Keyboard teleoperation (teleop_twist_keyboard) in ROS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the ROS Python client library.

ROS

import [1]

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

Arospy

Broslib

Crosnode

Drosmsg

Attempts:

3 left

💡 Hint

Common Mistakes

Using roslib instead of rospy

Forgetting to import rospy

The rospy library is used to write ROS nodes in Python, including teleoperation scripts.

2fill in blank

medium

Complete the code to create a publisher for velocity commands.

ROS

pub = rospy.Publisher('[1]', Twist, queue_size=10)

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

A/cmd_vel

B/vel_cmd

C/move_base

D/velocity

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect topic names like /velocity or /move_base

The /cmd_vel topic is the standard topic for sending velocity commands to a robot in ROS.

3fill in blank

hard

Fix the error in the code to read keyboard input without blocking.

ROS

key = getKey([1])

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

ATrue

BFalse

C0.1

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Passing True or False instead of a timeout value

Passing None which causes blocking

The getKey function uses a timeout in seconds to read keyboard input without blocking. Passing 0.1 seconds allows non-blocking behavior.

4fill in blank

hard

Fill both blanks to set linear and angular velocity from keyboard input.

ROS

twist.linear.x = [1]
twist.angular.z = [2]

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Aspeed

Bturn

Cvelocity

Dangle

Attempts:

3 left

💡 Hint

Common Mistakes

Using velocity or angle which are not defined variables in this context

The speed variable controls forward/backward linear velocity, and turn controls rotation (angular velocity).

5fill in blank

hard

Fill all three blanks to create a ROS node, initialize it, and set the rate.

ROS

rospy.init_node('[1]')
rate = rospy.Rate([2])
while not rospy.is_shutdown():
    [3]

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

Ateleop_twist_keyboard

B10

Cpub.publish(twist)

Dcmd_vel

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong node names

Setting rate to 1 or 100 instead of 10

Forgetting to publish the twist message

The node is named teleop_twist_keyboard. The rate is set to 10 Hz. Inside the loop, the velocity command is published with pub.publish(twist).

Practice

1. What is the main purpose of the teleop_twist_keyboard node in ROS?

easy

A. To control a robot using keyboard keys

B. To visualize robot sensor data

C. To simulate robot movements automatically

D. To compile ROS packages

Solution

1. Step 1: Understand the node's function

   The teleop_twist_keyboard node allows manual control of a robot using keyboard inputs.

2. Step 2: Compare options with the node's purpose

   Only To control a robot using keyboard keys describes controlling a robot with keyboard keys, which matches the node's purpose.

3. Final Answer:

   To control a robot using keyboard keys -> Option A

4. Quick Check:

   Keyboard control = A [OK]

Hint: Remember: teleop means tele-operation via keyboard [OK]

Common Mistakes:

• Confusing teleop with simulation or visualization
• Thinking it compiles code
• Assuming it runs robot automatically

2. Which command correctly runs the teleop_twist_keyboard node in ROS 2?

easy

A. ros run teleop_twist_keyboard teleop_twist_keyboard

B. ros2 launch teleop_twist_keyboard teleop_twist_keyboard.launch

C. ros2 run teleop_twist_keyboard teleop_twist_keyboard

D. ros2 start teleop_twist_keyboard

Solution

1. Step 1: Identify the correct ROS 2 run syntax

   In ROS 2, the command to run a node is ros2 run <package> <executable>.

2. Step 2: Match the command to teleop_twist_keyboard

   ros2 run teleop_twist_keyboard teleop_twist_keyboard uses the correct syntax and package/executable names.

3. Final Answer:

   ros2 run teleop_twist_keyboard teleop_twist_keyboard -> Option C

4. Quick Check:

   ros2 run + package + executable = B [OK]

Hint: Use 'ros2 run' for running nodes in ROS 2 [OK]

Common Mistakes:

• Using 'ros' instead of 'ros2'
• Using 'launch' instead of 'run' for this node
• Typing 'start' which is not a ROS command

3. Given the following keys pressed in teleop_twist_keyboard: i, j, k, what is the expected robot movement sequence?

medium

A. Turn left, move forward, stop

B. Move backward, turn right, stop

C. Stop, move forward, turn right

D. Move forward, turn left, move backward

Solution

1. Step 1: Recall key functions in teleop_twist_keyboard

   Key 'i' moves robot forward, 'j' turns left, 'k' moves backward.

2. Step 2: Match keys to movements in sequence

   Pressing 'i' then 'j' then 'k' results in moving forward, turning left, then moving backward.

3. Final Answer:

   Move forward, turn left, move backward -> Option D

4. Quick Check:

   i = forward, j = left, k = backward [OK]

Hint: Remember i=forward, j=left, k=backward keys [OK]

Common Mistakes:

• Mixing up 'j' and 'l' keys for turning
• Assuming 'k' stops movement
• Confusing forward and backward keys

4. You run ros2 run teleop_twist_keyboard teleop_twist_keyboard but pressing keys does not move the robot. What is the most likely cause?

medium

A. The robot is not connected or not receiving velocity commands

B. The keyboard keys are incorrect; use arrow keys instead

C. The teleop_twist_keyboard node must be launched with a launch file

D. ROS 2 is not installed properly

Solution

1. Step 1: Check common reasons for no robot movement

   If keys are pressed but robot doesn't move, often the robot is not connected or not subscribed to velocity commands.

2. Step 2: Evaluate other options

   Keyboard keys are correct as per documentation; launch file is not required; ROS 2 installation issues would prevent node running.

3. Final Answer:

   The robot is not connected or not receiving velocity commands -> Option A

4. Quick Check:

   No movement = no connection [OK]

Hint: Check robot connection before blaming keys or launch files [OK]

Common Mistakes:

• Assuming arrow keys must be used
• Thinking launch file is mandatory
• Blaming ROS 2 install without checking connection

5. You want to increase the robot's forward speed using teleop_twist_keyboard. Which method correctly achieves this?

hard

A. Press 'i' key twice quickly to double speed

B. Press 'w' key to increase speed while running teleop_twist_keyboard

C. Restart teleop_twist_keyboard with a higher speed parameter

D. Edit the robot's URDF file to increase max speed

Solution

1. Step 1: Understand teleop_twist_keyboard speed control

   The node allows speed adjustment during runtime using 'w' and 'x' keys to increase or decrease linear speed.

2. Step 2: Evaluate other options

   Editing URDF changes robot model, not teleop speed; restarting with parameters is possible but less direct; pressing 'i' twice does not increase speed.

3. Final Answer:

   Press 'w' key to increase speed while running teleop_twist_keyboard -> Option B

4. Quick Check:

   Use 'w' to increase speed live [OK]

Hint: Use 'w' and 'x' keys to adjust speed live [OK]

Common Mistakes:

• Trying to speed up by pressing movement keys repeatedly
• Editing URDF for speed instead of teleop parameters
• Restarting node instead of adjusting speed live