P18347: Baby Stroller with HVAC
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# Preliminary Detailed Design

 Table of Contents 1 Team Vision for Preliminary Detailed Design Phase 2 Engineering Analysis 3 Feasibility: Prototyping, Analysis, Simulation 3.1 Heat Transfer Analysis 3.2 Micro-Controller Selection 3.3 Electrical Circuit Diagrams & Micro-Controller Prototyping 3.4 Wire Research 3.5 Battery Benchmarking 3.6 Battery Enclosures 3.7 Material Research 4 Bill of Material (BOM) 5 Test Plans 6 Updated Engineering Requirements & Risk Assessment 7 Plans for next phase

During this phase, Team Climate Constroller worked to further refine their design from the previous phase. This included continuing to work on heat transfer calculations, updating physiological information of children, making decisions on the types of material and the type of microcontroller that will be used, and benchmarking basic battery information. Discussions were had with Dr. Robert Stevens, Dr. Margaret Bailey, and our customer Dr. Josa Hanzlik to get their thoughts and input on our ideas and calculations.

## Team Vision for Preliminary Detailed Design Phase

Accomplishments
• Insulation research and selection for seat insulation and plastic cover
• Schematic diagrams - heat transfer through system
• Matlab - heat transfer calculations
• Required spacing between heating coils to achieve desired heat output
• Heat lost from baby to the environment
• Optimal thickness for seat insulation and plastic cover
• Micro-controller selection
• Prototyping temperature sensor
• Shut-down system research
• Material bench-marking for heating coils
• Bench-marking electrical enclosures
• Preliminary bill of materials
• Preliminary test plan
• Physiological research
• Burn temperatures
• Baby's respiration rate
• Updated engineering requirements and risk assessment

## Engineering Analysis

Specific physiological questions were answered in order to move forward with heat transfer calculations as well as ventilation analysis.

The breath rate as well as tidal volume of the baby was determined. The tidal volume is defined as the amount of air breathed in/out in one breath cycle.

• Breath rate = 33 breaths/min
• Tidal Volume = 15 mL =~ 0.5 L/min

The time it takes for the baby to be burned was also analyzed. Because there is little information about burns on babies, this information will be inferred from that of adults.

• Assuming a skin temperature of 33 degrees C, a contact temperature of 44 C (109.4 F) is the minimum temperature that will burn the skin.
• It is assumed that a baby's skin thickness is about 1/5 that of an adult.

## Feasibility: Prototyping, Analysis, Simulation

### Heat Transfer Analysis

A heat transfer analysis was done using matlab to answer the following questions:

• What is the optimal spacing between Nichrome A wires to achieve desired heat output?
• How much heat is lost in the system?
• How thick does our polyurethane foam need to be?
• How thick does our thermo-polyurethane plastic need to be?

Revision 2: Matlab Document

Subject Matter Expert Meeting: Dr. Robert Stevens (10/27/2017)

#### Heat Generation within the Heated Seat

The diagram found below represents the spacing between the Nichrome A heating coils. Matlab was used to determine the increase in heat generated as the space between the coils decreased.

Heating Coil Spacing Diagram

Heating Coil Optimization Plot

#### Heat Lost from the System

Matlab was also used to find the heat lost from the system as the thickness of both the foam and plastic insulation are varied. Each surface plot represents an increase in atmospheric temperature, varying from -40 degrees C to 60 degrees C. These outputs can now be used to calculate our battery requirements.

Schematic: Resistive Network

Surface Plot: Heat Loss in System

### Micro-Controller Selection

Using the guidelines provided by Professor Slack a number of micro-controllers were investigated and compared. All evaluations are captured in the Microcontroller Master Sheet. Using a modified version of the provided selection matrix four micro-controllers were compared and the Arduino Uno Rev3 was determined to be the best selection.

Micro-controller selection matrix

### Electrical Circuit Diagrams & Micro-Controller Prototyping

Using the results of the Morphological Chart from the Systems Design Phase along with a list of potential inputs and outputs a high level block diagram of the complete electrical system was created. The brain of the system will be an Arduino Uno rev3 running on custom software written by Ian. A basic overview of the inputs and outputs for each subsystem to the Arduino are shown on the diagram below. Moving forward each individual subsystem will have a complete circuit schematic like that of the temperature sensing circuit further down the page.

