Sending custom MAVLink commands in Drone Programming - Time & Space Complexity

Time Complexity: Sending custom MAVLink commands

O(n)

Understanding Time Complexity

When sending custom MAVLink commands, it's important to know how the time to send commands grows as you send more commands.

We want to understand how the program's work changes when the number of commands increases.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

for command in commands_list:
    mavlink_message = create_custom_command(command)
    send_mavlink_message(mavlink_message)
    wait_for_acknowledgment()

This code sends each custom MAVLink command one by one, waiting for an acknowledgment before sending the next.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Loop over each command in the list.
• How many times: Once for every command in the commands_list.

How Execution Grows With Input

Each command requires creating, sending, and waiting for acknowledgment, so the total work grows directly with the number of commands.

Input Size (n)	Approx. Operations
10	10 command sends and waits
100	100 command sends and waits
1000	1000 command sends and waits

Pattern observation: The total time grows in a straight line as the number of commands increases.

Final Time Complexity

Time Complexity: O(n)

This means the time to send commands grows directly in proportion to how many commands you have.

Common Mistake

[X] Wrong: "Sending multiple commands at once will take the same time as sending one command."

[OK] Correct: Each command needs time to be created, sent, and acknowledged, so more commands mean more total time.

Interview Connect

Understanding how sending commands scales helps you design efficient drone control programs and shows you can think about program speed clearly.

Self-Check

"What if we sent all commands without waiting for acknowledgment? How would the time complexity change?"

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