Bizarre local spinning behaviour between certain world space angles

Questions & Answers
1

This problem is easily replicated in a 2D scene (camera facing down the Z axis) with a single 3D object, such as a cube. The object must have a rigidbody, and the following script:

using UnityEngine;

public class CubeMovement : MonoBehaviour
{	
	private Rigidbody body;
	
	private float currentTurningRate = 0;
	private float targetTilt;

	void Start()
	{		
		body = GetComponent<Rigidbody>();
	}

	void Update()
	{
		currentTurningRate = Input.GetAxis("Turn");
		body.transform.Rotate(Vector3.forward * -currentTurningRate, Space.World);

		targetTilt = body.transform.localRotation.eulerAngles.y - currentTurningRate * 10;
		body.transform.Rotate(Vector3.up * targetTilt, Space.Self);
	}
}

When the user presses left or right, the object should spin around the Z axis relative to the global space, and tilt slightly along the Y axis relative to its own space.

So what’s happening is that when the cube is rotated along the Z axis (Vector3.forward) between certain angles spanning about 180°, the next Rotate command causes it to spin like crazy around the Y axis (Vector3.up). When rotation leaves that range, the object responds as expected, where it looks like it tilts a little as it turns.

As you can see, I’ve pared the code right back and I’m still having the problem so I’m putting it down to me not quite getting how Rotate affects euler angles. Any ideas? Cheers!

3

Directly manipulating Euler angles by adding to them each frame doesn’t work. There is a degenerate point at where the Euler angles become meaningless. It’s typically pointing straight up. That’s why you have weird behaviour.

You can demonstrate this in the editor by watching the Euler angle values as you rotate an object. They don’t change smoothly. Hence you aren’t getting smooth rotation.

2

v3.forward will always spin the object along ITS axis. So when you spin along z then along y it will be checking z to assign y

Let me know if that’s what you need.