C:/Users/Andreas Schiffler/Desktop/SVN/NewGamePhysics/NewGamePhysics/Physics/FrictionModel.cs

// --------------------------------------------------------
// FrictionModel.cs
// (A. Schiffler, 2009)
// --------------------------------------------------------

namespace NewGamePhysics.Physics
{
    using System;
    using System.Collections.Generic;
    using System.Text;

    public enum RotationalFrictionType
    {
        None,

        Linear,

        Stribeck
    }

    public class RotationalFrictionModel
    {
        private RotationalFrictionType frictionType;

        private double linearFrictionCoefficient;

        private double stribeckStaticFriction;


        private double stribeckFrictionScale;

        public double LinearFrictionCoefficient
        {
            get { return linearFrictionCoefficient; }
        }

        public double StribeckStaticFriction
        {
            get { return stribeckStaticFriction; }
        }

        public double StribeckFrictionScale
        {
            get { return stribeckFrictionScale; }
        }

        public RotationalFrictionModel()
        {
            this.frictionType = RotationalFrictionType.None;
        }

        public RotationalFrictionModel(RotationalFrictionType f)
        {
            this.frictionType = f;
            switch (f)
            {
                case RotationalFrictionType.Linear:
                    this.linearFrictionCoefficient = 0.0005;
                    break;
                case RotationalFrictionType.Stribeck:
                    this.stribeckStaticFriction = 0.0001;
                    this.stribeckFrictionScale = 0.0002;
                    break;
            }
        }

        public void SetNone()
        {
            this.frictionType = RotationalFrictionType.None;
        }

        public void SetLinear(double linearFrictionCoefficient)
        {
            this.frictionType = RotationalFrictionType.Linear;
            this.linearFrictionCoefficient = linearFrictionCoefficient;
        }

        public void SetStribeck(double stribeckStaticFriction, double stribeckFrictionScale)
        {
            this.frictionType = RotationalFrictionType.Stribeck;
            this.stribeckStaticFriction = stribeckStaticFriction;
            this.stribeckFrictionScale = stribeckFrictionScale;
        }

        public double ApplyFriction(double omega)
        {
            // Friction difference
            double deltaOmega = 0.0;
            double o = Math.Abs(omega);

            // Adjust by type
            switch (this.frictionType)
            {
                case RotationalFrictionType.None:
                    // No friction
                    deltaOmega = 0.0;
                    break;
                case RotationalFrictionType.Linear:
                    // Linear friction  
                    deltaOmega = linearFrictionCoefficient * o;
                    break;
                case RotationalFrictionType.Stribeck:
                    // Stribeck friction
                    if (o < stribeckStaticFriction)
                    {
                        // Hinge stuck
                        return 0.0;
                    }
                    else
                    {
                        // Calculate friction as curve
                        deltaOmega = stribeckFrictionScale * (o - Math.Exp(-Math.Pow((o / 0.025), 0.3)) + Math.Pow(2.0 * o, (1 - 0.3)));
                    }
                    break;
            }

            // Handle discontinuity around zero
            if (omega > 0.0)
            {
                omega -= deltaOmega;
                if (omega < 0.0)
                {
                    omega = 0.0;
                }
            }
            else
            {
                omega += deltaOmega;
                if (omega > 0.0)
                {
                    omega = 0.0;
                }
            }

            return omega;
        }
    }
}

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