Inertia problems

[Stucuk]

Julio, can you post link on fullsize logo of Newton? We want to place it in the bootscreen of our project

- Click Here

[Julio Jerez]

Ok there are few things wrongs, the first I found is in the function that create the body for the ship, the mass is 100, but the inertia is 1,
and the make the body acts like a little black hole, meaning the mass distribution is concentrated at the origin.
Went that happens the auto sleep code is dominated by the linear momentum since there is very lithe change in angular momentum in the motion. Therefore when the linear momentum falls below the threshold the body stops moving.

This is a case when the laws of physics act very strange when the input data is different that the common sense is familiar to.
The reason the body spins a little is because you are setting the angular velocity directly but the body should be even more unrealistic than what you see with that data.

if you set the inertia according to the Mass distribution, it do not even have to be exact just close enough, the it will be fine.

Plus if you do no want the auto slepp code to kick in , the you need to set the autosleep on the body to zero. But for that you need to expose those functions of newton in your wrapper.

Do that and I believe you will be fine.

Bellow is teh funtion tah I beleiev need to be modified to do whe I say.

Code: Select all

        public static int AddBodyConvHull(int physic_World , TVMesh Mesh, double mass, double lin_damp, Vector3 ang_damp)
        {
            int count = Mesh.GetVertexCount();
            double[] points = new double[count * 3];
            int number;

            for (number = 0; number < count; number++)
            {
                float X=0, Y=0, Z=0, temp=0;
                int temp2 = 0;
                Mesh.GetVertex(number, ref X, ref Y, ref Z, ref temp, ref temp, ref temp, ref temp, ref temp, ref temp, ref temp, ref temp2);
                points[number * 3] = X;
                points[number * 3 + 1] = Y;
                points[number * 3 + 2] = Z;
            }
            Matrix mat = new Matrix();
            mat = MatrixTV2Matrix(Mesh.GetMatrix());

            Matrix mat2 = new Matrix();
            mat2.M11 = 1;
            mat2.M12 = 0;
            mat2.M13 = 0;
            mat2.M14 = 0;

            mat2.M21 = 0;
            mat2.M22 = 1;
            mat2.M23 = 0;
            mat2.M24 = 0;

            mat2.M31 = 0;
            mat2.M32 = 0;
            mat2.M33 = 1;
            mat2.M34 = 0;

            mat2.M41 = 0;
            mat2.M42 = 0;
            mat2.M43 = 0;
            mat2.M44 = 1;

            int shapeID = 0;
            int colis = NewtonWrapper.CreateConvexHull(physic_World, count, points, 24, 0.1f, shapeID, ref mat2);
           
            int body = NewtonWrapper.CreateBody(physic_World, colis);


            NewtonWrapper.BodySetMatrix(body, ref mat);
            NewtonWrapper.ReleaseCollision(physic_World, colis);

            NewtonWrapper.BodySetLinearDamping(body, lin_damp);
            Vector3 AngDamp = new Vector3(0.1, 0.1, 0.1);

            NewtonWrapper.BodySetAngularDamping(body, ref ang_damp);

            // I do no find the function to set auto sleep off yo unee to implmenet function
            void NewtonBodySetAutoSleep (const NewtonBody* body, int state);

            // you need to set the inertia matrix by using funxtion,
            // NewtonConvexCollisionCalculateInertialMatrix (const NewtonCollision* convexCollision, dFloat* inertia, dFloat* origin);   

            // setting the inertia to 1.0 causes the body to move in a very unrealistic way,
            // and because auto step was on then the auto frezze code kicks in and the bodis stop when eth lina moment reach zero, sicne the angual momentum is very, very small.
            NewtonWrapper.BodySetMassMatrix(body, mass, 1, 1, 1);

            NewtonWrapper.BodySetMaterialGroupID(body, 1);

            return body;

        }

[Aldeminor]

Thank you very much, Julio! You saved loads of nerves and time for us!
It's realy great!

[martinw]

I might be wrong but is the Newton dll not contained within the TV3D dll? I'm using TV3D6.5 without a Newton dll I think.

The reaosn I ask is we might be stuck with an old version of the Newton dll until the TV3D6.5 dll is updated?

Just a thought ..............

[Julio Jerez]

I do not know how they got the wraper but Aldeminor Team is using the latest version of newton in double presistion,

[martinw]

It looks pretty impressive