Converting controller speed directly to arcade collision force values

SpeedToCollisionForce.cs

// Copyright 2018 Andrew Maneri 
//
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// Related to article: http://www.yarsoft.com/2018/05/13/when-vr-hands-hit-digital-objects-believable-physics-conversion/

using UnityEngine;

public static class ArcadeCombatUtils
{
    /// <summary>
    /// Simple scalar for m/s into Newtons.  This value will make the average adult hit with a force of around 4500 newtons
    /// </summary>
    const float k_SpeedToForce = 740.0f;

    /// <summary>
    /// How long a 'collision' in this case is imparting force onto a target object
    /// </summary>
    const float k_CollisionTimeStep = 0.125f;

    /// <summary>
    /// Converts an impact velocity into a force that can be directly applied to a rigidbody with believable results
    /// </summary>
    /// <param name="impactVelocity">How fast the object was moving before it collided with a target</param>
    /// <param name="targetMass">How much mass the target object contains (rigidbody.mass) </param>
    /// <returns>A force that can be fed directly into RigidBody.AddForceAtPosition</returns>
    static Vector3 SpeedToCollisionForce(Vector3 impactVelocity, float targetMass)
    {
        // For lighter objects will reach a speed where the impacting object is no longer colliding, we estimate that here
        var timeApplied = targetMass / (k_SpeedToForce * k_CollisionTimeStep);

        // We then adjust the total force imparted by this reduced time step
        var forceMultiplier = k_SpeedToForce * Mathf.Min(k_CollisionTimeStep, timeApplied);

        // The impacting object will be delivering less force at the end of the impact, so we also estimate the impact of that effect here
        // In the case where where the target object accelerates away, we average the starting and ending forces (full and zero) to get .5
        if (timeApplied < k_CollisionTimeStep)
        {
            forceMultiplier *= 0.5f;
        }
        else
        {
            forceMultiplier *= 1.0f - (k_CollisionTimeStep/(timeApplied*2.0f));
        }

        return impactVelocity * forceMultiplier;
    }
}