RC signal loss failsafe in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when RC signal is lost?

Consider this drone control snippet that triggers a failsafe when the RC signal is lost for more than 3 seconds. What will be printed if the signal is lost at time 0 and no signal is received for 4 seconds?

Drone Programming

class DroneController:
    def __init__(self):
        self.signal_lost_time = None
        self.failsafe_triggered = False

    def receive_signal(self, time):
        self.signal_lost_time = None

    def check_signal(self, current_time):
        if self.signal_lost_time is None:
            self.signal_lost_time = current_time
        elif current_time - self.signal_lost_time > 3:
            self.failsafe_triggered = True

    def status(self):
        return 'Failsafe Active' if self.failsafe_triggered else 'Normal Operation'

controller = DroneController()
controller.check_signal(0)
controller.check_signal(4)
print(controller.status())

A Failsafe Active

B Normal Operation

C AttributeError

D Failsafe Active after 5 seconds

💡 Hint

Think about how the failsafe triggers after 3 seconds of no signal.

The failsafe triggers because the signal is lost at time 0 and remains lost at time 4, which is more than 3 seconds. So the status returns 'Failsafe Active'.

🧠 Conceptual

intermediate

What is the main purpose of an RC signal loss failsafe?

Why do drones implement an RC signal loss failsafe mechanism?

A To increase the drone's speed when signal is weak

B To automatically land or hover the drone safely when control signal is lost

C To disable the drone's motors permanently

D To send a notification to the pilot without changing drone behavior

💡 Hint

Think about safety when the pilot loses control.

The failsafe ensures the drone does not fly uncontrolled by automatically landing or hovering safely when the RC signal is lost.

🔧 Debug

advanced

Identify the error in this failsafe implementation

This code is supposed to trigger a failsafe after 2 seconds of signal loss. What error will it cause when run?

Drone Programming

class Failsafe:
    def __init__(self):
        self.lost_time = None
        self.active = False

    def signal_received(self):
        self.lost_time = None

    def check(self, current_time):
        if self.lost_time is None:
            self.lost_time = current_time
        elif current_time - self.lost_time > 2:
            self.active = True

failsafe = Failsafe()
failsafe.check(1)
failsafe.check(4)
print(failsafe.status())

A Failsafe Active

B TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'

C SyntaxError: invalid syntax

D AttributeError: 'Failsafe' object has no attribute 'status'

💡 Hint

Check if all methods used are defined.

The class does not have a 'status' method, so calling failsafe.status() raises an AttributeError.

📝 Syntax

advanced

Which option correctly implements a failsafe check with a ternary operator?

Fix the syntax error in this failsafe check line: failsafe_active = True if time_since_loss > 5 else False

A failsafe_active = True if (time_since_loss > 5) else False

B failsafe_active = True if time_since_loss > 5 else

C failsafe_active = True if time_since_loss > 5 else False

D failsafe_active = True if time_since_loss > 5

💡 Hint

Ternary operator requires both 'if' and 'else' parts.

Option C is the correct syntax for a ternary conditional expression in Python.

🚀 Application

expert

How many times will the failsafe trigger in this signal loss sequence?

Given this code that checks signal loss every second and triggers failsafe if loss lasts more than 3 seconds, how many times will 'Failsafe triggered' print? class Drone: def __init__(self): self.signal_lost_start = None self.failsafe_triggered = False def update_signal(self, signal_present, current_time): if signal_present: self.signal_lost_start = None self.failsafe_triggered = False else: if self.signal_lost_start is None: self.signal_lost_start = current_time elif current_time - self.signal_lost_start >= 3 and not self.failsafe_triggered: print('Failsafe triggered') self.failsafe_triggered = True # Signal presence over 7 seconds: [True, False, False, False, False, True, False] drone = Drone() signal_sequence = [True, False, False, False, False, True, False] for t, signal in enumerate(signal_sequence): drone.update_signal(signal, t)

A 1

B 0

C 3

D 2

💡 Hint

Failsafe triggers only once per continuous loss period after 3 seconds.

Failsafe triggers once at t=4 (after 3 seconds of loss). It resets when signal returns at t=5, so no second trigger at t=6.