Customer Solutions
Building Formula 1 Caliper and Brake Test Dynamometers Using NI LabVIEW 7.1 and NI-DAQmx
Author(s):
Paul Riley, Computer Controlled Solutions Limited
Industry:
Automotive
Product:
Data Acquisition, LabVIEW, Motion Control, PXI/CompactPCI
The Challenge:
Building a new type of dynamometer that could match the
high-speed and acceleration rates achieved by Formula 1 cars and carrying out these tests within the actual sections of car’s standard wheel and suspension assembly.
The Solution:
Basing the new system around an industrial Pentium 4 HT 3.2 GHz with 1 Gb RAM, using National Instruments data acquisition and control cards, and writing the software completely within NI LabVIEW.
AP Racing Builds Unique New Dynamometers
For more than 30 years, AP Racing has been a world leader in the technology and manufacture of brake calipers and race clutches. Building off the current dynamometer, AP Racing concluded that a unique new dynamometer would be a distinct advantage if it had the following capabilities:
- It could test the brake and caliper both on a rig mounting and within the actual wheel and suspension assembly.
- It had the power to accurately simulate Formula 1 speeds and acceleration rates.
- It could simulate the air flow around the caliper and allow for investigation into the airflows through different ducting designs.
- It could import track data on the braking profiles and acceleration profiles.
Because of the strong design capabilities of AP Racing, they decided that the rig would be built in house, which would provide cost benefits and absolute control on the system capabilities. For the software and electronics control system, AP Racing selected Computer Controlled Solutions (CCS) based on our experience in this field and the number of successful test machines previously provided and maintained for AP Racing.
The system was based around an industrial Pentium 4 HT 3.2 GHz with 1 Gb RAM and the following acquisition and control cards:
We wired these cards via various rack-based signal conditioning to control and measure the following:
- 288 kW inverter
- Extraction fan system
- 240 kph inlet air flow control
- Hydraulics servo control system for brake pressure application
- Torque, temperature, infrared temperature, pressure and speed measurement
- Invertors for control of the machine covers
- Water cooling and monitoring
- Bearing cooling and monitoring
- Disk wear capacitance displacement
We wrote the software completely within LabVIEW. The main design elements were as follows:
- Intuitive: We centred the design around the main menu so the operator can check all I/O, build tests, run tests, and analyze data. A simplified menu option also changes this screen to a basic run screen for running predesigned tests.
- Calibration screen: Making good use of dual TFT displays, we designed the calibration screen to provide a tabular view of all I/O on the left screen. These tables are best for the calibration engineer to view and check I/O. The right screen contained a complete mimic of the rig, which is useful in identification of the transducer and controller location upon the rig.
- Modular, simple test development: We broke down all aspects of a test into simple modules (i.e., apply brake, go to speed, loop, start and stop acquisition). The user could then build up a whole suite of tests by putting the modules together in a simple list.
- Intuitive run screen: Taking advantage of the speed of LabVIEW, we could present a full run screen, indicating position in the test, mimic, dual scrolling graph displays, and all status information.
Using The Latest Version of LabVIEW and the NI-DAQmx Controls
During final development of the system National Instruments released LabVIEW 7.1 and NI-DAQmx. After investigating the software, we decided to upgrade to this latest system, which provided the following key benefits:
- Smooth upgrade of LabVIEW versions: We had assisted in beta testing this product prior to release, which gave us initial confidence. We also found the new release to be stable and straightforward to upgrade.
- Faster data acquisition: The system was designed to control continuous save-to-disk and display mimics and graphs on dual screens at data rates up to 2 kHz per channel. By implementing the NI-DAQmx code, we saw acquisition rates increase approximately five times, which we took advantage of to free up the system for more complex real-time control and displays.
- Nonlinear acquisition: Using NI-DAQmx, we automatically applied a nonlinear fit to infrared temperature transducers, thus avoiding post processing and having real-time display of these linearized channels.
- Subpanel implementation: We used the newly implemented subpanels and showed the status of a particular point in the test in a subpanel on the main run screen. One advantage we experienced here was that the main panel kept the focus, which kept the abort button active while we carried out subpanel actions.
Design Challenges: High Speed Interdependent Closed-Loop Control
The system required the following closed-loop controls:
- Torque control: controlling the brake torque applied to match actual profiles, constant levels, or speed dependant levels
- Pressure control: controlling the brake under pressure to match actual profiles, constant levels, or speed dependant levels
- Air flow control: simulate air flow in the ducting and onto the brake based on output speed
- Speed control: control of the motor inverter
There are various servo control cards with analogue or DSP solutions for this application. However, we found the NI quad-axis motion controller suited this system best for the following reasons:
- It was completely controlled within the LabVIEW environment: This is important from a software maintenance view as it avoids having other software products and associated libraries which can create version control problems and extra complications in re-installing software.
- It was low cost: In comparison with other DSP implementations or servo controllers, for 4 channels the price-performance could not be matched.
- It had a high PID loop rate: PID loop rates of up to 16 kHz ensures that the PID control is a few orders of magnitude better control than some common servo controllers thus providing very smooth mechanical movement and control.
Note: Since implementation of this system, the NI FPGA cards have been introduced, which would also have been ideal for this application.
The system is now running successfully, testing all ranges of motorsport brakes and calipers for AP Racing development and Formula 1 teams. Our completion of this project has resulted in a unique and advanced method of brake testing. By designing the system to carry out full dynamometer brake testing within a section of the car, we have allowed an unparalleled source of data to be acquired and analyzed, thus feeding back accurate data to assist in optimum brake design. Using LabVIEW and associated hardware, we designed a stable system achieving complex control and maintaining operator ease of use. We are also looking into implementation of a vision system, which will provide a data-embedded video file.
For more information, contact:
Paul Riley
Computer Controlled Solutions Ltd
37 Park Street
Leamington Spa
Warwickshire, United Kingdom
CV32 4QN
Tel: +44 1926 430200
Fax: +44 1926 430209
E-mai: Paul@ccsln.com
Web: www.ccsln.com
