HBK Measurement Technology Optimises a Vehicle's Stay Rod

Universities from around the world participate in the Formula Student competition, including the FaSTDa team (Formula Student Team of Darmstadt University of Applied Sciences). Teams compete to see who can build the best race car in terms of construction, performance and cost.

The teams compete in the categories of combustion engine, electric drive and autonomous driving vehicles. Advantages for students: They gain practical experience in vehicle development, production and financing far beyond academic studies.

Challenge

To win the formula student competition, the Formula Student Team of Darmstadt University of Applied Sciences had to optimize the weight and load-bearing capacity of the stay rod.

Solution

To determine the actual normal force load applied to the stay rod and the max. bending load capacity based on the chassis geometry, the students designed a measurement setup using HBK strain gauges, data acquisition system and software.

Result

The results, obtained using HBK's precise and proven measurement technology, were to serve as a basis for subsequent lightweight design measures on the stay rod.

Application

As part of this competition, the students in Darmstadt worked on optimizing the weight and load-bearing capacity of a specific chassis component: the stay rod.

The stay rod aligns and stabilizes the wheel of a vehicle; it is connected directly to the chassis and the wheel. Each stay rod consists of two spherical buttons attached to the chassis, the two stay rod arms and a so-called "A" with a pressed-in ball joint to form a complete triangular stay rod.

The first task was to determine the actual normal force load applied to the stay rod, as well as the max. bending load capacity based on the chassis geometry. For that purpose, the students designed a measurement setup using HBK strain gauges (SG), HBK data acquisition system and HBK software for data visualization and analysis.

The measurement system, which was adapted to the application, was then installed in the vehicle to collect and evaluate data under various operating conditions. The resulting findings were to serve the team as a basis for decisions regarding design changes to the stay rod.

Measurement Setup

The stay rod arm was identified as the weakest point where strain should be most clearly measurable. Any deformation, e.g. the strain or compression of a component, causes a change in resistance in the strain gauge, which can be measured as a change in load strain.

In this test scenario, the students attached:

  • Two strain gauges offset by 90° on the stay rod to allow measurements of the tension/compression load.
  • Two strain gauges on opposite sides of the stay rod for measuring the bending strain.

Linear, half-bridge connected and self-compensating standard strain gauges were used in line with the required measurement tasks and normal ambient conditions.

The strain gauges were then wired and calibrated to expected normal forces. During this calibration, concrete force values resulting from the strain were assigned to the stress changes.

 

 

 

Fig. 2: Linear strain gauges with half-bridge circuit for measuring strain due to tension/compression (r.) and bending strain (l.)

 

Measurements

Once the stay rods equipped with strain gauges had been mounted back in the vehicle, it was time to take measurements under conditions that were as realistic as possible to obtain plausible and transferable results. The students carried out the measurement runs under ideal conditions in good weather on a karting track that resembled a race track in terms of the asphalted surface and layout.

The team defined three different driving scenarios that would produce maximum strain on the triangular stay rods:

  1. Driving multiple rounds of the track
  2. Start/Stop driving with maximum acceleration and maximum delay
  3. Cornering with braking

For the acquisition and analysis of the measured values, the Formula Team of Darmstadt University of Applied Sciences used components of the well-established HBK QuantumX data acquisition system and catman data acquisition software.

 

The strain gauge amplifiers in this series are particularly suitable for precise and reliable measurement data acquisition from strain gauges in full-bridge, half-bridge and quarter-bridge configurations, and are an ideal choice whenever strain and forces are measured and ambient temperature influences play a role. In conjunction with the QuantumX data recorder and the pre-installed catman software, the result is a highly precise and reliable data acquisition system suitable for mobile applications, which is easy-to-use in all operating steps – configuration, visualization, automation, evaluation, data management and reporting.

Conclusion

The analysis of the measurements of tensile/compressive and bending forces taken during vehicle operation showed that the values for normal forces were plausible, i.e. it can be assumed that they actually exist in that form. The bending strain measurement showed that there was only a minimal bending load on the stay rod.

These results, obtained using HBK's precise and proven measurement technology, can now serve as a basis for subsequent lightweight design measures on the stay rod.

About FaSTDa Racing

FaSTDa Racing was founded in 2007 by a small group of dedicated students from Darmstadt University of Applied Sciences. In the 2020 season, the team consists of 50 members from a wide range of technical and business majors. The skills of each member complement each other, making each component work harmoniously and efficiently to build a high-performance race car together as a team within 8 months. Every year FaSTDa Racing recruits new members and prepares for the international Formula Student competitions.


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