Report on the System Development for In-Situ
Characterization of Horse Racing Track Surfaces
Submitted to:
Dr. C. Wayne McIlwraith, BVSc, Ph.D., FRCVS
Director of Orthopaedic Research,
Colorado State University, Fort Collins 80523
By:
M. L. Peterson, Ph.D.
Stillwater River Technologies,
61 Bennoch Rd., Orono, ME 04473
Overview: This is a report that gives details of the first demonstration of a system that
will allow the strength and stiffness of a racetrack surface to be quantitatively evaluated.
Tens of millions of dollars are at stake on any given day, not to mention the lives of the
horse and jockey. However, the track condition is appraised in vague and qualitative
terms such as “fast and hard” or “wet.” This vague nomenclature can be very
misleading, since track material properties will make a huge difference on how a track
responds to the loading of a horse’s hoof under race conditions. Therefore, a
quantitative means is necessary to evaluate racetrack condition.
The soil loading conditions for horse racing are extreme with 9 kN of force applied at a
rate of 10 m/s. Moisture content, sand and clay composition, organic material content,
and tillage are traditionally the factors that are controlled in order to maintain a
consistent track. The work described has focused on developing a tool that replicates
the dynamics of the horse running on the track. A system has been developed that
replicates the strain rate and loads applied by the hoof to the soil. By replicating the
strain rate and load in a system, it is possible to measure the tangent modulus of the
track at the high strain rates encountered in horse racing. The system is now in the
process of being tested to provide quantitative base line data from tracks around the
country. This data will eventually be used to help superintendents to maintain and
control the track surfaces regardless of weather and other factors.
This report constitutes the final deliverable of a contract from Colorado State
University to Stillwater River Technologies. The purpose of the contract was to
develop a pilot system and report on the results that were obtained from track testing at
a California race track. Load versus time and position versus time results are reported.
Future work will include additional channels of acceleration data and repeatability
studies. From this initial result the range of the outputs has been obtained and the final
phases of the system design and calibration can begin. The data is not processed at this
time since the results are meant to only demonstrate the concept. Future work will
include pilot data which will demonstrate a protocol which can be used to do a
comparative study of tracks, and then a large scale comparative study of strength and
stiffness in racetrack surfaces.
TESTING APPROACH
While the vertical and horizontal
response properties of the soil have
been known to be important
parameters related to racetrack
performance, previous approaches
have not adequately taken into
account the complexity of the
problem. The non-linear, elastic,
plastic material characteristics with
strain rate dependence have not been
dealt with appropriately. For example,
complex
systems
have
been
developed for measuring the vertical
properties (or hardness) of the soil
Fig.1 A schematic of the five channels
[Clanton et. al. 1991, Oikawa et. al.
of instrumentation used for the track
2000, Ratzlaff et. al. 1997]. However,
testing apparatus.
the shear strength was predominantly
ignored. Only Clanton et al [1991]
quantified any of the shear strength properties. In one measure a load cell was placed in
the hitch of a harrowing device and in another loaded cadaver hooves were across the
track while measuring the drag force with a load cell. However, these tests only
partially accounted for the complexity of the shear strength of soil, since strain rates
similar to those encountered by the hoof at a gallop were not approximated. In the drop
tests the tangent modulus of the soil was not
measured and in many cases the load applies was
much smaller than what was required to test the
portion of the soil that would be important in the
loading of the leg. In some previous tests, loads as
small as 10 kg dropped from heights of less than 1
meter were used [Pratt 1985]. This type of test
represents the impact phase of the gait and does not
address issues with the shear strength of the soil. In
later tests, shear vane tests were performed,
however because of the small loads on the device
they were most appropriate to the early phases of
the shear loading of the soil during the impact
phase of the gait. The shear strength of the soil
during stance or breakover was not addressed.
In order completely address the shear strength
of the soil, it would be necessary to load the soil in
both the direction of the deceleration of the hoof as
well as in the direction of motion of the horse.
However, since both cases would require the
Fig. 2 A photo of the synthetic hoof
appropriate preload and strain rate, significant
and accelerometer. The load cell is
complexity is introduced by completely
in series with the gas spring.
duplicating the contact of the hoof with the
ground. The design of the initial system is focused on the impact and the stance phase.
The assumption made is that the deceleration of the hoof during the stance phase is
related to the shear strength of the soil. This assumption has some support in the
physics of the problem, but is a significant limitation of the work which should be
addressed in the future.
Thus the device that has been developed is essentially a variable speed drop
hammer, which impacts a synthetic hoof at an angle to the soil which is adjustable
based on biomechanical data in the literature and data obtained in associated work, fig 3
and fig. 4. The hoof is cast from a two part casting rubber (Smooth-On, Easton PA).
