Question RigidBody2D Causing Character to Move Slow?

Hey all, first time poster so I hope I'm doing this right. I'm following the "Ruby's Adventure" tutorial to try and get my feet wet with the Unity Engine workflow. Everything was going good until I got to the "World Interactions" section of the tutorial.

During this part, the tutorial had me add a collider to the main character and then replace my "transform" based movement system with a rigidbody2D based one. Essentially the code went from this:

Code (CSharp):

1. public class RubyController: MonoBehaviour {    
2. // Start is called before the first frame update  
3. void Start()     {              
4.  
5. }    
6.  
7. // Update is called once per frame    
8. void Update()     {        
9. float horizontal = Input.GetAxis("Horizontal");        
10. float vertical = Input.GetAxis("Vertical");                
11. Vector2 position = transform.position;        
12. position.x = position.x + 3.0f* horizontal * Time.deltaTime;         position.y = position.y + 3.0f * vertical * Time.deltaTime;        
13. transform.position = position;    
14. }
15. }

To this:

Code (CSharp):

1. public class RubyController : MonoBehaviour {  
2. Rigidbody2D rigidbody2d;        
3.  
4. // Start is called before the first frame update  
5. void Start()     {        
6. rigidbody2d = GetComponent<Rigidbody2D>();    
7. }  
8.  
9. // Update is called once per frame    
10. void Update()     {        
11. float horizontal = Input.GetAxis("Horizontal");      
12. float vertical = Input.GetAxis("Vertical");                
13. Vector2 position = rigidbody2d.position;        
14. position.x = position.x + 3.0f* horizontal * Time.deltaTime;         position.y = position.y + 3.0f * vertical * Time.deltaTime;        
15. rigidbody2d.MovePosition(position);    
16. }
17. }

I followed all the instructions to a "T" but when I finished implementing the code I noticed my character moved significantly slower. I've done some digging on the Unity forums and other parts of the internet but I couldn't find anything similar to my issue. If anyone knows what might be causing it I could really use some help!

 

The issue is rigidBody2D.MovePosition(). Because physics is updated with FixedUpdate and MovePosition only takes the last position it received. It will appear to slow down because its not receiving all the positions you are sending it. Why? FixedUpdate or what I call the physics update is called every 0.02s(50fps), on average Update is called every 0.016s(60fps). With physics "lagging behind" it moves slower using that method. I usually set the velocity directly or use AddForce to move a rigidBody using Update.

 

Thanks for the clarification! I ended up remedying my issue after reading what you said and watching a video about top down movement from Brackeys that detailed the difference between update and fixed update. I implemented a system where the player's input is taken in the regular update function, but all of the rigid body based movement happens in fixed update. It's working perfectly now!

I find it kind of crazy that an error like that was in an official Unity tutorial though. I can't have been the first person to run into that issue while following it. Did Unity handle updating differently in a previous version maybe?

 

Are we looking at the same tutorial? I took a screenshot of the instructions for Ruby's Adventure and they clearly put the rigidBody2D movement code in Update, not FixedUpdate:



This is an actual screencap from the tutorial itself.

 

That certainly is strange. I was following the version from the Unity Learn website so perhaps that one is outdated? Thank you for highlighting that it's correct in the final version though!

 

Awesome! Glad I was able to help dig up the issue!

 

Hi,
if you want i am currently creating top down shooting tutorial myself,
here i have posted video where i am creating movement script:

 

As of August 18 I'm following the same tutorial (Ruby's Adventure: 2D Beginner, awesome, by the way!) and I'm finding the same problem. While testing on Scene Ruby moves reaaaaaaaally slow. It's a bit hard to try colliders with GameObjects which are a bit far from her.

 

It's a little bit late, but since I have the same problem and solved it in a way nobody mentioned yet, there is a easier solution to your problem.
simply change Time.deltaTIme to Time.fixedDeltaTime in your original code and problem solved.
This fix is better, cause from a coder's point of view, it's does feel weird to introduce 2 local vars just to store some infor you should to able to retrieved from properties.
But it's your call anyway.

 

For those coming here with the same problem, here is a simple example of how to use RigidBody.MovePosition to move an object or character.

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. [RequiresComponent(typeof(RigidBody2D))]
4. public class Controller : MonoBehaviour
5. {
6.     RigidBody2D rBody;
7.     float moveSpeed = 2f;
8.     Vector2 moveInput;
9.  
10.     void Awake()
11.     {
12.         rBody = GetComponent<RigidBody2D>();
13.     }
14.  
15.     void Update()
16.     {
17.         moveInput = new Vector2(Input.GetAxis("Horizontal"), Input.GetAxis("Vertical"));
18.     }
19.  
20.     void FixedUpdate()
21.     {
22.         Vector2 pos = rbody.Position + moveInput * moveSpeed * Time.fixedDeltaTime;
23.         rBody.MovePosition(pos);
24.     }
25. }

Do not use Update with MovePosition it will not work correctly. You can also use this in 3D with a few simple changes.

@huangmai I'm not sure how your code is but if you are using Update and simply changing Time.deltaTime to Time.fixedDeltaTime, its still not working correctly. It will only accept the last value passed in before being processed in FixedUpdate. Also changing Time.deltaTime to Time.fixedDeltaTime does nothing to change what value is returned when used in FixedUpdate. The engine makes Time.deltaTime equal Time.fixedDeltaTime during FixedUpdate.

 

Hello. I am doing the 2D Ruby Adventure tutorial in Unity Learning page. It's october 2021. I have the same problem as the user you were replying a year ago. The code seems to not be updated or with some part missed. The code doesn't show the FixedUpdate function. Also, the character moves very slow after these changes.

Could you please help me and report the problem?

The code I can see in the tutorial is the next one (part 6 in tutorial, number 9 and 10):




EDIT:
It seems to work fine (at least for now) if you just change "Update" for "FixedUpdate". The character now seems to move correctly by doing this. So, the function "Update" should be renamed to function "FixedUpdate" with the same code inside. I would like to know if this is the correct or the "official" solution in the tutorial.
Anyways, could you please report the problem? This tutorial is amazing and very helpful. It would be great if they correct this problem.

 

This is a capture of what I see (accessing the tutorial using the same link you posted), this is right before step 10, when they show the code:



I am reading the tutorial in Spanish. Coud this be the problem? Maybe the image with the code is not updated in the Spanish course.

I don't know if it is made with some automatic translation or not, and if the courses in different languages show the same files or not. But I mentioned that just in case.

 

Thank you very much.

I just changed the language in my profile to English. Accessing again to the course, now I can see what you posted; the right code. So, somehow the problem seems to be that, the language of the course.

 

Nice to know.
Thank you for your help and your answers!

 

This 'issue' is not fixed for Korean tutorial version as of March 7, 2023. It still shows Update function only. And Ruby mooooovs very slow.
I hope the Korean tutorial version is also get fixed ASAP. Thanks.