Search Unity

  1. Unity 2019.1 beta is now available.
    Dismiss Notice
  2. The Unity Pro & Visual Studio Professional Bundle gives you the tools you need to develop faster & collaborate more efficiently. Learn more.
    Dismiss Notice
  3. We're looking for insight from anyone who has experience with game testing to help us better Unity. Take our survey here. If chosen to participate you'll be entered into a sweepstake to win an Amazon gift card.
    Dismiss Notice
  4. On February 28th the Feedback website will shut down and be redirected to the Unity forums. See the full post for more information.
    Dismiss Notice
  5. Want to provide direct feedback to the Unity team? Join the Unity Advisory Panel.
    Dismiss Notice
  6. Unity 2018.3 is now released.
    Dismiss Notice
  7. Improve your Unity skills with a certified instructor in a private, interactive classroom. Watch the overview now.
    Dismiss Notice

Simple pendulum movement

Discussion in 'Scripting' started by mrCharli3, Dec 8, 2018.

  1. mrCharli3

    mrCharli3

    Joined:
    Mar 22, 2017
    Posts:
    327
    I have a ball at the end of a string, the string is attached to a cube with the following script on it. The ball moves back and forth kind of like a pendulum, but with a constant speed. How can I make it so the speed is more like a pendulum? i.e slow down before changing direction.

    Here is the relevant logik I use, only for the x-axis to keep it short:

    Code (CSharp):
    1.  
    2. void Start()
    3.     {
    4.         _rotateUntil = transform.rotation.eulerAngles * -1; //sets the point of changing direction, i.e if I start at 30 degress, I change dir at -30 degrees.
    5.     }
    6.  
    7. void FixedUpdate()
    8.     {
    9.         transform.Rotate(_dir * Time.deltaTime * _currentSpeed);
    10.         Swing();
    11.     }
    12.  
    13. private void Swing()
    14.     {
    15.         float angle = 0;
    16.         float target = 0;
    17.         angle = (transform.rotation.eulerAngles.x > 180) ? transform.rotation.eulerAngles.x - 360 : transform.rotation.eulerAngles.x;
    18.          target = _rotateUntil.x;
    19.          if (angle <= target)
    20.               ChangeDir();
    21. }
     
  2. Kurt-Dekker

    Kurt-Dekker

    Joined:
    Mar 16, 2013
    Posts:
    3,146
    What you want is simple harmonic motion:

    https://en.wikipedia.org/wiki/Simple_harmonic_motion

    You can trivially get close to this in Unity by simply using the Mathf.Sin() of a steadily advancing variables, rather than pingponging linearly between to limits.

    I would just put a local pivot into the gameObject hierarchy and drive that directly.

    If you wanted that pivot to swing along the +Z axis, this would be the code:

    Code (csharp):
    1. float MaxAngleDeflection = 30.0f;
    2. float SpeedOfPendulum = 1.0f;
    3.  
    4. float angle = MaxAngleDeflection * Mathf.Sin( Time.time * SpeedOfPendulum);
    5. myPivotTransform.localRotation = Quaternion.Euler( 0, 0, angle);
    Speed of 1.0 implies a period of 2 * pi. Speed of Mathf.PI * 2 would be a period of one second.
     
    mrCharli3 likes this.
  3. mrCharli3

    mrCharli3

    Joined:
    Mar 22, 2017
    Posts:
    327
    I knew there had to be some way that didnt involve over 100 lines of code. This is exactly what I was looking for. You are the best!
     
    Kurt-Dekker likes this.