QMT Features: December 2014
Rattling boxes

A student racing team gets help with its metrology

The UPBracing Team of Paderborn University has been a regular contender on the Formula Student circuit since 2006, writes Harald Richter. The student racing team is one of the more experienced in the international constructors’ championship. But to compete with the best, some very special technology is needed.

Building a racing car is a bit like Lego, but at a much higher level. Everything is a bit more complex and a bit bigger, including the boys and girls who play with it. Anybody who ever received Lego as a present remembers the promising rattle when you shook the box. The mixture of excited anticipation and quiet self-doubt that came as you wondered whether you could really build it.

Christoph Wälter has never lost that feeling. Today, he’s not just receiving rattling boxes anymore, but entire crates of pipes, body parts, suspension components and more.

Christoph Wälter is chairman of UPBracing Team e.V., the racing team of Universität Paderborn. The team is made up of students from all faculties of the university, and they work together to design and construct a single-seater racing car for the Formula Student competition.

Formula Student has its origins in an American university competition that was founded by the SAE (Society of Automotive Engineers) in 1981. In 1998 the idea migrated across the Atlantic to Great Britain and in the years that followed, more and more international race tracks staged the constructors’ competition, one of them being the Hockenheimring. Since 2006, the Verein Deutscher Ingenieure (VDI) has been in charge of Formula Student Germany and this has opened the door to the race track for many German students.

The objective of the Formula Student project is to gain experience in car design and construction, and the commercial aspects of automotive engineering. To this end, the participants form a virtual production company that is focused on the development and construction of a racing car with the aim of producing a fully functional prototype.

Teams come together once or twice a year at famous race tracks throughout the world to race against each other. However, in Formula Student it is not necessarily the fastest car that wins, but the team with the best overall package of construction, racing performance, financial planning and promotional arguments.
The UPBracing Team of Universität Paderborn is one of the most experienced Formula Student racing teams in Germany, having produced their first racing car back in 2006. The team includes over 140 former and about 40 active members – and each one of them is familiar with the problem of the rattling boxes.

Building from loose parts
Says Christoph Wälter. “Of course, as a student team we don’t receive our vehicle components fully assembled as professional racing teams would. We are grateful when companies let us have some material and parts. It doesn’t matter if they come unsorted and loosely packed. The main thing is that we get what we need.”
Prime among these are the metal parts for the lattice tube frame of the planned competition vehicle. This is practically the race car’s skeleton, a hybrid chassis consisting of a steel lattice tube rear frame with a carbon fibre monocoque and a carbon fibre crash box.

“We had the steel tubes manufactured to our exact CAD data. They were delivered as individual parts,” explains Wälter. The content of the rattling box had to be welded together with millimetre precision to make up the lattice tube frame. Not an easy task – and not manageable without help.

That help came from Hexagon Metrology in the form of a ROMER Absolute Arm with a measurement range of 2.5 metres and a single point reproducibility of 0.02 millimetres.

The ROMER Absolute Arm is currently used by the racing team to accurately check the welded lattice tube frame elements. “This is not at all a trivial task”, explains team boss Wälter. “Each vehicle component has a precise position within the frame, which is defined to the millimetre. Even a minute deviation in the frame structure compared to the CAD data would have a fatal effect on function and safety. Without the ROMER Absolute Arm as a measuring tool we could never achieve the required precision – we would still be faced with a load of rattling boxes!”

It is fascinating to see how relaxed the team is as it goes about its business, in spite of the need for high-end precision.

With a surprisingly low weight of just 8 kilograms, the ROMER Absolute Arm is perfect for the team’s needs: its light weight is ideal for manoeuvring around the car, and measuring even in difficult to reach areas. This lightness is the result of the carbon fibre structure of the arm’s internal and external tubes. This is also the reason why the ROMER Absolute Arm does not require a temperature compensation device – unlike aluminium measurement arms.

Ease of operation applies to the ROMER Absolute Arm in another sense too. “You have to remember that none of us here is a metrology specialist”, says Wälter. “In spite of this we have found that using the arm is really easy. All a new team member needs is a short introduction to the ROMER Absolute Arm and they can start measuring immediately.”

Tips and tricks
The UPBracing Team has established a special forum that is dedicated to the application of the ROMER Absolute Arm. Everybody who uses it can enter his or her experiences, and add any tips or tricks.

The young constructors are clearly excited about the absolute encoders integrated into the arm’s movement axes, which assign an absolute value to the position of each joint. This technology makes encoder referencing and warm-up time unnecessary – the measuring arm is ready for operation immediately after it is switched on, even in a confined space. “You don’t have to mess about, you just do it,” says Mr Wälter of this unique feature.

Automatic probe recognition means that measurement probes can be swapped on the fly, without any need for recalibration. The team in Paderborn also makes use of the arm’s Wi-Fi connection and battery operation.

It will typically take months for a complete racer to be built from all of the parts in those rattling boxes before participating in its first race. From its transverse mounted Suzuki GSR 600 in-line four cylinder engine, the university racer produces about 92 horsepower, accelerating to a top speed of about 120 kilometres per hour. With power like that, and such accurate construction, there is no Formula Student team that is better equipped to build a racing car from a set of rattling boxes.
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