Optimized ski cross performance - with SoMat and nCode GlyphWorks

For a conquering start: rugged data acquisition and efficient data analysis

An Olympic sport since the 2010 games in Vancouver, ski cross is a particularly spectacular race as everyone got to see during the final days of the Sochi 2014 Olympics. The French team really shined and the tricolor flag dominated the winner’s podium as Jean-Frédéric Chapuis accepted the gold medal, Arnaud Bovolenta d’Arêche-Beaufort the silver, and Jonathan Midol the bronze.

HBM got the opportunity to take part in a performance optimization project undertaken by the French Skiing Federation (the FFS). "In this kind of competition, the start is especially critical with a huge impact on the rest of the race. To improve our performance at this level, we set up a system to analyze the behavior of athletes when their hands are on the starting grips. For this, we used HBM technologies," notes Nicolas Coulmy, director of the Sports and Science Department at the FFS.

Initially, the FFS had worked on starting techniques with an ergometer in a training room. To take things to the next level, they wanted to perform these tests under real-life racing conditions on a snow-covered mountain. This required instrumentation on the starting grips to record, and then process, the force values supplied by the sensors.

To ensure the success of its operation, the FFS enlisted the support of Des-I-D, headed by Pierre Désarmaux, who is highly specialized in project management. The company supports projects with a high potential for innovation and provides management for complex or multi-disciplinary projects. The director's experience in the company Salomon-Amer and his knowledge of the environment prompted the FFS to contact Des-I-D.

Things moved quickly, as Pierre Désarmaux explains: "We started by drawing up the functional schedule of requirements, which clearly defined the FFS's expectations. The application required installation of force sensors on the grips and recording and processing of the information received. Having known HBM for a long time, I knew that the company would have a total solution to address the whole problem, from the sensor to processing of the measurements. We then invited them to join the project. HBM proposed well adapted technical solution and put us in touch with the company, Astrym, to which we entrusted the development of the recording application".

HBM's solution involved low-temperature strain gage sensors, a SoMat data acquisition system, and nCode GlyphWorks data analysis software. In this system, the sensor required special developments, as Désarmaux of Des-I-D explains: "Together with the FFS and support from Claude Nanjod, a renowned expert in high-precision mechanics, we designed, developed and manufactured a custom cylindrical sensing element to be inserted between the support grips for the skiers and the frame supporting these grips. Each sensor features two adhesive strain gages to measure the forces exerted along two perpendicular directions. In order to ensure integrity of the device, special care had to be taken in the design of axial outputs with market-standard connectivity so that wires would not be in the starting gate zone where skiers are located.” The force on the grips at the starting time is high. The Application was designed for a total force of 200 daN, or 100 daN on each grip.

Recording the FFS application is relatively simple with just 4 data channels (two sensors on each grip) and no major metrological demands or dynamic constraints. "Although simple, there was a significant constraint. The data acquisition system would be used outdoors on a mountain and would need to be moved around a lot so it had to be compact, battery-powered. It also needed to be able to withstand hostile ambient conditions like cold, impacts, humidity and snow," says Désarmaux. The SoMat was selected to meet these needs because of its mobility and ability to function at temperatures of -20 °C. It was an especially good fit since it is available in a wide array of variants and scalable configuration whether large or small, not to mention the option for future expansions.

Astrym, which was contracted for the development of the application software, had already created several applications with HBM products, such as vibration measurement on a rail traction machine (for maintenance purposes) and strain measurement on a large 65,000-tonne press. "HBM is a true partner for us. Aside from providing high quality products, they help us with marketing support, which means a great deal to a young company like ours," imparts Sylvain Tremouilhac, Manager at Astrym.

The application software developed by Astrym was completed on a traditional PC with parameterization and processing software installed and supplied by HBM. The parameterizations were defined first to include the number of channels, scales, units of measurement, uncertainties, capture frequency (500 Hz), data record format, etc.
The data recorded were analyzed usingnCode GlyphWorks software. "We wanted software that was easy to use, offered powerful processing and that featured good reporting functionality since the purpose of the tests is to produce results that are easy to analyze without having to spend time converting and processing the data. nCode GlyphWorks offers all of these features," notes Sylvain Tremouilhac. During a demonstration for the FFS, Astrym developed an analysis process in GlyphWorks in just 15 minutes that would have taken two days with a Microsoft Excel® spreadsheet.

A particularly impressive feature in GlyphWorks is the ability to manage each individual test (or run) and automatically assigned a file name and date, which is far more practical to find them for data processing. During the tests on the skiing site, GlyphWorks and SoMat software was installed on a rugged tablet to directly control and display the results of the analysis.