This is a paper which got published in SAE Conference proceedings in October 2009.

1. 09CV-0117
Human Sensitivity in Forced Feedback Systems as a Function of Frequency and
Amplitude of Steering Wheel Vibrations
Nimmagadda, P., Tkacik, P.T., Merrill, Z. A., and Kadire, N. R.
The Department of Mechanical Engineering and Engineering Science
The University of North Carolina at Charlotte
Copyright © 2009 SAE International
ABSTRACT carrier, can be much more catastrophic than an
ordinary car accident. A typical fully-loaded large
A warning system is described as, that improves commercial truck can weigh 80,000 pounds or
safety in an over the road truck application by more, while an average passenger automobile
warning the driver with steering wheel vibration of weighs approximately 3,000 pounds. While
impending roll over. This work focuses on creating statistics show that truck drivers are generally
a Haptic feedback and the corresponding driver much more careful on the road than
response to a range of frequencies and amplitudes automobile drivers, and thankfully the incidence of
of vibration at the steering wheel. The haptic fatal crashes involving trucks and other large
feedback system is the endpoint of the entire vehicles has declined in recent years, large truck
warning system. An experimental road going crashes still accounted for 5,350 fatalities and
system is designed, presented, and tested. The 133,000 injuries in 2001.
experimental data reveals information about the
response of the human subject to the frequency of The subject of interest in this paper is over-turning
steering wheel vibration, while driving a vehicle. accidents and a system to avoid them by providing
Data variability is investigated through sampling of an effective warning. Haptic technology refers to
a population of drivers. The experimental setup technology that interfaces to the user via the sense
probing the amplitude and frequency information is of touch by applying forces, vibrations and/or
analyzed. Objective measurement anomalies in the motions to the user. In this case a mechanical
data were seen in the subjective tests as well. stimulation is used to warn a driver of a potential
Some conclusions are given about the applicability rollover. The system tested is comprised of a
of laboratory tests to moving vehicle tests. vibration causing device attached to a steering
wheel. The subject of interest is the human
INTRODUCTION response to a range of vibration amplitude and
frequency.
A traffic accident involving a commercial truck,
such as an eighteen-wheeler or other large freight

2. In this system, the vibration causing equipment adaptable system would have had a variable
starts the vibration ‘before’ a potential rollover. For eccentricity on a moving eccentric weight. The
giving a suitable range of values for the term dilemma was in hitting a driver’s hands and
‘before’ is a project in itself. But here, it is not in the distracting him/her while controlling a moving
scope to assess this numerical range but, to vehicle. The solution is shown in figure 3, in which
assess the range of frequencies that is apt to be the eccentricity is incorporated into a circular
perceived as a warning signal instead of creating flywheel.
panic in the driver.
EXPERIMENTAL SETUP (VEHICLE)
The experimental setup consists of an electronic
motor controller, a connecting control wire and a
steering wheel mounted motor/shaker system. For
reasons of application, it is a mobile system that
operates on 12 VDC and runs off of a vehicle
“cigarette lighter”.
Eccentric hole
in flywheel Flywheel
Electric motor
Figure 2. Image of the steering wheel shaker motor
being attached to truck steering wheel.
Control
Steering wire
Wheel
Figure 1. Schematic layout of steering wheel
shaker experimental system.
The Control Wire - has the appropriate connector
to the electronic motor controller plus a length of
coiled cable that is to be wrapped around a
steering wheel column and allows the control wire
to wind up and unwind while the steering wheel is
turned, (see figure 1).
Figure 3. Image of the steering wheel shaker motor
The Electric Motor with Clamp – is attached to
flywheel with the eccentric hole.
the steering wheel with a clamp that allows a wide
range of steering wheel sizes. Figure 2 shows it
The electronic controller has a collection of controls
being attached to a truck steering wheel but it was
on its top face. These include:
also able to attach to very small steering wheel
diameters.
• main power,
• motor direction,
The Flywheel With Eccentric Hole – generates
the shaking force on the steering wheel. The • a max speed function,
concern for safety with a spinning flywheel was the • engagement of motor braking,
determining factor on the design. A more • a variable speed potentiometer.

