Miniature Parachute-Probe Dynamics Test-Bed

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Miniature Parachute-Probe Dynamics Test-Bed

• Jessica Dooley
• Ralph Lorenz
• Aerospace and Mechanical Engineering Department,
  University of Arizona
• Lunar and Planetary Laboratory, University of
  Arizona

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Introduction

• Importance of detailed kinematics of descent
• Motions affect scientific measurements
• Wind shear response allows shears to be measured
• Critical review
• Complex degree-of freedom models
• Large cost for full-scale,
• instrumented vehicles

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Objective

• Create a miniature test-bed
• Low cost
• -Off-the-shelf components
• Easy to use
• -Small-scale parachute-sensor packages
• -Hand-dropped from within a building
• Gain familiarity with sensor data and
• corresponding motions of system

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Instrumentation

• Instrumentation on the probes
• BASIC Stamp 2 and Basic-X24 micro controllers
• Orthogonal triad of FGM-1 fluxgate magnetometers
• ADXL202 2-axis accelerometers
• MPi resonant piezo-electric rotation sensors
• Nutex wireless video camera
• Daventech SRF-04 sonar module
• Parachutes
• Apogee Rockets

Inside of multi-sensor probe
BasicX24 board, accel., gyro, SRF-04
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Testing and Set-up

• Testing Phases
• Preliminary pendulum
• Preliminary drops
• Compact probe drops
• Probe drops with on-board camera
• Multi-sensor drops

Camcorder footage of descent with yellow chute
Three versions of the parachute-probe Dynamics
test-bed
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Data Analysis (1 of 4)

• General visualization with camcorder data
• Vector between parachute apex and probe center
• Cannot capture swings and motion towards and away
  from the camera
• Possible solution- use length of vector to
  indicate motion in other plane

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Data Analysis (2 of 4)

• Horizontal and vertical velocity with camcorder
• Reveal general patterns associated with simple
  pendulum motion
• -sinusoidal pattern
• -horizontal velocity has double the period of
  vertical velocity

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Data Analysis (3 of 4)

• On-Board sensor data
• Z-axis acceleration record is asymmetric, not
  sinusoidal
• -Broad troughs and narrow peaks
• Spikes often superimposed

hand-guided pendulum test with 180
degree rotation at end-points
hand-guided pendulum test with 180
degree rotation at mid-points
Compact probe drop utilizing purple parachute.
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Data Analysis (4 of 4)

• On-board camera data
• Plot constructed from frame by frame
• camcorder analysis shown below
• Results inspired the use of gyros

3.06
3.13
3.26
3.33
3.46
3.53
3.63
3.73
3.86
3.93
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Simple Pendulum Model

• Assumes probe-parachute system is a rigid
  pendulum
• Parameters include length l, initial angular
  displacement theta0, phase, bias, and drag

Model rarely matched data for more than one
oscillation using measured values for model
parameters
Accelerometer data for 6th drop on June
10th (on-board camera data on previous slide).
No drag, relatively same effective l.
Drag0.40, l model2.8m (where l measured 2.11m)
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Summary

• Salient results
• Correlation of spin with bottom of swing
• Need for an effective pendulum l longer than
  measured l
• Miniature test-bed helped explore
• Descent kinematics of planetary probe through an
  atmosphere
• Interactions of parachute system with in-situ
  measurements
• Experiments
• Relatively inexpensive and easy to assemble
• May be useful in an educational setting

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