Obstacle avoidance in Unity - Mini Project: Build & Apply

Obstacle avoidance

📖 Scenario: You are creating a simple Unity game where a character moves forward and avoids obstacles automatically.Imagine a small robot that moves straight but stops or turns when it senses an obstacle in front.

🎯 Goal: Build a Unity script that makes a game object move forward and avoid obstacles by detecting them with a raycast and turning away.

📋 What You'll Learn

Create a float variable called speed with value 5f

Create a float variable called turnSpeed with value 90f

Use Physics.Raycast to detect obstacles in front within 2f distance

If an obstacle is detected, rotate the object to the right using transform.Rotate

If no obstacle is detected, move the object forward using transform.Translate

💡 Why This Matters

🌍 Real World

Obstacle avoidance is used in games and robotics to help characters or robots move safely without hitting objects.

💼 Career

Understanding obstacle detection and movement control is important for game developers and robotics programmers working on AI navigation.

1

Create movement speed variables

In a new C# script, create two float variables called speed and turnSpeed. Set speed to 5f and turnSpeed to 90f.

Unity

using UnityEngine;

public class ObstacleAvoidance : MonoBehaviour
{
    // Create speed and turnSpeed variables here
    // Your code here
}

Hint

Use public float speed = 5f; and public float turnSpeed = 90f; inside the class.

2

Add obstacle detection distance

Add a float variable called obstacleDistance and set it to 2f to define how far the raycast will check for obstacles.

Unity

using UnityEngine;

public class ObstacleAvoidance : MonoBehaviour
{
    public float speed = 5f;
    public float turnSpeed = 90f;
    // Add obstacleDistance variable here
    // Your code here
}

Hint

Define public float obstacleDistance = 2f; inside the class.

3

Detect obstacles with raycast

Inside the Update() method, use Physics.Raycast from the object's position forward to check if an obstacle is within obstacleDistance. Use if (Physics.Raycast(transform.position, transform.forward, obstacleDistance)).

Unity

using UnityEngine;

public class ObstacleAvoidance : MonoBehaviour
{
    public float speed = 5f;
    public float turnSpeed = 90f;
    public float obstacleDistance = 2f;

    void Update()
    {
        // Add raycast obstacle detection here
        // Your code here
    }
}

Hint

Use Physics.Raycast(transform.position, transform.forward, obstacleDistance) inside Update().

4

Move forward or turn to avoid obstacle

Complete the Update() method so that if an obstacle is detected, the object rotates right by turnSpeed * Time.deltaTime. Otherwise, it moves forward by speed * Time.deltaTime. Use transform.Rotate(0, turnSpeed * Time.deltaTime, 0) and transform.Translate(Vector3.forward * speed * Time.deltaTime).

Unity

using UnityEngine;

public class ObstacleAvoidance : MonoBehaviour
{
    public float speed = 5f;
    public float turnSpeed = 90f;
    public float obstacleDistance = 2f;

    void Update()
    {
        if (Physics.Raycast(transform.position, transform.forward, obstacleDistance))
        {
            // Rotate right to avoid obstacle
            // Your code here
        }
        else
        {
            // Move forward
            // Your code here
        }
    }
}

Hint

Use transform.Rotate(0, turnSpeed * Time.deltaTime, 0); to turn and transform.Translate(Vector3.forward * speed * Time.deltaTime); to move forward.

Practice

1. What is the main purpose of obstacle avoidance in Unity game programming?

easy

A. To help objects move without hitting obstacles

B. To make objects jump higher

C. To change the color of objects

D. To increase the speed of objects

Solution

1. Step 1: Understand obstacle avoidance concept

   Obstacle avoidance is used to prevent objects from colliding with obstacles in their path.

2. Step 2: Identify the correct purpose

   The main goal is to help objects move smoothly without hitting anything.

3. Final Answer:

   To help objects move without hitting obstacles -> Option A

4. Quick Check:

   Obstacle avoidance = prevent collisions [OK]

Hint: Obstacle avoidance means avoiding collisions [OK]

Common Mistakes:

• Confusing obstacle avoidance with speed control
• Thinking it changes object appearance
• Assuming it makes objects jump

2. Which Unity function is commonly used to detect obstacles ahead for avoidance?

easy

A. Update

B. Instantiate

C. Raycast

D. Destroy

Solution

1. Step 1: Recall Unity functions for detection

   Raycast is used to send an invisible line to detect objects in front.

