Team Vision for System-Level Design Phase
The objective of the System-Level Design phase was to identify the primary functions of the SailBot based on the requirements and constraints identified in the Problem Definition phase. In addition, our goal was to develop a high-level system design for the entire project, which will be broken down further in the Preliminary Detailed Design and Detailed Design phases. To do this, several steps were required:
- Functional decomposition, to identify high-level tasks.
- Additional benchmarking, to identify what has worked and what has not.
- Concept development, to show what concepts and methods could be used to accomplish the tasks identified in functional decomposition.
- Feasibility analysis, to begin answering analytical/practical questions that may arise during the course of our design and attempt to catch issues early on.
- Concept selection, to develop a screened morphological chart based on the results of concept development.
Updated House of Quality
After consulting with our customer following his review of our Problem Definition, some updates had to be made to customer and engineering requirements. Adding as many control methods as possible increased in priority and so did wireless communication. To compensate for the increase in attention towards adding control methods, the requirement for wind speed functionality was decreased. In addition, the ability to float/fully waterproof and the ability for the system to be touch-controlled were no longer required, and their priority rankings were set to zero. Finally, the ability for the system to implement eye tracking or brain scanning as a control mechanism was suggested and will be considered as a stretch goal. This would help a Sailor whose disability prevented them form moving any part of their body.
The following chart is an updated house of quality. A link to the live document can be found here. Changes from the house of quality found in our Problem Definition phase are denoted by yellow highlighting:
Updated House of Quality
The updated house of quality helped ensure that our scope was correct in evaluating the abilities and compromises of each subsystem
Given our customer and engineering requirements, a list of potential risks was developed and ranked by importance with respect to the project goals. Causes of each risk as well as actions to minimize or erase the risk altogether were also considered in preparation for the design phase. This risk assessment chart will continue to be updated, but at the end of this second phase our main risk concerns are with technical components and available resources, both of which will be critical for testing components in the next phase of design.
Updated Risk Assessment
After the system design review risks are added, the table will be broken down to establish more action items and plans to further the SailBot project.
The risk assessment document is linked here
Functional Decomposition was a tool used to help understand all the actions that SailBot will take. The functional decomposition chart was created by evaluating the basic task SailBot must complete (steer Sailboat). This function was broken down into further actions needed to complete this task (shown in Blue). This process continued until the actions were as specific as possible without having set ideas:
Functional Decomposition Chart
The functions in purple were used to further understand all tasks SailBot must complete. These could get further analyzed into concepts and designs for various subsystems of SailBot.
Sailing is a complex activity that demands physical action and prior experience. For sailors with disabilities, this recreational activity is not easily accessible. A solution to power assist the tiller for steering does exist. This system is implemented on a proprietary boat only, called the RS Venture Connect. Currently, this is the only product available on the market to fulfill the need for assisted steering.
- This system does work, but with some limitations and issues.
- The first issue being that the hydraulic ram does not have a limit to force provided or linear travel. The issue with this is that it can extend the tiller so far that it hits the back of the boat. The ram also has enough force to break the tiller and damage the rear hull. This has happened just recently and the customer had to spend $10,000 on repairs to the boat.
- If the instructor wants to take temporary control of steering, they must grab the same joystick that the Sailor is using; this can be intrusive to the experience.
- The system takes a long time to set up which can be difficult if there are many sessions in one day.
- Using the functional decomposition and the benchmarked product, these are the requirements that must be met:
- Steer the tiller
- Have multiple control methods
- Attaches to hull quickly with minimal actions.
Based on the functional decomposition chart, the bottom layer tasks were listed (as well as others) and evaluated in a concept development chart. Any method for completing each function was listed which helped inspire ideas for designs on each task.
A refined version of this chart is included under the Morphological Chart and Concept Selection section of this page. The main functions that SailBot needs to have, outlined in the functional decomposition chart, were expanded upon and used to categorize the concepts (methods) being brainstormed. Benchmarking against the RS Venture helped us eliminate concepts that are not as desirable while inspiring us to consider similar components which have been proven to work well. During the detailed design phase, our primary focus will be further analyzing many of these methods and prototyping the ones which we want to pursue further.
