Sprite moves at an angle that is 2x the rotation of the sprite.

Questions & Answers
1

I’m a complete newbie and learning 2D game development by trying to make a top-down tank driving game.

Here’s my code to control the tank sprite.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TankController : MonoBehaviour 
{

	// Rigidbody2D rb2D;

	public float maxForwardSpeed = 2.0f;
	public float maxRotationSpeed = 50.0f;

	void Start () 
	{
		// rb2D = GetComponent<Rigidbody2D>();
	}

	void Update ()
	{
		float forwardSpeed = Input.GetAxis("Vertical") * maxForwardSpeed;
		float rotationSpeed = Input.GetAxis("Horizontal") * maxRotationSpeed;

		transform.Translate(transform.up * forwardSpeed * Time.deltaTime);
		transform.Rotate(0, 0, -rotationSpeed * Time.deltaTime);

	}
}

It compiles and runs, and the tank forward and back movement is fine but when I rotate the tank to say 45 degrees (Northeast), the actual direction of movement when I press forward is +90 degrees (East). Similarly if I rotate the tank to 90 degrees (East) the actual direction of movement is down (South).

What is going on to cause this behaviour?

I expected the transform.Translate(transform.up * forwardSpeed * Time.deltaTime) statement to move the tank in the exact direction that the sprite is pointing.

2

Well, I got it working by keeping track of the direction using a user-defined variable and then setting position and rotation directly. Not sure why the above method doesn’t work or whether this is a good solution. Please comment if there is a problem with this or if you have a better solution.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TankController : MonoBehaviour 
{

	//Rigidbody2D rb2D;

	public float maxForwardSpeed;
	public float maxRotationSpeed;

	public float direction;

	void Start ()
	{
		//rb2D = GetComponent<Rigidbody2D>();
		direction = 0.0f;
	}

	void Update ()
	{
		float forwardSpeed = Input.GetAxis ("Vertical") * maxForwardSpeed;
		float rotationSpeed = Input.GetAxis ("Horizontal") * maxRotationSpeed;

		direction -= rotationSpeed * Time.deltaTime;

		transform.position = transform.position + transform.up * forwardSpeed * Time.deltaTime;
		transform.rotation = Quaternion.Euler (0, 0, direction);

	}
}