Question by Pzula · Jul 12, 2016 at 05:49 AM · rotation physics alignment angularvelocity

Rotate Rigidbody to Rotation Via AngularVelocity

Hello all,

I'm looking to get a rigidbody object to align its rotation with another object by moving the rigidbody via angular velocity/forces. The rigidbody is not effected by gravity and is motionless in space.

Here's a breakdown of what I'm trying to achieve:

Object A has a rigidbody
Object B is a gameobject with a rotation
Object A (Rigidbody) should add/set its angular velocity so its rotation matches Object B.

The rotation can be gradual.

The rotation is not limited to any axis; the object can rotate freely.

I'm really not great at rotations/quaternions and this is giving me a lot of problems.

Any help is much appreciated.

Thank you!

Add comment · Show 3

_Yash_ · Jul 12, 2016 at 08:44 AM 0

try this code:

  float dir = Vector3.Cross(A.transform.forward, B.transform.forward).y;
  A.GetComponent<Rigidbody>().angularVelocity = new Vector3(0f, Vector3.Dot(A.transform.forward, B.transform.forward)*dir, 0f) * lerpSpeed;

adjust lerpSpeed to change how quickly it matches the rotaion of B.

Pzula _Yash_ · Jul 12, 2016 at 12:32 PM 0

Hey, thanks for your response.

I gave your code a try and it works great, but it only rotates around the y axis. I tried implementing rotation for the other axes and while it worked at first, it becomes inaccurate at more extreme rotations.

_Yash_ Pzula · Jul 13, 2016 at 05:03 AM 0

Okey, you are right,
other solution i can think of is this,

 void FixedUpdate(){
     // if this doesn't work try "B.transform.eulerAngles - A.transform.eulerAngles" below
     Vector3 difference = A.transform.eulerAngles - B.transform.eulerAngles;
     Vector3 velocity = difference / Time.fixedDeltaTime;
     A.rigidbody.angularVelocity = velocity;
 
 }