Racecar Tire Testing Apparatus

Author(s):
B. Taylor Newill - Brigham Young University
Russell Aldridge - Brigham Young University

Industry:
Automotive, University/Education, Transportation, Research

Products:
CompactRIO, LabVIEW, DIAdem

The Challenge:
Acquiring the knowledge of tire parameters is vital to racing success, and purchasing tire data from third-party vendors is extremely expensive. The Brigham Young University Formula Racing Team needed to build a robust, versatile, low cost data acquisition system for testing key tire parameters under harsh conditions.

The Solution:
Building a tire testing machine using NI CompactRIO hardware and NI LabVIEW software that saved the team thousands of dollars and gave them a competitive edge.

Building a tire testing machine using NI CompactRIO hardware and NI LabVIEW software that saved the team thousands of dollars and gave them a competitive edge.

The BYU SAE team needed to build an inexpensive but effective tire testing machine that could operate in extreme temperatures, constant vibrations, moisture, and dust. The tire testing machine designed and built by the BYU team is towed behind a truck or SUV using the vehicle’s receiver hitch and trailer receptacle. This puts the challenge of powering the tire in the hands of automotive engineers. The tester tire turns the tire from left to right over a 30 degree range as dictated by a predefined program while strain gages and infrared thermocouples measure imparted forces and resultant temperature gradients. The heart of the system is the CompactRIO platform programmed LabVIEW software. This winning combination provides a durable, cost-effective solution for a challenging problem. 

When track times for the top drivers are within 0.2 percent of each other an accurate tire tester and tire model are crucial. Tire data is used to generate a comprehensive, mathematical tire model. The tire model information influences design factors such as suspension and steering geometry; spring and damping ratios; location of the center of gravity; and tire settings such as camber and caster.

System Benefits

A key benefit of the tow-behind tire tester is the ability to test tires in real-world conditions. Expensive tire testing machines are permanently located inside a building and use a continuous belt to simulate road travel with an extremely high friction coefficient. Ambient conditions such as temperature, solar radiation, and surface properties cannot be accounted for with this type of testing. Our tow-behind tester is durable enough to gather data in the real world.   

The tester was designed to be simple enough to be used by the average college freshman and versatile enough to be towed by most vehicles. With the Web-hosting feature of the CompactRIO Real-Time platform, anyone with a laptop and a Web browser can run the tester by connecting via a wireless router to the CompactRIO. Because of the wide input voltage range of the CompactRIO (11 to 30 V), the tester can be powered by any vehicle using a standard 7-pin trailer plug. 

Each time the tester is connected to a new power source, it automatically recalibrates its measurement system.             Because of the configurability of the system, the user can opt to run a variety of preset testing programs or generate a custom testing cycle to make custom tire models.

System Design

Automation, measurement, and data acquisition are controlled by the CompactRIO. As the vehicle travels in a straight line, the slip angle is varied using a linear actuator controlled by a 4-channel relay module. Feedback for the closed-loop system is achieved using a linear potentiometer. Power for the potentiometer is sent via an analog output card (+/-10 VDC), and a 4-channel analog input card (+/-80mV) measures the voltage. A timer runs the tire through its range of motion between two limit switches, which calibrate the output voltage from the potentiometer. Voltage at each limit is recorded and tire angle is calculated using an NI LabVIEW MathScript node, which converts this voltage signal into a degree measurement. 

Strain gages measure the forces imparted by the tire at different slip angles in lateral and longitudinal directions. An analog output card (+/-10 V) provides excitation voltage to two full Wheatstone bridges and one half bridge. A 4-channel analog input card (+/- 80 mV) measures voltage differentials across the bridges. 

A low-voltage analog input card also measures the voltage differentials created by the infrared thermocouples. These thermocouples actively record the temperature across the tread face and side wall. A GPS system transmits speed, distance, and direction to the CompactRIO via an RS-232 serial port communicating at 19,200 kbps. 

To develop this solution, the FPGA target was programmed with four parallel synchronous loops and 32 I/Os. The real-time target was similarly programmed and was responsible for the signal conditioning. On the real-time level, only the data-logging loop had to be controlled deterministically. This was necessary to visualize delta effects on key parameters. We also incorporated a timed loop operating at 50 Hz to help visualize key parameters. The generated data strings are concatenated with a GPS and a system time stamp and then written to flash memory later retrieval via the CompactRIO FTP server. The data files are saved in CSV format and the data is analyzed and reported using NI DIAdem software. 

A small 700 x 400 pixel-tabbed GUI gives the user quick access to key parameters such as tire temperature, force measurements, speed, and position. The user is also able to control which test programs run, when data logging begins, and the name of the data file. These systems work together to achieve a reliable tire-testing platform that accurately measures racecar tire parameters.

Building a tire tester similar to those used by professional tire testing companies on a Formula SAE budget seemed impossible, but with the help of NI software and equipment, the BYU Formula Team created an automated tire tester with enough money left to build a racecar.

For more information, contact:

 

Russell Aldridge

 

Brigham Young University

 

486 CTB, Provo, UT 84604

 

Tel: (801)494-9520

 

russellaldridge@gmail.com

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