"Topsy" - A Chassis Kinematics and Compliance Measurement Facility Topsy is a modular system designed for measurement of all composite inertial, kinematic, and compliance parameters that appear in today's sophisticated mathematical simulation models. The basic design is described in SAE Transactions for 1997. The emphasis in its design is not "production-line" testing, but research: the operator can observe the vehicle's reaction to developing forces; and as insights develop he can modify the test program as he goes along. Test errors are minimized by running all tests under servo control with continuous display of all data and recording of all known error sources, while the operators closely monitor the test and the developing data. The test facility is organized around an "infrastructure" consisting of baseplates; vehicle locating fixtures; scales; hydraulic and pneumatic power sources; interchangeable valve assemblies and actuators; and transducers. These are organized along with specialized devices into the several forms required for the different tests. Topsy uses the ATI/Heitz proprietary data acquisition system, which allows close monitoring of a test in progress, and useful review of completed test programs. All testing is videotaped, with raw transducer data recorded in serial binary form on one or more lines at the top of the picture. Voice, noises, and transducer outputs are recorded in synchronism continuously during the entire test on two-hour tapes, so that anomalies that might occur during or between test runs can later be investigated. Throughout the test, data is displayed as columns of numerics, twelve channels to a column, overlaid on the video picture, for visual monitoring. All processed data is referenced to hours, minutes, and seconds of tape time, so that final plotted data can be looked at while watching a replay of the test run.
The system is designed to use a maximum of nine "data lines" with 12 channels per line, for a total of 108 10-Hz data channels sampled at 60 Hz. However, it is also possible to devote some data lines to "high-speed" use, with two data channels sampled at 480 Hz or one data channel sampled at 960 Hz. A typical test program requires 24 to 36 "low-speed" 10 Hz channels.
Testing Protocols All Chassis Lab testing is performed in accordance with established standards or recommended practices, whenever such standards or recommended practices exist for obtaining the desired data. The Chassis Lab methodologies and the instrumentation accuracies listed herein are in accordance with SAE J1574 for all items covered by J1574, although the range of applied forces, moments, and displacements is greater. Roadholding tests are performed in accordance with numerous standard protocols as noted herein. We do not perform result-oriented tests.
Test Documentation Each test program is documented by one or more spiral-bound test reports and by unedited videotapes. Raw and processed data is made available on CDs.
All tests are videotaped, and all raw instrumentation data is anti-alias filtered, sampled 60 times per second, and recorded in 12-bit binary serial format in one to three video lines at the top of the screen, in a patented, proprietary process. Each video line carries 12 channels of data. Raw instrumentation data is also superimposed onto the video picture, in columns of twelve 3-digit numerics or in several other graphic forms, either during the test or during editing. Test videotapes are provided with and without on-screen timing, and with and without superimposed numerical data. Video formats can be VHS, S-VHS, or digital.
Test reports are completely objective (no value judgments) and include: purpose of the test; vehicle description and any departure from manufacturer's specification; description of methodology and instrumentation; plotted data; equations fitted to plotted data (in parameter measurements); still photographs of test set-ups; and copies of the protocols used.
In preparation of the reports raw data is filtered as required, by running average or Fourier methods, and zeroed. In cases where dynamic data is to be compared, the phase shifts caused by anti-aliasing filters are removed. The resulting data set, along with any auxiliary variables that must be obtained from recorded data by integration, etc., is saved as the "processed data set" for use in preparing data plots. Floppy disks containing both the original raw data and the processed data set are supplied on request, in binary or compressed ASCII files.
MEASUREMENT SERVICES CURRENTLY OFFERED
Whole vehicle center of gravity
Whole vehicle moments of inertia: Roll, Pitch, Yaw
Whole vehicle roll/yaw product
CG of sprung and unsprung masses separated
Driveline rotational inertia
Chassis Compliances Measurements with forces and moments in parallel (aiding) and opposing Force and moment levels to wheel slip.
Lateral force compliance steer
Lateral force compliance camber
Lateral force compliance deflection (X, Y, Z at reference point on spin axis)
Lateral force y-deflection at tire contact
Aligning moment compliance steer
Aligning moment tire twist
Aligning moment compliance camber
Roll center height by equilibrium jacking force method
Longitudinal Forces in parallel, forces opposing, forces applied to single wheel.
Longitudinal force compliance steer
Longitudinal force compliance camber
Longitudinal force caster change
Longitudinal force compliance deflection (X, Y, Z at reference point on spin axis)
Anti-dive angles by equilibrium jacking force method
Steering Effort Reaction
To aligning moment
To side force
To balanced thrust/braking
To unbalanced thrust/braking
RIDE/ROLL SPRING RATES & KINEMATICS
Measurements from compressed stops to wheel-off Roll centers can be unrestrained, or fixed at ground or at any height to 3.5 inches below bottom of body.
Normal forces at wheels
Ride spring rates
Ride coulomb friction
Roll spring rates
Roll coulomb friction
Tire spring rates
Roll stiffness distribution
Swing arm lengths
X,Y,Z displacements of reference point on spin axis
X,Y displacements of tire contact
Roll center heights by displacement method
Shock absorber travel
Steering System Measured Lock-to Lock
Wheel steer vs handwheel angle
Overall steering ratio vs handwheel angle
Steering axis inclination angle
X,Y,Z displacements of reference point on spin axis