How to set the distance my character can dash?

I'm trying to give my character the mechanic of dashing but I want to set the distance it can dash. Right now it works fine but I want it to feel nicer. It freezes the y position while dashing, and it removes collisions so you can dash through walls/avoid incoming damage. The only problem is that it dashes depending on speed, which means if I make the speed higher, the character dashes further away.

How should I go about restricting the length of the dash so that if I increase the dash speed it just goes faster within that distance, rather than further?

Here is my code:

public Rigidbody2D rb;
private BoxCollider2D coll;

//Dashing variables
[SerializeField] private float dashDuration = 0.5f;
[SerializeField] private float dashSpeed = 15.0f;

public void Dash()
{
    StartCoroutine(DashRoutine());
}

IEnumerator DashRoutine()
{
    movementAllowed = false;
    coll.isTrigger = true;

    rb.constraints = RigidbodyConstraints2D.FreezePositionY; //Freeze y position while dashing

    if(rb.velocity.x < 0)
    {
        rb.velocity = new Vector2(-dashSpeed, transform.position.y);
    }
    else
    {
        rb.velocity = new Vector2(dashSpeed, transform.position.y);
    }

    Debug.Log("Im dashing!");

    yield return new WaitForSeconds(dashDuration);
    rb.constraints = RigidbodyConstraints2D.None;
    coll.isTrigger = false;
    movementAllowed = true;
}

Speed, Distance, Time formulae:

S = D / T
D = S * T
T = D / S

In Context:

dashSpeed = dashDistance / dashDuration
dashDistance = dashSpeed * dashDuration
dashDuration = dashDistance / dashSpeed

To keep the distance of the dash the same while increasing speed, you need to decrease the dash time. You can determine the dash time by solving the formula for time T=D/S

eg. dashDuration = dashDistance / dashSpeed

Alternatively to this great answer:

Well instead of waiting a fixed dashDuration you can rather go by the distance traveled (or combine both and stop dashing on whichever finishes first)

...

[SerializeField]
private float maxDashDistance;

...

private IEnumerator DashRoutine()
{
    ...

    Debug.Log("Im dashing!");

    var startPosition = rb.position;
    // it is slightly cheaper to compare square magnitude
    var sqrMaxDistance = maxDashDistance * maxDashDistance;
    
    // iterates until either the dashDuration or the maxDashDistance is exceeded
    for (var timePassed = 0f; 
         timePassed < dashDuration && (rb.position - startPosition).sqrMagnitude < sqrMaxDistance; 
         timePassed += Time.deltaTime)
    {
        yield return null;
    }

    rb.constraints = RigidbodyConstraints2D.None;
    coll.isTrigger = false;

    // assuming this ensures you stop moving with the dashSpeed
    movementAllowed = true;
}

or if the for loop condition looks too ugly to you you can also drag it in like

for (var timePassed = 0f; timePassed < dashDuration; timePassed += Time.deltaTime)
{
    if((rb.position - startPosition).sqrMagnitude >= sqrMaxDistance) break;

    yield return null;
}

Hopefully I can help out The issue is that you're simply setting the velocity of the rigidBody; Thus, if the velocity is greater, the object will travel further. A better approach would be to somehow smoothly move from the current position to a desired distance; In other words, we could linearly interpolate, or lerp. You can read the documentation. You can use the rigidbody's position for the start position, and then get the end position by adding the current position with some vector (distance).