Companion computer integration (Raspberry Pi) in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of MAVLink message parsing code

What is the output of this Python code snippet running on a Raspberry Pi receiving MAVLink messages?

Drone Programming

from pymavlink import mavutil

master = mavutil.mavlink_connection('udp:127.0.0.1:14550')
msg = master.recv_match(type='HEARTBEAT', blocking=True)
print(f"System ID: {msg.get_srcSystem()}, Component ID: {msg.get_srcComponent()}")

A AttributeError: 'NoneType' object has no attribute 'get_srcSystem'

B System ID: 1, Component ID: 1

C System ID: 0, Component ID: 0

D TimeoutError: No message received

💡 Hint

The code waits for a heartbeat message and prints its source IDs.

The code connects to a MAVLink UDP endpoint and blocks until it receives a HEARTBEAT message. The typical system and component IDs for a simulated vehicle are 1 and 1.

🧠 Conceptual

intermediate

Purpose of companion computer in drone systems

What is the main role of a companion computer like a Raspberry Pi in a drone system?

A To act as a GPS receiver only

B To control the drone's motors directly

C To replace the flight controller entirely

D To provide advanced processing and run custom algorithms alongside the flight controller

💡 Hint

Think about tasks that require more computing power than the flight controller.

The companion computer runs complex tasks like computer vision, path planning, or data logging, while the flight controller handles low-level motor control and stabilization.

🔧 Debug

advanced

Identify the error in MAVLink connection code

What error will this Raspberry Pi Python code produce when trying to connect to a drone via serial port?

Drone Programming

from pymavlink import mavutil

master = mavutil.mavlink_connection('/dev/ttyUSB0', baud=57600)
msg = master.recv_match(type='ATTITUDE', blocking=True)
print(msg)

A SyntaxError: invalid syntax in baud parameter

B AttributeError: 'NoneType' object has no attribute 'recv_match'

C FileNotFoundError: [Errno 2] No such file or directory: '/dev/ttyUSB0'

D TimeoutError: No ATTITUDE message received

💡 Hint

Check if the serial device path exists on the Raspberry Pi.

If the serial device '/dev/ttyUSB0' is not connected or does not exist, Python raises a FileNotFoundError when trying to open it.

📝 Syntax

advanced

Correct syntax for sending MAVLink command

Which option correctly sends a MAV_CMD_NAV_TAKEOFF command using pymavlink on a Raspberry Pi?

Drone Programming

master = mavutil.mavlink_connection('udp:127.0.0.1:14550')

# Send takeoff command here

A master.mav.command_long_send(master.target_system, master.target_component, mavutil.mavlink.MAV_CMD_NAV_TAKEOFF, 0, 0, 0, 0, 0, 0, 0, 10)

B master.mav.command_long_send(master.target_system, master.target_component, MAV_CMD_NAV_TAKEOFF, 0, 0, 0, 0, 0, 0, 0, 10)

C master.mav.command_long_send(master.target_system, master.target_component, mavutil.MAV_CMD_NAV_TAKEOFF, 0, 0, 0, 0, 0, 0, 0, 10)

D master.mav.command_long_send(master.target_system, master.target_component, mavutil.mavlink.MAV_CMD_NAV_TAKEOFF, 1, 0, 0, 0, 0, 0, 0, 10)

💡 Hint

Check the full path and parameters for the MAV_CMD_NAV_TAKEOFF constant and command_long_send signature.

The correct constant is mavutil.mavlink.MAV_CMD_NAV_TAKEOFF. The first parameter after command is confirmation (0 means no confirmation). The altitude is the last parameter (10 meters).

🚀 Application

expert

Number of GPS fix messages received in 10 seconds

A Raspberry Pi companion computer listens to GPS_RAW_INT MAVLink messages at 5 Hz. How many GPS fix messages will it receive in 10 seconds?

A 50

B 100

C 5

D 10

💡 Hint

Multiply the message frequency by the time interval.

At 5 messages per second, in 10 seconds the total messages received are 5 * 10 = 50.

Practice

1. What is the main role of a Raspberry Pi when used as a companion computer in drone programming?

easy

A. To add smart features and process data alongside the drone's flight controller

B. To replace the drone's flight controller completely

C. To act as a remote control for the drone

D. To charge the drone's batteries during flight

Solution

1. Step 1: Understand the companion computer concept

   A companion computer like Raspberry Pi works alongside the drone's flight controller to add extra processing power and smart features.

2. Step 2: Identify the Raspberry Pi's role

   It does not replace the flight controller but supports it by handling tasks like image processing or advanced navigation.

