Setting a maximum XZ plane velocity of a rigid body

Hey all.

I'm learning how to make a FPS controller. However, I was never able to force the player to a top speed in Unity 5. Let's attach this script to a 3D capsule and call it our player. I have also attached a zero friction Physic Material to our player so he never slows down by friction. We want to limit the player's top speed on the XZ axis to 1 while the ASDW keys are being pressed. The following code should cap the speed exactly to 1 (walkSpeed) but it doesn't. The speed exceeds 1 (actually goes up to 6.6 on my computer until it stops increasing) while I keep pressing ASDW. If I stop pressing ASDW the player it slows down to 1, the desired top speed, and stays there until I press ASDW again.

Why does the speed exceed the walkSpeed limit while pressing ASDW? The if (xzVelocity.sqrMagnitude > walkSpeed*walkSpeed) should never let it exceed WalkSpeed which equals 1.

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class PlayerMovementScript : MonoBehaviour {
5.  
6.     public float walkAccel = 10000f;
7.     public float walkSpeed = 1f;
8.  
9.     Rigidbody playerBody;
10.  
11.     void Start () {
12.         playerBody = GetComponent<Rigidbody> ();
13.     }
14.  
15.     void Update() {
16.         playerBody.AddRelativeForce (Vector3.forward * Input.GetAxis ("Vertical")
17.                                      * walkAccel * Time.deltaTime);
18.         playerBody.AddRelativeForce (Vector3.right * Input.GetAxis ("Horizontal")
19.                                     * walkAccel * Time.deltaTime);
20.  
21.         Vector2 xzVelocity = new Vector2 (playerBody.velocity.x, playerBody.velocity.z);
22.  
23.         if (xzVelocity.sqrMagnitude > walkSpeed*walkSpeed) {
24.             float yVelocity = playerBody.velocity.y;
25.             xzVelocity = xzVelocity.normalized*walkSpeed;
26.             playerBody.velocity = new Vector3(xzVelocity.x, yVelocity, xzVelocity.y);
27.         }
28.     }
29. }

 

First, put your code in FixedUpdate. Any physics stuff goes there.

Would this work?

Code (CSharp):

1.     void FixedUpdate()
2.     {
3.         Vector3 targetVelocity = new Vector3(Input.GetAxis("Horizontal"), 0f, Input.GetAxis("Vertical")).normalized * walkSpeed;
4.         Vector3 clampedVelocity = Vector3.ClampMagnitude(targetVelocity - transform.InverseTransformDirection(playerBody.velocity, maxWalkSpeed));
5.         clampedVelocity.y = 0f;
6.         playerBody.AddRelativeForce(clampedVelocity);
7.     }
8.  

set walkSpeed to something like 50, and max walk speed to something like 2.
The reason walkSpeed is higher than walk speed, is because we are using the default addforce, which uses ForceMode.Force, which is similar to multiplying the value by Time.deltaTime (or Time.fixedDeltaTime). If we used ForceMode.VelocityChange, then the walkSpeed would be something like .05f

 

Your code works great. The only problem is I'd like the player to accelerate and deaccelerate much faster than it does with this code (while keeping the same top speed) . How would I do that?

 

I used Forcemode.VelocityChange and got this to work as i wanted. Thanks a lot