3. DB300-0 CD Brush Motor Driver
Common (ground)
On/Off
Maximum speed
Forward/Reverse
Motor braking s/w no
Motor speed
s/w no
Figure 6. LabView screenshot of motor control
program GUI.
s/w no
s/w no
12 VDC in
2 KΩ potentiometer
0 – 10 VDC power out to
shaker motor
Figure 4. Shaker motor control wiring diagram.
Figure 7. LabView block diagram control and data
acquisition program.
Figure 5. The motor controller box and both main Figure 5 shows the motor controller. Also shown is
power and coiled motor wiring. the arrangement of the coiled motor power wire.

4. The yellow wire at the bottom is the main power tricky venture. All tests were done at low speeds
wire plugged into the 12 VDC “cigarette lighter” and on the UNC Charlotte campus (light traffic
outlet. This eccentric hole flywheel was used for all areas).
moving vehicle tests.
The motor controller was small enough to fit easily
into a moving vehicle without issues.
For additional control, a LabView program was
incorporated into the system that allowed exact
voltage control of the motor, (see figure 7.). This
bypassed the potentiometer of figure 4 and
provided the voltage directly.
An accelerometer was mounted to the shaker and
provided the frequency response at these voltages.
Figure 6 shows a screenshot with the round
voltage control dial on the left and the frequency
spectrum plot, data file, and amplitude vs. time
plots. Figure 8 shows the connections between the Figure 9. Vehicle test with accelerometer on
components of the experimental setup. steering wheel shaker.
Figure 8. Flow Diagram of the Experimental setup.
Figure 10. Moving tests with vehicle underway.
EXPERIMENTAL TESTS (VEHICLE)
The most significant feature of the moving tests
The experiments in the vehicle were done both was the large vibration required to overcome the
stationary and with the vehicle moving. natural vibration levels found on a truck. Whereas
on the stationary tests we recorded “not
In figure 9, the small box ahead of the controller is noticeable”, “very weak”, and “weak” vibrations; in
the charge amp for the accelerometer and the the moving tests, there was no “very weak” level.
small box to the rear of the controller is the That is, it was either “weak” or “not noticeable” with
National Instruments I/O interface. These all fit on nothing in between.
the center console of the truck.
EXPERIMENTAL SETUP (LABORATORY)
In figure 10, it was found that while driving a
vehicle with multiple wires connected to the The laboratory based experimental setup is as
steering wheel, despite great efforts to keep them shown in the Figure 9. It consists of gaming
from knotting up in the steering wheel, this was a steering wheel with the vibration causing

5. equipment with a accelerometer installed on it. It The shaker system mounted easily and allowed a
also has the motor controller, the NI-USB 6008 wide range of subjects. Since it wasn’t particularly
DAQ card, the Kistler dc charge amplifier and the heavy, it could also be transported to a variety of
LabView installed Laptop. locations.
The accelerometer output is given as an input to The polar moment of inertia and the diameter of
the coupler (charge amplifier) which then amplifies the game console steering wheel is considerably
the signal and outputs it through the USB lower than for a actual vehicle steering wheel, (see
connector to the Labview software. The Labview figure 9 and 10). This had two major effects. First,
program is also used to control the speed of the the steering wheel did not have the ‘normal’ feel of
motor by controlling the voltage input to the motor a steering wheel in a vehicle. It felt like what it
through the NI-DAQ USB 6008 device. was, a game console steering wheel.
Second, since the inertia was lower, the ratio of
inertias between the laboratory based steering
wheel and the shaker eccentric was such that the
vibrations were stronger, (see figure 12). This was
considered a positive effect as the eccentric wheel
proved to supply a weak vibration signal in the
truck. At the game console, the amplitude of
vibration seemed more appropriate for this
experiment.
Figure 11. Steering Wheel Shaker Laboratory
setup
Figure 13. Driver’s view of laboratory based
experiment.
Figure 12. Close up of lab based experiment. RESULTS
The laboratory based system used a popular video Tests were performed in three conditions; the
game steering wheel console clamped to a table. laboratory tests, the stationary vehicle tests, and
tests in a moving vehicle.

