INTRODUCTION: "To turn, a skier manipulates the orientation and loading pattern of skis to generate a reaction force from the snow surface that allows redirection of trajectory and regulation of speed" (Reid et al., 2020). Therefore, measurement edging angles allow for information about ski snow interaction and turning technique (Snyder et al., 2021). In this study, an algorithm is presented that allows us to measure ski orientation in 3D space using IMUs. METHODS: Two IMUs (1000 Hz, 6-DOF, 16-bit, ± 2000°/s, ± 16 g) are mounted to the back of the ski boot. Beforehand, IMU axis are adjusted and rotated to account for manufacturing inaccuracies. Measurements are performed by experienced ski instructors and coaches (n = 3) by doing 3 trials. Every trial started with a five-second zero-movement-phase in a flat area to calculate the gyroscope offset and calculate the mounting orientation. Movement tasks in each trial are skidding and stopping, snowplow and carving. In post-processing, raw data is filtered (10 Hz Butterworth lowpass), and the Madgwick filter is applied. Received quaternions are converted into Euler angles. RESULTS: Overall, the algorithm delivers plausible results. However, if the accelerometer saturates (e.g. on icy/bumpy slopes), edging angles drift. Adjusting the filter`s gain improves results. No reference system was used so far, but further measurements using a reference method will be presented at the congress. DISCUSSION/CONCLUSION: Overall, the Madgwick filter is a promising approach to measure edging angles. Adjusting gain setting (dynamically) is subject to further testing. Also, mechanical dampening of the IMU could further improve results.
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