Chain & Shoal

The CoCoRo project is driven by a ‘big vision’, a search and rescue scenario where a swarm of autonomous underwater vehicles (AUVs) is deployed at the surface of a body of water. Their task is to find something, the black box of a downed plane for instance. As the swarm shoals to the bottom it must leave behind a ‘relay chain’ of AUVs to maintain communication with the surface. The swarm explores the sea bed, and the chain must follow it, always maintaining the communication line. As the swarm shoals further from the origin, where a team of anxious humans awaits the discovery of the black box, the chain must get longer. Hence, AUVs must dynamically re-assign themselves between chain and shoal functions. This can’t go on forever, eventually there won’t be any shoaling AUVs left. At this point the shoal should be informed that it must turn around, and not stretch the chain to breaking point. In this manner, the chain grows (and can also shrink) and moves with the shoal as it tries to locate the black box.

This is a hard problem, directed communication underwater is short range (at least on our robots), they can’t see each other very well, they are trying to navigate a 3D environment, and they have a tendency to float off and lose contact with the group. We’ve been working on shoaling in recent months, and have some solutions – at least in simulation – to this problem. Chain formation, navigation and dynamic reallocation of AUVs is harder still. But we are getting close. Below is a video showing proof of principle that it is possible, again, in simulation at least (it’s 3.7Mb, give it a second to load…)

There are some other assumptions made in the video: we have assumed for now that AUVs can locate one another’s relative position very well. In reality they will have to use bluelight LEDs and sensors, and can only determine the distance to another AUV within a 120 degree cone. But if you can’t make it work using “underwater GPS” then its certainly not going to work using bluelight. Getting this onto real platforms will be challenging, and cracking it will be quite an achievement. Check back here in 6 months!

Oh, in case anyone is interested, here’s a promotional video for CoCoRo with AUVs choreographed to do what we are now creating actual algorithms to accomplish autonomously (its pretty, but remember it’s not real).