P18046: The Overcomer
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Systems Design

Table of Contents

Team Vision for System-Level Design Phase

The systems level design phase is a crucial part of the Overcome It project for numerous reasons. This phase was intended to take the team through several exercises that would ultimately produce a high level systems design concept. The key phrase there is "several exercises". We learned that it is very important to keep an open mind when generating concepts, and not to jump to conclusions about what the design should look like. This is especially crucial to the success of this project because we are designing a prototype that will ultimately be manufactured on a larger scale. Along with that, it was important for the team to fully vet each concept that we generated, so that we were able to foresee risks and challenges in our design concepts.

Ultimately, our team accomplished an overall systems design concept, which we will now be able to translate into subsystem and full system detailed designs.

Functional Decomposition

The functional decomposition defines the list of functions and subfunctions delivered by the final design. The functions are derived from the customer and engineering requirements identified in the first cycle. The functional decomposition is organized such that the blocks underneath a block explain how that block will be accomplished and the block above explains why the blocks below it are relevant.

Inputs and Source

  1. Project Objectives.
  2. Engineering Requirements.
  3. Benchmarking Data.

Outputs and Destination

  1. Complete list of functions that must be provided in order to satisfy the functional requirements of the entire project.
  2. Engineering Requirements are written to measure how well the functions are performed.
  3. Concepts are generated around functions identified here.

A link to the working Functional Decomposition can be found here.

Functional Decomposition

Functional Decomposition

Benchmarking

Although there are no direct product comparisons to the Overcomer, we found a few related products to benchmark product weights, costs, performance, and adjustability / ease of use.

Inputs and Source

  1. PRP.
  2. Project Objective.
  3. Function Decomposition.
  4. Prior MSD EDGE sites.
  5. Customers.
  6. Vendors and users of existing or similar solutions.

Output and Destination

  1. List of best available concepts and embodiments.
  2. Criteria used for selection of best.
Benchmarking

Benchmarking

A link to the working Benchmarking document, with links to the benchmarked products, can be found here.

Feasibility: Prototyping, Analysis, Simulation

For the feasibility portion of the systems level design phase, most of our feasibility work consisted of prototype various system concepts we had. These prototypes, shown below, were all quickly made using cheap, common materials such as foam core, rubber bands, and nails.

Images of prototypes are displayed below. From left to right: Spring and Arms Prototype position one and two, Dustpan Prototype front and side view.

public/prototype3.jpg public/prototype1.jpg public/prototype2.jpg public/prototype2b.jpg

Some simple dynamic calculations were done to investigate the magnitude of the force needed to to be transmitted to common types of balls on common types of surfaces so that the ball travel 10-30 meters. In the formula used, below, the variables used consist of:

image:formula.png

The results from this analysis can be found below. Ultimately we determined that we will need to transmit between 5 and 25 Netwons of force to the ball.

public/plot1feas.png

Morphological Chart and Concept Selection

The Morphological chart is intended to to brainstorm actions and concepts to accomplish certain tasks. Our product is broken up into three main functions: trapping an object, controlling/moving an object, and launching an object.

Morphological Chart for the Trapping Mechanic

Morphological Chart for the Trapping Mechanic

Morphological Chart for the Controlling Mechanic

Morphological Chart for the Controlling Mechanic

Morphological Chart for the Launching Mechanic

Morphological Chart for the Launching Mechanic

Inputs and Source

  1. Project Objectives.
  2. Engineering Requirements.
  3. Function Decomposition.
  4. Concept Development.
  5. Benchmarking criteria.
  6. System Architecture.

Outputs and Destination

  1. A complete set of concepts that provide all of the functionality required.
  2. Fall back options to substitute for the most risky concepts.

Concept Development

The team came up with many initial design concepts. Sketches of these concepts can be found below.

public/concepts collection.jpg

The original sketches for some of these concepts can be found in the following image files: Dustpan Concept 1, Dustpan Concept 2, Dustpan Concept 3, Concept 4, Concept 5, Concept 6, Concept 7

After brainstorm these ideas individually, we worked together to look into the advantages and challenges of each concept. We then broke into groups to develop next iteration concepts. These concepts are shown below.

public/frame.png public/angled arms.png public/dustpan.png

Concept Selection

This consists of two elements:

The real value in this step of the process is not the comparison matrix you generate to compare your concepts, but the analysis and discussion you do to support your evaluation.

Selection Criteria

Selection Criteria

Selection Criteria

Pugh Charts

Pugh Chart

Pugh Chart

Although the results of our Pugh chart analysis show that the Dustpan and Cannon design is relatively better than the other two, our team decided that we will be moving forward with that design, as well as a combination of the Angle Arms and Spring & Arms design. At this point in the design process, we feel as though we do not have enough information to fully settle on one design concept. Additionally, by moving forward with two design options, we are engaging in contingency planning in the event that we discover that one design is not feasible for some reason.

Systems Architecture

Systems Architecture

Systems Architecture

While our Systems Architecture is simple, it is designed to indicate the potential simplicity of our overall system. Our main goal for the system is that it performs the intended function, and gives the user an indication that they succeeded in their task.

Inputs and Source

  1. Engineering Requirements.
  2. Functional Decomposition.
  3. Concept Development.

Outputs and Destination

  1. High level description of the total system that support concept selection.
  2. Interface definition for subsystem design.

Risk Assessment

Since risk management is a continuous task, our team updated our risk assessment chart throughout the system design phase. As we conducted more detailed research including getting to look at various types of wheelchairs and observe our target market, we were able to much better understand the likelihood and severity of the risks we had already identified in cycle 1. We were also able to come up with new risks that we had not previously had the insight to come up with.

In assessing risks, our hope that bringing awareness to any potential problems so that we can take actions to reduce the likelihood of these problems. From an overall standpoint, we can try to quantify the uncertainty of our project by looking at the risks we have identified, and summing the product of each likelihood and severity to come up with an overall risk level for any point in time. As we remove, update, and add risks this number will change as as we progress into MSD II we hope to drive down our risk level. A plot of our risk over time can be found here.

Design Review Materials

Our Phase 2 design review slides can found on our Google Slides link, System Design Level Review Presentation.

Plans for next phase

At the conclusion of phase 2, our team reflected on the work we did for the System Design phase and the way we went about completing that work. We went back to our Individual Plans for Cycle 2 that we created at the end of Phase 1. We reviewed our predictions for what tasks we would work on and then compared those predictions to what we actually worked on. We also reflection on some of the lessons we learned during the Systems Design phase.

Then, to be better prepared for the next phase, our team took a look at the tasks and deliverables due for the the Preliminary Detailed Design phase. Then we individually came up with a prediction for the work that we would complete during that phase to contribute to our Phase 3 Design Review. The Individual Plans for Cycle 3 were created as a Google doc and will be updated after the completion of Phase 3 with what we actually did and learned during Phase 3.

In terms of overall project planning, the next phase will primarily be focused on improving and adding detail to our systems level design concepts, the dustpan and the L-shaped arms. In addition to building out our designs more fully, we will make decisions about materials and components, and begin to identify suppliers to order from. These materials and components will be arranged to form our Bill of Materials (BOM). We will also focus on defining our product testing plans, to be used in MSD II while we build the prototype. Finally, we will continuously document and update our risk management documents.

Our team has begun using Trello to track and assign individual task information. Our Trello board can be viewed here.


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