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Jeremy Wright, 01/31/2013 03:51 pm

Shepard Test Stand Preliminary Design

This is a newer document based on this one , and you should refer to that original version if you want to see the revision history.

Introduction

The preliminary design discussion is broken down into two parts in the forums.

  1. Mechanical systems
  2. Data Acquisition (DAQ) Systems

Most of this preliminary design work was done via Google+ Hangout. The meeting minutes from those hangouts will be distilled down into a form suitable for this document, but in the meantime you can find links to the raw meeting minutes below. You will most likely need to request permission to view the document.

  1. Mechanical Hangout Minutes
  2. Data Acquisition Hangout Minutes

Note: Need to get all of the minutes linked here

Preliminary Mechanical Design

  • STSPM 1.1 FreeCAD will be used as the base CAD program for this project.
    • STSPM 1.1.1 Files will be stored on Open Design Engine in the default FreeCAD file format.
    • STSPM 1.1.2 For milestone versions STEP files will also be provided for models, and PDF files will be provided for drafts.
  • STSPM 2.1 The overall design will be composed of three principle components:
    • STSPM 2.1.1 The structure will hold the other system elements (both mechanical and DAQ related) with sufficient weight to prevent movement.
    • STSPM 2.1.2 The rail system will limit the motor's movement to the thrust axis.
      • STSPM 2.1.2.1 The rail system will be a duplicate of the version 1.0 rail system .
      • STSPM 2.1.2.2 A shield made out of HVAC ductwork material will prevent the rail system from being fouled by motor exhaust particulates.
    • STSPM 2.1.3 The motor mount will connect the motor under test to the rail system.
    • STSPM 2.1.3.1 The motor mount will be a duplicate of the version 1.0 motor mount .
    • STSPM 2.1.3.2 A new contact pad will be used to adapt the surface of the motor mount to the face of the selected force sensor.
  • STSPM 2.2 The thermocouple will be attached to the motor casing with metalized foil tape.
    • STSPM 2.2.1 The thermocouple leads will be routed away from the motor exhaust and in such a way that it won't interfere with the movement of the motor mount on the linear guide.
  • STSPM 2.3 The selected force sensor will be attached to the structure using double stick tape such that it will interface properly with the motor mount.
    • STSPM 2.3.1 The type of double stick tape used must not be too thick or have too much elasticity so as to affect the thrust measurements.
  • STSPM 2.7 Selected design concept: back plate and beam body (covering a concrete block for added weight), ball bearing drawer guide rail system, and Estes motor mount with a plumbing t-connector

You can refer back to the version 1.0 preliminary design items STSPM 2.2 through STSPM 2.4.3 for competing design choices for the structure.

Preliminary Mechanical Cost Estimates (For One-Off Quantities)
Item Cost (Shipping to Midwest U.S.) Approx Total Link
8' 2x10 pine board $7.75 $7.75
8' 2x4 pine board $2.50 $2.50
4"x8"x16" solid concrete block $1.50 $1.50
Small Ball Bearing Drawer Guide $6.00 $6.00
Pulley $3.00 $3.00
Estes D/E Motor Mount $9.00 $9.00 http://bit.ly/Rrn330
Estes Motor Adapters $6.00 $6.00 http://bit.ly/MYMnNg
Copper T-Fitting $3.00 $3.00
High Heat Spray Primer $8.00 $8.00
High Heat Spray Paint $5.00 $5.00
Misc Hardware $5.00 $5.00
Total $56.75

Note: Need to address shielding in the cost table above.

Preliminary Data Acquisition Design

  • STSPD 1.1 An Arduino Uno will be used as the data collection platform which includes the ADC interface with the load cell and thermocouple(s).
  • STSPD 1.2 A Force Sensing Resistor (FSR) will be used for the load cell. We will need to watch for hysteresis issues with this type of load sensor.
  • STSPD 1.3 A type K glass braid insulated thermocouple will be used to measure the casing temperature of the motor.
    • STSPD 1.3.1 An Adafruit thermocouple amplifier will be used to condition the thermocouple signal for the Arduino's analog inputs. This requires SPI communication with the Arduino.
  • STSPD 1.4 The data will that is recorded by the Arduino will be streamed over the USB connection unless it is found that is not fast enough.
    • STSPD 1.4.1 The data format will consist of a data point coupled with a simple time stamp.
    • STSPD 1.4.2 Data processing will be handled by the computer. This will include the conversion from voltage to force due to the logarithmic nature of the force sensing resistor.
  • STSPD 1.5 The Wiring programming language will be used to program the Arduino, and Processing will be used for any computer-side code.
Preliminary DAQ Cost Estimates (For One-Off Quantities)
Item Cost (Shipping to Midwest U.S.) Approx Total Link
Arduino Uno R3 $29.95 + shipping $35 http://bit.ly/N5kizl
1.5 Inch Square FSR $7.95 + shipping $16 http://bit.ly/Pd3ztz
TLV2374 Op Amp $1.71 + shipping $8 http://bit.ly/OcVA12
560 Ohm Resistor x 2 $0.20 (combined w/ shipping above) $0.20 http://bit.ly/M3duBJ
Type-K Glass Braid Insulated Thermocouple $10.00 + shipping $13.87 http://bit.ly/NPRosE
Adafruit Thermocouple Amplifier $17.50 + shipping $21.50 http://bit.ly/OqVc2A
Misc (Wire, etc) $5.00
Total $99.57

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