P16214: Bicycle Power Meter
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Detailed Design

Table of Contents

This page shows our MSD team's accomplishments during the Detailed Design phase. The goal of this phase was to finalize the design for our Bicycle Power Meter. This phase focused on the low risk items that still need to be mitigated which account for roughly 10% of our design. Along with finalizing these design choices our MSD team also began to perform some initial testing with our chosen components that served to verify that our design choices were correct and would be able to satisfy the design needs. Original documents and live documents for this phase can all be found within the Detailed Design Documents sub-folder.

Team Vision for Detailed Design Phase

During this phase our MSD team plans to have our design for the Bicycle Power Meter completely finalized. We also plan to continue conducting testing to verify that our design decisions were correct and accurate. By completing this testing now while in the design phase of MSD I, this will better suit our MSD team by finding possible errors in our design calculations and making any necessary changes now rather than in MSD II. The goal at the end of this phase is to have our design ready to begin building and testing at the start of MSD II.

Prototyping, Engineering Analysis, Simulation

Strain Gauge Testing

During this phase our MSD team wanted to test our strain gauges to ensure that we could in fact get the degree of accuracy that we had calculated for. In order to perform this testing we first needed to test our amplifier circuit to ensure that it was working correctly before we would be able to connect the amplifier to the strain gauges to test the strain gauges. The amplifier circuit was built on a breadboard based on the amplifier circuit that was designed in the previous phase. The amplifier circuit with a wheat-stone bridge built into it is shown below:

Amplifier Circuit with Wheat-Stone Bridge

Amplifier Circuit with Wheat-Stone Bridge

This circuit was then implemented and constructed on a breadboard.

public/Photo Gallery/Building Amplifier Circuit.JPG public/Photo Gallery/Constructed Amplifier Circuit.jpeg

The image on the left shows Connor constructing the amplifier circuit on a breadboard based on the amplifier circuit that was designed by our MSD team. The image on the right shows the amplifier circuit after it had been constructed. The chip at the bottom of the picture is the amplifier IC while the wires and the resistors seen at the top of the picture is the wheat-stone bridge. The wires going out of the frame of the picture from the wheat-stone bridge are connected to the strain gauges. In order to receive signals and readings from the stain gauges wires needed to be soldered to our strain gauges. The following images show how the wires were soldered to the strain gauges:

1.) public/Photo Gallery/Strain Gauge Solder Image_1.JPG 2.) public/Photo Gallery/Strain Gauge Solder Image_2.JPG

3.)

Images 1.) and 2.) show that the stain gauge was taped to a piece of sheet metal. The reason for taping the strain gauge was to keep it from moving and flexing which would potentially damage the strain gauge. The sheet metal also helped to act as a heat sink so as not to apply too much heat to the strain gauge and damage its accuracy. Once the strain gauge was taped in place the same action was performed on the wires to keep them in place so as not to damage the pads of the stain gauges by accidentally tugging and pulling at them. Once both the strain gauge and the wires were taped in place, the wires were then soldered to the pads of the strain gauge being extremely careful not to apply heat for too long that it would potentially damage the strain gauge. Image 3.) show a picture of the whole piece of sheet metal with the strain gauge and wires taped to it. This model was then used as a basis to test the operation of the amplifier circuit.

However, upon trying to solder wires to the strain gauges our MSD team came to the realization that this is not a very feasible task which led us to think of other ways in which we could attach wires to our strain gauges. Our MSD team seeked out the assistance of a strain gauge specialist on RIT's campus who was able to give us some advice on the usage and application of our strain gauges. The strain gauge specialist showed us strain gauges that are manufactured with wire leads already attached to them which would be a lot more feasible for our MSD team to accomplish. The strain gauge specialist also applied the strain gauge on our crankset for no added cost. The following figure shows the new strain gauge that our MSD team will be using for this project as it has been applied onto the crankset:

