Motor and propeller physics basics in Drone Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate thrust using motor power and propeller efficiency.

Drone Programming

thrust = motor_power * [1]

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

Abattery_voltage

Bmotor_speed

Cpropeller_efficiency

Dpropeller_diameter

Attempts:

3 left

💡 Hint

Common Mistakes

Using motor speed instead of efficiency

Using battery voltage incorrectly

The thrust produced depends on the motor power multiplied by the propeller efficiency.

2fill in blank

medium

Complete the code to calculate motor torque from power and angular velocity.

Drone Programming

torque = [1] / angular_velocity

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

Aangular_velocity

Bmotor_power

Cthrust

Dpropeller_efficiency

Attempts:

3 left

💡 Hint

Common Mistakes

Using angular velocity as numerator

Using thrust instead of power

Torque is calculated by dividing motor power by angular velocity.

3fill in blank

hard

Fix the error in the code to correctly calculate thrust coefficient Ct.

Drone Programming

Ct = thrust / (0.5 * air_density * [1] ** 2 * propeller_area)

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

Apropeller_diameter

Bbattery_voltage

Cangular_velocity

Dmotor_speed

Attempts:

3 left

💡 Hint

Common Mistakes

Using motor speed instead of diameter

Using angular velocity incorrectly

The thrust coefficient Ct uses the square of the propeller diameter in the denominator.

4fill in blank

hard

Fill both blanks to compute power coefficient Cp from power and propeller parameters.

Drone Programming

Cp = [1] / (0.5 * air_density * [2] ** 3 * propeller_area)

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

Amotor_power

Bpropeller_diameter

Cmotor_speed

Dthrust

Attempts:

3 left

💡 Hint

Common Mistakes

Using motor speed or thrust incorrectly

Mixing diameter with speed

The power coefficient Cp is power divided by half air density times propeller diameter cubed times propeller area.

5fill in blank

hard

Fill all three blanks to create a dictionary of motor parameters filtered by efficiency.

Drone Programming

motor_params = {motor_id: [1] for motor_id, [2] in motors.items() if [3] > 0.8}

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

Aefficiency

Bparams

Cparams['efficiency']

Dmotor_speed

Attempts:

3 left

💡 Hint

Common Mistakes

Using motor_speed instead of params

Filtering by wrong variable

The dictionary comprehension uses params['efficiency'] as value, params as the second variable, and filters by params['efficiency'] greater than 0.8.

Practice

1. Which factor directly increases the thrust generated by a drone's propeller?

easy

A. Lowering the drone's weight

B. Increasing the motor speed (rpm)

C. Reducing the battery voltage

D. Decreasing the propeller size

Solution

1. Step 1: Understand thrust formula basics

   Thrust depends on the square of the motor speed (rpm) and the propeller area.

2. Step 2: Identify which factor increases thrust

   Increasing rpm increases thrust because thrust ∝ rpm² x propeller area.

3. Final Answer:

   Increasing the motor speed (rpm) -> Option B

4. Quick Check:

   Thrust ∝ rpm² [OK]

Hint: Thrust grows with rpm squared, so speed up motor [OK]

Common Mistakes:

• Thinking smaller propellers increase thrust
• Confusing power with thrust
• Ignoring rpm's squared effect

2. Which of the following is the correct Python syntax to calculate power given rpm and propeller_area variables?

easy

A. power = rpm ** 2 + propeller_area

B. power = rpm * 3 * propeller_area

C. power = rpm ^ 3 * propeller_area

D. power = rpm ** 3 * propeller_area

Solution

1. Step 1: Recall Python exponent syntax

   Python uses ** for exponentiation, so rpm cubed is rpm ** 3.

2. Step 2: Match formula for power

   Power depends on rpm cubed times propeller area, so multiply rpm ** 3 by propeller_area.

3. Final Answer:

   power = rpm ** 3 * propeller_area -> Option D

4. Quick Check:

   Use ** for power, not ^ or *3 [OK]

Hint: Use ** for powers in Python, not ^ or * number [OK]

Common Mistakes:

• Using ^ instead of ** for exponent
• Multiplying rpm by 3 instead of cubing
• Adding instead of multiplying

3. What is the output of this Python code snippet?

rpm = 1000
propeller_area = 0.05
thrust = rpm ** 2 * propeller_area
print(round(thrust, 1))

medium

A. 50000.0

B. 50000

C. 50000.00

D. 50.0

Solution

1. Step 1: Calculate rpm squared

   rpm ** 2 = 1000 * 1000 = 1,000,000.

2. Step 2: Multiply by propeller_area

   1,000,000 * 0.05 = 50,000.0.

3. Step 3: Check print rounding

   round(50000.0, 1) = 50000.0 and print outputs 50000.0.

4. Final Answer:

   50000.0 -> Option A

5. Quick Check:

   Thrust = 1000² x 0.05 = 50000.0 [OK]

Hint: Square rpm, multiply by area, then round [OK]

Common Mistakes:

• Misreading rounding precision
• Calculating rpm squared incorrectly
• Confusing thrust with power

4. Identify the error in this Python code that calculates power:

rpm = 1200
propeller_area = 0.04
power = rpm ^ 3 * propeller_area
print(power)

medium

A. Multiplying instead of adding propeller_area

B. Missing parentheses around rpm and 3

C. Using ^ instead of ** for exponentiation

D. Incorrect variable names

Solution

1. Step 1: Check exponentiation operator

   In Python, ^ is bitwise XOR, not exponentiation. Use ** for powers.

2. Step 2: Understand impact on calculation

   Using ^ causes wrong calculation or unexpected result, not power of rpm.

3. Final Answer:

   Using ^ instead of ** for exponentiation -> Option C

4. Quick Check:

   Use ** for powers, not ^ [OK]

Hint: Remember ** means power, ^ is bitwise XOR [OK]

Common Mistakes:

• Confusing ^ with **
• Assuming parentheses fix ^ operator
• Ignoring operator precedence

5. You want to program a drone to maintain constant thrust while reducing motor speed to save battery. If you reduce rpm by 20%, how should you adjust the propeller area to keep thrust constant? (Thrust ∝ rpm² x propeller_area)

hard

A. Increase propeller area by 56.25%

B. Increase propeller area by 25%

C. Decrease propeller area by 20%

D. Keep propeller area the same

Solution

1. Step 1: Calculate new rpm ratio squared

   Reducing rpm by 20% means new rpm = 0.8 x original rpm. Squared: 0.8² = 0.64.

2. Step 2: Find required propeller area increase

   To keep thrust constant, propeller_area x 0.64 = original propeller_area. So, new propeller_area = 1 / 0.64 ≈ 1.5625 times original, or 56.25% increase.

3. Final Answer:

   Increase propeller area by 56.25% -> Option A

4. Quick Check:

   Thrust constant -> area ∝ 1 / (rpm²) = 1/0.64 = 1.5625 [OK]

Hint: Square rpm ratio, invert it for area change [OK]

Common Mistakes:

• Forgetting to square rpm ratio
• Adding instead of multiplying percentages
• Assuming area stays same