6. Figure 14 shows the relationship between the weight was sensitive to the truck steering system.
voltage to the motor and the fundamental It appeared that at some motor speeds, the
resonance or motor speed. As would be assumed, eccentric appeared to be out of phase with the
the Natural Frequency, or First Harmonic of the shaker system and a vibrational damping occurred.
system is tied to the rotational speed of the At other motor speeds, these two would resonate
eccentric weight. together and add to the amplitude.
What is most significant about the plots is the
relationship of the test methods to motor speed.
That is, between the lab test and the stationary
steering wheel test, at the same motor voltage, the
lab test spins much faster and resonates at a
higher frequency. The frequency or speed
difference grows with motor voltage. It was felt that
this was logical as the lower inertia of the lab
steering wheel allowed for it to ‘ring’ at a higher
frequency and thus the motor rotated faster as
well.
Curiously, in the mobile tests for the same
conditions this trend reversed and the large truck
steering wheel then allowed the motor to turn
faster. This counter-intuitive result may have been
a result of the power steering of the truck while
moving or an interaction of vibrational frequencies Figure 15. Accelerometer Natural Frequency
that naturally permeate the steering system. vibration amplitude versus motor voltage during the
stationary truck test.
It was also possible to drive the truck and sense
the additive effect and damping effect at these
different eccentric motor speeds. That is, as the
motor voltage increased and the motor speed
increased, the vibration would get larger, then
subside, and then at a higher spedd, re-excite and
vibrate even more.
Figure 14. Natural Frequency (Hz) of the three test
systems as a function of motor voltage.
Figure 15 revealed a vibrational pattern that could
be sensed by the driver during the driving test. The
amplitude values plotted are selected from the
vibration of the accelerometer on the shaker
system at the natural frequency. This revealed that
the harmonic resonance of the motor eccentric Figure 16. Data plot of the response of the subjects
vs the voltage input to the motor for laboratory test

7. ‘moderate’. That is, at the accelerometer dip in
amplitude (figure 15), there was a corresponding
change in the opinion from ‘strong’ to ‘moderate’.
At higher voltages and motor speeds, the vibration
continued as expected to rise and the trends in
vibration amplitudes and respondants opinions
returned to the stronger vibration levels.
In table 1, the values corresponding to the four
catagories of responses are the medians of motor
voltage. For example, as can be seen in Figure 16,
the median motor voltage for moderate is 1.2 V. It
is observed that the ratio is around 0.66, which
implies that lab test produces the similar human
response at 0.66 times the motor voltage of a
stationary on-vehicle test.
Figure 17. Data plot of the response of the subjects
vs input to the motor during a stationary truck test CONCLUSION
Human Lab A warning system is described as the one that
response test On vehicle Ratio improves the safety in an over the road truck
application by warning the driver with steering
Very Weak (V) 0.5 0.8 0.63 wheel vibration of impending roll over. This work
focuses on the driver response to a range of
Weak (V) 0.8 1.1 0.73 frequencies and amplitudes at the steering wheel.
It does not depend on, but is in collaboration with a
Moderate (V) 1.2 1.8 0.67 (heavy truck) trailer rollover sensor.
Strong (V) 1.8 2.9 0.62 An experimental road going system, a stationary
vehicle test and a laboratory based steering wheel
Table 1. Center Voltage for each response and the shaker are designed, presented, and tested. The
ratio experimental data reveals information about the
sensitivity of the human driver as a function of
During testing, the respondant was told to describe steering wheel shake frequency and amplitude.
the vibration. The descriptive terms were defined
to the respondant prior to testing. “Moderate” was On the stationary tests we recorded “not
defined as a vibration that was not so strong as to noticeable”, “very weak”, and “weak” vibrations; in
cause a sense of panic but not too weak that it the moving tests, there was no “very weak” level.
couldn’t be felt at all. “Very Strong” was described That is, it was either “weak” or “not noticeable” with
as a vibration that might startle the respondant nothing in between.
when driving a vehicle. “Weak” and “Strong” were
intermediate levels and “Unnoticeable” was Data variability was investigated through sampling
described as just that. “Very Weak” was defined of a population of drivers, and found to be in sync
as a vibration as the edge of perception. with the anomalies in the vibration measured. The
experimental setup probing the amplitude and
When reviewing figure 15, it was noticed that the frequency information was analyzed. For this
resonance was present in the desktop tests as system, it was found that there was a correlation
well. It is noticed that the truck test vibration at 1.5 between the laboratory test and the stationary
volts has a dip in the amplitude of vibration, see vehicle test. Comparing the median motor voltage
figure 15. In figure 16, at 1.5 volts, the percentage between the two tests showed that there was a
of respondants gave a subjective opinion that also 0.66 ratio of shaker motor voltage to the human
showed an increase from ‘strong’ back to response between the tests.

