Help Filo - Calculating weight on cable point

[MarcPilgaard]

Hi,

If you're interested only in the vertical component, you need to:

- Multiply the impulse direction (accesible as cablejoint.Jacobian) by the impulse magnitude.
- Project it onto the gravity vector (a simple dot product).
- Use the magnitude of the projection as your new impulse magnitude.

If you're after the full force regardless of directionality, you need to:

- Project the gravity vector onto the jacobian (again a dot product, since the jacobian has unit length)
- Use the length of the projected gravity vector as your new acceleration.

I have tried implementing the measurement of the full force, I do get some numbers but I am unsure if these are calculated correctly.

The weights I calculate are:
- All weights are negative
- When I move my crane around, slowly, the weight fluctuates alot, much more than I would have expected, sometimes the calculated weights briefly becomes 0.0. But the element we are moving is being moved very slowly, so I doubt it is because the cables starts to slack.
- The summed weight for all four cables are close to the mass of the rigid body they are suspending. Mass of rigidbody 30.000 ~ Total weight across four cables 30.800.

Current implementation:

Code:

   private void FixedUpdate()
   {
       //Last joint where the weight is attached
       CableJoint joint = cable.Joints[cable.JointCount - 1];

       //The gravitional acceleration vector
       Vector3 grav = new Vector3(0, -9.82f, 0);

       //Projecting the gravitational vector onto the Jacobian vector
       float dot = Vector3.Dot(grav, joint.Jacobian);

       //The projected gravity vector
       Vector3 gravProj = joint.Jacobian * dot;

       // Calculate force by diving Impulse with Time
       float force = joint.ImpulseMagnitude / Time.fixedDeltaTime;

       //Calculate the weight by dividing the force with the magnitude of the projected gravity vector
       weight = ((force / gravProj.magnitude));
   }