Can't get AddRelativeForce to work

I'm trying to make a player controller script for a tank based 2d top down game. The tank will rotate just fine but will not move forward (or any direction) with the code I'm using. Can anyone tell me what's wrong with it?

Cheers

Code (CSharp):

1. public byte speed = 70;
2.     public Rigidbody2D rb;
3.     // Start is called before the first frame update
4.     void Start()
5.     {
6.         rb = GetComponent<Rigidbody2D>();
7.     }
8.  
9.     // Update is called once per frame
10.     void Update()
11.     {
12.  
13.        
14.         if (Input.GetKey("left"))
15.             transform.Rotate(Vector3.forward * Time.deltaTime * speed);
16.         else if (Input.GetKey("right"))
17.             transform.Rotate(Vector3.back * Time.deltaTime * speed);
18.  
19.         if (Input.GetKey("up"))
20.         {
21.             rb.AddRelativeForce(Vector3.forward * Time.deltaTime * speed);
22.         }
23.  
24.     }

 

Try increasing the value of speed. The force you're applying as written is going to be incredibly small.

Also, add forces in FixedUpdate, not Update.

 

Hi, I've moved the input checks to FixedUpdate and changed speed to 1000 just for testing, the tank still rotates just fine but does not move in any direction.

 

No, do all input checks in Update. Move all forces to FixedUpdate.

As your code is written above though, just do the math first. If your game is running at 120 FPS currently, that will result in a force of:

0.0083 * 70 = 0.581

With 1000 speed:
0.0083 * 1000 = 8.3

At 8.3 that might still not be large enough to overcome whatever friction your tank has with the terrain. If your FPS is even higher (with simple games this is common) then the force will be much smaller. That is because multiplying force against deltaTime means the faster the FPS the smaller the force you are applying. Move all forces to FixedUpdate still, and when you do that you no longer need to multiply against deltaTime anyways.

There may well be a problem with your code still, but first try actually applying a large force before anything else.

 

Ive done as you said, and changed the it to 10000000 and still the tank will turn but not move in any direction. There is no terrain its a 2d top down, the tank is just there on screen with nothing else, is that the problem? I've changed its drag properties and gravity to 0 (otherwise it just drops off screen) but still no effect.