P17316: Light Rail

Preliminary Detailed Design

Table of Contents

Files related to this phase can be found in the Detailed Design Documents directory.

Team Vision for Preliminary Detailed Design Phase

The goals for this phase were . . .

The team completed . . .

The team still needs to discuss details of the presentation with Dr. Edmunds as he was unable to attend this review.

Updated Functional Decomposition

public/Detailed Design Documents/Schematics/Functional Decomposition Diagram 1.3.jpg

Mechanical System

Rail Structure, Height Adjusting Stands

Prototyping, Engineering Analysis, Simulation

The prototyping for the mechanical system was limited to calculations, improved cost feasibility, and the selection of one mechanical design. A beam deflection calculation will help confirm that whatever material type is selected for the rail will not deflect. A weight limit on the rail has been decided based on research on various tripod stands. We will not exceed their allowable weights with the weight of the rail. Cost options for materials have been detailed in the bill of materials.

Feasibility: Prototyping, Analysis, Simulation

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Calculations used to select rail cross section and material.

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Calculations used to select stands for each end of the rail.

Clickhere for the full document.

Drawings, Schematics, Flow Charts, Simulations

public/Detailed Design Documents/Schematics/Schematic.PNG

Electrical System

LEDs, Power Source, Interface with the Software

Prototyping, Engineering Analysis, Simulation

The circuit comprises of a simple diode resistor circuit. The power is supplied by an external five volt supply and the ground is controlled by a BJT sink. The LED will be controlled by a 74hc595 shift register that has its serial data input given from a microprocessor. The shift register will output the data in parallel and bias the BJTs to sink the LED which turns it on.

Feasibility: Prototyping, Analysis, Simulation

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Circuit Prototype. See the video in the link to watch the raspberry pi control the LEDs. Link to Electrical Prototype Video

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Oscilloscope capture from prototype circuit shown above.

Drawings, Schematics, Flow Charts, Simulations

public/Detailed Design Documents/Schematics/MSD1 LED Circuit.JPG

public/Detailed Design Documents/Schematics/Single Shift Register with 8 LEDs.JPG

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Bill of Material (BOM)

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Click here for the link to the document.

Mechanical Test Plans

The following mechanical engineering requirements will be tested to the following specs after project completion.


To ensure the weight requirement for the finished product is met, the entire apparatus (Mechanical and Electrical Components) will be weighed using a scale after completion of the project. The product will be designed with weight in mind so the estimated weight of the final design will be below the maximum acceptable value of 50 lbs.

Stored Footprint

To ensure the product fits within the required storage footprint, the Light Rail will be disassembled into the storage state. The summation of maximum length, width, and height combination of the disassembled apparatus will be recorded. This value will create a single metric to compare to the engineering requirement.


The maximum load on the mechanical system will be determined. The worst case location for stress and cyclic loading will be analyzed to predict number of cycles until failure (fatigue analysis) and maximum acceptable loading (buckling analysis).

Height Range

The Light Rail vertical structure will be raised to it’s maximum operating height and this value will be measured and compared to the engineering requirement for height.

Ease of Setup/Teardown

The teardown and setup time for the Light Rail will be measured for 5 trials. The average of these times will be compared to the engineering requirement for ease of setup/teardown. The test can be repeated with people who have received written instructions for setup and teardown if it is deemed necessary by the design team.

Electrical Test Plans

The following electrical engineering requirements will be tested to the following specs after project completion.

Power Consumption

The Light Rail will be a low-power device. LED lights do not consume much power and the Raspberry Pi does not as well. The maximum power for a 120 Volt/15 Amp wall outlet is 1800 Watts but the Light Rail will not consume nearly that much power. The LED lights that we have chosen have a forward current of 20mA at 5V which is 0.1W per LED. Our design will use 40 lights so the lights will consume about 4 Watts of power. The 74HC595 shift register IC has a very low power consumption, 80-µA Max ICC. There is remaining power for the microcontroller as well as anything else electrical.

Min to Max Speeds

The Light Rail will cover a wide range of speeds simulating speeds up to 90 MPH over a 20 foot range. Testing will be done to ensure that the lights are in fact moving to simulate up to 90 MPH. Using the clock cycle from the microcontroller and the total number of LEDs (40), the total time can be calculated using the number of clock cycles required to have the 40 LEDs on. With the time, velocity can be calculated by finding the quotient of the total length (20 feet) and the time required to turn all 40 of the LEDs on.

Max Error Allowed in Calculation

The Light Rail must be accurate down to the millisecond. However, the microcontroller is not a perfectly engineered device and therefore there will be a very slight error in the timing. The microcontroller may also be performing many different tasks at a given time and this will also affect the accuracy acting as an interrupt to the process. Testing trials will be performed to ensure that the microcontroller is accurate and consistent with the necessary timing down to the millisecond.

Software Test Plans

The following software engineering requirements will be tested to the following specs after project completion.

Max Error Allowed in Calculation (Code)

The Light Rail’s upper and lower boundaries for accuracy must be discovered and outlined. This will be done by setting the light speed to as low/high as possible for a test trial. The same process will be applied to the upper bounds. This ties into the engineering requirement ‘Max Error Allowed in Calculation’. Extensive testing will be done on the three desired/predetermined speeds requested by the customer to ensure accuracy.

Profile Storage

At least 1000 test user profiles will be made to ensure that the storage available is adequate for long term use. A user profile will also be exported to prove that concept.

Design and Flowcharts

public/Photo Gallery/Light Rail Chart 1.1.jpg

Risk Assessment

The project's risks have remained minimal for this phase. For the full document please click here.

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Plans for next phase

Mechanical -

  1. Stability Analysis on Cymbal Stand: Meet with Dr. Boedo.
  2. Light Rail Connection to Support StructurE Design and Analysis. (Ideas: Pulley with Rope, Hinge Bracket, Pin and Slot Connection)
  3. Light Rail Connection between Members. (Ideas: Hinge Bracket, Clamped Collars)
  4. Visit to Local Drum Shop to see Specified Cymbal Stand

Electrical -

  1. Decide on specific components based on power requirements. Are we actually able to power everything using only the Raspberry Pi? Or do we need a voltage regulator to cut the voltage?
  2. Decide on third party power supply vs. designing linear voltage regulator. The concern is the Raspberry Pi itself may not be able to power the entire circuit and we may need external circuitry.
  3. Decide on the housing/mounting for each LED circuit pod as well as circuit placement.
  4. Call/visit Dr. Edmunds regarding the display, keyboard with touch panel, etc. We need to get his approval and give him some options regarding the peripherals.
  5. Evan and Charles will be doing much of the physical design between now and the next review.

Software -

  1. Using C, Code a variable clock that may be used as the controller of the speed for the light rail.
  2. Create code that can control LEDs

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