P18250: Smart Buoy
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Systems Design

Table of Contents

Team Vision for System-Level Design Phase

The ultimate goal of this phase is to come up with a system level design concept. This is done by taking the customer requirements engineering requirements and translating them into systems, subsystems, and components. There are many steps to this process, starting with a functional composition. Through several techniques, we plan do break down the specific functions the ‘Smart Buoy’ needs to perform. We will then brainstorm ways to meet these functions, and compare these brainstormed concepts. Finally, a preliminary feasibility analysis will be conducted and a design concept will be generated. We also plan to continue to update and address our risk assessment, as well as start developing a test plan.

Over the course of Phase 3, the team met all of our panned goals for the phase. The in depth details of these accomplishments are documents below. A functional decomposition was conducted using a “function tree” and “Transformation diagram”. A morph chart was then used to brainstorm ideas to meet these functions and to generate concepts. A pugh chart was used to compare these concepts and ultimately select one. Lastly feasibility analysis was conducted all of the major aspects and components of the systems level design to verify our concept would be possible within the constraints and scope of the project. Knowing our subsystems and components, we were then able to start coming up with a plan of testing. calibration, and validation. We were also able to update our risk assessment, which involved adding items, removing items, and editing items due to our improved knowledge of the problem and system. Lastly, we successfully presented our progress and results from this phase in our Phase 3 review.

Functional Decomposition

The following two diagrams were developed to to flow down the customer requirements and engineering requirements into specific functions that must be met by our system.

The first diagram is a “Function Tree” which breaks down high level functions of the system ino system functions.

Function Tree Diagram

Function Tree Diagram

The second figure is a “Transformation Diagram” which maps out the transfer of energy and information through the system.

Transformation Diagram

Transformation Diagram

Benchmarking

The microcontroller benchmark table is shown below:

The main functionalities that will be considered for this project are the system architecture and serial ports.

Microcontroller Benchmark Table

Microcontroller Benchmark Table

Morphological Chart and Concept Development

With the main functions of the ‘Smart Buoy’ identified, the next step in the design process is top find ways to meet these functions. For each sub function, we brainstormed as many ideas as possible that could possibly conduct that function. Doing this resulted in the “Morph Chart” below.

Morph Chart

Morph Chart

Concepts were then selected by choosing different components from each row of the morph chart. Some examples of this process can be seen below.

Morph Chart with Options Chosen

Morph Chart with Options Chosen

Ultimately each team member went through this activity and came up with a design concept. These concepts are shown below:

Morph Chart Summary

Morph Chart Summary

Concept Selection

With a variety of concepts developed, the next step was to funnel them down into 1 selected concept. This was accomplished through a pugh analysis. To conduct this pugh analysis, 13 critical design criteria were chosen to judge each concept relative to a baseline. The list of criteria can be seen in the first column of the “Pugh Chart”. After a baseline was chosen, each design was then compared to the baseline based on the chosen criteria.

Pugh Chart

Pugh Chart

In order to fully understand the important aspects of our system and have an opportunity to see things from a different perspective, we ran this analysis again by selecting a different baseline. This second run can be seen below:

Pugh Chart 2nd Round

Pugh Chart 2nd Round

Results:

From doing this pugh analysis, we were able to identify which aspects of each concepts were the most effective, and which collection of substems were complementary, thich resulted in the following selected concepts for our components:

Pugh Chart Summary

Pugh Chart Summary

Concept

Concept

Feasibility: Prototyping, Analysis, Simulation

In order to validate the decisions we made in our concept selection and assess the overall feasibility of the project, we conducted a feasibility analysis for all major subsystems, and the key customer/engineering requirements.

Stay Afloat

A catamaran was chosen as the hull type for the smart buoy as the emans for it to stay afloat. Some of the key factors regarding this decision are that a catamaran is more stable and easier to maneuver/control than a monohull, and is cheaper and easier to build than trimaran

The following are preliminary calculations of buoyancy and hull size.

FB=Buoyant Force p=fluid density=1000 kg/m3 Vd=volume of fluid displaced g=acceleration due to gravity=9.81m/s2 W=total Weight of Buoy=100lb=444.8N (From ER's)

Assumptions: We want 1/3 of the hull submerged Use 12in diameter PVC for the Hulls

Hull Calculations

Hull Calculations

Results:

Therefore, in order to float the ER weight with the pontunes 2/3 out of the water and a diameter of 12in, each pontoon needs to be 3ft long. This is a very reasonable number.

The footprint limit from the ER’s is 5’ x 6’. Thes calculations show that the footprint of the hull will easily be below that footprint limit.

Provide Thrust

Thrust requirement is dependant on buoy weight and drag. The buoy will face three types of drag: surface (viscous) drag, form drag, and effects of waves. The drag resulting from wave action typically far outweigh the others and are heavily dependant on hull shape and weather conditions. Because of the difficulty in analytically determining required thrust benchmarking was used. Accepted industry rule of thumb states that a trolling motor should provide 2-2.5 lbs of thrust per 100 lbs of boat. Therefore based on this rule of thumb a 45 lb thrust motor will be more than sufficient to control a 100 lb buoy.

