public unsafe static void SetMotorTarget(this HingeConstraint obj, ref OpenTK.Quaternion qAinB, float dt)
 {
     fixed(OpenTK.Quaternion *qAinBPtr = &qAinB)
     {
         obj.SetMotorTarget(ref *(BulletSharp.Math.Quaternion *)qAinBPtr, dt);
     }
 }