Instant velocity change in physics engine question.

Hi, Im trying to use the mouse or even the left/right arrows to make my game object change velocity instantly (from moving left, then snapping to moving right). I need to keep physics on the object. I searched around the forums and tried some things but I cant think of a way. Im using forcemode velocity change and have mass and all drag settings low as possible but it still has to slow down before it goes the opposite direction. I read not to use rigidbody.velocity in fixedupdate. Anyone know a proper way to do this?

 

There's no way to have instant velocity changes with pure physics; they don't work that way (in real life or PhysX). You have to directly alter rigidbody.velocity if you want to do that.

--Eric

 

I think you want something like this?

Code (csharp):

1.  
2. var speed=10.0;
3.  
4. function Update(){
5.     x=(Input.GetKey("a")? -1.0 : 0.0) + (Input.GetKey("d") ? 1.0 : 0.0);
6.     if(x!=0.0){
7.         rigidbody.velocity=Vector3.right * x * speed;
8.     }
9. }
10.  

What Eric5h5 said is correct. The only way to do it is by controlling the velocity directly. So in the case I gave an example of how to do it. I deliberately didn't use GetAxis because it has a slowing effect on this particular operation.

 

ForceMode.VelocityChange works. If your velocity is not zero, just add the difference between your desired velocity, and rigidbody.velocity.

Tell that to a baseball!

 

Wouldn't this do it:

Code (csharp):

1.  
2. rigidbody.AddForce(newVelocity - rigidbody.velocity, ForceMode.VelocityChange);
3.  

 

A baseball is bouncing off something.

--Eric

 

I know this is older but I had the same question and found this post.

I used bigmisterb's theory and applied it with the Horizontal access

Code (CSharp):

1. float h = Input.GetAxis("Horizontal");
2.         rigidbody2D.AddForce(Vector2.right * h * Speed);
3.         rigidbody2D.transform.position = new Vector2(Mathf.Clamp(rigidbody2D.transform.position.x, minX, maxX), 8f);
4.  
5.         if (h != 0.0f && rigidbody2D.velocity.x != 0.0f)
6.         {
7.             rigidbody2D.velocity = Vector2.right * h * Speed;
8.         }

 

This is the retro platform jumper movement I usually use:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class PlayerMove2D : MonoBehaviour
{
public Rigidbody2D rb;
public float moveSpeed = 50f;
public float jumpForce = 10;
public LayerMask groundLayer;
public Transform groundChecker;
public float maxVelocity = 50f;
private Vector3 currScale = Vector3.one;

void Update()
{
//Moving left or right
float moveX = (Input.GetKey("a") ? -1.0f : 0.0f) + (Input.GetKey("d") ? 1.0f : 0.0f);

if(!IsGrounded()) //Gliding movement in air
{
if (Mathf.Abs(rb.velocity.x) < maxVelocity)
{
rb.AddForce(transform.right * moveX/2);
}
}
else //Sticky movement on ground
{
rb.velocity = new Vector2(moveX * moveSpeed, rb.velocity.y);
}
//Check which way the sprite should be
if (moveX != 0)
{
currScale.x = Mathf.Sign(moveX) * 1;
transform.localScale = currScale;
}
//Jump
if(Input.GetButtonDown("Fire1"))
{
if (IsGrounded())
{
rb.AddForce(Vector2.up * jumpForce);
}
}
}
bool IsGrounded()
{
return Physics2D.Raycast(groundChecker.position, -transform.up, 0.4f, groundLayer);
}
}