Sending custom MAVLink commands in Drone Programming - Mini Project: Build & Apply

Sending Custom MAVLink Commands

📖 Scenario: You are working with a drone that uses MAVLink protocol for communication. You want to send a custom command to the drone to perform a specific action, such as changing the LED color or triggering a buzzer.

🎯 Goal: Build a simple program that sends a custom MAVLink command with specific parameters to the drone and prints the confirmation of the command sent.

📋 What You'll Learn

Create a dictionary called custom_command with keys command_id, param1, param2, param3, param4 and their exact values.

Create a variable called target_system and set it to the exact integer 1.

Write a function called send_mavlink_command that takes target_system and custom_command as parameters and returns a string confirming the command sent.

Print the result of calling send_mavlink_command with target_system and custom_command.

💡 Why This Matters

🌍 Real World

Sending custom MAVLink commands is useful for controlling drones with specific instructions that are not covered by standard commands, such as turning on LEDs or activating special sensors.

💼 Career

Understanding how to send custom commands via MAVLink is important for drone developers, robotics engineers, and anyone working with UAV communication protocols.

1

Create the custom MAVLink command data

Create a dictionary called custom_command with these exact entries: 'command_id': 300, 'param1': 1.0, 'param2': 0.0, 'param3': 0.0, 'param4': 0.0.

Drone Programming

# Create the custom_command dictionary with specified keys and values
# Your code here

Hint

Use curly braces {} to create a dictionary with the exact keys and values.

2

Set the target system ID

Create a variable called target_system and set it to the integer 1.

Drone Programming

custom_command = {
    'command_id': 300,
    'param1': 1.0,
    'param2': 0.0,
    'param3': 0.0,
    'param4': 0.0
}
# Create the target_system variable and set it to 1
# Your code here

Hint

Just assign the number 1 to the variable target_system.

3

Write the function to send the MAVLink command

Write a function called send_mavlink_command that takes parameters target_system and custom_command. The function should return the string: f"Command {custom_command['command_id']} sent to system {target_system}".

Drone Programming

custom_command = {
    'command_id': 300,
    'param1': 1.0,
    'param2': 0.0,
    'param3': 0.0,
    'param4': 0.0
}
target_system = 1
# Define the function send_mavlink_command with parameters target_system and custom_command
# Your code here

Hint

Use an f-string to format the return message with the command ID and target system.

4

Print the confirmation message

Print the result of calling send_mavlink_command with target_system and custom_command.

Drone Programming

custom_command = {
    'command_id': 300,
    'param1': 1.0,
    'param2': 0.0,
    'param3': 0.0,
    'param4': 0.0
}
target_system = 1

def send_mavlink_command(target_system, custom_command):
    return f"Command {custom_command['command_id']} sent to system {target_system}"

# Print the confirmation message by calling send_mavlink_command
# Your code here

Hint

Use the print function to show the message returned by send_mavlink_command.

Practice

1. What is the main purpose of sending custom MAVLink commands to a drone?

easy

A. To update the drone's firmware automatically

B. To control the drone with commands beyond the standard set

C. To recharge the drone's battery remotely

D. To change the drone's GPS coordinates manually

Solution

1. Step 1: Understand MAVLink command basics

   MAVLink commands include standard and custom commands to control drones.

2. Step 2: Identify the role of custom commands

   Custom commands allow sending special instructions not covered by standard commands.

3. Final Answer:

   To control the drone with commands beyond the standard set -> Option B

4. Quick Check:

   Custom MAVLink commands extend control [OK]

Hint: Custom commands add new controls beyond defaults [OK]

Common Mistakes:

• Confusing custom commands with firmware updates
• Thinking commands recharge battery
• Assuming manual GPS change via commands

2. Which of the following is the correct way to send a custom MAVLink command with 3 parameters in Python using pymavlink?

easy

A. vehicle.mav.command_long_send(target_system, target_component, command_id, 0, param1, param2, param3, 0, 0, 0, 0)

B. vehicle.send_command(command_id, param1, param2, param3)

C. vehicle.mav.send_command_long(command_id, param1, param2, param3)

D. vehicle.command_long_send(command_id, param1, param2, param3)

Solution

1. Step 1: Recall pymavlink command_long_send syntax

   The correct method is vehicle.mav.command_long_send with parameters: target_system, target_component, command, confirmation, and up to 7 params.

