Shepard Test Stand Preliminary Design v1.0¶

• Shepard Test Stand Preliminary Design v1.0
  • • Introduction
    • Preliminary Mechanical Design
    • Preliminary Data Acquisition Design

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

Preliminary Mechanical Design¶

• STSPM 1.1 We're going to attempt to use FreeCAD as the base CAD program for this project.
  • STSPM 1.1.1 Files will be stored on "Open Design Engine":opendesignengine.net in the default FreeCAD file format.
  • STSPM 1.1.2 For milestones STL versions will be saved for models, and DXF and PDF formats will be saved for draft files.
• STSPM 2.1 The frame design will somewhat follow the RepRap family of frames by using threaded rod, smooth rod, and bearings.
  • STSPM 2.1.1 Each end of the frame consists of a triangle of threaded rod with plastic corner caps in a Mendel assembly configuration.
  • STSPM 2.1.2 The cross members that tie the two ends of the frame together will be smooth rod, again in the vein of the Mendel assembly
  • STSPM 2.1.3 The cross members will not be much longer than the motor mount.
  • STSPM 2.1.4 Springs will be placed at the exhaust end of the cross member rods to absorb any recoil from the parachute charge.
  • STSPM 2.1.5 Linear bearings will ride on the smooth rod cross members, and the motor mount carriage will mount to those.
  • STSPM 2.1.6 There will be one linear bearing per cross member rod.
  • STSPM 2.1.7 Clearance will be built into the plastic corner caps so that there is enough room for the linear bearings to run.
• STSPM 2.2 Body tube and motor mount components from a "Big Daddy" style rocket will be sourced and used as the motor mount that attaches to the rod bearings.
  • STSPM 2.2.1 The body tube will have a 2" to 3" inside diameter.
  • STSPM 2.2.2 The body tube will be cut off 1" above the top bulkhead. The "top" bulkhead being defined as the bulkhead closest to the nose cone.
  • STSPM 2.2.3 Three fin slots will be cut in the body tube at angles around the circumference to match the vertices of the frame triangles.
  • STSPM 2.2.4 The balsa wood used for the fins will be of the standard weight used in the "Big Daddy" rocket, but will be cut with rectangular profiles rather than the typical chamfered design.
  • STSPM 2.2.5 Motor adapters will be used to adapt B through D size motors to the E size motor tube inherent in the "Big Daddy", and adapters for the A size motors will be custom made.
  • STSPM 2.2.6 Balsa wood attachment points will be used between the fins and the rod bearings.
  • STSPM 2.2.7 The fins will be run through the body tube and glued directly to the engine mount tube in a standard "Big Daddy" configuration.
  • STSPM 2.2.8 The body tube will need to have a nose of some sort to push on the load cell.
• STSPM 2.3 Some sort of shielding such as chicken wire will be used to protect observers from runaway rockets.
• STSPM 2.4 The thermocouple will be attached to the motor casing with Kapton tape.
  • STSPM 2.4.1 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 carriage.
  • STSPM 2.5 A Mount will be created for to attache the selected load cell to the triangular end cap opposite the exhaust end of the motor.

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 1.2.1 A unity gain amplifier will be used to obtain measurable output from this 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.