3.  Chassis Lab Services offered by ATI

3.0  "Topsy" - The Chassis Parameter 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 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's development, test methodologies, equipment, and procedures are described in SAE Paper 971056 "Topsy - A Modular Chassis Parameter Measurement System", which was presented at the SAE International Congress in February 1997. An updated description based on that paper is available for download (http://www.atiheitz.com/download.htm).

All measurements made on Topsy are in accord with SAE J 1574/1 "Measurement of Vehicle suspension Parameters for Directional Control Studies - Rationale, Test Equipment, and Procedures", wherever that standard is applicable. In general, measurements on Topsy are extended to higher force levels than those suggested in J1574; and a number of parameters are measured in addition to those covered by that standard.

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, overlayed 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.

3.1  Measurement Services Currently Offered

3.1.1  Inertial Measurements

3.1.2  Chassis Compliances

Measurements with forces and moments in parallel (aiding) and opposing
Force and moment levels to wheel slip.


Forces in parallel, forces opposing, forces applied to single wheel. Steering Effort Reaction

3.1.3  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.

3.1.4  Steering System

Measured Lock-to Lock

3.2  Measurement Methodologies

Inertial Measurements
Vehicle is locked to baseplate Frame. For CG measurements Frame is mounted on knife edges, and is cycled through tilt angles by a vertical linear actuator, equipped with a load cell and mounted on a torque arm. CG is normally measured at several ride heights, to permit CG estimation under different loadings. For roll and pitch inertia Frame is mounted on knife edges and linear springs. For yaw inertia Frame sits on "yaw cradle", which is attached to the floor through a large-diameter ball bearing with torsion bar spring restraint. Separation of sprung and unsprung masses by measurement of total vehicle CG height at several different ride heights is theoretically simple. However, because of body beaming deflection and the compliance of engine/suspension subframe rubber mounts, the results have been so far insufficiently accurate. Development of the methodology is continuing.

Chassis Compliance
Vehicle sprung mass is locked to the Frame, with tires on ball-bearing low-friction tables mounted on platform scales. Hydraulic servo cylinders equipped with load cells apply forces and moments at the tire contact patches. Compliances are measured from a transducer plate mounted on lugnut extensions to a ball-slide follower mechanism attached to the sprung mass, or from the tire contact surface to the Frame.

Ride/Roll Spring Rates and Kinematics
Vehicle rests on scales and ball bearing tables. Sprung mass is restrained laterally and fore/aft by vertical posts in linear ball bearings. Four hydraulic servo cylinders apply ride and roll forces. Vertical posts are unrestrained vertically for ride motions. For roll motions they can be left unrestrained so vehicle "finds its own" roll center; or they can be locked to define roll centers at ground level or at any level from 4 inches below ground to 3.5 inches below the sprung mass bottom of body. Deflections are measured from a transducer plate mounted on lugnut extensions to a ball-slide follower mechanism attached to the sprung mass, or from the tire contact surface to the Frame.

Vehicle rests on scales with ball bearing tables, restrained by unlocked vertical posts. The steering wheel is cycled slowly by hand or by geared electric motor through full lock. Measurements of displacements of reference point on the spin axis are made from a transducer plate mounted on lugnut extensions to a four-axis ball slide assembly (X,Y,Z, steer angle) attached to the sprung mass. Caster and steering axis inclination are computed from camber and caster changes.

3.3  Specification of Kinematics and Compliance Tests

3.3.1  Standard Conditions
All tests are run at, or referenced to, curb trim height. All kinematics tests are run with engine stopped. Steering system tests are run with engine running and with engine stopped. Only handwheel torque is plotted for the engine stopped condition, as explained in the Notes below. Front lateral force and aligning torque compliances with forces or torques adding are run with engine running; and with forces and torques opposing the engine is stopped; as explained in the Notes below. Front longitudinal force compliance tests are run with engine running. All rear compliance tests are run with engine stopped.

3.3.2  Equations Fitted to Plotted Data
Third-order least-squares polynomial equations are fitted to most data plots. Where dictated by the character of the data, three-element linear plots (thru-center, and positive and negative extremes) are used instead. Examples of the latter are steer tests, where roadwheel steer angle vs aligning torque usually shows a distinct difference between on-center and off-center slopes; and wheel loads in ride and roll, where rates change as bump or rebound stops are engaged.

