P20250: Finger Lakes Explorer ROV
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Systems Design

Table of Contents

Team Vision for System-Level Design Phase

During this phase our team planned to produce a feasible upper level design to gain a better understanding of the lower level design that will occur in the next phase. This was based off the feedback from our team Guide, Customer, and general MSD guidelines. This design also allowed for the easy identification of multiple sub-systems that will need to be later designed in the next phase. There was also general brainstorming of solutions for each subsystem which gave us some preliminary design ideas The ideas generated will be utilized later for the specific sub-system designs. The most important lesson learned was that this portion of the phases put in perspective how much work we need to do to produce a fully functional prototype.

Our team started the phase by creating a Function Tree and a Transformation Diagram in order to better understand the flow of information within the system. At that point, we did not allow for anything other than the Engineering and Customer Requirements to dictate our decisions. From there, we created a morphological chart to generate concepts based on the different functions that our team came up with from the Function Tree. Each of us created our own completed concept idea to be utilized in a Pugh Matrix. This allowed us to identify key functions and concepts to be implemented in our proposed solution. Once all of these ideas were presented, a completed concept was chosen to proceed with.

Systems Architecture

The System Level Architecture is shown below. The flows for the Energy (Red), Materials (Green), and the Information (Blue) is shown from the Launch Station to the ROV. Generally Power and Material travel in one direction but as for Information, it travels both from the User Input to the Sensors and then back through to the HUD as shown below.
System Level Architecture Flow Chart

System Level Architecture Flow Chart

Functional Decomposition

Purpose

A decomposition was obtained from customer and engineering requirements and arranged in a logical and hierarchical way. This functional hierarchy can be seen in the figure below.
Function Tree Hierarchy

Function Tree Hierarchy

Benchmarking

In order to narrow down the list of possible solutions to our sub-functions and finalize our design, one method used was benchmarking. By researching potential components for our solution that are already on the market, we were able to quickly gain insight on a matter and make an education decision moving forward.

Benchmarking was done for such components as the mechanical shell, handles, tether and winch in addition to electrical components like sensors, motors, lights and controllers.

Link to the mechanical benchmarking document

Link to the electrical benchmarking document

Lights

The lighting schemes of 6 LED diving lights, outlined below, provides a potential direction our team should follow for lighting the path of the ROV underwater. We will likely buy (1) LED light that can emit at least 500 lumens, with a beam angle of at least 60. An additional light might be needed, or a larger beam angle, but this will be finalized in the next Phase. If possible, buying a light with adjustable brightness (to accommodate distance and close up videos) would be preferred. Based on this benchmark, the light could cost around $100, so this might limit the likelihood of buying multiple lights.
LED Diving Lights

LED Diving Lights

Link to the lighting benchmarking document.

Temperature Sensor

A temperature sensor is one of our customer requirements, and as such, is an important addition to the ROV. This will be useful for both transmitting information to the HUD as well as factoring into the controls system architecture. This makes finding a high quality temperature sensor a necessity. The only engineering requirement for this sensor is that it has an accuracy of at most 1 degree Fahrenheit. Anything less would be greatly preferred. Other factors such as physical size and range of operation are also taken into account. As can be seen in the table below, it is very easy to find temperature sensors that meet these requirements, thereby making other details such as compatibility with I2C or SPI more important. When our team starts finalizing our design, there will be a better understanding of which route to take.
Temperature Sensor Benchmark

Temperature Sensor Benchmark

Feasibility: Prototyping, Analysis, Simulation

Visibility

To get a grasp of visibility at depth in the target launch sight of Conesus Lake, a rough prototype was constructed with a GoPro Hero 3 Black as the camera sensor. The testing apparatus, shown below, consisted of a weight to reach the bottom and a float to hold the camera steadily off the bottom. The tether was 1/8" woven nylon anchor line.
Testing Apparatus

Testing Apparatus

On a very sunny day, footage was taken from the bottom of the lake at 4', 7', 15', 27', 35', 44', and 55'. Aside from a few animal encounters, this test was important because it validated the need for a lighting system on board the ROV. Visibility was almost gone at 55', which is slightly over half of the target depth of 100'. Additionally, it was learned that water clarity is not constant through out the lake, which surface visibility (depth around 3') being much further at the 4' collection site than the 55' collection site.

Here are links to the videos from 4', 7', 15', 27', 35', 44' and 55'.

Note: If the video links don't play, you can download the files from here.

Pressure

From a mechanical standpoint, the one of the biggest risks is hull collapse and/or leakage at depth due to the pressure exerted by the water of the ROV. Assuming constant density of water, and that the density of lake water is somewhere between that of distilled water and saltwater, it was found that the ROV will be subject to pressures of 4 Atm at the target depth of 100', and almost 9.5 Atm at the stretch goal of 276'.

A graph showing the pressure as a function of depth. The target goal is shown in green while the stretch is shown in orange.

A graph showing the pressure as a function of depth. The target goal is shown in green while the stretch is shown in orange.

Pressure is the amount of force exerted over area. Once a final hull shape is determined in the subsystem design phase, the pressure can be used to find out what and where the maximum force will be applied. This will drive hull design accordingly.

