Unexpected behaviour of rb.velocity on a Cubes Movement.

I'll get right to the problem, I am moving a Cube on a platform which is made of small cube using queue to make a procedural infinity moving platform and i am using rb.velocity to move a player (also a cube) over these cubes/platform but the cube sometime start rotating, i want it slide smoothly and not rotate, i applied a physics material on both player and platform cube for zero friction but it didn't work.

Video Demo

Pictures:
https://drive.google.com/open?id=1QC7dLNpWF8oJ-MyUCVKy_LQLbnCGzX_e
https://drive.google.com/open?id=1UCmry-W6LuApVNUitu0qEj7OAl9RebJY
https://drive.google.com/open?id=1t1ZbUExrbRkRnFUNgJ-8Y01V96uddMtB
https://drive.google.com/open?id=1rl0nA2ckoT6YR3lBJF20_xhDACfaSUmg

PlayerMovement Script:

Code (CSharp):

1. void FixedUpdate()
2.     {
3.         //Movement
4.         rb.velocity = new Vector3(forceSpeed, rb.velocity.y, 0);
5.      
6.         //CheckifGrounded
7.         CheckIfGrounded();
8.  
9.         //Jump;
10.         if (Grounded && jump)
11.         {
12.             rb.velocity = new Vector3(rb.velocity.x, jumpForce, rb.velocity.z);
13.             Grounded = false;
14.         }
15.      
16.     }
17.     void Update()
18.     {
19.         //DistanceTravelled
20.         distanceTravelled = transform.localPosition.x;
21.  
22.         //TouchControls
23.         if (CrossPlatformInputManager.GetButtonDown("Jump"))
24.         {
25.             jump = true;
26.         }
27.         else
28.         {
29.             jump = false;
30.         }
31.  
32.         //Resize.Shrink
33.         if (CrossPlatformInputManager.GetButtonDown("Shrink"))
34.         {
35.             if (!shrink)
36.             {
37.                 shrink = true;
38.                 //transform.localScale = Vector3.one * 0.5f;
39.                 Invoke("Reverse", timer);
40.             }
41.         }
42.         anim.SetBool("Shrink", shrink);
43.  
44.         //Velocity Check
45.         speed = rb.velocity.magnitude;
46.  
47.         if (speed <= 0.1f)
48.         {
49.             FindObjectOfType<Game>().EndGame();
50.          
51.         }
52.  
53.         //LightMode
54.         if(distanceTravelled > 100)
55.         {
56.             light.enabled = false;
57.             n++;
58.         }
59.  
60.     }
61.  
62. void CheckIfGrounded()
63.     {
64.         rayDown = new Ray(new Vector3(transform.position.x, transform.position.y - transform.localScale.y / 2 + 0.1f, transform.position.z), Vector3.down);
65.  
66.         RaycastHit hit;
67.  
68.         //Bottom
69.         if(Physics.Raycast(rayDown, out hit))
70.         {
71.             Vector3 distance = rayDown.origin - hit.point;
72.             if(distance.y <= rayLength)
73.             {
74.                 Debug.DrawLine(rayDown.origin, hit.point,Color.red);
75.                 Grounded = true;
76.             }
77.             else
78.             {
79.                 Debug.DrawLine(rayDown.origin, hit.point,Color.blue);
80.                 Grounded = false;
81.             }
82.         }
83.      
84.     }

PlatfromSpawning Script:

Code (CSharp):

1. void Start () {
2.         platformQ = new Queue<GameObject>();
3.         for(int i=0;i<numberofObjects;i++)
4.         {
5.             platformQ.Enqueue(Instantiate<GameObject>(prefab));
6.         }
7.         nextPosition = startPosition;
8.         for(int i=0;i<numberofObjects;i++)
9.         {
10.             Recycle();
11.         }
12.     }
13.  
14.  
15.     void Update () {
16.         if(PlayerMovement.distanceTravelled > platformQ.Peek().transform.position.x + recycleOffset)
17.         {
18.             Recycle();
19.         }
20.  
21.         if (PlayerMovement.distanceTravelled > 150)
22.         {
23.             minGap.x = 4;
24.             maxGap.x = 10;
25.         }
26.  
27.         if (PlayerMovement.distanceTravelled > 250)
28.         {
29.             maxGap.x = 6;
30.         }
31.         if (PlayerMovement.distanceTravelled > 300)
32.         {
33.             maxGap.x = 5;
34.             minGap.x = 2;
35.         }
36.     }
37.  
38.     void Recycle()
39.     {
40.         Vector3 scale = new Vector3(Random.Range(minSize.x, maxSize.x), Random.Range(minSize.y, maxSize.y), Random.Range(minSize.z, maxSize.z));
41.  
42.         Vector3 position = nextPosition;
43.         position.x += scale.x * 0.5f;
44.         position.x += scale.x * 0.5f;
45.  
46.         GameObject o = platformQ.Dequeue();
47.         o.transform.localPosition = nextPosition;    
48.         platformQ.Enqueue(o);
49.  
50.         nextPosition.x += Random.Range(minGap.x, maxGap.x);
51.         nextPosition.y = Random.Range(minGap.y, maxGap.y);
52.  
53.     }
54. }

 

https://docs.unity3d.com/Manual/class-Rigidbody.html

All you need to do is freeze the rotation of the cube.