How would I get collision at different speeds?

Hello all, I have been working on a huge commercial project and have come to a stop where I am not too familiarized in the mathematical side and conditional statements part of programming in C#.

What do I want?

  1. My helicopter can travel at speeds and with this speeds I would like a different affect on collision at each speed.

  2. My helicopter has been built using Rigidbody, mainly AddForce and AddTorque. I wouldn’t even know how to get the speed value of the Rigidbody.

  3. I would like the helicopter to be able to collide with the terrain at different speeds.

I have gone ahead and made some pseudocode to display to show you all what I am trying to achieve. I imagine I have been stuck for over 7 hours now and I guess all the research I have been doing has not lead me to the correct solution.

using UnityEngine;
using System.Collections;

public class CollisionTerrain : MonoBehaviour {

	public GameObject terrain;
	public ParticleSystem PlayP1;
	public ParticleSystem PlayP2;
	public ParticleSystem PlayP3;
	public GameObject WH;

	void OnCollisionEnter(Collision collision) {
		if(helicopter.velocity.magnitude > 10);  //If Helicopter is faster than a velocity of 10
		PlayP1.particleSystem.enableEmission = true;	 //Helicopter will emit a black smoke and make a damage sound 
		PlayP1.AudioSource.Play(); // Ignore if wrong
		 if(helicopter.velocity.magnitude > 25); //If Helicopter is faster than a velocity of 25
		PlayP2.particleSystem.enableEmission = true;	{ Helicopter will emit a deeper black smoke and make a more intense damage sound}
		PlayP2.AudioSource.Play(); // Ignore if wrong
		 if(helicopter.velocity.magnitude > 50); //If Helicopter is faster than a velocity of 25
		PlayP3.particleSystem.enableEmission = true;	{ Helicopter will emit a deeper black smoke and make a more intense damage sound}
		PlayP3.AudioSource.Play(); // Ignore if wrong
		WH.Instantiate.WreckageObject. //Blown up Helicopter

First, lets get the speed of your object. Put this at the top of your script:

public float velocity; //The velocity of our object.
Vector3 previous; //The previous position of our object.

now, lets use the Update function to get the speed of our object. Like so:

	void Update () {
		velocity = ((transform.position - previous).magnitude) / Time.deltaTime;
		previous = transform.position;

next, lets check that velocity if we hit something.

	void OnTriggerEnter(Collider col){
		if (col.tag == "Terrain") {
			if(velocity > 0 && velocity < 10){
				if(velocity >= 10 && velocity <= 50){
				if(velocity > 50){

your code is really not that far off. you can call rigidbody.velocity to get a rigidbody’s velocity (as a vector3) and you can get the magnitude for a scalar value.

the problem in your code snip is mostly that if your speed is > 50, all lines will be called (if something is larger than 50, it is also larger than 10, 25, and 30).

a simple way of solving this would be something like

void OnCollisionEnter(Collision c){
 float speed = helicopter.rigidboy.velocity.magnitude;

 if(speed > 50) DoHighestEffect();
 else if (speed > 25) DoMediumEffect();
 else if (speed > 10) DoLowEffect();
 else DoMinimumEffect();


You may want to have a single CollisionEffect(float speed) method instead that takes the speed as a parameter, depending on how you implement having different effects.