New Strain Gauge Applied to the Crankarm

New Strain Gauge Applied to the Crankarm

Once the amplifier circuit was tested and was verified that it was working correctly as well as the strain gauge being applied to the crankarm, the test could now begin to start verifying the types of values that we expect to see from the strain gauges as calculated when forces are applied to the crankarm. The following pictures show the test setup that was used for the strain gauge test are shown below:

public/Photo Gallery/Crankset Test Setup_1.jpeg public/Photo Gallery/Crankset Test Setup_4.jpeg

The pictures above show that the crankarm with the strain gauge attached to it was placed in a vice to keep the crankset from rotating. The wires coming from the new strain gauges were then connected to the amplifier circuit and the output of the amplifier circuit was hooked up to a data acquisition unit to record the output voltages of the amplifier. With the crankset in place weights were added to the crankarm to record the voltages that get produced from the strain gauges. The results of the strain gauge test are shown below:

Crankset Test Results

Crankset Test Results

Continued Battery Feasibility Analysis

Along with conducting the testing on the strain gauges more feasibility analysis was performed on our battery power supply. When our MSD performed our initial feasibility analysis we did not take into account how large the batteries would be. We ordered the batteries that we had initially designed for and when our MSD team received the batteries they were larger in size than anticipated. This led our team to revisit the feasibility analysis of our battery. Upon revisiting the battery feasibility we adjusted our calculations to provide enough power to sufficiently provide power strictly for the ImagineRIT event. The following graph shows the adjusted battery consumption graph that was created in the previous phase:

public/Photo Gallery/Detailed Design/Power Consumption Chart_12-8-15.JPG

The graph above shows the total battery power (green), the maximum power consumption our microcontroller is able to draw from a power supply (blue), and the total power consumption we expect to see (red). The original document for the updated battery consumption feasibility can be found within the Detailed Design Documents sub-folder

Preliminary Smartphone App Layout

Our MSD team also decided to create a preliminary layout for the user interface for the smartphone app that will be used to display the power meter information. The user interface is shown on an iPhone because that is the ideal smartphone that our MSD team is designing for. The preliminary user interface layout is shown below:

public/Photo Gallery/Detailed Design/Smartphone App Layout.JPG

The phone image shown on the left above is the main screen that the user will see when they first initialize the app. This main screen shows two different selections that the user can choose from. The top button that says 'Reset' is used to calibrate the power meter. Once the second button that says 'Start New Ride' is pressed this will take the user to the screen shown on the right above. The image shown on the right will then start to record the riders calories burned as well as their power output. It can also be seen that below the power output will be a graph that displays the rider's power output as a function of time.

Bill of Material (BOM)

After making minor changes in the design of the Bicycle Power Meter and adding things to the design our MSD team updated the Bill of Material to reflect these changes in the finalized design. The updated bill of material can be seen below:

Updated Bill of Material

Updated Bill of Material

It can be seen in the bill of material which items we have purchesed and received already. Our MSD team also added a small list of items that we know we will need to purchase in the future. While these items are shown on our bill of material they are not taken out of our total remaining budget. The original and live document for our MSD team's bill of material can be found in the Bill of Materials Spreadsheet.

Test Plans

The timeline for some of the test plans of our subsystems and components have been shifted due to some minor changes in our finalized design. The updated test plan schedule is shown below:

Updated Test Plan

Updated Test Plan

The updated test plan not only shows the shifted testing schedule but it also shows the updated tests that have been completed. The original and live document that shows the updated schedule along with the results of these tests can be found in the Subsystem Test Plan Document. Along with the test plan schedule the subsystem test plan document was updated. The test plan document contains the instructions of each test that was conducted as well as the results to each test. The test plan document can be found in the Detailed Design Documents.

