introduction of operating method

The Underwater Roboswimmer uses principles from soft robotics for the actuation of its tail. Upon designing our robot, the team explored a variety of different soft robotics principles and actuation methods. The team down-selected to two different forms of actuation for our robot: pneumatic actuation and tendon actuation. These two actuation methods were most applicable to our robot design, and would prove most effective as well. 

One important consideration in choosing an actuation method from the two listed above is the fact that the robot will be swimming underwater. While both actuation methods can be used for underwater operation, one would prove easier for implementation. While pneumatic actuation is a very feasible option for underwater actuation, the components of the air channels must be completely waterproof to prevent any water from entering the channels. Based on the materials we had to work with (3D printed parts), the team decided that this method would not be well suited for our specific design, especially when considering the shape of our robot. Therefore, the team decided to continue with tendon actuation. 

Key components of operation

Tendon actuation has been a proven way to operate soft robots. Our tendon actuation uses a series of fishing line (the tendons) and a servo that can actuate the fishing line. The ends of the fishing line not connected to the motor are anchored to the tail end of the robot, and goes through a variety of tapering oval-shaped tail parts to create a streamline design. 

The servo utilizes a double-arm, which means each side of the center of the servo has an arm. The team utilized one fishing line through each side of the robot, meaning that two fishing lines had to be actuated. The team is using a pull-pull system to operate the tendons, meaning that each fishing line attaches to one end of the double-arm. This allows for the pull-pull system to actuate the tail of the robot, along with the tapering oval-shaped tail parts. The video below shows the soft robot actuation operation:

Operational electronics

Servo

As seen in the video, and mentioned above, the team utilizes a servo as the motor for actuation. The servo the team is using for operation is waterproof, and can operate at a speed that is suitable for reliable and quick actuation of the tail (see fabrication page for a link to the exact servo used). 

The importance of utilizing a waterproof servo is so the team can prioritize a smaller housing for all on-board electronics and only storing the necessary components that need to be waterproofed, that will be described below.

Arduino Nano

To operate the servo, the team explored a couple methods. One was to manually control the servo via an external servo tester, which means a wire would have to be extending from the soft robot outside of the water tank. While this method is easy to implement, the team wanted to prioritize complete on-board electronics with no external electronics. Because of this, the team decided to utilize an arduino nano that is programmed to actuate the servo from one extreme to the other, allowing continuous and autonomous operation of the servo while the robot is in the water. The arduino nano also utilizes an external button, that is programmed to start and stop the code that actuates the servo. The button is located on the outer shell of the robot to allow for ease of operation.

Originally, the team utilized a single servo speed. However after initial testing, the team determined that using various speeds of the servo actuation would help the team tune the robot to maximize its performance underwater. Therefore, the button also can change the delay time for the servo. When the robot is inactive, the button will begin operation at its slowest speed. When the button is pushed again, it operates at a medium speed. When the button is pushed again, it operates at its fastest speed. Another push of the button will turn off the robot. Having this feature was very helpful to the team when it came to determine the robot's optimal performance relative to the structure.