P16045: Motorized Pediatric Stander for the market
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

The primary objectives to address for the preliminary detailed design phase are:
- Analyze and debug P15045 stander.
- Develop preliminary schematics and test code with due consideration to the pitfalls and shortcomings in P15045.
- Solidify electrical and mechanical part selection and order them.
- Test environmental sensory.

Each of these tasks were addressed and currently being iteratively improved upon.

Lesson's Learned

While working on the previous iteration of the stander, the team had a strong opportunity to evaluate why the previous iteration of the stander had not been moving in a straight line. Realizing that the previous team didn't take advantage of implementing a PID controller properly, this years team decided to attempt to implement a rough PID controller to see if a steady state between the two motors could be reached. In attempts to tackle this task, a library for PID controllers was found. After reading up on the design that went into the library and the simplicity of implementation, it was implemented in a test to see if the motors could be spun forward at matched speeds.

The results of the PID implementation can be seen here.

As can be seen from the results of the PID test, the PID controller was effective in matching the movement of the motors. The next step in evaluating the PID was to see how the controller/stander operated on the floor (as opposed to suspended). It was when conducting this test that we found that the stander was still drifting (there was an initial deviation from straight line travel that was a result of having not perfected the parameters of the PID controller, but once the controller matched the motors the stander should have driven straight)despite positive results while suspended.

The results of this testing on the floor can be seen here.

From these tests we reached a few conclusions as to potential issues in the stander not being able to implement straight line travel.

We had found in tests leading up to these two tests that the encoders weren't reliable. It was thought that perhaps there was some weight issue that impeded the encoders already unreliable feedback while the weight of the stander was applied.
Since having performed the test, this seems like a less likely cause, but it was thought that while the weight of the stander was applied to the wheels/structure, there was some force acting on the wheels/motor in such a way that it was causing the unit to indefinitely turn despite the PID's attempt to straighten out.
It was suggested to us that the motor was attempting to draw more current than allowed by the motor driver. After consideration, this is something that could very well be the issue. Due to the timing of this diagnosis, no tests were able to be conducted to verify but test plans for the incoming motor kit have been drafted to validate this hypothesis.

Mechanical Systems - Motors

Revisited Motor Analysis

The motor analysis was revisited to determine the total effects of change in friction coefficients and ramped surfaces. Due to the number of public ramps that are not within ADA compliance, it should be noted that the ramped surface calculations were completed with 15 degree incline for worse case scenario modeling. Overall, it was seen that the maximum torque was not effected greatly by the change from a flat surface to a ramped surface.
Flat Surface Conditions

Flat Surface Conditions

Flat Surface - Static

Flat Surface - Static

Flat Surface - Dynamic

Flat Surface - Dynamic

Ramped Surface Conditions

Ramped Surface Conditions

Ramped Surface - Static

Ramped Surface - Static

Ramped Surface -Dynamic

Ramped Surface -Dynamic

Speed Requirements

Speed Requirements

The latest version of the document should be referenced at all times.

Weight Distribution Testing

This testing was completed to determine weight force on all wheels. This can be utilized to determine the potential for mechanical failure of the wheel drive shafts.
Weight Applied Front to Back and Left to Right

Weight Applied Front to Back and Left to Right

Motor Selection

Motor Requirements Comparison

Motor Requirements Comparison

Motor Building Requirements

Motor Building Requirements

Motor Diagram of Built-from-Scratch Motor

Motor Diagram of Built-from-Scratch Motor

Overall, the team advises moving forward for the time being with the Parallax Motor Kit, but exploring the option of changing out the encoders with ones that are more robust and do not require the toothed gear configuration.

Schematics and Software

Schematic

In efforts to begin the redesign of the electrical system inside the previous stander a new electrical schematic has been started specific to this iteration of the project. Using what the team learned from the behavior of the previous stander, looking at the electrical components implemented, and the accompanying software it is the belief of this group that some redesign in the electrical and software portions of the project will lead to the new implementation working better and having been implemented in a more proper fashion.

The original revision (Rev 0) of the schematic can be found by clicking here.

Software

With regards to software, there had been a lot of research taking place at the last review regarding implementation of PID controllers. Among our research we had found an identically functioning PID controller in Arduino with a GUI to observe the data graphically in real time, multiple PID controllers in the Arduino environment used to level out quad copters, and a simple Arduino library was found.

After looking further into the Arduino PID library, the author provided documentation on the functionality and design of the code, and it was found that this library – though simple – was robust enough for our needs. As mentioned we implemented it and through suspended tests on the stander we found that the code worked well. This provided the team with a solid base on the code that needed to be implemented for moving the stander in a straight line. This in addition with our flow charts on the hierarchy of command, provides the team with a good outline on how the final code should look and eases the design.

Also, as can be noted with some of the details in the way analog inputs were set up in the schematic, the functionality of the code should be significantly improved as it very may well be a possibility that a solution has been found for implementing interrupts to identify times when the analog inputs need to be read as opposed to polling. This improvement along with the hierarchal improvements we are making should improve the functionality of our team’s code over the last implementation, and should also make our code easier for people who weren’t the authors to read/understand our work.

Test Plans

Mechanical

Motor Testing Parameters consist of the following:

These parameters are depended upon the motor configurations, motor placement, and environmental conditions. These dependent parameters are:

Motor Characterization Matrix

Motor Characterization Matrix

The current version of the test matrix for motor characterization can be found here. All documentation regarding the results from these characterization tests will be logged in this document for future reference.

Electrical

With regard to electrical test plans, specifics as far as the testing have the potential to vary depending on the final implementation. At this point, the testing required for the electrical portion of the design would be primarily focused on meeting with SME’s to discuss design flaws, and obvious issues related to the implementation we are trying to move forward with. After getting our design cleared with SME’s we’ll be able to create a test template to perform and record current analysis and verify the circuit for power management.

Software

With software, the testing will be simpler in that the team can design an automated test bench. This would call for the need in implementing rigorous code sessions to identify edge cases with known inputs and expected outputs. This cannot be designed until the final code has been finished as expected outputs aren’t necessarily known yet, but implementation of such a tool will allow for proper testing of the system’s software.

Industrial Design

Story 1

Story 1

Story 2

Story 2

Story 3

Story 3

Story 4

Story 4

Charging Detail

Charging Detail

Custom Bumper

Custom Bumper

Enclosure Internals

Enclosure Internals

Exploded Back

Exploded Back

Exploded Front

Exploded Front

LED Detail

LED Detail

Money Stander

Money Stander

Money Stander 2

Money Stander 2

Sensor Feasibility

Environmental Sensory Testing

HC-S04 Ultrasonic sensor testing

HC-S04 Ultrasonic sensor testing

HC-S04 Ultrasonic sensor testing environment

HC-S04 Ultrasonic sensor testing environment

HC-S04 Ultrasonic sensor testing environment

HC-S04 Ultrasonic sensor testing environment

HC-S04 Ultrasonic sensor testing video

Bill of Materials

The current BOM can be obtained here

Risk Assessment

Updated Risk Analysis

Updated Risk Analysis

Please refer to the current risk chart for the live document, and to see the overall changes in risk identified from the problem definition design review to the preliminary detailed design review.

Key Changes in Risk Analysis Chart

The additions to the risk analysis chart come from the troubleshooting of the 15045 stander, and creating preliminary designs for the new stander. These include:

Plans for next phase

MSD 1 Timeline

Task Status

Task Status

Excel Document

Individual 3-Week Plans

Individual Plan - Jenna Hopkins

Individual Plan - Max De Sousa

Individual Plan - Jack DeGonzaque

Individual Plan - Holman Chung


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