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MEASURING DEVICE FOR THE DETERMINATION OF ROLLING RESISTANCE OF ROLLER SKIS

University of Innsbruck Department of Sport Science. MEASURING DEVICE FOR THE DETERMINATION OF ROLLING RESISTANCE OF ROLLER SKIS. Kurt Schindelwig, Florian Hoppel, Michael Hasler and Werner Nachbauer. Introduction. Roller skis are used in: roller ski competition

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MEASURING DEVICE FOR THE DETERMINATION OF ROLLING RESISTANCE OF ROLLER SKIS

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  1. University of Innsbruck Department of Sport Science MEASURING DEVICE FOR THE DETERMINATION OF ROLLING RESISTANCE OF ROLLER SKIS Kurt Schindelwig, Florian Hoppel, Michael Hasler and Werner Nachbauer

  2. Introduction • Roller skis are used in: • roller ski competition • cross country training • If rolling friction is smaller than gliding friction • changes in movement technique • higher injury risk in races on asphalt with downhill parts

  3. Introduction • Determination of μR: • towing a weighted sledge by the Boer et al. (1987), Hoffmann et al. (1990) • variability of 20% of μR • motorized treadmillAinegren et al. (2008), Steiner et al. (2009) • - good reliability of μR • - but the heavy measurement equipment • is not transportable

  4. Aim • Develop a measuring device that enables • anexact and fast determination of μR. • Measuring device must be transportable. • Second aim • examine the effects of • ambient temperature • loading • different manufacturers • to μR of roller skis

  5. Method Weight sledge Roller ski Flywheel (18kg) Electric motor Incremental rotary encoder

  6. Method Warm up phase of 3 min with a Load 150N Circumferential velocity 7m/s

  7. Method • After the warm up phase • Motor removed • Measure the flywheel movement for 15s with 100Hz

  8. Determination of μR I * (w2- w1)= MR * Δt MR = FR· r μR = FN / FR I…moment of inertia (Flywheel) r…radius of flywheel w1…angular velocity at t1 w2…angular velocity at t2 Δt…t2 – t1 FR…Friction force FN…Normal force

  9. Determination of I 1. From the geometric and mass data of the flywheel I= ½ [m1 r1² + m2 (r1²+r2²) + m3 (r2² +r3²)]

  10. Determination of I w1 =0 m, v1 =0 h1 2. With an experiment t2 t1 w2 m, v2

  11. Determination of I t1 t2

  12. Method • Determination of μR • Load: 150, 175, 200, 225 and 250N (22°C) • Ambient temperature: 18, 20, ….30°C • (load 200N) • 4 different manufacturers

  13. Results: Moment of Inertia I • From the geometric and mass data of the flywheel: • I = 1.3104 kg/m² • 2. With 20 tests • mean: Im = 1.3124 kg/m² • standard deviation: Ist= 0.0024 kg/m²

  14. Results: Reliabilty 6 wheels - 15 measurements every wheel μR [ ] wheel Range of μRfor every wheel < 0.0009

  15. Results: Loading 6 wheels - 5 measurements each load μR [ ] 150 175 200 225 250 loading [N] loading 150 - 250N  µR6%

  16. Results: Temperature 6 wheels - 5 measurements each temperature μR [ ] 18 20 22 24 26 28 30 temp. [°C] temperature 18 – 30°C  small influence to µR

  17. Results: Manufacturers 10 wheels for every manufacturer - 5 measurements each wheel μR [ ] Maximum Minimum BarthelmesI-Gliti DMSMarwe Large differences of μR between wheels of some manufactor between manufactors

  18. Discussion Reliability: very high …with constant temperature and constant load Loading µR6%  disadvantage heavier athletes Example: 10 km with 300m difference in altitude Two athletes: 60kg and 80kg A60: 27min:15s A80: 27min:37s  time difference: 22s

  19. Conclusion Different manufacturers: Range of µRover 50% For a fair rollerski competition an exact determination of µRis needed!

  20. Thank You!

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