P16229: Robofish 3.1 - Navigation
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Subsystem Design

Table of Contents

Team Vision for Subsystem-Level Design Phase

Goals: To begin assess the subsystems of the design this phase was intended to involve prototyping of high risk subsystems.

Summary of Progress:

Feasibility: Prototyping, Analysis, Simulation

Purpose

Feasibility Analysis was also performed at the Subsystem Level. The feasibility of certain systems, ideas, and technology at the system level gave way to integrated subsystems. Proof of concept testing, mock-up designs, and simulations for subsystems are integral to the functionality of the entire system.

Swimming Algorithm - LED Implementation

A proof of concept test was executed to visually show the potential operation of the swimming motion. Using the Arduino Mega, a script was written which used a ongoing counter to drive digital output signals high and low at designated times.

Previously, a sinusoidal approach was attempted to perform the task in MATLAB. Due to overlap issue, this idea was changed to a pure timing control, not involving a mathematic function.

Five parameters can be used to adjust the swimming profile. T represents the swimming period or speed in seconds. Alpha, Beta, Gamma, and Delta represent the amount of overlap for A, B, C, and D signals respectively. Setting these overlap parameters to 0 corresponds to no overlap. A positive number between zero and one will increase the length of the signal, while a negative number will decrease the length, as a percentage of the remaining time.

The theoretical analysis was derived as is pictured.

LED Swimming Testing Theory

LED Swimming Testing Theory


The length equations represent how long that specific signal is to stay on for while the start equations represent where in time the signals should activate.

Swimming Theory Equations 1

Swimming Theory Equations 1

Swimming Theory Equations 2

Swimming Theory Equations 2


The videos which demonstrate the LED operation are shown here. Please note that to watch the mp4 files, right-click on the "display" link and click "save link as". Saving the file will allow for download of the video.

A flowchart of the code structure is shown.

Swimming Theory Equations 1

Swimming Theory Equations 1


A link to the actual code and details found in a README file are contained here.

Preliminary Battery Testing

Several batteries which were identified in the systems review were purchased and tested for charging/discharging performance. The overall results were unfavorable, the battery appeared to dramatically under-perform as per their specification.

Further Investigation: It is possible that the current draw from the batteries was too high, forcing this unexpected result. Testing will begin at a lower current draw to determine if this prolongs the battery life. Also, a name-brand battery will be purchased and tested as a control group.

UltraFire 18650 Analysis with R=2Ohm

UltraFire 18650 Analysis with R=2Ohm


UltraFire 18650 Analysis with R=5Ohm

UltraFire 18650 Analysis with R=5Ohm


UltraFire 18650 Wh rating with R=2Ohm

UltraFire 18650 Wh rating with R=2Ohm


UltraFire 18650 Wh rating with R=5Ohm

UltraFire 18650 Wh rating with R=5Ohm


Tail Mock-Up

A wood tail mock-up was created in order to test the feasibility of the tail design in terms of structure and mechanics. The T-shaped structure was constructed after the current design of the tail at this stage. For simplicity cables were used in place of the McKibben muscles which could be "actuated" by hand.

Tail Mock Up in Resting Position

Tail Mock Up in Resting Position




A series of images that follow show the tail mock-up actuating back and forth once. The cables were pulled alternating sides. The back sections of the tail (section B as was called in systems level design) re-positioned itself passively due to the friction between the piece and the table top. This will lead to further investigations into the feasibility of having a passive re-positioning system in section B.

Tail Mock Section A moving

Tail Mock Section A moving

Tail Mock Up Section B Re-positioning

Tail Mock Up Section B Re-positioning

Tail Mock Up Section A moving

Tail Mock Up Section A moving

Tail Mock Section B Re-positioning

Tail Mock Section B Re-positioning

Additionally, the maximum relative change in length of the cable and that from rest were determined in order to characterize better how feasible the direct muscle attachment system is or additional problems which will need to be addressed to achieve this goal.

A gif was created to show to tail motion in an animated fashion.

Animation of Tail Actuation

Animation of Tail Actuation

SolidWorks Body Design

A preliminary body was designed in SolidWorks which will be used as a basis for further design considerations and decisions. The purpose of this model is to generate a physical concept upon which future improvements and considerations can be made as well as to allow for computer based modeling to begin on the system.

This design was based off of the carp, the fish form most similar to the desired state of the Robofish envisioned in Phase 1.

Generic Image of a Common Carp

Generic Image of a Common Carp

The model was constructed in order to maintain a relatively high aspect ratio (having to take into account the profiles of the internal components), a morphology amenable to attaching skin, and a face plate truncated in order to allow for the addition of P16029's head.

Front Oriented View of SolidWorks Model

Front Oriented View of SolidWorks Model

Rear Oriented View of SolidWorks Model

Rear Oriented View of SolidWorks Model

In addition to this, simplified models of several of the internal components of the fish were constructed and the rest will be added as the internal composition is resolved. To these simplified model we intend to apply custom material properties in order to well characterize the centers of mass and buoyancy of the fish.

These parts were all created separately from the body such that they can be reoriented within SolidWorks to determine the optimal placement. The balanced (aligned center of mass and buoyancy) computer model can then be translated into a physical fish body.

This is not expected to be perfect, however, it should minimize the amount of imprecise adjustments that need to be made.

Mathematical Modeling

In order to assess whether or not the proposed design for the tail could be actuated by the McKibben muscles attached to the tail as proposed mathematical calculations were initiated. Below are two images of a work in progress which should in the end determine the feasibility of directly attached Mckibben muscles in the proposed tail system.

Mathematical Model Pt 1

Mathematical Model Pt 1

Mathematical Model Pt 2

Mathematical Model Pt 2

Inputs and Source

  1. Engineering Requirements
  2. Concept Selection

Outputs and Destination

  1. Feasibility
  2. Risk
  3. Concept Selection

Drawings, Schematics, and Flow Charts

The system was described using a system architecture schematic.
High Level System Block Diagram

High Level System Block Diagram

Bill of Materials (BOM)

A bill of materials was constructed which began with the materials available to our team from the previous team and to this was added the components purchased by our team.

A link to the live BOM can be found here.

Risk Assessment

Updated assessment from Systems Design and link location. Attempts have been made and concepts have been proposed in order to minimize risks.
Update Items to Risks

Update Items to Risks

A link to the live document can be found here.

Design Review Materials

None at this time

Plans for next phase

The Robofish electrical team will be expanding on its swimming algorithms and testing input signals to implement turning while swimming mode is operational. Extensive testing with ultrasonic sensor will continue in order to confirm viability within the next 3 weeks otherwise image processing will be pursued. Power regulation boards will be manufactured or ordered based on previous design which will remain the same. An estimated budget for the electrical team will be compiled based on decision of sensors and board needs.

The Robofish mechanical team will construct a metal version of the tail model which can be used for testing the muscles (electrical systems if possible as well). On this platform will be a system for adjusting the attachment points of the muscles and testing attachment methods. Concepts will be pursued as far as achieving the necessary length change of the muscles required by actuation. Additionally, the mathematical model will be continued and computer based modeling will begin.


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