Morphological Chart and Concept Selection
After brainstorming and breaking down SailBot into its specific functions, a morphological chart was created to organize potential design concepts by the functions associated with them. This chart provides a tool for analyzing different combinations of designs and ensuring every function is accounted for when the entire system design is decided on.
In this chart, each concept was talked about and researched in order to understand all the benefits and limitations of each one. These would be the concepts used in the Pugh analysis charts
Based on the functions listed in the morphological chart, a Pugh analysis was conducted on each different designs in order to pinpoint the best options while removing bias. Design options were ranked according to 12 system-level criteria (listed along the left side) which were selected based on customer and engineering requirements:
- Installation Difficulty
- Comfort (User)
- Precision/Degrees of control
- When evaluating, some systems use precision to discuss the accuracy of the system. Others were based off degrees of control which evaluated how much control a user had over the system
- Modifications to Boat
A scale from 1 - 5, with 5 being the best, was used and the top weighted choices are highlighted in red. Some criteria were difficult to apply to some designs which is why there are rows filled in with zeros. Moving forward, these top choices will be the first to be analyzed and prototyped in various combinations during the next design phase.
Pugh analysis for tiller control
Pugh Analysis for Installation
Pugh Analysis for Tiller Attachment
Pugh Analysis for Reading the Tiller Position
Pugh analysis for User input methods
Since some of the functions in the morph chart are directly dependent on other subsystems, we did not use them in the Pugh analysis. In addition, the User feedback options are not being evaluated against one another and therefore did not get a Pugh analysis. The Pugh analysis forced each idea to be fully inspected and understood. The information and points discussed are going to be used to focus on prototypes and feasibility.
Systems Architecture and Design Flowchart
Based on the actions of the morphological chart and functional decomposition, A system architecture chart was created to display the basic flow of energy and information through the system.
After installation, the system is split into five inputs (tiller attachment, user input, electronics/power, sensors, and user feedback) which all flow into the main output which is tiller control and movement to ultimately steer the sailboat in a desired direction.
The system operation is further broken down into more specific elements to understand how all systems interact with each other
The System level architecture and flowchart lead to the creation of each overarching subsystem.
Feasibility: Prototyping, Analysis, Simulation
What power usage allows for a 2 hour battery life using a 12v 18Ah battery?
What power usage allows for a 4 hour battery life using a 12v 18Ah battery?
Which user control (input) design will be most intuitive for sailors? Which design will be compatible for use with the greatest range of disabilities?
Taking which disabilities are most common and pinpointing a design which can be used under most, if not all, situations. Interviewing electric wheelchair users on aspects they like/dislike about the controls.
Creating models for shape variations and comparing comfort felt with each one.
How fast is the Sonar going to be able to turn once the SailBot is attached, i.e. what will it’s maximum rotational velocity be?
- Determine the minimum and maximum speeds that the boat will be operating at with the device.
Determine how quickly the tiller actuator will be able to respond to the user input. Some benchmarking of electronic components as well as analysis of the actuator itself in terms of degrees of freedom and turn angle will be required to answer this.
Develop a mathematical model for determining high/low rotational speeds. This can be simulated or found experimentally via a small prototype.
Turning Speed Estimation
What is the maximum speed the tiller can rotate?
150:1 Gear Ratio
SailBot actuator moves at the same rate as the tiller.
Use standard stepper motor.
Use estimate gear ratio
In order to determine the torque required by the tiller controller, the maximum load torque applied to the tiller in real life scenarios must be calculated.
Remote Connection to User Inputs
Examine the viability of multiple wireless transmit and receive methods as well as the power and processing requirements for each, some method to be explored are listed below.
- UART Serial Wired Communication (as a baseline)
- 2.4GHz Wifi Communication
Design Review Materials
Plans for next phase
- Refine our concept selection to a specific design we want to pursue, at least as a starting point.
- Develop proof of concept for the specific design
- Perform analysis, simulation and prototyping of subsystems, specifically those with components we want to compare multiple options for
- Begin organizing design outputs (drawings, process flow diagrams, simulation documentation)
- Continue communicating with Rochester Yacht Club and go on site to measure their boats and see the facilities we may use for testing
Below are the three-week plans for each individual team member of the next phase: