Preliminary Design Review

The purpose of the Preliminary Design Review (PDR) is to formalize all of the information regarding your project into something that anyone without prior knowledge would be able to understand what was being attempted. It will also help clear up any issues or misunderstandings between the customer and the team. This blog post provides information about what documentation is required and some examples of how to create them.

The PDR can be considered to be made up of two main sections, the project documentation and the project plan / schedule. The project documentation focuses on details about what the team will be designing and involves things such as the requirements, system block diagram, and software block diagram. The project plan / schedule outlines how the team plans to complete the project within the semester. You will be required to complete and present both for the PDR presentation.

Outline

The objective of the Preliminary Design Documentation is to lay out the preliminary “technical” design of the project as defined by the Level 1 and 2 requirements, system design, and modeling. While the preliminary design needs to provide a clear description of the project, it is understood that the creation process follows the System Engineering Method and is therefore iterative by nature. You can consider this being a snapshot of the design process for future students to learn from if they continue working on the next generation of the robot.

Title Slide / Cover Page

This section of the presentation / document should contain the following:

  • Name of project and current school term
  • Team member names and respective division assignments
  • Project related picture or illustration.

I.E.

Goliath

EE 400D Spring 2017

Person X (Project Manager)

Program and Project Objectives / Mission Profile

The process begins with the identification of the problem to be solved, and/or product to be built as defined by the customer and codified by the Program Objective Statement. Although the Program Objective may be in the form of a requirement, it is typically a qualitative statement of what the customer wants. These “objectives” are not developed in isolation or at a fixed point in time but like all elements of the engineering method, evolve over the life of the project.

For example, after a system design is selected and the manufacturing element of the project comes to the fore, you may need to ask the customer about how easily the widget needs to be put together or taken apart for repair. The answer may require a redrafting of the program objectives, program requirements, system/subsystem requirements, and associated verification tests.

The Mission Profile documents how the product will be operated by the customer and is focused on the conceptual operation (ConOps). For many of our robots, the Mission Profile is defined by the course it will run on the day of the Final. This can also lead to additional requirements being generated as you find issues that were not considered.

Quality Control and Safety

Present Constraints on the project imposed by The Robot Company and Project Stakeholders.
Specifically include company (i.e., University) safety standards and those safety standards associated
with the product (e.g., Children’s Toys).

This will be covered in more detail with the Constraints lecture. You may attempt to address this section in your presentation but it is not required.

Requirements

From the mission objectives statement, Program and Project Requirements are written. Often the simple (only by appearance) process of defining a program requirement, will require rethinking program objectives and introduce new calculations that need to be performed, trade-off studies to be conducted, new models / prototypes that will need to be built, and experiments to be conducted. In other words each step in the engineering design process sends ripples both up and down the project.

  • Each requirement should be numbered for later reference.
  • While each requirement must be paired with one or more verification tests, this second step will be implemented in the next iteration of this document. You should indicate your initial thoughts on how to verify the requirement. This will help identify if you have worded the requirement properly. I.E. L1-13 will be verified by demonstration on the day of the final or L2-7 will be verified by measurement from testing.
  • Clearly indicate which level the requirement falls under. Make sure that the linkages for each level are apparent. I.E. The level 1 requirements clearly show they were derived from the mission profile or project objectives. Level 2 requirements directly follow from Level 1 requirements.

Once a system design is selected, the subsystems are defined. Definition of the subsystems is in
the form of Subsystem Requirements and Design Specifications (Level 2 requirements). Like the layers of requirements preceding them, each requirement level (program, project, system, subsystem), must be responsive to higher level requirement(s). They may never stand alone. To clarify, Level 2 requirements respond to Level 1 and Level 1 requirements respond to the project objectives / mission profile.

Design Innovation (If Applicable)

Once a first draft of the program/project requirements is done, the project team searches for creative design solutions (design ideas) for potential problems or issues that need to be addressed. This is where the creativity methods discussed in class can help.
This section only applies to your project if you have a problem to solve that does not already have a clearly defined solution provided by the customer. If you are working on a previous generation of a robot, there may not be a problem to resolve.

The focus of this section is to present the problem(s) to be solved and the potential creative solutions you are considering. You may reference solutions that was done by others as long as it provides evidence that the idea can work. The creative exercise is meant to help you consider as many potential solutions as possible and try to find if someone has done something similar to provide a starting point.

Systems / Subsystems Design

Product Breakdown Structure

The major subsystems comprising the system are defined in the Product Breakdown Structure (PBS). Please refer to this link for more information about the distinction between the PBS and WBS. The WBS will be covered in the Project Plan / Schedule section of this post. The important thing about this section is that the lowest level should be clearly assigned to a specific person.

Software Design

This section includes any material that helps portray how the software will need to work. It can consist of program flowcharts, block diagrams, or any other visual aid to show how the final code will perform. If your project needs to incorporate the Arxterra Control Panel or ArxRobot app in any way, you will need to show how it will be used. It also should indicate if any custom code will need to be generated as well. As things are being planned out, you may use placeholder names for the functions needed as long as it is relevant (does not need an explanation for what the purpose is). Typically, you will want two separate slides for this. One to show how the program should operate while executing the mission and another one to present the different parts of the code to develop.

Electronic System Design

System Block Diagram

Another aspect of the system design is the clear definition of the subsystems and the interfaces that exist between them. From an electrical engineering perspective, this definition is predicated by the System Block Diagram, followed by a description of the subsystems, their interfaces and requirements.

This diagram should clearly define all of the subsystems that make up your project and show how they interact (number of wires connecting them, direction of communication, type of communication protocol used, etc). One additional detail that would be helpful is to show how the subsystems fit together. For example, many subsystems will physically be within the chassis of your robot. It would be useful to represent that and show the interconnections on the inside.

Do not overload the diagram with long paragraphs describing each subsystems function. Be prepared to explain this verbally during the presentation.

Interface Matrix / Definitions

For a microcontroller based design, the electronic interface definition begins with the Interface Matrix and is finally documented by detailed schematic(s). Often the breadboard testing is documented by Fritzing diagrams. When two or more projects are subsystems of a larger project, they will need to coordinate how those subsystems interact. That results in the interface control document (ICD), which explains how the different interfaces of each project should be defined to keep everything organized.

There should be an interface matrix for each microcontroller or printed circuit board (PCB) to indicate the different wires and their function on that board. Shown below is an example of how this should be done. While it may be tedious, you should indicate all available pins for the device and indicate when that resource has been taken.

Atmega 328p (Arduino Uno) PinsCustom PCB PinsUltrasonic Sensor Pins
Pin 10 (VCC)3.3VVCC
Pin 11 (GND)GNDGND
Pin 12 (MISO)MISOX
Pin 13 (MOSI)MOSIX
Pin 14 (SCK)SCKX
Pin 15 (SS)SS1X
Pin 16 (PD6)XTRIG
Pin 17 (PD5)XECHO
Custom PCB PinsMagnetometer PinsLED PinsAtmega 328p (Arudino Uno) Pins
Pin 1 (VCC)VCCXPin 10 (VCC)
Pin 2 (GND)GNDGNDPin 11 (GND)
Pin 3 (MISO)MISOXPin 12 (MISO)
Pin 4 (MOSI)MOSIXPin 13 (MOSI)
Pin 5 (SCK)SCKXPin 14 (SCK)
Pin 6 (SS1)SSXPin 15 (SS)
Pin 7 (LED1)XVCCX

Mechanical Design

From a mechanical engineering perspective, the system design is predicated by a 3D mechanical rendering of the system with subassemblies clearly identified. This is typically done with an Exploded View of the system, followed by a description of the subsystems, their interfaces and requirements. Ideally, the best representation of the system will be from SolidWorks models but the complexity of the project may make it difficult. If you feel the model is lacking, include additional material (sketches) only if they add to the presentation.

Design and Unique Task Descriptions

After a first pass through the Engineering Process, you should have a fairly complete set of Task Definitions. These definitions include a short description of each task that needs to be performed and its duration. Once these tasks are defined, the projects take them to the divisions where engineers are assigned to complete them across the division. For example, if multiple projects need to know more about the characteristics of a servo, then only one engineer needs be assigned to gather information, define a test plan, and then conduct and document the test results.

Each member should develop the list of tasks that they will be focusing on in the coming weeks. A brief explanation of how they plan to approach it should be provided. For example, the E&C engineer is responsible for the custom PCB design and they may plan to breadboard the individual components that will go on the PCB to confirm how the wiring should be done before developing the schematic.  It may take two weeks or more for breadboard testing, evaluations of the design, and revisions before being complete.

These tasks can include applicable sketches, back of the envelope, trade-off studies, models, etc. Trade off studies must begin and end with requirements that are the key factors in making a choice. Trade-off studies must be quantitative. Avoid words like: Typically small, Large Torque, Very accurate and precise, Highly efficient, Has reserve power and torque, more likely to malfunction if subjected to overload, precise positioning, stable, quick starting and stopping, small step  distance, it’s possible to “skip” steps with high loads, draws maximum current constantly, low self-discharge, very high energy density, A little expensive, high shelf life. Provide exact values if possible from datasheets or calculations to allow for accurate comparisons.

The main focus of this section is to lay out what are the critical things each team member will be working on and how they may plan to do them. Once that is covered, you should present the results from any experiments that you have performed. For example, any breadboarding or back of the envelope calculations that were performed should be discussed here.

Do not simply copy-paste material from previous generations of documents. Give proper credit for any work that you not responsible for.

Preliminary Project Plan / Schedule

Work Breakdown Structure

The WBS is a hierarchical breakdown of the work necessary to complete the project. (NASA System Engineering Handbook Section 4.3.2.1 Product Breakdown Structure). We will use the terms Work Breakdown Structure (WBS) and Product Breakdown Structure (PBS) synonymously, as they apply to the functional decomposition of the project.

Your WBS should be taken to a level such that tasks within each structural element are assigned to a single engineer. Specifically, organize all your tasks into groups in some hierarchical tree structure where each node (group) is the responsibility of only one engineer. Normally, the hierarchy will fall along Division/Section/Group lines.

Project Schedule

The top level schedule provided in this section should be developed using Microsoft Project or Project Libre. The top level schedule should be built from (linked to) WBS modules. Each module should in turn be linked to system/subsystem level tasks. These tasks may include trade-off studies and modeling (including rapid prototyping) as described in the next section and defined in the Preliminary Design Document.

From Microsoft Project, create a table of tasks needed to implement the project at the System and Subsystem level as defined by your WBS. A time estimate with uncertainty should be attached to each task. These tasks should be in response to those tasks defined in the Preliminary Design Document.

If you have any other project management software that can generate this, feel free to use that as an alternative to Microsoft Project or Project Libre. Please indicate what that software is.

Burndown

The purpose of the burndown diagram is to show the projects progress up to this point. Depending on how the project schedule is defined, it should give an estimation of how work should be progressing.

The percent of project completion is computed as follows. When a task is started, 50% of its weight is assigned as completed. When a task is completed, the remaining 50% is added to the score. Task completion must be approved by the president or the vice president. Proof of completion (blog post, documentation, etc) needs to be provided for each task before it can be considered finished. There are two approaches to how to define the burndown diagram.

Each task can be evaluated based on percentage completion or the number of hours it would take to finish.

For the first method, the total number of tasks needs to be considered. As each task is completed, you compare it to that total. I.E. 5 tasks are completed with another 4 that have started. That would correspond to 7 tasks (1 for each task done and 0.5 for each started) out of a total of 30. Therefore the total percentage done would be 23.33%.

For the second method, the total number of hours needs to be considered. As each task is completed, you compare it to that total. I.E. each task may vary for the number of hours needed. Assume the average is 4 hours for each task. For 5 tasks completed and 4 that have started, it would correspond to a total of 28 hours (4 for each completed task and 2 for each started task). If the total for the project is 84 hours, the total percentage would be 33.33%.

System Resource Reports

Resource Reports as they are applicable to the project provide information about how things are distributed among the subsystems. For example, power allocation/estimate for each subsystem module help to evaluate the total needed for the battery. Each resource should have a margin attached to it based on the uncertainty in the estimate. It should also show contingency, where contingency is defined as the project allocation minus the estimate and total margin.

One important consideration for these resource reports is that the project allocation for that resource needs to be justified or derived from a requirement. Typically, this is arbitrary due to the freedom of a student project. However, to be realistic, there is some form of a constraint that limits what is allowed. Therefore, the project allocation for each resource needs to be clearly defined as it shows how the design may run into problems with the choice of components and leads to the specifications of what is needed (operating voltage, etc).

Mass Shared Resource Report / Allocation

This section is dedicated to the total mass of the project. Also in a tabulated format, it should contain the expected weight, measured weight, percent uncertainty, and margin for each respective resource being used in the project. Lastly, it should contain total expected weight, total margins, project allocation, and contingency.

Power Shared Resource Report / Allocation

This section shows the different power demands of the various components used. There are several ways to represent the power (watts, mA, or mAh), so make sure to pick one. Typically represented in a tabulated format, it should include an expected current drawn, measured current drawn, percent uncertainty, and margin for each resource consuming power (for the mA case). Lastly, it should contain total expected current, total margins, project allocation, and contingency clearly showing the power source selected will support the project.

Other Shared Resource Report(s) / Allocation

Any other resources tracked by the system engineer. For example, 3DoT projects using a 3D printer have an 9 hr. (3/3/3) resource requirement that must be tracked.

Cost

Within the introduction of this section, please indicate the funding source for this project.
This is a table containing a parts list of all items to be purchased in support of the project. Each line item should include a margin if the actual item to purchase has not been defined. It is important that the estimate be as comprehensive as possible. Please do not leave off the list items for which you are know you will need but currently have not identified a model number/source. For example if you know you are going to need a servo but am not sure about which one then research the cost of servos and use the mean cost as an estimate with an uncertainty that makes sense. Finally, at the end of the table add a margin. This is to cover any contingencies including broken parts, parts you forgot about, etc. This margin should decrease with time as the project becomes better defined. If there are any parts that you will be borrowing from the cabinets or previous generations, please indicate those as well on this list and consider their actual cost to be 0. Add a note that it is being provided from previous semesters.

PDR Grading Rubric

The following list are all of the parts of the PDR presentation that will be graded.

  • Title Slide
  • Program Objectives & Mission Profile
  • Requirements
  • Design Innovation (If applicable)
  • System Design
    • Product Breakdown Structure
    • Software Design
  • Electronic System Design
    • System Block Diagram
    • Interface Matrix
  • Mechanical Design
  • Design and Unique Task Descriptions (Subsystem Task Descriptions)
    • The bulk of the work has been defined for the project manager and MST engineer at this point and they will continue to develop those items (system block diagram, etc).
    • This is why the main focus will be on what the E&C and MFG engineers are responsible for.
  • Project Plan / Schedule
    • Work Breakdown Structure
    • Project Schedule
    • Burndown
  • Resource Allocations
    • Mass
    • Power
    • Other
  • Cost