Sensor calibration (accelerometer, compass, gyro) in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accelerometer offset correction code

What is the output of this accelerometer offset correction code snippet?

Drone Programming

def calibrate_accel(raw_values, offset):
    return [v - offset for v in raw_values]

raw = [1024, 1030, 1018]
offset = 1020
corrected = calibrate_accel(raw, offset)
print(corrected)

A [1020, 1020, 1020]

B [-4, -10, 2]

C [1024, 1030, 1018]

D [4, 10, -2]

💡 Hint

Think about subtracting the offset from each raw value.

The function subtracts the offset (1020) from each raw accelerometer reading, so 1024-1020=4, 1030-1020=10, 1018-1020=-2.

🧠 Conceptual

intermediate

Purpose of gyro bias calibration

Why is gyro bias calibration important in drone sensor calibration?

A To remove constant drift errors in gyro readings

B To increase the gyro's measurement range

C To align the gyro axes with the compass

D To reduce noise from external magnetic fields

💡 Hint

Think about what happens if the gyro always reads a small value even when still.

Gyro bias calibration removes constant drift errors that cause the gyro to report rotation even when stationary, improving accuracy.

🔧 Debug

advanced

Identify error in compass calibration code

What error does this compass calibration code raise when run?

Drone Programming

def calibrate_compass(raw_readings, hard_iron_offset):
    calibrated = []
    for x, y, z in raw_readings:
        calibrated.append((x - hard_iron_offset[0], y - hard_iron_offset[1], z - hard_iron_offset[2]))
    return calibrated

raw = [(30, 45, 60), (32, 47, 62)]
offset = [5, 5]
result = calibrate_compass(raw, offset)
print(result)

A IndexError: list index out of range

B No error, outputs [(25, 40, 55), (27, 42, 57)]

C TypeError: unsupported operand type(s) for -: 'tuple' and 'int'

D ValueError: too many values to unpack

💡 Hint

Check the length of the offset list compared to how many elements you subtract.

The offset list has only 2 elements but the code tries to access offset[2], causing IndexError.

📝 Syntax

advanced

Syntax error in gyro calibration function

Which option contains the correct syntax for this gyro calibration function?

Drone Programming

def gyro_calibrate(raw_data, bias):
    calibrated = []
    for reading in raw_data
        calibrated.append(reading - bias)
    return calibrated

A Replace 'append' with 'add' method

B Add colon after for loop: for reading in raw_data:

C Change 'return calibrated' to 'return calibrated;'

D Indent 'return calibrated' inside the for loop

💡 Hint

Look carefully at the for loop syntax.

The for loop is missing a colon at the end, causing a syntax error.

🚀 Application

expert

Calculate final calibrated gyro reading

Given raw gyro readings [0.05, -0.02, 0.01] rad/s and a bias of [0.01, 0.00, -0.01], what is the final calibrated reading?

A [0.06, -0.02, 0.00]

B [0.05, -0.02, 0.01]

C [0.04, -0.02, 0.02]

D [0.04, 0.02, 0.00]

💡 Hint

Subtract bias from each raw reading element-wise.

Subtracting bias from raw readings element-wise: 0.05-0.01=0.04, -0.02-0= -0.02, 0.01-(-0.01)=0.02.

Practice

1. What is the main purpose of calibrating the accelerometer in a drone?

easy

A. To update the drone's firmware automatically

B. To increase the drone's battery life

C. To improve the drone's camera quality

D. To ensure the sensor measures acceleration accurately

Solution

1. Step 1: Understand accelerometer function

   The accelerometer measures acceleration forces acting on the drone.

2. Step 2: Purpose of calibration

   Calibration adjusts the sensor to give accurate acceleration readings.

3. Final Answer:

   To ensure the sensor measures acceleration accurately -> Option D

4. Quick Check:

   Accelerometer calibration = Accurate acceleration [OK]

Hint: Calibration fixes sensor errors for accurate readings [OK]

Common Mistakes:

• Confusing calibration with battery or firmware updates
• Thinking calibration improves camera quality
• Assuming calibration is optional for flight safety

2. Which of the following code snippets correctly starts the compass calibration process in a drone's program?

easy

A. startCompassCalibration()

B. compass.calibrate()

C. calibrateCompass.start()

D. beginCompassCalibration()

Solution

1. Step 1: Identify correct method call syntax

   In drone programming, sensor objects often use method calls like compass.calibrate().

2. Step 2: Check method naming conventions

   compass.calibrate() uses the correct object and method name format.

3. Final Answer:

   compass.calibrate() -> Option B

4. Quick Check:

   Correct method call = compass.calibrate() [OK]

Hint: Use object.method() format for sensor calibration calls [OK]

Common Mistakes:

• Using function names without object context
• Incorrect method chaining or naming
• Assuming calibration starts with 'start' prefix

3. Given the following code snippet for gyro calibration, what will be the output if the calibration succeeds?

if gyro.calibrate():
    print("Calibration successful")
else:
    print("Calibration failed")

medium

A. Calibration successful

B. SyntaxError

C. No output

D. Calibration failed

Solution

1. Step 1: Understand the if condition

   The method gyro.calibrate() returns True if calibration succeeds.

2. Step 2: Check output for True condition

   If True, the program prints "Calibration successful".

3. Final Answer:

   Calibration successful -> Option A

4. Quick Check:

   gyro.calibrate() True = "Calibration successful" [OK]

Hint: True return prints success message [OK]

Common Mistakes:

• Assuming calibration returns False by default
• Confusing print outputs
• Expecting syntax errors from correct code

4. The following code is intended to calibrate the accelerometer but does not work as expected. What is the error?

def calibrate_accel():
    accel.calibrate
calibrate_accel()

medium

A. accel object is not defined

B. Incorrect function name

C. Missing parentheses to call the calibrate method

D. Indentation error in function

Solution

1. Step 1: Check method call syntax

   The line accel.calibrate references the method but does not call it.

2. Step 2: Fix by adding parentheses

   Adding parentheses accel.calibrate() calls the method properly.

3. Final Answer:

   Missing parentheses to call the calibrate method -> Option C

4. Quick Check:

   Method call needs () to execute [OK]

Hint: Always use () to call functions or methods [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Assuming function name is wrong without checking syntax
• Ignoring error messages about callable objects

5. You want to calibrate all three sensors (accelerometer, compass, gyro) in sequence and confirm each calibration succeeded before flight. Which code snippet correctly implements this logic?

def calibrate_all():
    if accel.calibrate() and compass.calibrate() and gyro.calibrate():
        print("All sensors calibrated successfully")
    else:
        print("Calibration failed on one or more sensors")
calibrate_all()

hard

A. The code correctly checks all calibrations and prints success only if all pass

B. The code only checks the accelerometer calibration

C. The code will print success even if one sensor fails

D. The code has syntax errors and will not run

Solution

1. Step 1: Analyze the if condition combining calibrations

   The condition uses and to require all calibrations to return True.

2. Step 2: Confirm output logic

   If all succeed, it prints success; otherwise, it prints failure.

3. Final Answer:

   The code correctly checks all calibrations and prints success only if all pass -> Option A

4. Quick Check:

   All calibrations True = success message [OK]

Hint: Use 'and' to ensure all calibrations succeed before proceeding [OK]

Common Mistakes:

• Using 'or' instead of 'and' causing false success
• Not checking all sensors in the condition
• Misunderstanding boolean logic in if statements