I'm not sure how to stop it from accelerating forever.
[SerializeField] float moveSpeed;
[SerializeField] float turnSpeed;
[SerializeField] float maxForwardVelocity;
private Rigidbody rigidbody;
private void Start()
{
rigidbody = GetComponent<Rigidbody>();
}
private void Update()
{
if(Input.GetAxis("Vertical") != 0)
{
float rotateInput = Input.GetAxis("Horizontal") * turnSpeed * Time.deltaTime;
transform.eulerAngles += new Vector3(0f, rotateInput, 0f);
}
float forwardInput = Input.GetAxis("Vertical") * moveSpeed * Time.deltaTime;
rigidbody.AddRelativeForce(new Vector3(forwardInput, 0f, 0f));
}
First, you should do physics calculations in FixedUpdate.
Second, using some vector math you can calculate the acceleration to apply. Explanation in comments:
float rotateInput;
float forwardInput;
private void Update()
{
rotateInput = 0f;
if(Input.GetAxis("Vertical") != 0)
{
rotateInput = Input.GetAxis("Horizontal") * turnSpeed;
}
forwardInput = Input.GetAxis("Vertical") * moveSpeed;
}
void FixedUpdate()
{
transform.eulerAngles += new Vector3(0f, rotateInput * Time.deltaTime, 0f);
// How much the current frame wants to change velocity in the forward direction
float uncappedForwardDS = forwardInput
* Time.deltaTime * Time.deltaTime / rigidbody.mass;
// How fast are we going in the forward direction
float curForwardSpeed = Vector3.Dot(transform.forward, rigidbody.velocity);
// prevent braking effect when going forward (don't "accelerate" less than 0)
float availableForwardDS = Mathf.Max(0f, maxForwardVelocity - curForwardSpeed);
// Cap the relative delta speed
float cappedRelDS = Mathf.Min(uncappedForwardDS, availableForwardDS);
// Mass and deltaTime of frame already accounted for, so apply with VelocityChange
rigidbody.AddRelativeForce(new Vector3(cappedRelDS, 0f, 0f),
ForceMode.VelocityChange);
}