3. Final Answer:

   To add smart features and process data alongside the drone's flight controller -> Option A

4. Quick Check:

   Companion computer = extra smart features [OK]

Hint: Remember: companion computer supports, not replaces flight controller [OK]

Common Mistakes:

• Thinking Raspberry Pi replaces the flight controller
• Confusing companion computer with remote control
• Assuming it charges the drone

2. Which of the following is the correct way to import the DroneKit library in a Python script running on a Raspberry Pi?

easy

A. import DroneKit

B. from dronekit import connect

C. import dronekit

D. import drone_kit

Solution

1. Step 1: Recall DroneKit import syntax

   The DroneKit library is imported using 'from dronekit import connect' to access the connect function directly.

2. Step 2: Check case sensitivity and module name

   Python is case sensitive; 'DroneKit' or 'drone_kit' are incorrect module names.

3. Final Answer:

   from dronekit import connect -> Option B

4. Quick Check:

   Correct import syntax = from dronekit import connect [OK]

Hint: Use exact lowercase 'dronekit' and import needed functions [OK]

Common Mistakes:

• Using wrong capitalization in module name
• Trying to import the whole module without specifying functions
• Misspelling the library name

3. Given the following Python code snippet on a Raspberry Pi connecting to a drone via UDP:

from dronekit import connect
vehicle = connect('udp:127.0.0.1:14550', wait_ready=True)
print(vehicle.mode.name)

What will this code output if the drone is in GUIDED mode?

medium

A. guided

B. Mode GUIDED not found

C. GUIDED

D. SyntaxError

Solution

1. Step 1: Understand vehicle.mode.name output

   The mode name property returns the mode as an uppercase string, e.g., 'GUIDED'.

2. Step 2: Check the print output for GUIDED mode

   Since the drone is in GUIDED mode, the output will be 'GUIDED' in uppercase.

3. Final Answer:

   GUIDED -> Option C

4. Quick Check:

   vehicle.mode.name returns uppercase mode [OK]

Hint: DroneKit mode names print in uppercase strings [OK]

Common Mistakes:

• Expecting lowercase mode names
• Confusing attribute access syntax
• Assuming code causes syntax error

4. You wrote this code on your Raspberry Pi to connect to a drone via serial port:

from dronekit import connect
vehicle = connect('/dev/ttyUSB0', baud=57600, wait_ready=True)
print(vehicle.battery.level)

But you get an error: TypeError: connect() got an unexpected keyword argument 'baud'. What is the fix?

medium

A. Change 'baud' to 'baudrate' in the connect() call

B. Remove 'wait_ready=True' from connect()

C. Use 'baud' but set it to 115200 instead

D. Change '/dev/ttyUSB0' to 'udp:127.0.0.1:14550'

Solution

1. Step 1: Identify the correct parameter name for baud rate

   The connect() function expects 'baudrate' not 'baud' as the keyword argument for serial speed.

2. Step 2: Fix the parameter name in the code

   Replace 'baud=57600' with 'baudrate=57600' to fix the TypeError.

3. Final Answer:

   Change 'baud' to 'baudrate' in the connect() call -> Option A

4. Quick Check:

   Correct parameter name = baudrate [OK]

Hint: Use 'baudrate' keyword, not 'baud' in connect() [OK]

Common Mistakes:

• Using 'baud' instead of 'baudrate'
• Changing connection type unnecessarily
• Removing wait_ready without cause

5. You want your Raspberry Pi companion computer to monitor the drone's battery and land the drone automatically if battery level falls below 20%. Which code snippet correctly implements this logic using DroneKit?

hard

A. if vehicle.battery.level < 20:
vehicle.mode = vehicle.mode.LAND

B. if vehicle.battery.level < 20:
vehicle.mode = vehicle.mode.name('LAND')

C. if vehicle.battery.level < 20:
vehicle.mode = vehicle.mode('LAND')

D. if vehicle.battery.level < 20:
vehicle.mode = 'LAND'

Solution

1. Step 1: Understand how to set vehicle mode

   To change the drone mode, assign a string like 'LAND' directly to vehicle.mode.

2. Step 2: Check the battery level condition

   If battery level is below 20%, set vehicle.mode = 'LAND' to command landing.

3. Final Answer:

   if vehicle.battery.level < 20: vehicle.mode = 'LAND' -> Option D

4. Quick Check:

   Set mode by assigning string name directly [OK]

Hint: Assign mode as string like 'LAND' to vehicle.mode [OK]

Common Mistakes:

• Trying to call mode as a function
• Using mode.name or mode.LAND incorrectly
• Not comparing battery level properly