2. Step 2: Match the correct parameter order

   vehicle.mav.command_long_send(target_system, target_component, command_id, 0, param1, param2, param3, 0, 0, 0, 0) correctly uses target_system, target_component, command_id, 0 (confirmation), then params, filling unused with zeros.

3. Final Answer:

   vehicle.mav.command_long_send(target_system, target_component, command_id, 0, param1, param2, param3, 0, 0, 0, 0) -> Option A

4. Quick Check:

   Use command_long_send with full parameters [OK]

Hint: Use command_long_send with all 11 parameters [OK]

Common Mistakes:

• Omitting target_system or target_component
• Using wrong method names
• Not filling unused params with zeros

3. Given this Python snippet using pymavlink:

vehicle.mav.command_long_send(
    1, 1, 300, 0, 10, 20, 30, 0, 0, 0, 0
)

What does the number 300 represent in this command?

medium

A. The command ID for the custom command

B. The first parameter value

C. The confirmation flag

D. The target system ID

Solution

1. Step 1: Identify parameter positions in command_long_send

   Parameters are: target_system, target_component, command, confirmation, param1...param7.

2. Step 2: Locate the third argument

   The third argument (300) is the command ID, which specifies which command to execute.

3. Final Answer:

   The command ID for the custom command -> Option A

4. Quick Check:

   Third argument = command ID [OK]

Hint: Third argument is always command ID [OK]

Common Mistakes:

• Confusing command ID with target system
• Mixing confirmation flag with command ID
• Thinking parameters come before command ID

4. You wrote this code to send a custom MAVLink command but the drone does not respond:

vehicle.mav.command_long_send(1, 1, 400, 1, 5, 10, 15)

What is the likely problem?

medium

A. The command ID 400 is invalid

B. Target system and component IDs must be zero

C. The confirmation flag should be 0, not 1

D. Missing required parameters; command_long_send needs 11 arguments

Solution

1. Step 1: Check command_long_send argument count

   command_long_send requires 11 arguments: target_system, target_component, command, confirmation, and 7 params.

2. Step 2: Identify missing arguments

   The code only provides 7 arguments; missing the last 4 parameters which should be zero if unused.

3. Final Answer:

   Missing required parameters; command_long_send needs 11 arguments -> Option D

4. Quick Check:

   command_long_send needs 11 args [OK]

Hint: Always provide 11 arguments to command_long_send [OK]

Common Mistakes:

• Passing fewer than 11 arguments
• Assuming confirmation must be zero
• Using invalid target IDs

5. You want to send a custom MAVLink command that sets a drone's LED color using command ID 2100 with parameters for red, green, and blue values. Which Python code snippet correctly sends this command assuming target system and component IDs are 1 and 1, and you want red=255, green=100, blue=50?

hard

A. vehicle.mav.send_command(2100, 255, 100, 50)

B. vehicle.mav.command_long_send(1, 1, 2100, 1, 255, 100, 50)

C. vehicle.mav.command_long_send(1, 1, 2100, 0, 255, 100, 50, 0, 0, 0, 0)

D. vehicle.command_long_send(2100, 1, 1, 0, 255, 100, 50, 0, 0, 0, 0)

Solution

1. Step 1: Use correct method and argument order

   command_long_send requires target_system, target_component, command_id, confirmation, then 7 params.

2. Step 2: Fill unused parameters with zeros

   Only 3 parameters used for RGB; remaining 4 must be zero to complete 7 params.

3. Step 3: Confirm target IDs and confirmation flag

   Target system and component are 1, confirmation is 0 (no confirmation needed).

4. Final Answer:

   vehicle.mav.command_long_send(1, 1, 2100, 0, 255, 100, 50, 0, 0, 0, 0) -> Option C

5. Quick Check:

   Correct method, full params, proper IDs [OK]

Hint: Fill unused params with zeros, use confirmation=0 [OK]

Common Mistakes:

• Omitting zeros for unused parameters
• Using wrong method name
• Swapping target system and component order