Popular flight controllers (ArduPilot, PX4, Betaflight) in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of ArduPilot mode selection code

What is the output of this Python code simulating ArduPilot flight mode selection?

Drone Programming

modes = {0: 'Stabilize', 1: 'AltHold', 2: 'Loiter', 3: 'Auto'}
selected_mode = 2
print(f"Selected mode: {modes[selected_mode]}")

A KeyError

B Selected mode: Auto

C Selected mode: AltHold

D Selected mode: Loiter

💡 Hint

Look up the value for key 2 in the dictionary.

The dictionary maps 2 to 'Loiter', so the print statement outputs 'Selected mode: Loiter'.

🧠 Conceptual

intermediate

Understanding PX4 parameter update behavior

In PX4 flight controller, which statement best describes how parameters are updated during flight?

A Parameters can be updated live and take effect immediately without reboot.

B Parameters require a full reboot of the flight controller to take effect.

C Parameters update only after landing and disarming the drone.

D Parameters cannot be changed once the flight controller boots up.

💡 Hint

PX4 supports dynamic parameter updates.

PX4 allows live parameter updates that apply immediately without rebooting, enabling in-flight tuning.

❓ Predict Output

advanced

Betaflight PID tuning output

What is the output of this Python snippet simulating Betaflight PID tuning adjustments?

Drone Programming

pid = {'P': 40, 'I': 30, 'D': 23}
pid['P'] += 5
pid['I'] -= 10
print(pid)

A {'P': 45, 'I': 30, 'D': 23}

B {'P': 45, 'I': 20, 'D': 23}

C TypeError

D {'P': 40, 'I': 20, 'D': 23}

💡 Hint

Check how the dictionary values change after the increments and decrements.

P is increased by 5 (40+5=45), I is decreased by 10 (30-10=20), D remains 23.

🔧 Debug

advanced

Identify error in PX4 parameter code

What error does this Python code produce when simulating PX4 parameter access?

Drone Programming

params = {'SYS_AUTOSTART': 1001, 'COM_RC_IN_MODE': 1}
print(params['SYS_BAUDRATE'])

A KeyError

B SyntaxError

C TypeError

D No error, prints 1001

💡 Hint

Check if the key 'SYS_BAUDRATE' exists in the dictionary.

The key 'SYS_BAUDRATE' is not in the dictionary, so accessing it raises a KeyError.

🚀 Application

expert

Calculate total flight time from ArduPilot battery data

Given this Python code simulating battery voltage readings from ArduPilot, what is the total flight time in minutes?

Drone Programming

voltages = [12.6, 12.4, 12.1, 11.8, 11.5]
interval_seconds = 60
flight_time = (len(voltages) - 1) * interval_seconds / 60
print(flight_time)

A 6.0

B 5.0

C 4.0

D Error

💡 Hint

The total time spans (number of readings - 1) intervals. Multiply by interval and convert seconds to minutes.

There are 5 readings taken 60 seconds apart, covering 4 intervals: (5-1)*60 = 240 seconds = 4 minutes.

Practice

1. Which flight controller is mainly designed for racing drones?

easy

A. PX4

B. ArduPilot

C. Betaflight

D. Mission Planner

Solution

1. Step 1: Understand flight controller purposes

   Betaflight is known for its focus on fast, agile racing drones.

2. Step 2: Compare with other controllers

   ArduPilot and PX4 support many drone types, not just racing.

3. Final Answer:

   Betaflight -> Option C

4. Quick Check:

   Racing drones use Betaflight [OK]

Hint: Betaflight = racing drones, ArduPilot/PX4 = versatile [OK]

Common Mistakes:

• Confusing ArduPilot as racing-only
• Thinking PX4 is only for racing
• Selecting Mission Planner (it's a software, not a controller)

2. Which of the following is the correct way to start the PX4 flight controller using the command line?

easy

A. start px4

B. px4 start

C. px4.launch

D. launch px4

Solution

1. Step 1: Recall PX4 command syntax

   The PX4 flight controller is started with the command px4 start.

2. Step 2: Check other options

   Options like start px4, px4.launch, and launch px4 are incorrect commands.

3. Final Answer:

   px4 start -> Option B

4. Quick Check:

   PX4 starts with 'px4 start' command [OK]

Hint: PX4 command line starts with 'px4 start' [OK]

Common Mistakes:

• Reversing command order
• Using '.launch' as a command
• Confusing with graphical launch commands

3. Given this ArduPilot code snippet, what will be the output?

mode = 'AUTO'
if mode == 'AUTO':
    print('Autonomous flight enabled')
else:
    print('Manual control active')

medium

A. Autonomous flight enabled

B. Manual control active

C. SyntaxError

D. No output

Solution

1. Step 1: Check the value of mode variable

   The variable mode is set to the string 'AUTO'.

2. Step 2: Evaluate the if condition

   The condition mode == 'AUTO' is true, so the first print statement runs.

3. Final Answer:

   Autonomous flight enabled -> Option A

4. Quick Check:

   mode == 'AUTO' triggers autonomous message [OK]

Hint: Check if condition matches variable value exactly [OK]

Common Mistakes:

• Assuming else runs when mode is 'AUTO'
• Confusing string case sensitivity
• Expecting syntax error from simple if

4. Identify the error in this Betaflight configuration snippet:

def set_pid(p, i, d):
    pid = {'P': p, 'I': i, 'D': d}
    return pid

config = set_pid(40, 30)
print(config)

medium

A. Missing one argument in set_pid call

B. Incorrect dictionary keys

C. Syntax error in function definition

D. Print statement missing parentheses

Solution

1. Step 1: Check function parameters and call

   The function set_pid requires 3 arguments: p, i, d.

2. Step 2: Compare with function call

   The call set_pid(40, 30) provides only 2 arguments, missing the third.

3. Final Answer:

   Missing one argument in set_pid call -> Option A

4. Quick Check:

   Function needs 3 args but only 2 given [OK]

Hint: Count function args and call parameters carefully [OK]

Common Mistakes:

• Assuming default values exist
• Thinking dictionary keys are wrong
• Ignoring Python 3 print syntax

5. You want to program a PX4 drone to switch between manual and autonomous modes based on a variable mode. Which code snippet correctly implements this logic?

hard

A. if mode != 'MANUAL'
control_manual()
else
control_auto()

B. if mode = 'MANUAL':
control_manual()
else:
control_auto()

C. switch(mode) {
case 'MANUAL': control_manual(); break;
default: control_auto();
}

D. if mode == 'MANUAL':
control_manual()
else:
control_auto()

Solution

1. Step 1: Check correct Python syntax for condition

   The correct code uses if mode == 'MANUAL': which is correct for equality check in Python.

2. Step 2: Verify function calls and else block

   The correct code calls control_manual() if true, else control_auto(), matching the logic.

3. Final Answer:

   if mode == 'MANUAL': control_manual() else: control_auto() -> Option D

4. Quick Check:

   Python uses '==' for comparison, correct if-else structure [OK]

Hint: Use '==' for comparison, not '=' in conditions [OK]

Common Mistakes:

• Using '=' instead of '==' in if condition
• Using switch-case syntax in Python
• Missing colons or indentation in if-else