GhostBot Knifes Its Way Into Aquatic Automation

Taking their cue from nature, researchers at Northwestern University have created the GhostBot, a robotic knifefish that can swim both horizontally and vertically.

Humankind is excellent at building machinery that has no corollary in nature - cars and plans are loose approximations on large animals and birds but are slow and ponderous in comparison. A recent wave of environmental scholarship has led to a number of designs which incorporate aspects of the natural in the robotic rather than trying to out-do what nature has created, and so it is with the robotic knifefish known as GhostBot.

Brainchild of Malcom MacIver, Oscar Curet and Neelesh Patankar, the GhostBot is a robotic approximation of the black ghost knifefish, which hunts at night in the Brazilian Amazon basin. Using a weak electric field to detect its prey in the murky waters, the knifefish has a long ribbon-like fin on the bottom of its body to drive its movement forward. This alone was enough to interest the team, but their curiosity piqued when they saw a captive knifefish stop its forward motion and suddenly begin moving vertically almost instantly.

What they discovered was that when the fish was moving forward or backward, only one wave was being created by its ribbon fin - front to back or back to front, but when it chose to move upward, two waves were created, one running in from head to tail and one from tail to head. These "inward counterpropogating waves" met in the middle of the fish and funneled down into a jet that drove the fish up.

This discovery fuelled the team to create GhostBot, which they designed with 32 independent motors that allow for individual movement of 32 fin layers. On its first test run, GhostBot was able to accurately simulate the movement of the knifefish, leading to hopes of underwater robots that may one day be as mobile as fish themselves.

Nature specializes in creatures that feature high mobility in order to track and capture prey or to elude predators, something most macro-sized robot designers ignore in favor of brute strength.

Thankfully, the GhostBot is not simply something we hear going bump in the night.

Source: Northwestern University