3.3.3  Choice of Data to Be Plotted
Raw data (vs time) required for all plots will be supplied on floppy disks for all tests, and will be included in the test charge. All of the plots in the following listing can be generated from the floppy disk format. Since many of the data plots in the listing are useful only in some simulation models, and the quotation for Data Processing includes a separate charge for each plot, costs will be minimized by circling only those plots actually intended for use, or those for which fitted equations are desired.

3.3.4  Organization of Data Plots
Data plots are organized into four groups:

Test type and configuration      
    Non-standard test conditions if present           
                Parameter plotted
Examples of non-standard test conditions are engine running or stopped, non-curb ride heights, etc. For example, a front compliance test at 30 mm jounce instead of curb height would be coded as FC-30J-SFA, etc.


  1. In front steering and compliance tests, side forces adding and aligning torques adding include steering column compliance, which can be significant with power steering inoperative because the engine is stopped. With power steering in operation the steering column is affected only by steering wheel effort. Forces and moments opposing will tend to balance at the steering gear, and so do not load the steering column.
  2. The self-centering effect of front end geometry is best evaluated with power steering inoperative.

3.4 Quotations

Quotations are based upon the following components of cost:

  1. Incoming vehicle inspection: listing of vehicle specifications, departures from manufacturer's specifications, dimensional measurements, topping up or draining gas tank, cleaning of underside of accumulated dirt, preliminary vehicle wheel weights, etc.
  2. Mounting and centering of vehicle on test fixture.
  3. Ballasting of vehicle, if necessary.
  4. Installation of vehicle clamping devices, or of Ride/Roll actuators and scales.
  5. Setting and recording installed ride height per test specification.
  6. Calibration of equipment and instrumentation.
  7. Installation of special equipment and instrumentation appropriate to each test.
  8. Performance of the test.
  9. Data Processing.
  10. Plotting of data.
  11. Preparation of report.
  12. Removal and restoration of the test vehicle to as-received condition.
  13. Post-test calibration checks and restocking of instrumentation. and equipment.
Whole-car CG and Moments of Inertia
Whole-car center of gravity and moments of inertia are all measured with a single vehicle setup on the testing Frame. The principal cost items are 1 through 7 above. Current (March 1996) approximate quotations are: $2000 for CG height at specified trim and two additional trim heights or loading conditions; $500 each for roll, pitch, and yaw moments of inertia. For litigation-involved projects, we can provide as an extra-cost option, an on-camera, stepwise multipoint calibration of each measuring system, with computed linearity, measuring tolerance, and confidence limits for the particular test.

Kinematics and Compliance Testing
Compliance tests done alone might be done with hydraulic, electric or manual actuators in the vehicle positioning system, with hydraulic servoactuators used to generate tire side forces and aligning torques. Kinematics testing requires hydraulic servoactuators for body jounce, pitch, and roll motions. When Kinematics and Compliance tests are both to be run, the same setup of hydraulic actuators in the Ride/Roll crossmember fixtures is used for both tests, with useful cost savings. Items to be measured are selected from the list of identification codes. Of these, items to be plotted and those to be curve-fitted are selected, and a quotation is made based on all of these considerations.

As noted under "Specification of Kinematics and Compliance Tests", raw data for all items measured are supplied on floppy disks. Some costs can be saved by plotting only items certain to be needed: others can be plotted by the Customer or by HCL at any time later.

Time & Material Quotes
For exploratory "cut & try" tests with a customer's engineer present, a quotation can be prepared with a fixed price covering defined items, with time & materials for "messing around" negotiated separately.


3.5 Rates and Charges 

Fixed Price Services
When the testing services required or the character of the final work product are sufficiently defined, ATI prefers to provide such services at an agreed-upon quoted price, on a "not to exceed" basis.

Equipment Used
The use of equipment owned by HCL, including test facilities, instrumentation, data acquisition, video, and computation equipment, is included in the rates quoted above, or in fixed-price quotes.

Other Project Expenses
Project expenses that are included in time & material charges as line items, at HCL's cost, include (but are not necessarily limited to) subcontracted work, special printing and reproduction, and shipping charges.

3.8 Terms and Conditions of Agreement

last modified 05/11/2006