P18347: Baby Stroller with HVAC
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Integrated System Build & Test

Table of Contents

Team Vision for Integrated System Build & Test Phase

Phase 3 Team Vision Phase 3 Accomplishments Phase 4 Team Vision
Electrical
  • Complete the heater system
  • Debug and develop code of the main loop
    • Fix noise in temperature sensor
    • Program UI
    • Program input buttons
  • Convert breadboard components to PCB
  • Develop a battery charging method to be user friendly
  • Completed the heater system
  • Finalize system code
  • Solder components to PCB
    • Regulator circuits
    • Temperature sensing circuit
    • Heater control circuit
    • UI circuit
  • Finish battery charging method
Mechanical
  • Mount all components to stroller (battery, seat, wiring, micro-controller)
  • Complete micro-controller CAD modeling and determine how it will be manufactured
  • Connect the plastic covering and zipper to the stroller
  • Mounted seat to stroller (sewed seat cover); drilled holes for components in boxes
  • Completed micro-controller CAD modeling, determined an alternative
  • Connected plastic covering to stroller and zipper to plastic cover
  • Finish mounting components to stroller
  • Measure final stroller weight and footprint
Test Plans
  • Continue to test heated seat functionality
  • Controller testing (user interface)
  • Usability- ease of movement
  • Overall electrical charge on stroller
  • Foam Thickness Test
  • Ambient Temperature Testing
  • Heated Seat Functionality
  • Charge on the stroller
  • Ease of movement
  • "Crash" testing
  • System shutdown and start-up
  • User interface
Status of Tasks

Status of Tasks

The following chart shows the status of the tasks from this phase. The tasks in green and the tasks in yellow are still in progress. There are a few parts we are still waiting for to arrive and tests that we need to perform. The tasks in red we have not gotten to yet. We plan on doing all tests and validation in the next phase.

Manufacturing Results

Sewing

P18437 Sewing Plans

STEP 1 STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 STEP 7
 Determine Measurements and spacing for harness straps and fixtures.

Determine Measurements and spacing for harness straps and fixtures.

 Cut 3 sheets of fabric for the cover oversized to account for material thickness.

Cut 3 sheets of fabric for the cover oversized to account for material thickness.

 Secure 2 edges of 2 sheets together with pins to prevent sliding.

Secure 2 edges of 2 sheets together with pins to prevent sliding.

 Sew the secured edges together and turn inside out to see finish product. Repeat with the other sheet on the other 2 edges.

Sew the secured edges together and turn inside out to see finish product. Repeat with the other sheet on the other 2 edges.

 Measure and mark openings for harness straps.

Measure and mark openings for harness straps.

 Cut material to create openings and sew excess fabric down.

Cut material to create openings and sew excess fabric down.

 Invert material and see finished cover.

Invert material and see finished cover.

Visor was removed to sew plastic cover to the fabric using a Singer Futura sewing machine. Plastic was cut to a length that touched the tray. Two mirrored sheets of plastic were cut the distance from the tray to the foot support. Edges of the plastic were sewn together, covered in nylon to hide and protect the stitch. Zipper was sewn to the plastic cover using the sewing machine. Extra fabric was attached to the bars beneath the foot support and needs to be hand stitched using the back stitching technique for strength.

Plastic Cover

Plastic Cover

Machining

Tabs from injection molding removed with mill to allow more space within enclosures. Holes drilled into battery box and microcontroller box for mounting, buttons, and cable glands.

Enclosure Tabs Before

Enclosure Tabs Before

Enclosure Tabs After

Enclosure Tabs After

Electrical Subsystem Integration

Seat Heater: Over break the final iteration of the seat heater was completed. The nichrome wire, which acts as the heating element, was bent and divided into four separate ~7.5 Ohm heaters which have a one inch spacing from wire to wire. These four heaters were then connected together in parallel to create one large heating element which covers the entire surface area of the seat.
View of the completed nichrome seat heater

View of the completed nichrome seat heater

User Interface: After speaking with both the customer and engineering team a cardboard mock up of the user interface was created. The user interface has two input buttons for temperature control along with a LCD display which will show the user the temperature setting of the stroller along with the current temperature readings of both ambient and seat temperatures. Additionally an emergency stop button is positioned above the temperature setting buttons as a means of shutting of the heater in case of emergency. This system will be enclosed in a waterproof container which is currently being modified to hold the electrical components.

Cardboard mock up of stroller's user interface

Cardboard mock up of stroller's user interface

System Functionality: During this phase each individual subsystem was evaluated and checked to ensure proper functionality as a complete system. The system was tested briefly on a breadboard with a single 12V power source to ensure that each voltage regulator circuit works individually while also working to power their correlated subsystems. Additionally the user inputs where checked to ensure functionality along with the display to ensure it shows the temperature readings. At this time the team is waiting on one last order to arrive with parts so the system can finish being soldered together and attached to the stroller. Rough sketches of the P18347 Electrical System Wiring Plans can be found in the previous hyperlink.

P18347 Integrated Electrical Subsystem Circuit

P18347 Integrated Electrical Subsystem Circuit

Test Results Summary

Tests Completed This Phase:

Test Setup:

Thermocouple Placement

Thermocouple Placement

Three thermocouples were used to temperature readings. One was placed directly on the center of the foam seat (T1), one under the visor (T2) and one underneath the tray (T3).
Test Setup

Test Setup

The stroller was covered with plastic to simulate the completed enclosed stroller.

Test Results:

All tests were stopped after one part of the seat reached 109 F because it was predetermined that this temperature is the maximum temperature allowed without burning the baby.

The first test run was to determine how the ambient temperature inside the stroller changes as the heated seat warms up. Temperatures were taken at three different points on the seat for each test. The green and orange lines, representing the ambient temperatures below the visor and tray, both reached a temperature of around 75 F when the heated seat reached a temperature of 115 F. The opening at the back of the stroller greatly affected the ambient temperature underneath the visor.

Ambient Temperature in Stroller vs. Time

Ambient Temperature in Stroller vs. Time

The second test run was to determine how long it takes for the seat to heat to the maximum specified temperature. It takes 8.5 minutes for one part of the seat to reach a surface temperature of 109 F. At this point, the heated seat would turn off to cool and restart its heating cycle.

Time for Heated Seat to Warm

Time for Heated Seat to Warm

The third test run was to determine how long it takes for the seat to cool from the maximum specified temperature to an ambient temperature. It takes about 7 minutes for the seat to cool from its max allowed temperature of 109 F.

Time for Heated Seat to Cool

Time for Heated Seat to Cool

This information tells that a realistic cycle time for our heated seat would be around 16 minutes (8.5 minutes to heat to 109 F, 7 minutes to cool to 75 F).

Full test report here:P18347 Ambient Temperature Testing Report

Financial Update

P18347 Integrated Systems Design Costing Update

P18347 Integrated Systems Design Costing Update

We have continued to update our BOM and a Purchase order checklist (POC) accordingly. A separate finance sheet is maintained and updated, keeping track of all expenses along with each purchase made along with date and price of item. 95% of the items in the BOM have been ordered and rest 5% pending on certain decisions at this point of time.

P18347 Integrated Systems Design Costing Breakdown for Build

P18347 Integrated Systems Design Costing Breakdown for Build

The above pie chart shows the breakdown of cost in terms of how much money the team spent on manufacturing, testing and shipping.

Risk and Problem Tracking

Problem Tracking Document

Problem Tracking Document

Future Plans for Project

Plans for the Project:

Recommended Senior Design Improvements:

Plans for next phase

Verification and Validation Schedule

Verification and Validation Schedule


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