8. In summary, it has been determined that the and Dr. Peter Tkacik is an Assistant Professor of
laboratory based steering wheel shaker test can Mechanical Engineering and Engineering Science
provide stationary on-vehicle test results by using a in the Lee College of Engineering of the University
0.66 correction factor on the motor voltage. of North Carolina at Charlotte. They can be
Therefore, on-vehicle tests may be simulated in the reached pnimmag1@uncc.edu for Mr.
laboratory using this correction. Nimmagadda, nkadire@uncc.edu for Mr. Kadire,
and ptkacik@uncc.edu for Dr. Tkacik. Additionally,
ACKNOWLEDGMENTS Dr. Tkacik can be reached at (704) 687-8114.
The authors want to acknowledge the support for
equipment and resources donated by the
Mechanical Engineering and Engineering Science
Department of UNC at Charlotte. Also the help
extended by many of the friends and colleagues.
REFERENCES
1. Giacomin, J., Fustes, F., “Subjective
equivalence of steering wheel vibration and
sound”, International Journal of Industrial
Ergonomics, 35 (2005) 517-526.
2. Mandayam A. Srinivasan, Ki-Uk Kyung et.al
“Perceptual and Bio mechanical Frequency
Response of Human Skin: Implication for
design of Tactile Displays”,IEEE First Joint
Eurohaptics Conference and symposium on
Haptic Interfaces for Virtual Environment and
Teleoperator Systems, 0-7695-2310-2/05.
3. Roberts J.R, Jones R., et al,Evaluation of
vibrotactile sensations in the ‘feel’ of a golf
shot, Elsevier Science ‘Journal of Sound and
Vibration’ 285 (2005) 303 – 319.
4. Anthony J Champagne, “Correlations of Electric
power Steering Vibration to Subjective
Ratings”, SAE 2000 World Congress, Human
Factors in 200: Driving, Lighting, Seating
Comfort, and Harmony in Vehicle Systems (SP-
1539).
5. Cebon D, “Heavy Vehicle Vibration – a case
th
study.” Proc.9 IAVSD symposium on The
Dynamics of Vehicles on Roads and on
Tracks., Linkoping, Sweets and Zeitlinger,
1985.
6. http://arts.bev.net/roperldavid/rollovers.pdf
7. Lamri Nehaoua, Hakim Mohellebi et al,“Design
and Control of a Small-Clearance Driving
Simulator” IEEE Transactions on Vehicular
technology, Vol.57, No.2, March 2008.
CONTACT
Prajwal Nimmagadda and Nishanth Reddy Kadire
are working on their Masters of Science degrees