Basic Electrical System Block Diagram

Temperature Sensing Schematic

Using components that were left over from freshman practicum the circuit diagram shown above was created in hardware using a breadboard and an Arduino Uno Rev 1 that Ian already had. Ian created code based on the datasheet for the AD22100TK thermal sensor used in the circuit to convert the voltage output into a digital signal that the Arduino could then continuously read from. From there a simple if else loop was created that triggered a print output of "Heater ON" or "Heater OFF" depending on the average temperature read by the two sensors. Additionally two digital I/O pins were set to outputs and were triggered on and off to visually signal the heater on/off output even when the system is not connected to a PC.

Temperature Sensing system code

### Wire Research

NiChrome Resistance

This chart represents the percentage of increase resistance with relation to wire temperature for Nichrome A and C.

NiChrome Wire Resistance Chart

This table shows the wire resistance at various gauges.

DIAMETER The smaller the wire, the higher the resistance per foot. As the diameter increases in size (AWG decreases) the resistance decreases. As the diameter decreases (AWG increases) the resistance increases. It is easier to move an electrical current through a large wire, than it is a small wire.

LENGTH The longer the wire, the higher the overall resistance. As length increases, the resistance increases. As the length decreases, the resistance decreases. The more wire you have, the more resistance it creates.

Grafoil Properties

Grafoil properties looked at in depth.

### Battery Benchmarking

Battery Benchmarking

Battery Properties

Benchmarking of various types of batteries and properties.

### Battery Enclosures

Enclosure Ratings

The Different types of ratings we looked into for the enclosures.

Enclosure Selection

The type of enclosure we choose and the reason why we choose it.

### Material Research

The following tables show the different types of materials researched. The seat will be made of a type of foam material and then covered in a fabric. The type of plastic that will be used to enclose the system are also shown. The materials that have been selected are boxed in red.

Foam Seat Material Benchmarking

After looking at multiple types of foam used in car seats, cushioning, and types of insulation, it was decided that polyurethane foam would be the best to use for the seat.

Polyurethane Flexible Foam

This table shows some basic information of different forms of polyurethane foam.

Fabric Material Benchmarking

In order to make sure the heated seat does not burn the child, the foam will need to have a fabric covering. Nylon fabric was determined to be the best fabric because it is lightweight and easy to wash.

Plastic Covering Material

There are many different types of plastic that could be used for the plastic covering. However, it is very important for this project that the plastic has low toxicity, it is weatherproof, and it is a flexible material. Similar systems were researched, such as hospital bubbles and inflatable walking water bubbles.

## Bill of Material (BOM)

A preliminary Bill of Materials was created in preparation for the purchasing of items needed for testing and prototyping.

Item Status:
Items in GREEN have been completed. Items in YELLOW are in progress. Items in RED have not been started.

Preliminary BOM

## Test Plans

A preliminary test plan was developed to outline the tests required based off of the engineering requirements created in the problem definition phase.

Preliminary Test Plan

Each test is further explained in a more detailed document.

## Updated Engineering Requirements & Risk Assessment

The team has updated our customer requirements, engineering requirements, and risk assessment to account for our final design concept choice.

#### Customer Requirements

Cells highlighted in ORANGE: item has been updated to reflect Phase 3 design changes.
Rows highlighted in RED: requirement no longer applies to our project.

Customer Requirements: Phase 3 Revisions

#### Engineering Requirements

Cells highlighted in ORANGE: item has been updated to reflect Phase 3 design changes.
Rows highlighted in RED: requirement no longer applies to our project.

Engineering Requirements: Phase 3 Revisions

#### Risk Assessment

Rows highlighted in GREEN: action has been taken to mitigate this risk during Phase 3.
Rows highlighted in RED: event no longer applies to our project.

Risk Assessment: Phase 3 Revisions

## Plans for next phase

Team's Plan

Final Detailed Design Phase Plan

The following chart shows the timeline of where the team wants to be by the end of the final phase of MSD I. We would like to have most, if not all, materials and components sourced and decided on so we can order them over winter break. We plan on using the frame of the stroller we have already purchased to start with.

The team has already started looking into the ventilation system design and development.

Subject Matter Expert Meeting: Dr. Margaret Bailey (11/06/2017) Customer Meeting: Dr. Josa Hanzlik (11/08/2017)

Individualized 3 Week Plans Combined list of individual phase four three week plans