessly like a pogo stick. Then the scientists strengthened centralized control by re-weighting its chassis to make it move more coherently.

“The metronomes on the platform are mechanical coupling, and our robot coordinates control that way,” Neveln said. “You can change the mechanical coupling of the robot by repositioning its weights. We were able to predict the changes this would make by using the measure we developed from the cockroach.”

Cockroach Surprises

The researchers also wired up specific roach muscles and neurons to observe their syncopations with the scurry waves. Seventeen cockroaches took 2,982 strides to inform the principles and math, and the bugs also sprung surprises on the researchers.

One stuck out: The scientists had thought signaling centralized more when the roach sped up, but instead, both central and local signaling strengthened, perhaps doubling down on the message: Run!

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