Design and Flowcharts

The design and flow of our system design has not changed much from the previous phase. Similar to last phase the architecture of the Bicycle Power Meter flows as follows:

Systems Architecture

Systems Architecture

With this systems architecture in mind our MSD team created a full systems electrical schematic which includes all of the wiring and connections that will be needed between our microcontroller, accelerometer, the strain gauges, as well as our amplifier and wheat-stone bridge circuitry. The electrical engineers on the team created the circuit schematic using Orcad. The full systems schematic that was created can be seen below:

Full Systems Schematic

Full Systems Schematic

The original files for the full schematic can be found in the Schematics sub-folder of the Detailed Design Documents.

Along with this systems architecture and the electrical schematics, a set of mechanical drawings were also created to show the sizes and dimensions of all of the various components that will be used for the bicycle power meter. The drawings also show the components as they will be placed on the crankset with the various dimensions as well. The CAD drawings were created by the mechanical engineer on the team. The dimensioned CAD drawings are shown below:

Battery

Battery

Battery Holder

Battery Holder

Amplifier Circuit PCB

Amplifier Circuit PCB

Microcontroller

Microcontroller

Accelerometer

Accelerometer

Plug for Accelerometer

Plug for Accelerometer

Complete Assembly

Complete Assembly

The following links will show the pdf version of each of these drawings to allow for better clarity and quality of the drawings and their dimensions:

2032 Battery Drawing

Battery Holder Drawing

Amplifier Circuit PCB Drawing

Microcontroller Drawing

Accelerometer Drawing

Plug for Accelerometer Drawing

Complete Assembly Drawing

After all of the component placement was finalized and the final dimensions were known the team then created a rough idea for a housing to protect the components on the crankset. The housing was updated to include an on and off switch for the battery supply power to the rest of the bicycle power meter. Also some preliminary dimensions were added to the housing. Pictures to show both the housing dimensions and the location of the on/off switch are shown below:

Crankarm Housing with Dimensions

Crankarm Housing with Dimensions

Crankarm Housing with On/Off Switch Added

Crankarm Housing with On/Off Switch Added

These CAD drawings are only preliminary drawings and dimensions. These dimensions and drawings will change as the final location and position of all of the components gets completely finalized. This housing will have the on/off switch which will allow the battery to supply power to the power meter or disconnect the power. The housing will also protect the components on the crankarm from getting damaged by any accidental kicks or being knocked on.

Risk Assessment

After going through the Detailed Design phase our MSD team updated our risk assessment to show the risks as we see them at this point in the project. The updated risk assessment can be seen below:

Risk Assessment

Risk Assessment

The original and live document of the updated risk assessment can be found in the Detailed Design Documents folder. The updated risk assessment is different from the last phase in that we have changed the severity of risk item number 4 (the smartphone app does not function as intended in the design) from a 3 to a 1. The reason for reducing this severity is because we have a backup plan for the power meter not being able to function with the smartphone app. We have already tested the bluetooth communication and know that it will communicate with both a smartphone as well as a microcontroller. Therefore if we do not get the smartphone app operating correctly we will use a second microcontroller to process the information in place of the smartphone app and then send this information to a display. Also the likelihood of the last risk item (item number 11) has been reduced from a 3 to a 2 because our MSD team has created a preliminary housing for these components that we know will cover all of the components to prevent them from getting damaged.

Design Review Materials

For the Detailed Design Review our MSD team decided to create a powerpoint presentation to display our progress throughout this phase. The following link is a link to the Detailed Design Phase Powerpoint Presentation

After the detailed design gate review our MSD team was given some advice as to what to accomplish by the start of MSD II. The advised plans of action are shown below:

Plans for next phase

After the design phases of MSD I our MSD team is getting prepared for the building and testing portion of MSD II. The following shows a list of what we plan to accomplish in MSD II:

Our MSD team also came up with a list of deadlines that we hope to meet to keep us on track to completing a working product for our customer by ImagineRIT. The list of deadlines is shown in the table below:

Task to be Completed Deadline
Subsystem test plan complete End of February
App prototype complete Mid March
Housing prototype printed Beginning of April (1st)
Overall system test complete Mid April (15th)
App complete Mid April (15th)
Housing finished Mid April (22nd)

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