CASESTUDY
CASESTUDY
NTNU used OAV Air Bearings to build a high-precision tribometer capable of testing full-sized cross-country skis on laboratory-grown dendritic snow with high precision.
CUSTOMER
NTNU
INDUSTRY
Research & Academics
APPLICATION
Ski-Snow Friction Testing
PRODUCT USED
Linear Air Bearing Guide
BENEFIT
Stable Resonances & Precise Measurements
CASESTUDY
Ski-snow friction plays a large role in cross-country ski performance, but accurately measuring it in a laboratory is challenging. International restrictions on fluorinated ski waxes have led to an increase in research to minimize ski-snow friction. Although laboratory friction studies have been conducted, existing test setups had limitations such as severe snow polishing and restricted sample size.
Replicating realistic skiing conditions requires more than just measuring friction on a small snow sample. The researchers needed a system capable of testing full-sized cross-country skis while accurately controlling speed and applied load over a long testbed. At the same time, the measurement system needed to reduce unwanted mechanical resistance so that forces generated by the test apparatus would not interfere with the relatively small ski-snow friction forces being measured.
CASESTUDY
A full-scale ski-snow tribometer was developed by the Department of Civil and Environmental Engineering at the Norwegian University of Science and Technology to investigate ski-snow friction using the OAV Dovetail Linear Air Bearing. The performance of the tribometer varied based on snow type, speed, and surface preparation.
The tribometer was capable of testing full-sized cross-country skis at speeds up to 8 m/s on testbeds made with laboratory-grown dendritic snow. This setup provided better control and could produce the same type of snow repeatedly, allowing for more precise measurements of ski-snow friction.
Consisting of a mobile carriage driven by a servo motor, the modified tribometer carriage included a fork, air bellow, the OAV Dovetail Linear Air Bearing, two vertical load cells, a horizontal load cell, and a system for data acquisition and transmission. During the runs, there were phases of acceleration, constant speed, and deceleration, with the length of the constant speed phase varying from 2.50 to 5.50 m depending on the chosen acceleration of the motor. The vertical load could be adjusted from 50 N to 800 N, and the applied load was distributed over the entire length of the binding with the center of mass approximately 12 cm behind the front of the binding, similar to a skier's weight distribution and center of mass over a ski.
Minimizing mechanical friction within the measurement system was important because the tribometer measures relatively small friction forces between the ski and snow. The OAV Dovetail Linear Air Bearing reduced resistance from the carriage and guidance system, allowing the measured forces to more closely represent the ski-snow interaction. Combined with controlled speed and adjustable vertical loading, the system allowed the researchers to evaluate ski-snow friction under repeatable test conditions.
Fig 2. Collected data (a) carriage speed, (b) horizontal force, (c) vertical force. The highlighted area is the measurement area.
Fig 1. Schematic of the friction track with the carriage optimized for cross-country skis. Insert a) shows the ‘frictionless’ sliding OAV Dovetail Linear Air Bearing and the position of the load cells while insert b) shows the detailed components of the carriage.
CASESTUDY
The OAV Dovetail Linear Air Bearing allowed for the ski-snow friction to be measured with incredibly accurate precision. The sliding mechanism of the air bearing allowed the ski to glide without any friction, providing greater control for precise measurements, which is critical for developing and testing new ski wax and base materials that align with the international ban of fluorine-containing waxes and ski bases.
The system measured ski-snow friction using the horizontal force recorded during each run, while two vertical load cells measured the applied normal force. These measurements were used to calculate the coefficient of friction and evaluate the repeatability of the tribometer across consecutive runs, parallel tracks, and different testbeds.
The researchers evaluated the precision of the tribometer at multiple levels, including repeatability across consecutive runs on a single track, and measurements across different testbeds. This allowed them to assess both the repeatability of individual measurements and the overall consistency of the system under varying test conditions.
To further evaluate the system at low friction levels, the researchers tested a classic roller ski. Across 50 consecutive runs at 6 m/s, the measurements produced a standard deviation of 0.000227, corresponding to a reported precision of 0.96%. The results demonstrated that the tribometer could maintain high measurement precision even at friction levels comparable to racing cross-country skis.
Achieved 0.96% precision across 50 consecutive test runs at 6 m/s
Enabled precise friction measurement at levels comparable to racing cross-country skis
Provided repeatable testing of full-size skis on laboratory-grown snow
Minimized measurement interference with frictionless linear motion
The study demonstrates how low-friction linear motion can support precise and repeatable ski-snow friction measurements under controlled laboratory conditions. By minimizing mechanical resistance within the test system, the OAV Dovetail Linear Air Bearing helped researchers evaluate ski performance at friction levels representative of racing cross-country skis.
CASESTUDY
Uitzonderlijke prestaties worden gesmeed vanuit de zeer fundamentele wortels van een doel. Voortdurende verbetering van die wortels zal de weg vrijmaken voor enorme prestaties en vorderingen. Bij OAV Air Bearings benadrukken we dat een sterke basis de essentie is van groei. De wrijvingsloze en nauwkeurige mogelijkheden van OAV Air Bearings zorgen voor de groei van ongelooflijk unieke en monumentale inspanningen. Hemelse activiteiten zijn zo'n voorbeeld.
Satellietcommunicatie en aardobservatie hebben op tal van manieren invloed op het leven. Van communicatie tot onderzoek en data, satellieten zijn een cruciaal onderdeel van wat we vandaag weten en gebruiken. Door het gebruik van cubesats is Open Cosmos gespecialiseerd in kritische satellietcommunicatie en -observatie. Cubesats zijn miniatuursatellieten, gebaseerd op een grootteconfiguratie tussen 10 cm en 30 cm, in de vorm van een vierkant die door de inzet in een baan om de aarde worden gelanceerd. Deze nanosatellieten zijn verantwoordelijk voor het verzamelen van een breed scala aan gegevens, van wereldwijde rampen tot wetenschappelijke onderzoeken, tot energie en hulpbronnen, tot communicatie en logistiek.
Het montage- en testteam van Open Cosmos produceert en test deze apparaten om aan hun doelstellingen te voldoen. Door het gebruik van de nieuwe OAV Roller Air Bearing is het team in staat om met succes satellieten in een baan om de aarde te simuleren en het standcontrolesysteem te testen. Het luchtlager wordt op een standaard geplaatst en het ruimtevaartuig op het luchtlager. Door wrijvingsloze beweging rond één as te bieden, stelt het luchtlager het team in staat om het houdingscontrolesysteem de ene as na de andere te testen. Vanuit de aarde is Open Cosmos in staat om met de OAV Air Bearing een vrijwel wrijvingsloze en microzwaartekrachtomgeving te creëren voor hemelonderzoek.
Voorafgaand aan het gebruik van OAV Air Bearing-producten verzamelde het team deze gegevens door middel van simulatieberekeningen en analyses. Een primaire uitdaging in deze periode was de onzekerheid over hoe nauwkeurig de simulaties en berekeningen werkelijk waren. Door het gebruik van het luchtlager kan het team dergelijke scenario's nu fysiek simuleren om hun berekeningen te bevestigen voor het genereren van volledige nauwkeurigheid.
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Afbeelding* Open Cosmos SatCubes Space Infrastructure
Dit materiaal is gebaseerd op werk ondersteund door Open Cosmos LTD. www.open-cosmos.com