How do I smooth the movement of three transforms moving at different rates along a single axis?

Questions & Answers
1

I’m moving three cubes along their Z axis by their transform component at different rates while having a camera following one of them.
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How would I be able to rid of the jerkiness that represents from the other two if they are moving at random rates every update to have all three cubes appear smooth?

using UnityEngine;
using System.Collections;

public class CarControllerAI : MonoBehaviour {
	private float speed;
	private Transform _endPoint;

	void Start() {
		//The point we want our transform to reach.
		_endPoint = GameObject.FindGameObjectWithTag("FinishLine").GetComponent<Transform>();
		//The speed from .1 to 1 for our lerp
		speed = Random.Range(.1f, .5f);
	}

	void Update() {
		speed = Random.Range (.1f, .5f);
	}

	void FixedUpdate() {
		transform.position = Vector3.Lerp (transform.position, new Vector3(transform.position.x, transform.position.y, _endPoint.position.z), speed * Time.deltaTime);
    }
}
3

I would recommend you not use Lerp function to move, as long as you have other options. Most people don’t really understand and freak when get unexpected behaviour. @kingcoyote’s solution will wok if you are using constant speed, but still I wouldn’t use Lerp. Anyways, if you don’t want to use constant speed then you can use SmoothDamp to move. In that you’ll have to set the smoothTime using your previous velocity and present velocity.

Vector3 lastSpeed = Vector3.zero;
Vector3 currentSpeed = Vector3.zero;

void Update(){
    float newSpeedMagnitude = Random.Range(1, 5);
    var deltaTranform = Mathf.Abs((currentSpeed * newSpeedMagnitude - lastSpeed)) * Time.deltaTime;
	tansform.positon = Vector3.SmoothDamp(tansform.positon, transform.positon + deltaTranform, currentSpeed, Time.deltaTime);
	lastSpeed = currentSpeed * newSpeedMagnitude;
}

I do have to warn you that this isn’t a good way to move either. It’s just suitable for you situation where you are randomly change speed. You probably shouldn’t use random speed, that does give it odd behaviour.

Hope this works out, I haven’t tried it. Comment if it does or not.

2

First off, if they change speed every frame, of course it’s going to be jerky! Is that what you really wanted, or did you want each object to move steadily at a random rate that is defined on start?

Second, you might want to change how you are using Vector3.Lerp. That might be a part of your problem. Rather than doing a small, almost fixed size linear interpolate between current position and end position, you should linear interpolate between start and end, and smoothly grow the intermediate value. Like this:

 using UnityEngine;
 using System.Collections;

 public class CarControllerAI : MonoBehaviour {
     private float speed;
     private float _location;
     private Transform _startPoint;
     private Transform _endPoint;

     void Start() {
         //The point we want our transform to reach.
         _endPoint = GameObject.FindGameObjectWithTag("FinishLine").GetComponent<Transform>();
         // The starting point
         _startPoint = transform;
         // the speed should be the number of 1/s where s is the 
         // number of seconds needed to get to the end.
         speed = 1 / Random.Range(5, 10);
         // default the location to 0
         _location = 0;
     }

     void Update() {
         // increment the location based on speed. 
         _location += speed * Time.deltaTime;
         transform.position = Vector3.Lerp(
             _startPoint.position, 
             _endPoint.position), 
             _location);
     }
 }