DEVELOPING A SYSTEM DYNAMICS EXPERIMENT FOR
REMOTE LABORATORIES
Katie Hauser and Jitesh Panchal
School of Mechanical and Materials Engineering
INTRODUCTION
WSU’s School of Mechanical and Materials Engineering now offers an ME
degree program at Olympic College in Bremerton, WA. While many courses in
the program will be taught at Olympic College, other courses will be taught
remotely from WSU. One of the challenges of remote learning is the simulation
of laboratory experiences, which are an important component of engineering
programs. While it makes little sense to teach a lab-only course remotely, it
could be beneficial to students’ learning if distance lecture courses included
supplementary remote experiments and demonstrations.
Creating the experiment is the first step in determining whether an experiment,
located at WSU and controlled over the Internet, would improve distance
students’ learning of concepts in engineering lecture courses. The goal of this
project was to develop a mass-spring system with features to facilitate its future
development into a remote experiment for the course ME 348: Dynamic
Systems.
PROCESS
The design process for the system dynamics simulation began with determining
objectives, which are the desired attributes of the final design; functions, which
are actions the design must perform; and constraints, which are strict limits the
design must adhere to in order to be acceptable.With these in mind, a list of
needed components was made, and options for each component were found or
later designed.
Objectives
•Modular in design
•Scientifically useful
•Resistant to wear and tear from repeated student use
•Cost-effective
•Conducive to remote procedure development
Functions
•Hang springs, dampers, masses
•Output displacement and force data
•Force mass-spring system in a step, ramp, or sinusoidal manner
Constraints
TESTING
Tests were conducted on the components of the apparatus to ensure their
viability before creating the final design.
Springs and Masses
In order to make sure the PASCO springs and masses would be compatible, each
mass was hung from each spring and set oscillating.
Results:
•Alone, the 10 & 20 g masses do not displace any of the springs
•The 1 kg mass will overstretch springs when the effective spring constant is
less than 40 N/m
•Displacing by pulling downwards beyond a system’s maximum amplitude
often causes the mass to fall off the spring; displacing by pulling upwards
does not
Damping
With mathematical tests it was determined that dampers from Ace Controls
would be too strong for the PASCO springs and masses. After obtaining a
sampleAirpot dashpot, whose damping coefficient is adjustable, it was
determined that these would be suitable for the apparatus and would be more
repeatable than magnetic damping made in-house.
Sensors
Due to the cost of ready-for-use PASCO sensors, sensors from Sharp and
Flexiforce were tested first with the idea that if they did not work well enough,
the PASCO sensors would be tried.
Sharp Infrared Proximity Sensor GP2Y0A21YK
These sensors output a voltage that varies as the target object moves from 10
cm away to 80 cm away.
Initial test results:
•At a given distance, the sensor readings (taken every 10 ms) had a
significant upward trend
•Periodically (about once per second), a single reading would jump much
higher than its surrounding readings
After programming the Arduino microprocessor to print the average of 1 ms
readings every 10 ms and powering the sensor with 3.3 V instead of 5 V (thus
increasing the range of possible output values), the standard deviation of
outputs in each trial was greatly reduced, and the sensor was then calibrated.
No particular constraints were determined initially. By reviewing design
progress often, any unwanted features could be noted and removed without
having spent significant time on developing them.
FINAL DESIGN
The final design incorporates:
•Six PASCO springs of three spring constants
•Four Airpot dashpots with different, fixed
damping coefficients
•Nine PASCO hooked masses
from 10 g to 1 kg
•Three Flexiforce pressure sensors along the
top of the frame
•Three adjustable-position Sharp IR Sensors
•One Arduino microprocessor and
electronics
•Two 1.7 kg PASCO A-frame rod stands
•Two 90 cm PASCO rods
•One computer running Linux and Kst for
plotting sensor output in real time
The design also incorporates a number of
custom parts:
•One 16 in top bar with hooks
•One 16 in bottom bar/track for sensors
•Five 2x1 in sliding platforms for
displacement sensors and forcing motors
•Brackets for connecting springs, dampers,
and masses in various configurations
CONCLUSIONS & FUTURE WORK
The system dynamics simulation described by this design will function as a
normal, in-person experiment. However, key features of the current design will
facilitate its development as a remote experiment:
•Interchangeability of springs and dampers
•Computer integration
•Low-profile, easily-modified frame
•Highly controllable sensor behavior and precision
•Customizable real time data plotting
Components
•Frame – supports system, hangs springs and dampers, holds sensors in place
•Springs – at least six, same length, multiple spring constants
•Masses – various weights, easily hung from springs
•Damping – repeatable, various damping coefficients
•Forcing – repeatable, variable
•Force & Displacement Sensors – precise, connect to computer
•Computer – display sensor data graphically
Screenshot of Kst, a real-time graphing program
Future design work will include such tasks as:
•Automating spring arrangement and displacement
•Developing a interface for remote users
•Developing a secure network over which to broadcast visuals and data
Once the remote experiment has been fully developed, research will be done to
determine whether it is a useful learning tool. The understanding and success of
four groups of students in ME 348: Dynamic Systems will be compared:
A Sharp IR sensor (lower left) connected to an Arduino microprocessor
Components (clockwise from top):
1. PASCO Springs (40, 20, & 10 N/m)
2. PASCO Masses (500, 200, & 100 g)
3. PASCO Weighted Base
4. Airpot Dashpot (Damping Device)
•Local students who performed the experiment in person
•Local students who did not perform the experiment
•Remote students who performed the experiment remotely
•Remote students who did not perform the experiment
FlexiforcePressure Sensor (25 lbs)
These are piezoresistiveforce sensors; the greater the force on the sensor, the
lower the output resistance. Initial tests of the sensor showed that its outputs
tended to increase over time, making calibration difficult. Conditioning the
sensor may ease this problem. The team expects to have the resources to
condition the sensor properly within the next few weeks, after which the sensor
can be calibrated for use in the apparatus.
ACKNOWLEDGEMENTS
Many thanks go out to Dr. Carl Hauser for assisting with programming, Ken
Lafleur from Airpot Corp. for his advice in choosing dashpots, and Henry Ruff
for helping with the design and building of the custom parts.
This work was supported by the National Science Foundation’s REU program
under grant number EEC 0754370