2. Step 2: Match function to obstacle detection

   Raycast detects obstacles ahead, while Instantiate creates objects, Update runs every frame, and Destroy removes objects.

3. Final Answer:

   Raycast -> Option C

4. Quick Check:

   Obstacle detection = Raycast [OK]

Hint: Raycast checks ahead for obstacles [OK]

Common Mistakes:

• Choosing Update which runs every frame but doesn't detect
• Confusing Instantiate with detection
• Selecting Destroy which deletes objects

3. What will be the output if the following Unity C# code runs and an obstacle is detected by the raycast?

void Update() {
    if (Physics.Raycast(transform.position, transform.forward, out var hit, 5f)) {
        transform.Rotate(0, 90, 0);
        Debug.Log("Obstacle detected, turning right.");
    } else {
        transform.Translate(Vector3.forward * Time.deltaTime * 3);
    }
}

medium

A. The object moves forward continuously without turning

B. The object moves backward

C. The object stops moving and no message is logged

D. The object turns right and logs "Obstacle detected, turning right."

Solution

1. Step 1: Analyze raycast detection and response

   If the raycast hits an obstacle within 5 units, the object rotates 90 degrees on Y axis and logs a message.

2. Step 2: Understand else behavior

   If no obstacle is detected, the object moves forward at speed 3 units per second.

3. Final Answer:

   The object turns right and logs "Obstacle detected, turning right." -> Option D

4. Quick Check:

   Obstacle detected = turn right + log message [OK]

Hint: If raycast hits, rotate and log; else move forward [OK]

Common Mistakes:

• Ignoring the rotation when obstacle detected
• Thinking object stops instead of turning
• Assuming object moves backward

4. Identify the error in this obstacle avoidance code snippet:

void Update() {
    if (Physics.Raycast(transform.position, transform.forward, 5f)) {
        Debug.Log(hit.distance);
        transform.Rotate(0, 90, 0);
    }
}

medium

A. The Rotate method parameters are incorrect

B. The Raycast method is missing the 'out RaycastHit' parameter

C. The if condition should use '==' instead of parentheses

D. The Update method should be named FixedUpdate

Solution

1. Step 1: Check Raycast method signature

   Physics.Raycast requires an 'out RaycastHit' parameter to store hit info when using this overload.

2. Step 2: Verify Rotate and method names

   Rotate parameters are correct for rotation; Update is valid for frame updates.

3. Final Answer:

   The Raycast method is missing the 'out RaycastHit' parameter -> Option B

4. Quick Check:

   Raycast needs 'out RaycastHit' [OK]

Hint: Raycast needs 'out RaycastHit' to detect hits [OK]

Common Mistakes:

• Omitting the out parameter in Raycast
• Confusing Rotate parameters
• Thinking Update must be FixedUpdate

5. You want your Unity object to avoid obstacles smoothly by turning gradually instead of instantly. Which approach should you use in your obstacle avoidance script?

hard

A. Use Quaternion.Slerp to rotate smoothly when obstacle detected

B. Use transform.Rotate(0, 90, 0) instantly on detection

C. Stop the object completely when obstacle is detected

D. Ignore obstacles and keep moving forward

Solution

1. Step 1: Understand smooth rotation methods

   Quaternion.Slerp smoothly interpolates rotation over time, creating gradual turns.

2. Step 2: Compare with instant rotation

   transform.Rotate(0, 90, 0) turns instantly, which is not smooth.

3. Final Answer:

   Use Quaternion.Slerp to rotate smoothly when obstacle detected -> Option A

4. Quick Check:

   Smooth turn = Quaternion.Slerp [OK]

Hint: Use Quaternion.Slerp for smooth turning [OK]

Common Mistakes:

• Using instant rotation causing jerky movement
• Stopping object instead of turning
• Ignoring obstacles completely