The speed of the hoof at impact replicates the velocity of impact of the hoof, with a
secondary loading of the hoof through an adjustable gas spring. The adjustable gas
spring replicates the compliance of the leg and because current information on the
compliance of the leg is incomplete, adjustability is built into the design. A stiff mass is
attached above the hoof which replicates the mass of the hoof which initially impacts
the track. Attached to the mass is a three axis 100g accelerometer (Model
CXL100HF3-Al, Crossbow Technologies Inc, San Jose, CA). Load is transferred into
the gas spring from the hoof mass using a dynamic load cell (Model 208C05, PCB
Piezotronics, Depew NY) with a DC to 36 kHz bandwidth. The position of the hoof on
the drop rail is determined using a string potentiometer (Model LX-PA, Unimeasure,
Corvalis OR). The redundant data from the acceleration and the velocity is sued to
estimate the penetration into the soil and to calculate the velocity of the hoof at impact.
The angle of the hoof with respect to the soil is adjustable from 0 degrees to 20 degrees.
Unlike the hoof during the gait, the angle is fixed during impact. The system does
however replicate the strain rate, the loads and the hoof velocity of the horse.
Comparison of the data will be made to high speed video data and acceleration data
obtained from instrumented horse shoes when available.
RESULTS AND CONCLUSIONS
Tests are ongoing with the system and only preliminary results are available at this time.
Initial system testing was performed
7.5
in January of 2004 at Santa Anita
Raceway in Arcadia California. Fig.
7
5 shows an uncalibrated graph of
6.5
some of the initial data from the
6
system. The peak forces obtained
from the system are less than 4500 N
5.5
with an impact velocity at the soil
5
interface of 2.5 m/s. An air cylinder
4.5
will be used to initially accelerate
the carriage to match the speed and
4
1.2
1.3
1.4
1.5
1.7
1.8
1.9
2.0
peak loads from the biomechanics
Time (sec.)
studies. Initial tests were done at an
Fig. 3 Example of position and load data
impact angle of 5 degrees with an
obtained from initial system testing.
unshod hoof.
Amplitude (volts)
Position
Load
Fig. 4 Test system mounted to rear of vehicle at Santa Anita Park.
Fig. 5 View of system prior to release over an area of the track that has just been
prepared for racing.
Fig. 6 Hoof print below raised carriage. Print is qualitatively similar to horse under
racing conditions.
REFERENCES
Carpenter, Gary, 2003, Race Track Industry Symposium, December 11, Tucson AZ.
Clanton, C., C. Kobluk, R. A. Robinson and B. Gordon, 1991 “Monitoring Surface
Conditions of a Thoroughbred Racetrack” JAVMA Vol. 198(3), p. 613-620
Johnston C, G. Hjerten, and S. Drevemo, 1991, “Hoof landing velocities in trotting
horses” Equine Exercise Physiology Vol. 3, p. 167-172.
Nunamaker, D, 2003, e-mail communication, November 3, 2003
Oikawa, M., S. Inada, A. Fujiswa, H. Yamakawa and M. Asano, 2000, “The Use of a
Racetrack Hardness Measurement System” Equine Practice, Vol. 22 (4), p. 26-29.
Pratt, G.W., 1985, “Racetrack Surface Biomechanics” Equine Veterinary Data, Vol. 6
(13), p. 193-202.
Reiser, Raoul, M. L. Peterson, C.W. McIlwraith and B. Woodward, 2000, “Simulated
Effects on Racetrack Material Properties on the Vertical Loading of the Equine
Forelimb”, Sports Engineering Vol. 3 (1), p. 1-11
Ratzlaff, M. H., M. L. Hyde, D. V. Hutton, R. A. Rathgeber and O. K. Balch, 1997,
“Interrelationships Between Moisture Content of the Track, Dynamic Properties of
the Track and the Locomotor Forces Exerted by Galloping Horses” Journal of
Equine Veterinary Science Vol. 17 (1), p. 35-42
Appendix
Data for a number of impacts with the track are shown. Analyses of this data will
require additional testing and completion of the calibration of the system.
8
Data set 1, at rail
7
Position
Filter Load
6
Voltage
5
4
3
2
1
0
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
1.2
1.3
1.5
1.6
1.7
1.8
2.0
Time (sec.)
11
Data set 2, at rail
Position
10
Filter Load
9
Voltage
8
7
6
5
4
3
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
Time (sec.)
1.2
1.3
1.5
1.6
1.7
1.8
2.0
10
Data set 3, at rail
9
Position
Filter Load
8
Voltage
7
6
5
4
3
2
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
1.2
1.3
1.5
1.6
1.7
1.8
2.0
Time (sec.)
10
Data set 1, At Center
9
Position
Filter Load
8
Voltage
7
6
5
4
3
2
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
Time (sec.)
1.2
1.3
1.5
1.6
1.7
1.8
2.0
10
Data set 3, At Center
9
Position
Filter Load
8
Voltage
7
6
5
4
3
2
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
1.2
1.3
1.5
1.6
1.7
1.8
2.0
Time (sec.)
10
Data set 4, At Center
9
Position
Filter Load
8
Voltage
7
6
5
4
3
2
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
Time (sec.)
1.2
1.3
1.5
1.6
1.7
1.8
2.0
10
Data Set from Chute
9
Position
Filter Load
8
Voltage
7
6
5
4
3
2
0.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
Time (sec.)
1.2
1.3
1.5
1.6
1.7
1.8
2.0