P15029: Air Muscle Underwater Fish Phase 2 - Buoyancy

Detailed Design

Table of Contents

Design Overview

The overall design of Phase II of the Underwater Robotic FIsh consists of the following major systems:


The buoyancy system is modeled after a ballast tank and utilizes 2” inch diameter, 7” length PVC pipe with corresponding end caps as the main structure. This size can hold around 0.02L of water, which has been proven through analysis to be more than the required amount of around .01L needed to float and sink. It will utilize a larger pump as the inlet and a small aquarium pump as the outlet to move water in and out of the tank, with two proportional valves controlling the flow in and out.


The tail structure has been recycled from Phase I’s design and prototype. It has been reduced to two sections, instead of three, with the struts being aligned to follow the shape of the bass profile, while still maintaining body caudal fin motion. It uses tensioning cables attached to the air muscles connected at each pivoting segment to actuate movement and produce body caudal fin motion.


The electronics will have a main board PCBA. The microcontrollers used will be ATMEGA328P chips. In addition there will be a PCBA for depth sensor, which can be used to determine the depth of the fish in the water. An IR sensor will also be placed at the front of the fish for obstacle detection. The fish will be able to to be controlled manually through RC in addition to having an autonomous mode.

Body Structure:

The fish is modeled after a bass profile and will be mimicked utilizing a composite shell for the front half of the fish and Eco-Flex mold for the aft end of the fish. The composite material will protect and secure the vital components of the fish, while the Eco-Flex will help streamline the movement of the tail and add to the overall fish-like appearance. The vital components will all be situated around a central channel, with the air muscles and valves centered and the tail secured to the aft end of the channel.

Air Muscles

The four air muscles that will be utilized are a smaller version of last year’s air muscles but, with the same house clamp connectors and screw tubes to connect to the tensioning cables. Despite their size, these air muscles still actuate with the same force as last year’s muscles, allowing for a comparable speed as last year’s and minimizing the overall size of the fish. There will be two to three way valves controlling the water flow to and from the air muscles. Furthermore, the air muscles have been designed to be inline with the tail to help eliminate any tensioning cable strain or breakage.

All of the above major components, reflect the robustness of the overall design of Phase II of the Underwater Robotic Fish and have been evaluated to meet the customer’s needs and requirements. Below you will find a comprehensive overview of the design, including testing, prototyping, drawings, electrical schematics, risk assessment, bill of materials, and project plan moving forward into MSD II, the build phase.

Drawings and Models

The PDFs for all of the individual component drawings can be downloaded here.



Main Board

The PDF of the Main Board Schematic can be viewed here.

Depth Sensor

The PDF of the Depth Sensor Schematic can be viewed here.


Main Board

Depth Sensor
Front Image of PCBA Back Image of PCBA Physical PCB

The Gerbers for the Depth Sensor PCB can be downloaded here.

Power Consumption

Signal Flow Charts

Main Signal Flow

Forward Swimming Subroutine

Turning Subroutine

Testing and Prototyping

Fish Tail

Full Tail Motion: This video shows the full motion of the tail motion while being actuated by the air muscles.

Half Tail Motion: This video shows the motion of the just the second tail segment while being actuated by the air muscles.

Buoyancy System

Buoyancy Test: This video shows some of the testing with the initial ballast tank design. It shows the ballast tank both descending and rising as water is pumped in and out.

Air Muscles

Air Muscle Test: This video shows the testing of the air muscles. Specifically it shows that the air muscle has enough force to handle a 1lbs load.


Eco-Flex Test: This video shows the testing of the elasticity of the Eco-Flex, ensuring that it would not tear as it stretched to match the tail movement. In addition, it was tested that the actuation force of the tail would be able to overcome the elasticity of the Eco-Flex and still be able to move.

Risk Assessment

The Full Risk Assessment can be viewed here.

The Risk Analysis and Solutions Presentation can be viewed here.

Bill of Materials

The BOM can be viewed here.


Current Status of Meeting Customer Requirements

Current Status of Meeting Engineering Requirements

MSD II Project Plan

The complete MSD II Project Plan can be viewed here

Design Review Presentations

The Week 12 Design Review Presentation can be viewed here.

The Final Design Review Presentation can be viewed here.

Table of Contents MSD I

Problem Definition Systems Design Subsystems Design Detailed Design

Project Statement

Customer Requirements

Engineering Requirements

House of Quality


Week 3 Review Presentation

Functional Decomposition

Morphological Chart


Concept Development

Systems Architecture


Risk Assessment

Systems Design Review

Electrical Subsystems

Buoyancy Subsystem

Tail Structure

Full Skeletal Structure

Air Muscles



Subsystems Design Review

Design Overview

Drawings and Models

Electronic Schematics

PCB Layouts

Signal Flow Charts

Testing and Prototyping

Risk Assessment

Bill of Materials


Design Review Presentations

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