Link to pressure analysis document.

Weight

It is a specification that the ROV be under 50 lbs in weight. If we assume neutral buoyancy, which is common in underwater applications, then this weight constraint also limits the maximum volume of the ROV. Analysis shows that for the ROV to remain under 50 lbs and be neutral buoyancy, it must occupy less than 0.023 cubic meters of water. To put this into perspective, that would be a cube of 11" on each side, or a sphere that is 1'2" in diameter. The conclusion drawn from this analysis is that the ROV and the subsystems that are chosen for it must be small enough to fit the weight requirement.

Link to weight analysis document.

Signal Latency Due to Tether Length

Once of the main requirements for this project is that the camera feed from the ROV should be viewable "live" by the user controlling the ROV. There was consideration about whether wireless data communication would be a viable way of transmitting this video feed which would be "more live", or have lower latency, than transmitting the video feed through hundreds of feet of wire along the tether. Analysis was done to determine how much latency would be caused by a 100ft tether of variable makeup, and the conclusion is that latency on the order of nanoseconds caused by the tether will not significantly impact the user's ability to make decisions based on the "live" video feed.

Link to latency analysis document.

Voltage Drop Across a Long Wire

One of the risks with using a pair of long wires for power delivery to the ROV is voltage drop and power losses across the wires. Analysis was performed to compute the voltage drop across a 400 foot wire loop for different gauge wires. It was found that increasing the thickness of the gauge of the wire, while holding the voltage source potential and the impedance of the load constant, the overall resistance of the wire dropped.

Link to voltage drop analysis document.

Morphological Chart

The Morphological Chart is a collection of concepts organized based on what function they accomplish. As a part of brainstorming, no concept is too ridiculous because an idea that might be thought of as not possible may open the door to other possibilities that were not previously imagined. Our team came up with a total of 126 concepts over 22 different sub-functions based on our engineering requirements. The color code was used to differentiate the concepts that our team will go forward with for our preliminary design. A green box is our primary concept for its particular sub-function, a yellow box is our secondary option, and a red box indicates a sub-function that we will need more information on before proceeding.

Morph Chart

Morph Chart

Concept Development

Using the Morphological Chart generated as a team (see abovesection), each team member selected a solution for each sub-function identified, and generated an alternative concept solution. These concepts were then used in our Pugh Matrix, to ultimately create a hybrid solution. Each individual concept solution is outlined below.

Individual Concept Generation

ROVie the Riveter - Lainey Celeste

This concept is composed of a 3D printed plastic enclosure, surrounded by a PVC frame designed to protect the ROV and provide a more user-friendly means of transporting the ROV. The frame also has 4 physical probes to sense the bottom of the lake, and can be disassembled and attached to the PVC frame for easier transportation. Motion is activated with a series of vectored thrusters, and a buoyancy compensator to descend into the water. An x-box controller allows the user to navigate the ROV, while the laptop displays the HUD. Transmission of data is wireless, which allows for the tether to be released from the ROV, as a fault reaction system, if the tether gets entangled underwater.

ROVie The Riveter Design Sketch

ROVie The Riveter Design Sketch

Scotty Puff Jr. - Scott Couwenhoven

This concept is designed around a metal canister which houses all of the critical on-board electrical components for the ROV. It is driven by a single aft propeller and controls direction with a rudder and horizontal, wing-shaped fins. The ROV is controlled via a laptop keyboard, and the user gains visual information through a HUD which will be displayed on the laptop screen. The HUD consists of information from a GoPro camera, a thermocouple, and a pressure sensor. The tether consists of an ethernet cable for information, a power cable to supply power from the launch boat battery, and a physical line to provide some mechanical strength. It is deployed through a manual winch to avoid entanglement and breakage.
Scotty Puff Jr. Design Sketch

Scotty Puff Jr. Design Sketch

Golden Explorer - Joseph Mantione

The Golden Explorer was primarily designed to accommodate for feasibility. Throughout the design, the simplest concepts were incorporated to make the production of the rover as simple as possible. First off, the tether end on the boat would have a Xbox controller and a Laptop for easy HUD and maneuverability of the ROV. The tether line then travels down to the ROV using Cat6 to only transmit data as the power source will be on the ROV. The shell of the ROV is made from a cheap plastic molding with a very basic cylinder shape to save on money. The camera would then stick out on a glass opening for easy viewing and the caterpillar motors would be placed on a rotating platform to adjust for different angles. The sensors, handles, and light will sit as shown.
Golden Explorer Design Sketch

Golden Explorer Design Sketch

Puffer McFishy - Scott Mann

This design was based around the idea of trying to make an ROV containing almost everything needed for operation on board, with a unique propulsion system based more on air than motors. This means that it utilized a pneumatic system to move horizontally, with a series of ballast tanks and a buoyancy compensator to control vertical motion. Physically, the design was based around a puffer fish. Its exterior is soft and flexible so hard objects cannot damage it, while an inflation device will allow the ROV to surface if damage is detected. Information is transferred wirelessly, making a cable unnecessary, while power is supplied via batteries on-board the ROV so that a power cable is not needed as well.

