Group 14
Derek Burney
Barnabas Fekete
Jason Hood
Fred Nguyenloc
Project Sponsor
Dr. Joel House
4
Taylor Impact Test
Velocity
Measurement System
_______________________________________________________________
Fall 2007 Final Design
________________________________________________________________
Outline




Taylor Impact Test
Problem Statement
Project Scope
Design Ideas
 Decision
Matrix
 Initial and final designs

Spring semester Progress
 Bracket
design
Taylor Impact Test

Used to study strain rate
properties of materials during
high velocity collisions.
High
speed camera
captures the collision
between the specimen
and the anvil.
The average test
speed is 200m/s.
Taylor Impact Test

Currently two methods are used to measure the velocity
of the test specimen.
1. Optical Barrier – 2 lasers
spaced apart a certain
distance. When the
beam breaks, it allows
us to know the time
frame.
2. Pressure Transducer –
pair of transducers
recording pressure at a
certain distance apart
Same concept as lasers
Problem Statement

Recently the laser detectors have been producing
erroneous velocities.


Signal from second optical barrier has a delayed response.
The measured velocity is lower compared to the pressure
transducers and the expected velocity calculated from the
propellant load.
Project Scope
•Update laser velocity measurement system such that it:
• Provides accurate velocity measurement of
projectiles with average speed of 200m/s using noncontact methods.
• Must be accommodating of test samples with
diameters of .21’’ to .50’’.
• New equipment must easily integrate into the
existing system.
Initial Design Ideas

Four Ideas to Fix Problem
 Sound Detectors
 Eddy Current Detector
 Chronograph
 Lasers
“Optical Chronograph.” 01 October 2007
http://kurzzeit.com/e_bmc17.htm
“Eddie Current Velocity Measurement.”
Sensorland.com. 31 September 2007
<www.sensorland.com/AppPage048.html>
Decision Matrix
Design Criteria
Weight
Factors
Material
Limitations
Strobe
Interference
System
Compatibility
Durability
Cost
Safety
Total
**
0.236
0.208
0.180
0.152
0.125
0.097
0.998
Detector Types
Rate
WF
*
Rate
WF
*
Rate
WF*
Rate
WF
*
Rate
WF
*
Rate
WF
*
Laser
4.95
1.16
4.50
0.94
4.16
0.74
5.00
0.76
0.67
0.08
4.5
0.44
4.12
Infrared
4.95
1.16
3.50
0.73
4.16
0.74
5.00
0.76
0.67
0.08
5.0
0.48
3.95
Eddy
Current
4.00
0.94
5.00
1.04
0.52
0.09
0.50
0.08
1.33
0.16
4.0
0.39
2.70
Sound
5.00
1.18
5.00
1.04
2.60
0.46
0.75
0.11
2.50
0.31
5.0
0.48
3.58
* WF = Rate x Weight Factor
** Total is sum of WF
Initial Design Ideas
Edmund Optics®
photodiode receiver modules (3)
5.6mm laser diodes
Custom brackets
From Decision matrix, the
laser barrier method
proved to be the best
option.
Helium Neon lasers
replaced with laser
diodes
Improve the
Reliability of the
system by
adding 3 optical
barriers
Problems Encountered with Initial Design
• Edmund Optics receivers were too large to
integrate three into the design.
•Purchasing laser diodes and receivers
would set us 30% over our budget.
Final Design


Incorporates currently used lasers so we do not exceed budget.
Two Edmund Optics® photodiode receiver modules with power
supply
Final Design
Bracket Design
Design Consideration

Is the measured velocity a representation of
the impact velocity.
Point 1 – Force of the
propellant and
Friction in the tube
Point 2 – Friction from
contact and Drag
Point 3 – Drag
VIMPACTt  V MEASURED  VFRICTION  VDRAG
Velocity Between 2 and 3
Acceleration due to propellant
equals 0 at point 2
FFriction  mg
a  g
v loss 
adrag 
2a x
Cd  A s   v
2
2 mspecimen
vdrag  2 adrag x
1.http://www.fas.org/man/dod-101/navy/docs/es310/ballstic/Ballstic.htm
VIMPACT  V MEASURED
Low Velocity Test

Measure the velocity of a Nerf Dart using two
methods and compare the results.
One – Measured the distance the dart
traveled horizontally from a fixed vertical distance and
apply Newton’s Law to projectile motion
 Method Two – Measure the velocity with the opticla
barrier system
 Method
Method One – Projectile Motion



The Gun was fired
horizontally from a
fixed position 40
times
The Level was set
with a pendulum
The x-distance was
measured
Method One – Projectile Motion
1 2
y  yo  gt
2
1
x  xo  v x t  ad t 2
2
Cd D 2 v 2
FD 
8
Fd
a 
mdart
Because of the
darts low mass
(0.21kg) Drag
could not be
assumed
negligible.
Method One – Projectile Motion

The drag deceleration is a function of the
projectile velocity which changed over the xdistance
Initial Velocity = 36+0.8 m/s
Method II - Optical Barriers


The optical barrier
uses interruption to
measure time to
travel a set x-distance
The time was
measured using a
computer based
oscilloscope
Method II - Optical Barriers
Voltage (V)
Detector One .50 cal 200m/s Test
0
100
200
300
400
500
600
700
Time (us)
Theoretical
Actual
The initial run of the demonstrated that the detectors functioned
opposite of expected and that they where flooded by ambient light.
680nm specific filters were ordered and the test resumed
Velocity Measurement Phase I
Measured the velocity of
40 samples with the
optical barrier system
Velocity Measured
from the gun =
37.3+2.3m/s
Method II - Optical Barriers
Results
 VPROJ = 36.0 + 0.75m/s
 VBAR = 37.3 + 2.3m/s
 The projectile method had the higher
accuracy due to the interpretation of the
time from the graphs. The system used on
site was expected to prevent the excess
error

Velocity Measurement Phase I
Performed Projectile Velocity Test to
Determine Average Nerf Dart Velocity
 Compared the Detector Velocities to the
Projectile Tests
 Average System Reading = 23.5 m/s +
0.95 m/s
 Average Nerf Dart = 24.6 m/s + 1.7 m/s

High Velocity Test


Install new detectors
at Eglin site
The 200m/s
projectile passed
through the barriers
before the detectors
could change in
voltage
High Velocity Test




The diodes in the detectors had a time to
peak voltage of 300μs.
The optical barrier is only blocked for 10μs
with a 200m/s test specimen
The diode only rose approximately 1/30th of
the peak voltage
The group initially determined the high
voltage gain of the detector circuit would
compensate for the slower rise time.
Corrective Recommendations

After review of the technical
manual for the current in use
detectors:
 Replace
the detector
photodiodes. A suitable
replacement with a 1530 ns
peak time is available for
$14.85.
 Replace the Helium-Neon
Lasers. They have an average
life span of two years. Current
lasers are twenty years old.
Proposed Solution
1. Complete Package
Unit
2. Rated for
Projectiles of 5000
m/s with 1%
accuracy
3. Estimated Cost
₤8000. (
http://www.compulink.co.uk/~msinstruments/pdf/858_optical_detector.pdf
Questions?