[SOLVED] Rigidbody physics addtorque to aim at target with lerp

Good day.

I'm struggling getting my spaceship to aim at a target without wildly over compensating when adding torque.

The ship ends up wiggling like a fish as it tries to maintain it's target, but is never able to directly aim at it's target.

Is there a way to smooth the torque so it does not wiggle? (Video

)

I'm using this function:


public Transform target;
public float force = 0.1f;

void LockOnTarget() // Face target direction
{
// find distance between object and target
Vector3 targetDelta = target.position - transform.position;

//get the angle between transform.up and target delta
float angleDiff = Vector3.Angle(transform.up, targetDelta);

// get its cross product, which is the axis of rotation to
// get from one vector to the other
Vector3 cross = Vector3.Cross(transform.up, targetDelta);

// apply torque along that axis according to the magnitude of the angle.
GetComponent<Rigidbody>().AddTorque(cross * angleDiff * force);

}

 

I've not tried experimenting with rigid body forces much in Unity, but I believe you may be better off looking at https://docs.unity3d.com/ScriptReference/Rigidbody.MoveRotation.html

I assume the oscillation you are seeing is simply an under-damped response to the inputs - if you imagine your ship in space, free from any external forces: As soon as you apply a torque to it there will be a corresponding angular acceleration, until an opposing torque is applied - angular velocity will change depending on the torque / time profile used. The chances of you applying an equal and opposite torque at the correct time is quite unlikely without some significant control logic.

I hope that helps, sorry I cannot add more. I did take a look at the ForceMode options in case there was some sort of cheat, but I don't think there is. Perhaps someone more knowledgeable has a simpler answer.

 

Control logic shouldn’t be so hard for this. Try to also add a force counteracting the angularVelocity:

rb.AddTorque(-rb.angularVelocity * factor)

The factor will need some fiddling and there is a spring/damper ratio that will not overshoot.. but that I‘d have to look up.

alternatively you can also just increase angular damping on the rigidbody in the inspector

 

Wow! I can't believe how simple that solution is. Thank you
@tjmaul !

 

For anyone that happens to stumble upon this thread Ive made a method that replicated this for 2D rigidbodies:

Code (CSharp):

1. /// <summary>
2.     /// Use AddTorque() to face a specific angle. For 2D physiscs. Should be used in every FixedUpdate() frame.
3.     /// </summary>
4.     /// <param name="currentVec"> vector representing the direction we are currently pointing at. (transform.right) </param>
5.     /// <param name="targetVec"> vector representing the direction we want to point at. </param>
6.     /// <param name="rb"> Rigidbody to affect. </param>
7.     /// <param name="maxTorque"> Max torque to apply. </param>
8.     /// <param name="torqueDampFactor"> Damping factor to avoid undershooting. </param>
9.     /// <param name="offsetForgive"> Stop applying force when the angles are within this threshold (default 0). </param>
10.     public static void TorqueTo(Vector3 currentVec, Vector3 targetVec, Rigidbody2D rb, float maxTorque, float torqueDampFactor, float offsetForgive = 0)
11.     {
12.         float targetAngle = FindAngle(targetVec);
13.         float currentAngle = FindAngle(currentVec);
14.         float angleDifference = AngleDifference(targetAngle, currentAngle);
15.         if (Mathf.Abs(angleDifference) < offsetForgive) return;
16.  
17.         float torqueToApply = maxTorque * angleDifference / 180f;
18.         torqueToApply -= rb.angularVelocity * torqueDampFactor;
19.         rb.AddTorque(torqueToApply, ForceMode2D.Force);
20.     }

This method does use other "helper" methods, to make my life easier in general. Here they are:

Code (CSharp):

1. public static float AngleDifference(float a, float b)
2.     {
3.         return ((((a - b) % 360f) + 540f) % 360f) - 180f;
4.     }

Code (CSharp):

1. /// <summary>
2.     /// Returns the angle (in degrees) in which the vector is pointing.
3.     /// </summary>
4.     /// <returns>0-360 angle </returns>
5.     public static float FindAngle(Vector2 vec)
6.     {
7.         return FindAngle(vec.x, vec.y);
8.     }
9.     public static float FindAngle(float x, float y)
10.     {
11.         float value = (float)((System.Math.Atan2(y, x) / System.Math.PI) * 180);
12.         if (value < 0) value += 360f;
13.         return value;
14.     }

 

your script didn't work for me but I managed to do:

Code (CSharp):

1.  private void Update_PhysicsModel()
2.     {
3.         for (int i = 0; i < Physics_Model.Length; i++)
4.         {
5.             float Difference = GetDiff(Target_Model[i].transform.eulerAngles.z, Physics_Model[i].transform.eulerAngles.z);
6.             float Distance = Mathf.Abs(Difference);
7.  
8.             TorqueLerp(Physics_Model[i], Difference, Distance);
9.         }
10.     }
11.  
12.     private static float GetDiff(float A, float B)
13.     {
14.         A = Mathf.Repeat(A + 180, 360) - 180;
15.         B = Mathf.Repeat(B + 180, 360) - 180;
16.         return (A - B);
17.     }
18.  
19.     private static void TorqueLerp(Rigidbody2D rb, float Diff, float Dist)
20.     {
21.         float Force = Diff * (Dist / 2);
22.         rb.angularVelocity = Force;
23.     }