Puffer McFishy Design Sketch

Puffer McFishy Design Sketch

Lean Green Keats Machine - Harrison Keats

The LGKM is based on two radical function solutions. Primarily, the idea that if a PVC frame existed to prevent impact damage to the ROV, a watertight plastic bag would be sufficient for containing the electronics underwater. This would save considerably on cost of design and of labor time to support design activities, but would present new, specific and reasonable risks for puncturing the bag and damaging electronics. Secondly, user input could be translated to micro commands for ROV subsystems from the userÍs position, and relayed by a series of power buses to the ROV instead of by communication with a microcontroller on the ROV. Controlling multiple power lines over the length of the tether would have drastically increased losses, but would present less risk for loss of communication and would reduce the cost of components underwater in the event of losing the ROV.

Lean Green Keats Machine Design Sketch

Lean Green Keats Machine Design Sketch

ROVI - Trevor Sherrard

This design was based around the concept of ease of user operation. The ROV itself has the ability to move in the horizontal direction making use of impellers powered by D.C motors. The ROV has the ability to strafe side to side using a pair of vectored thrusters. The pitch of the craft is controlled by actuating a mass on a linear actuator. The vertical motion of the ROV is controlled by a buoyancy control unit. The ROV is controlled through use of an Xbox controller connected to a base-station that will translate and transmit user input to the ROV, while displaying a live stream of ROV camera frames and sensor data from pressure and temperature sensors. LED lights will provide artificial lighting for ease of user navigation.

ROVI Design Sketch

ROVI Design Sketch

Selection Criteria

This section outlines the selection criteria used to evaluate the generated system designs objectively in the Pugh Matrix.

Concept Screening

The list below outlines 9 useful system-level selection criteria, which was used on our first Pugh Matrix.

  1. Transportability by 1 person
  2. Ease of use for user interface
  3. Quality of protection from (water and storage) environment
  4. Degrees of freedom of movement
  5. Ease of extraction from water
  6. Quality of crash prevention system (for lake bottom)
  7. Time of Development
  8. Cost of development
  9. Duration of Dive

Concept Improvement

Modifications were made to the above list, to more accurately represent differences in alternative concepts generated in terms of the characteristics listed on our Morphological Chart. This selection criteria was used on the second Pugh Matrix our team generated. For example, we realized while completing the first Pugh Matrix, that some of the selection criteria were required design features (for example, "move in 5 degrees of freedom"), so every design was built to accomplish that, and thus that was not a good selection criteria to use to compare our ideas. Instead, the new set of selection criteria was designed to be more specific while still being solution-independent, to more accurately represent differences in each of our approaches.

  1. Transportability by 1 person
  2. Ease of use for user interface
  3. Quality of protection from (water and storage) environment
  4. Power efficiency of movement
  5. Maneuverability
  6. Floor Detection
  7. Fault Reaction
  8. Time of Development
  9. Cost of development
  10. Duration of Dive

Link to the selection criteria document.

Pugh Matrix

Another use for the Morph Chart is to brainstorm different products utilizing what concepts are listed. In our team, we each concocted a different overall design that would accomplish the necessary criteria. These were then compared twice in Pugh Matrices, which can be seen below. For each matrix, a design was chosen at random as a datum to which all of the other designs were compared to, based off of our selection criteria. The positives and negatives of each design were added up to show which ideas worked well.

Pugh Matrix Part 1

Pugh Matrix Part 1

Pugh Matrix Part 2, with modified Selection Criteria

Pugh Matrix Part 2, with modified Selection Criteria

Designs and Flowcharts

Functional Flowchart

Based on functional decomposition and initial discussions on concept design, a flowchart was constructed which accounted to help identify subsystems and components as they could logically be grouped and as they interacted with elements outside the design scope of this project.
Functional Flowchart

Functional Flowchart

Software Functional Flowchart

Based on functional decomposition and initial discussions on concept design, a flowchart was constructed to outline a software functional relationship between the base station and ROV domains.
Software Functional Flowchart

Software Functional Flowchart

Systems Timing Flowchart

Based on use case, an estimate of the time required for each process was generated and compiled over the entire process, providing insight on to the full process run-time.
Temporal use case

Temporal use case

Initial Concept Design

Top View of ROV

Top View of ROV

Opened Back View of ROV

Opened Back View of ROV

Isometric View of ROV

Isometric View of ROV

Internal View of ROV

Internal View of ROV

Risk Assessment

The project risks were re-evaluated and compared with those from phase 1 to generate a risk curve. This curve will monitor the overall risk associated with the project through out the development phase. As expected, the total risk increased as the details of the subsystems come to light.
Risk Curve Through Phase 2

Risk Curve Through Phase 2

Risk Assessment For Phase 2

Risk Assessment For Phase 2

Link to the risk management document.

Design Review Materials

Plans for next phase

The team plans for next phase are listed in the Gantt chart under project planning. Screenshots are shown below for convenience.
Gantt Chart For Phase 2

Gantt Chart For Phase 2

Link to the Gantt chart document.


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