ROS 1 vs ROS 2 overview - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize a ROS 1 node.

ROS

ros::init(argc, argv, [1]);

Drag options to blanks, or click blank then click option'

Aros::NodeHandle

Binit_node

Cnode_handle

D"my_node"

Attempts:

3 left

💡 Hint

Common Mistakes

Using NodeHandle instead of a string for node name.

In ROS 1, ros::init requires the node name as a string.

2fill in blank

medium

Complete the code to create a ROS 2 node using rclcpp.

ROS

auto node = rclcpp::Node::make_shared([1]);

Drag options to blanks, or click blank then click option'

A"my_node"

Binit

Cnode_name

DNodeHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a variable without quotes or wrong type.

In ROS 2, nodes are created with make_shared and the node name is a string.

3fill in blank

hard

Fix the error in the ROS 1 publisher creation code.

ROS

ros::Publisher pub = node.advertise<std_msgs::String>([1], 10);

Drag options to blanks, or click blank then click option'

A"chatter"

Bstd_msgs::String

C10

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using an integer or type instead of a string for topic name.

The topic name must be a string, so it should be in quotes like "chatter".

4fill in blank

hard

Fill both blanks to create a ROS 2 subscription with a lambda callback.

ROS

auto sub = node->create_subscription<std_msgs::msg::String>([1], 10, [2]);

Drag options to blanks, or click blank then click option'

A"chatter"

B10

C[&](const std_msgs::msg::String::SharedPtr msg) { RCLCPP_INFO(node->get_logger(), "%s", msg->data.c_str()); }

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong types for topic name or callback.

The first blank is the topic name as a string, the second is the lambda callback function.

5fill in blank

hard

Fill all three blanks to process callbacks in a non-blocking loop and clean up a ROS 1 node.

ROS

while (ros::[1]()) {
  ros::[2]();
}
ros::[3]();

Drag options to blanks, or click blank then click option'

AspinOnce

Bok

Cspin

Dshutdown

Attempts:

3 left

💡 Hint

Common Mistakes

Using ros::spin() which blocks indefinitely.

Forgetting the while(ros::ok()) loop with spinOnce().

Check ros::ok() in the while condition, use spinOnce() to process callbacks non-blockingly, and call shutdown() to clean up.

Practice

1. Which statement best describes the main difference between ROS 1 and ROS 2?

easy

A. ROS 1 is older and simpler, while ROS 2 supports real-time and better scalability.

B. ROS 1 supports real-time better than ROS 2.

C. ROS 2 is older and less flexible than ROS 1.

D. ROS 1 and ROS 2 have the same features and design.

Solution

1. Step 1: Understand ROS 1 characteristics

   ROS 1 is the original version, simpler but limited in real-time and scalability.

2. Step 2: Understand ROS 2 improvements

   ROS 2 was designed to fix these limits, adding real-time support and better scalability.

3. Final Answer:

   ROS 1 is older and simpler, while ROS 2 supports real-time and better scalability. -> Option A

4. Quick Check:

   ROS 1 simpler, ROS 2 modern and scalable = A [OK]

Hint: Remember ROS 2 is the newer, more advanced version [OK]

Common Mistakes:

• Thinking ROS 2 is older than ROS 1
• Believing ROS 1 has better real-time support
• Assuming both versions have identical features

2. Which of the following is a correct way to describe ROS 2's communication middleware?

easy

A. ROS 2 does not support middleware communication.

B. ROS 2 uses DDS (Data Distribution Service) for flexible communication.

C. ROS 2 uses TCP only for all communication.

D. ROS 2 uses HTTP protocol for message passing.

Solution

1. Step 1: Identify ROS 2 communication method

   ROS 2 uses DDS, a middleware standard, for flexible and scalable communication.

2. Step 2: Check other options

   TCP only or HTTP are not used as the main middleware in ROS 2.

3. Final Answer:

   ROS 2 uses DDS (Data Distribution Service) for flexible communication. -> Option B

4. Quick Check:

   ROS 2 middleware = DDS [OK]

Hint: DDS is the key middleware in ROS 2 communication [OK]

Common Mistakes:

• Confusing TCP with DDS
• Thinking ROS 2 lacks middleware
• Assuming HTTP is used for ROS 2 messages

3. Consider this code snippet in ROS 1 and ROS 2:

node = Node('example_node')
node.create_publisher(String, 'topic', 10)

What is a key difference in how this code behaves in ROS 1 vs ROS 2?

medium

A. ROS 2 does not support publishers.

B. ROS 1 uses create_publisher with QoS settings; ROS 2 ignores QoS.

C. Both ROS 1 and ROS 2 use create_publisher identically.

D. ROS 1 does not support create_publisher method; ROS 2 does.

Solution

1. Step 1: Check ROS 1 publisher creation

   ROS 1 uses rospy.Publisher or roscpp::Publisher, not create_publisher.

2. Step 2: Check ROS 2 publisher creation

   ROS 2 uses create_publisher with QoS settings for flexible communication.

3. Final Answer:

   ROS 1 does not support create_publisher method; ROS 2 does. -> Option D

4. Quick Check:

   ROS 2 uses create_publisher, ROS 1 does not [OK]

Hint: Remember ROS 2 introduced create_publisher method [OK]

Common Mistakes:

• Assuming ROS 1 has create_publisher method
• Thinking QoS is ignored in ROS 2
• Believing ROS 2 lacks publisher support

4. You try to run a ROS 2 node but get an error about missing rclcpp::init. What is the likely cause?

medium

A. The error means your topic name is invalid.

B. ROS 1 nodes require rclcpp::init but ROS 2 does not.

C. You forgot to initialize the ROS 2 client library before creating nodes.

D. You used ROS 1 syntax in a ROS 2 project.

Solution

1. Step 1: Understand ROS 2 initialization

   ROS 2 requires calling rclcpp::init before creating nodes to set up communication.

2. Step 2: Check error cause

   Missing rclcpp::init causes runtime errors when nodes try to start.

3. Final Answer:

   You forgot to initialize the ROS 2 client library before creating nodes. -> Option C

4. Quick Check:

   Missing rclcpp::init means no ROS 2 initialization [OK]

Hint: Always call rclcpp::init before node creation in ROS 2 [OK]

Common Mistakes:

• Confusing ROS 1 and ROS 2 initialization steps
• Assuming topic name causes this error
• Ignoring the need for client library init

5. You want to build a robot system that requires real-time control and works on multiple platforms including Windows and Linux. Which ROS version should you choose and why?

hard

A. Choose ROS 2 because it supports real-time control and multi-platform compatibility.

B. Choose ROS 1 because it is simpler and supports all platforms equally.

C. Choose ROS 1 because ROS 2 does not support Windows.

D. Choose ROS 2 but only if you use Linux, not Windows.

Solution

1. Step 1: Identify real-time and platform needs

   The project needs real-time control and multi-platform support including Windows and Linux.

2. Step 2: Match requirements to ROS versions

   ROS 2 supports real-time features and runs on Windows and Linux, unlike ROS 1 which is limited.

3. Final Answer:

   Choose ROS 2 because it supports real-time control and multi-platform compatibility. -> Option A

4. Quick Check:

   Real-time + multi-platform = ROS 2 [OK]

Hint: ROS 2 is designed for real-time and multi-platform use [OK]

Common Mistakes:

• Assuming ROS 1 supports Windows well
• Thinking ROS 2 lacks real-time features
• Believing ROS 2 only works on Linux