Sending custom MAVLink commands in Drone Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send a custom MAVLink command using the drone object.

Drone Programming

drone.[1](command_long_encode(0, 0, command_id, 0, param1, param2, param3, param4, param5, param6, param7))

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

Asend_mavlink

Bdisconnect

Cconnect

Dreceive_mavlink

Attempts:

3 left

💡 Hint

Common Mistakes

Using receive_mavlink instead of send_mavlink

Trying to connect or disconnect instead of sending commands

The send_mavlink method is used to send custom MAVLink commands to the drone.

2fill in blank

medium

Complete the code to import the MAVLink command encoder function.

Drone Programming

from pymavlink.dialects.v20 import common as mavlink
command_long_encode = [1]

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Amavlink.MAVLink_command_long_encode

Bmavlink.MAVLink_command_short_encode

Cmavlink.MAVLink_heartbeat_encode

Dmavlink.MAVLink_param_request_read_encode

Attempts:

3 left

💡 Hint

Common Mistakes

Using command_short_encode which is for short commands

Using heartbeat or param request functions by mistake

The MAVLink_command_long_encode function encodes the long command message needed to send custom commands.

3fill in blank

hard

Fix the error in the code to correctly send a MAVLink command with parameters.

Drone Programming

drone.send_mavlink(command_long_encode(0, 0, [1], 0, 1, 2, 3, 4, 5, 6, 7))

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AMAV_CMD_DO_CHANGE_SPEED

BMAV_CMD_NAV_TAKEOFF

CMAV_CMD_COMPONENT_ARM_DISARM

DMAV_CMD_DO_SET_MODE

Attempts:

3 left

💡 Hint

Common Mistakes

Using a navigation command instead of an arm/disarm command

Using a mode set command without proper parameters

MAV_CMD_COMPONENT_ARM_DISARM is a common command to arm or disarm the drone, often used with parameters.

4fill in blank

hard

Fill both blanks to create a dictionary of commands with their parameter count.

Drone Programming

commands = { [1]: 7, [2]: 3 }

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AMAV_CMD_DO_SET_MODE

BMAV_CMD_NAV_LAND

CMAV_CMD_COMPONENT_ARM_DISARM

DMAV_CMD_NAV_TAKEOFF

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up commands and their parameter counts

Using commands that don't fit the parameter counts given

MAV_CMD_DO_SET_MODE typically uses 7 parameters, and MAV_CMD_NAV_LAND uses 3 parameters.

5fill in blank

hard

Fill all three blanks to filter commands with 5 or more parameters.

Drone Programming

filtered = {cmd: params for cmd, params in commands.items() if params [1] 5 [2] cmd != [3]

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A>

B>=

Cand

DMAV_CMD_NAV_LAND

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '>=' which excludes commands with exactly 5 parameters

Not excluding the land command properly

The filter keeps commands with parameters greater or equal to 5 and excludes the land 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