Rolling and Turning a Ball

Unity Engine
1

Hey Guys, looking for a little help with rotation here. I have a ball that I’m trying to roll along the ground. The left and right arrows turn the ball in the x-z plane, while the forward and backward arrows move it forward and backward. (This is all being done with physics and rigidbodies, rather than transforms.) My only problem is that I can’t use the default ‘forward’ vector of the transform since the ‘forward’ of a rolling ball is often pointed towards the ground or the sky, or any number of non-useful directions.

So what I’m trying to do is find the y angle rotation of the ball, then get a vector that is that rotation around the global ‘up,’ and use that as the new forward. It mostly works, except that somehow in my code there this weird course-correction thing happening. I’ll be rotating the ball and then hit forward and it will start for a second to roll in the correct forward direction for the ball, but then it will suddenly veer off to a slightly altered vector and I don’t know why. I was hoping someone could double-check my code and see if you can tell me what I’m doing wrong…

	void FixedUpdate () {

		//SPHERE MOVEMENT
		float hor = Input.GetAxis("Horizontal");
		float ver = Input.GetAxis("Vertical");
				
		//turning
		if (Mathf.Abs(hor) > deadZone) {
			rigidbody.AddTorque(Vector3.up * turnSpeed * Input.GetAxis("Horizontal"));	
		}

		//get the y rotation value 
		float yRot = transform.rotation.eulerAngles.y;
			
		//apply the y rotation to the global 'forward' vector3 to get the 
		//forward vector direction that our sphere is moving in
		Vector3 newForward = Quaternion.AngleAxis(yRot, Vector3.up) * Vector3.forward.normalized;		
		
		//forward
		if (Mathf.Abs(ver) > deadZone) {
			//move forward in that direction			
			rigidbody.AddTorque(newForward * forwardSpeed * Input.GetAxis("Vertical") * -1);	
		}
             }
1 Like
2

Allow me to rephrase, since I suspect I might be doing this completely wrong.

What I want is to get a 2D rotation around the Y axis that corresponds to how much the side arrows have been pressed. When I press ‘forward’ I would like for the ball to roll in the direction of that rotation. Is this the correct way of doing so?

3

If you want the ball only to roll and spin either left or right (2D). Then you could do something as simple as the code below.

#pragma strict
var speed = 10;

function Start () {

}

function Update () {

	if (Input.GetKey(KeyCode.RightArrow))
	{
	rigidbody.AddTorque(0,0,speed);
	}
	else if (Input.GetKey(KeyCode.LeftArrow))
	{
	rigidbody.AddTorque(0,0,-speed);
	}
}

This will spin the ball around the Z axis and also move the ball left and right to make it look like it’s rolling. Adjust speed to make it move and spin faster.

4

I think this is sort of what I’m already doing for left and right - but the problem is rolling forward. The ball starts to tilt to the side, so that its right-side directional vector is no longer parallel to the ground. Because of this, it begins to tilt and roll in odd directions. I need to get it to stop doing that.

5

Ball control is never really about ball position and rotation as it is about camera position and rotation.

Left is always Camera left.

This is a basic example, using a “cheater” object.

Transform cheat;

void Start(){
cheat = new GameObject().transform;
}

void FixedUpdate(){
float hor = Input.GetAxis("Horizontal");
float ver = Input.GetAxis("Vertical");

Vector3 dir = new Vector3(hor, 0, ver);
Vector3 rot = new Vector3(ver, 0, hor);


cheat.position = transform.position;
cheat.rotation = Camera.main.transform.rotation;
Vector3 lookAt = cheat.position + cheat.forward;
lookAt.y = transform.position.y;
cheat.transform.LookAt(lookAt);

rigidbody.AddTorque(cheat.TransformDirection(rot) * forwardSpeed * 0.5f);
rigidbody.AddForce(cheat.TransformDirection(dir) * forwardSpeed * 0.5f);
}