Question about WheelCollilder - vehicle not going straight

New Unity user here, playing around with Wheel Colliders.

I've made a simple "vehicle" consisting of a resized "Cube" GameObject with 4 empty child objects with WheelCollider components attached, one in each corner of the vehicle. The vehicle is situated on a plane:



I've the made a small script that sets the motorTorque on the two rear wheels, and the vehicle moves forward, as expected. However, it doesn't move in a straight line, but turns slightly to the left. Everything is set up symmetrically on the vehicle, and the plane is level. Shouldn't the vehicle then run in a straight line?

My controller script (C#):

Code (csharp):

1.  
2. using UnityEngine;
3.  
4. public class BasicCarController : MonoBehaviour
5. {
6.  
7.     // Private member variables
8.     private WheelCollider[] wheelColliders;
9.    
10.    
11.     void Start()
12.     {
13.         wheelColliders = new WheelCollider[4];
14.         wheelColliders[0] = gameObject.transform.Find("Wheels/FrontLeft").GetComponent<WheelCollider>();
15.         wheelColliders[1] = gameObject.transform.Find("Wheels/FrontRight").GetComponent<WheelCollider>();
16.         wheelColliders[2] = gameObject.transform.Find("Wheels/RearLeft").GetComponent<WheelCollider>();
17.         wheelColliders[3] = gameObject.transform.Find("Wheels/RearRight").GetComponent<WheelCollider>();
18.     }
19.    
20.     void FixedUpdate()
21.     {
22.         wheelColliders[2].motorTorque = 15;
23.         wheelColliders[3].motorTorque = 15;
24.     }
25. }
26.  

The Project can be downloaded from
http://debian1.vegardw.com/WheelColliderTest/WheelColliderTest.zip

Webplayer showing the vehicle turning at
http://debian1.vegardw.com/WheelColliderTest/WebPlayer/WebPlayer.html

 

A small update, if anyone else is having the same problem

Using these friction settings for the wheel colliders:

Extremum Slip = 0.01
Extremum Value = 1.0
Asymptote Slip = 0.04
Asymptote Value = 0.6
Stiffness Factor = 50000​

from this forum thread: http://forum.unity3d.com/threads/24872-Wheel-Friction-Curve-and-PhysX-a-discussion-about-settings.

seems to fix the problem, the vehicle is going straight with those settings.

 

The reason for the drifting seems to be some kind of bug related to fixed timestep. The drifting can be removed by reducing the timestep, see animated gif below for a before and after.

 

Yes, it fixed thank you but I wonder that would this adjustment ruin any other settings? Did you check it?

 

Hello everyone! I have the same problem in my game! I tried to do like this but I couldn't fix the problem! My vehicle not going straight! How can I fix that! You can also watch at this video!
First video >>>

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Second video >>>

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How can I fix that problem! Your posts didn't helped me to fix that problem!