Motor Location (Bow vs. Stern)

Locating the motor at the bow will make it easier to point the bow in the desired direction. This will be especially effective at station keeping when faced with cross winds or currents, as these transverse forces would help turn the heading towards that force as opposed to away from it.

Motor Location

Motor Location

Steering

Steering will be accomplished by rotating the motor Control systems for this method of steering are cheaper than buying a second motor The control systems used to accomplish this will be a gear on the motor, and a gear on a servo, attached with a chain. This is a cheap and simple method. Pontoons of the hull will act as keels, and if not sufficient additional keels can be added

Visibility

A common size of a marker used in sailing regattas is a 1x1x1 m Tetrahedron. These can cost $1000+ In order to provide an equivalent amount of visibility, a brightly colored sheet will be tarped around a frame in a square based pyramid shape with similar dimensions. This will be cheap, effective, and easy to build

Mark Rounding

Mark Rounding

Prevent Water Damage

We have a waterproof box already in stock, pictured below. May need additional protective storage for the battery, but we are yet to size all of the components

Sense Location, Heading, and Tilt Angle

GPS will be used to sense location as it’s the industry standard and cheap. A Magnetometer will be used to sense heading. A GPS can be used to calculate heading, but our buoy will be moving too slow to get an accurate heading calculation from the GPS.

  1. A Gyroscope will be used to sense tilt angle as it is easily integratable and cheap.

Store Energy

The majority of the power consumed will be due to high amp draw from the thrust motors as well as the winch motor. These events will happen in small time intervals throughout a typical day of sailing dependent on the amount of times course needs to be changed and the buoy needs to be moved.

The figure below shows an example instantaneous energy usage curve for the buoy. By taking the area under the curve over some time period, we get an average power draw over that time period.From this we can estimate the capacity of the battery that we will need.

Example Energy Usage of Buoy

Example Energy Usage of Buoy

An example power calculation is shown below as well as the estimated battery capacity needed.

Example Energy Usage of Buoy

Example Energy Usage of Buoy

The full power estimations spreadsheet can be found here.

Battery selection is not only depended on the capacity of the battery, but also the type. Different applications require different batteries (SLI, Deep-Cycle, Lithium-Ion, etc).Typical car batteries will not be able to supply our system, as they can only supply high currents for very short amounts of time, and can only discharge up to around 20% of there total capacity.

Ideally, we will want a deep-discharge battery that can discharge 60% to 80% of its total capacity, and handle relatively large currents for minutes at a time. A non-spillable battery, such as an AGM or Gel, is preferred because it will mitigate the risk of having battery leakage, and will allow us to orient the battery in any way we like.

Comparison of Different Battery Types

Comparison of Different Battery Types

Solar Panel

Specifications for an appropriately sized solar panel were used to approximate the amount of electrical energy that would be produced by a horizontal panel mounted on top of the buoy. Solar data for Rochester, NY was used and it was assumed that the buoy would be in operation for the eight hours between 8am and 4pm.

Solar panel size: 26.5*40.2in^2

Efficiency: 14.6%

Nominal Power Output: 100 W

Peak sun hours: 5 hr/day

Adjustment for operating conditions: .75

Adjustment for buoy operating period: .8

Power Generated: 300 W*hr/operating period

Data Transmission

The range from our customer requirements was set at around 1 mile data transmission range. However, after considering a new risk, the range has been increased to 6-10 miles. The new risk is that the range on datasheets for transceivers and such will say the range of the product in ideal conditions with certain antennas, and our application will likely have things interfering with it with less than optimal antennas.

With the new range requirement, the options that seemed most appealing were RF transceivers and drones. XBee RF transceivers were chosen because they are very cheap and have certain things like USB dongles available that will help with PC integration.

Drones ended up being way too expensive to achieve our required range, and would likely require additional components to interface with a PC, and those components are not readily available.

User Interface

The two most user friendly user interfaces we could use that wouldn’t add extravagant hardware to be bought or configured were PCs and mobile phones.

PC interface was chosen for its ease of integration. A phone would add convenience for the User, but problems arose when choosing a phone over a PC:

After considering these problems, we determined that the added convenience would take a lot more time and be decently more complex to implement, making a PC the better choice.

Stay in a Desired Location

Winch Calculations

Winch Calculations

The winch and anchor system will use less energy throughout the use period and provide better conditions for a sailing race.

Systems Architecture

Electronic Subsystem Diagram

Electronic Subsystem Diagram

Risk Assessment

Risk Assessment Chart

Risk Assessment Chart

The full document updated for Phase 2 can be found here.

Design Review Materials

The power point presentation can be found here.

Plans for next phase

Gantt Chart for Phase 3

Gantt Chart for Phase 3

The full Gantt Chart document can be found here.


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