Robotic Fish

             

 Robotic Fish:       

SoFi is a fairly small robot, about a foot and a half long and weighing in at just 3.5 pounds. A hydraulic pump moves water in its soft rubber tail from side to side, allowing it to swim in a fish-like motion. Electronics including a Linux PC, along with a fisheye lens, are stored in the robot's head. It runs off a small battery similar to what you would find in your smartphone, and in its current iteration it can swim for about 40 minutes at a time. A robot fish is a type of bionic robot, which has the shape and locomotion of a living fish.MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) have built a fish robot that can swim in the open water alongside the very animals it is researching. Robotic fish have become increasingly sophisticated in recent years. They are now "secret agents" that can infiltrate schools of fish in controlled scenarios. The new CSAIL robofish called SoFi appears to set a new standard in its ability to blend into open water.SoFi a soft robotic fish that can independently swim alongside real fish in the ocean.During test dives in the Rainbow Reef in Fiji, SoFi swam at depths of more than 50 feet for up to 40 minutes at once, nimbly handling currents and taking high-resolution photos and videos using  a fisheye lens.

SoFi had to swim in the ocean  at multiple depths. This meant waterproofing, buoyancy control, tweaking weight distributions and figuring out an unobtrusive way to share information underwater. It also meant compact equipment.

Design  and Structure:

            The basic biomimetic robotic fish is made up of three parts a streamlined head, a body, and a tail.

SoFi's parts are 3D-printed, making it relatively easy and inexpensive to reproduce.

1:The head is often made of a rigid plastic material and contains all control units including a wireless communication module, batteries, and a signal processor. 

2:The body may be made of multiple jointed segments, which are connected by servomotors. Servomotors control the rotation angle of the joint. Some designs have pectoral fins fixed on both sides of the body to ensure stability in the water.

3: An oscillating caudal  fin connected with joints and driven by a motor provides motive power.

How it works:

In contrast, SoFi has a much simpler and more lightweight setup, with a single camera, a motor, and the same lithium polymer battery that’s found in consumer smartphones. To make the robot swim, the motor pumps water into two balloon-like chambers in the fish’s tail that operate like a set of pistons in an engine. As one chamber expands, it bends and flexes to one side; when the actuators push water to the other channel, that one bends and flexes in the other direction. These alternating actions create a side-to-side motion that mimics the movement of a real fish. By changing its flow patterns, the hydraulic system enables different tail maneuvers that result in a range of swimming speeds, with an average speed of about half a body length per second.

The authors show a number of technical achievements in fabrication, powering, and water resistance that allow the robot to move underwater without a tether,” says Cecilia Laschi, a professor of biorobotics at the Sant'Anna School of Advanced Studies in Pisa, Italy. “A robot like this can help explore the reef more closely than current robots, both because it can get closer more safely for the reef and because it can be better accepted by the marine species.” The entire back half of the fish is made of silicone rubber and flexible plastic, and several components are 3-D-printed, including the head, which holds all of the electronics. To reduce the chance of water leaking into the machinery, the team filled the head with a small amount of baby oil, since it’s a fluid that will not compress from pressure changes during dives.Indeed, one of the team’s biggest challenges was to get SoFi to swim at different depths. The robot has two fins on its side that adjust the pitch of the fish for up and down diving. To adjust its position vertically, the robot has an adjustable weight compartment and a “buoyancy control unit” that can change its density by compressing and decompressing air. Katzschmann says that the team developed SoFi with the goal of being as nondisruptive as possible in its environment, from the minimal noise of the motor to the ultrasonic emissions of the team’s communications system, which sends commands using wavelengths of 30 to 36 kilohertz.