Ball Addforce Acceleration Speed

Questions & Answers
1

Hello,
I am not too good with scripting in Unity and I have come across a few problems. I have tried for weeks to get it working but with no success.

Basically, I am trying to make a game where the player has to navigate a level using a wooden ball. They use the arrow keys to controll the rolling of the ball.

I have made a script using AddForce with Rigidbodies on my ball object but the ball rolls incredibly slow and takes ages to change direction.

I want to be able to have a fast acceleration and be able to change directions fast but still have a relatively low top speed.

Here is my script so far:

function FixedUpdate () {

	if (Input.GetKey ("up")) 
		{
			rigidbody.AddForce (Vector3.forward * Time.deltaTime * 5, ForceMode.Acceleration);
		}
	
	
	if (Input.GetKey ("down")) 
		{
			rigidbody.AddForce (Vector3.forward * Time.deltaTime * 5, ForceMode.Acceleration);
		}
	
	
	if (Input.GetKey ("left")) 
		{
			rigidbody.AddForce (Vector3.left * Time.deltaTime * 5, ForceMode.Acceleration);
		}
		
		
if (Input.GetKey ("right")) 
	{
		rigidbody.AddForce (Vector3.right * Time.deltaTime * 5, ForceMode.Acceleration);
	}

I really need help with getting this script to work how I have described. Any help would be greatly appreciated.

2

You're on the right track, except for some specifics-

  1. If you use ForceMode.Acceleration, there will be virtually no top speed. It's basically emulating gravity!
  2. There isn't really an inbuilt way to give a rigidbody a 'top speed' as such- you can, however, give it relatively high drag and low mass, and it will stop moving soon after you stop putting a force on it.
  3. Is there any reason why you need to be using discrete inputs here? Why can't you use the Input.GetAxis("Horizontal/Vertical")? If you do something like that, you could fake out your drag to give a better response time, and still control the desired velocity.

This is how I would do it:

public float desiredSpeed;
public float maximumDrag;
public float forceConstant;
void Update()
{
    Vector3 forceDirection = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
    //This reduces drag when the player adds input, and makes it stop faster.
    rigidbody.drag = Mathf.Lerp(maximumDrag, 0, forceDirection.magnitude);
    // this reduces the amount of force that acts on the object if it is already
    // moving at speed.
    float forceMultiplier = Mathf.Clamp01((desiredSpeed - rigidbody.velocity.magnitude) / desiredSpeed);
    // now we actually perform the push
    Rigidbody.AddForce(forceDirection * (forceMultiplier * Time.deltaTime * forceConstant));

}