Sending custom MAVLink commands in Drone Programming - Full Explanation

Introduction

When controlling drones, sometimes you need to send special instructions that are not part of the usual commands. This is where custom MAVLink commands come in handy. They allow you to tell the drone exactly what to do beyond standard controls.

Explanation

Understanding MAVLink Commands

MAVLink is a communication protocol used to send instructions to drones. It has many built-in commands for common tasks like takeoff or landing. Each command has a unique ID and parameters that tell the drone what to do.

MAVLink commands are structured messages that control drone behavior through specific IDs and parameters.

Why Use Custom Commands

Sometimes the built-in commands do not cover all the special tasks you want your drone to perform. Custom commands let you create new instructions tailored to your needs. This flexibility helps in advanced drone applications.

Custom commands extend drone control beyond standard options by allowing new, user-defined instructions.

Creating a Custom MAVLink Command

To create a custom command, you assign a unique command ID that does not conflict with existing ones. You then define the parameters your command will use. This command is sent just like standard commands but requires the drone to understand it.

Custom commands need unique IDs and defined parameters to be recognized and executed by the drone.

Sending the Custom Command

You send the custom command through the MAVLink communication channel, usually via a ground control station or onboard computer. The command message includes the ID and parameters. The drone’s software must be programmed to recognize and act on this command.

Sending custom commands requires both transmitting the message and drone software support to handle it.

Safety and Testing

Because custom commands can change drone behavior, it is important to test them carefully in safe environments. Incorrect commands might cause unexpected drone actions. Always verify the command’s effect before using it in real missions.

Testing custom commands safely prevents unintended drone behavior and ensures reliable operation.

Real World Analogy

Imagine you have a remote control car with buttons for forward, backward, and stop. But you want it to do a special dance move. You create a new button on the remote and teach the car what to do when you press it. This new button is like a custom MAVLink command for drones.

MAVLink Commands → Standard buttons on a remote control for basic car moves

Custom Commands → A new button added to the remote for a special dance move

Creating a Custom Command → Designing what the new button does when pressed

Sending the Custom Command → Pressing the new button to send the instruction to the car

Safety and Testing → Trying the new button in a safe area to make sure the car dances correctly

Diagram

Diagram

┌─────────────────────────────┐
│ Ground Control Station (GCS) │
└─────────────┬───────────────┘
              │ Sends MAVLink Command
              ↓
┌─────────────────────────────┐
│        Drone Flight Controller│
│  ┌─────────────────────────┐│
│  │ Recognizes Command ID    ││
│  │ Executes Custom Action   ││
│  └─────────────────────────┘│
└─────────────────────────────┘

This diagram shows how a ground control station sends a custom MAVLink command to the drone's flight controller, which recognizes and executes it.

Key Facts

MAVLink → A communication protocol used to send commands and receive data from drones.

Command ID → A unique number that identifies each MAVLink command.

Custom MAVLink Command → A user-defined command with a unique ID and parameters not included in standard MAVLink.

Flight Controller → The drone’s onboard computer that processes commands and controls the drone.

Ground Control Station → A device or software used to send commands and monitor the drone remotely.

Common Confusions

Custom commands can be sent without modifying the drone software.

Custom commands can be sent without modifying the drone software. Custom commands require the drone’s flight controller software to be programmed to recognize and handle them; otherwise, the drone will ignore or reject them.

Any number can be used as a command ID for custom commands.

Any number can be used as a command ID for custom commands. Custom command IDs must be unique and not conflict with existing standard MAVLink command IDs to avoid unexpected behavior.

Summary

MAVLink commands control drones using unique IDs and parameters.

Custom commands let you add new instructions beyond standard ones by defining unique IDs and parameters.

Sending custom commands requires both transmitting the message and drone software support to act on it safely.

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