Question First Bullet Spawned is sometimes Faster then later bullets

I am following the AI tutorial and am on the acceleration chapter of the tanks, The first bullet spawned sometimes moves faster then the latter bullets. I have the following code for the shells

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Shell : MonoBehaviour
6. {
7.     public GameObject explosion;
8.  
9.     public float acceleration;
10.     public float gravity = -9.8f;
11.     public float zSpeed;
12.     public float mass = 100f;
13.     public float force = 1000f;
14.     public float gravityAcceleration;
15.     public float ySpeed;
16.  
17.     void OnCollisionEnter(Collision col)
18.     {
19.         if (col.gameObject.tag == "tank")
20.         {
21.             GameObject exp = Instantiate(explosion, this.transform.position, Quaternion.identity);
22.             Destroy(exp, 0.5f);
23.             Destroy(this.gameObject);
24.         }
25.     }
26.  
27.     // Start is called before the first frame update
28.     void Start()
29.     {
30.        
31.     }
32.  
33.     // Update is called once per frame
34.     void Update()
35.     {
36.  
37.      
38.         acceleration = force / mass;
39.      
40.         zSpeed += acceleration * Time.deltaTime;
41.         this.transform.Translate(0.0f, 0.0f, zSpeed);
42.      
43.         force = 0.0f;
44.  
45.  
46.  
47.  
48.     }
49. }
50.  

 

You're doing this every frame.

Code (CSharp):

1.         acceleration = force / mass;
2.         zSpeed += acceleration * Time.deltaTime;
3.         this.transform.Translate(0.0f, 0.0f, zSpeed);
4.         force = 0.0f;

But because of the

force = 0

part, only the first frame of acceleration actually happens. After that you're stuck with whatever your zSpeed was after one frame. Now the amount you accelerated after one frame was dependent on Time.deltaTime, because you did

acceleration * Time.deltaTime

.

In other words - your code is framerate-dependent. it will behave differently at different framerates. Your objects will get a bigger final speed when the frame took a long time to render. The first frame of a scene often takes longer than others because there is a lot of initialization going on.

TL;DR you're doing some weird stuff with your speed/acceleration variables etc. and you're ending up with a framerate-dependent final speed for your bullets.

 

How do i make each bullet framerate independent

 

Just give it a constant speed that doesn't depend on deltaTime. Don't overcomplicate things:

Code (CSharp):

1. public float speed = 10f;
2.  
3. // Update is called once per frame
4. void Update()
5. {
6.     transform.Translate(0.0f, 0.0f, speed * Time.deltaTime);
7. }

That being said you should really be moving this thing via a Rigidbody if you're trying to get collisions working...

 

https://docs.unity3d.com/ScriptReference/MonoBehaviour.FixedUpdate.html
https://docs.unity3d.com/ScriptReference/Rigidbody.AddForce.html
https://docs.unity3d.com/ScriptReference/ForceMode.html