How To Choose The Right Motors And Propeller For Different Drone Applications?

When it comes to drones, one of the most critical factors determining their ability to carry weight is the relationship between motor thrust and payload. The payload refers to any additional weight the drone is carrying—such as cameras, sensors, or cargo—while thrust is the force generated by the drone’s motors and propellers to lift the entire system off the ground. For a drone to lift off, the total thrust must exceed the combined weight of the drone itself and its payload. This article explores how thrust and payload interact, the role of motor and propeller factors in determining thrust, and how to select the right components for different drone applications.

Relationship between drone Payload and thrust of a motor

The payload of a drone is primarily determined by the thrust generated by its motors. Thrust is the force produced by the motors and propellers to counteract the drone's weight and any additional weight from the payload. For a drone to lift and carry a payload, the total thrust must exceed the combined weight of the drone and the payload. Here’s a comprehensive explanation of how payload and thrust are related:

1. Thrust vs. Payload

  ●Thrust is the force generated by the drone's motors and propellers to counteract the drone's weight (the force due to gravity).

  ●Payload is the additional weight the drone is carrying (e.g., cameras, sensors, cargo, etc.) beyond its own weight.

For a drone to lift off the ground, the thrust generated by its motors must exceed its total weight (including both the drone’s body weight and the payload).

The general rule is:

  ●Total Thrust≥Drone Weight+Payload Weight

2. The Role of Thrust in Payload Capacity

Excess Thrust: To carry a payload, the drone needs extra thrust beyond its own weight. Typically, drones are designed to generate at least 1.5 to 2 times their weight in thrust to ensure adequate lifting capacity and provide sufficient maneuverability. For example, a drone with a total weight of 2 kg would need to generate at least 3 kg of thrust (1.5 times its weight) to lift itself and a 1 kg payload.

3. Thrust-to-Weight Ratio

The thrust-to-weight ratio (TWR) is the ratio of the total thrust produced by the motors to the total weight (drone + payload):

  ●TWR=Total Thrust/Total Weight

  ●TWR > 1: The drone can lift off.

  ●TWR = 1: The drone is just hovering.

  ●TWR < 1: The drone will not be able to lift off or hover.

4. How Payload Affects Thrust Requirements

As you add payload to a drone, the required thrust increases. Here’s how:

  ●Without Payload: The drone only needs enough thrust to counteract its own weight.

  ●With Payload: The total weight increases, so the required thrust must increase in proportion.

For example:

  ●If a drone weighs 2 kg and can produce 4 kg of thrust, it can carry a payload of up to 2 kg (since 2 kg + 2 kg = 4 kg thrust).

  ●If the drone weighs 3 kg and can still produce 4 kg of thrust, it can carry a payload of 1 kg.

What factors determine the thrust of a motor?

The thrust of a motor is determined by the interaction of the motor, propeller, and environmental conditions. Below is a step-by-step explanation and the relevant formulas.

1. Motor Factors

  ●Torque (Tm): The motor must provide enough torque to spin the propeller at a required RPM.

  ●RPM: The motor's KV value and input voltage determine its rotational speed, which affects thrust.

  ●Power: Available power affects how effectively the motor can drive the propeller.

2. Propeller Factors

  ●Diameter (D): Larger propellers move more air, generating more thrust.

  ●Pitch (P): Higher-pitch propellers move air faster, affecting thrust and speed.

  ●Design and Efficiency (CT): Aerodynamic properties influence how effectively the propeller converts torque into thrust.

3. Environmental Factors

Air Density (ρ): Thrust increases in denser air, which depends on altitude, temperature, and humidity.

How do they affect the Thrust?

1. Torque

  ●Impact: Torque is indirectly related to thrust, as it determines the motor's ability to maintain the required RPM under load.

  ●Role: Higher torque allows the motor to spin larger or higher-pitch propellers, which require more force to overcome air resistance and generate more thrust.

  ●Key Insight: A motor with insufficient torque cannot achieve the necessary RPM for a given propeller, reducing thrust.

2. RPM

  ●Impact: Thrust increases quadratically with RPM.

  ●Role: Higher RPM means more air is displaced per second, increasing the force generated by the propeller.

  ●Key Insight: Doubling the RPM quadruples the thrust, making RPM a critical factor for small, lightweight propellers.

3. Diameter

  ●Impact: Thrust increases with the fourth power of the propeller diameter.

  ●Role: Larger propellers sweep a much larger area of air, significantly increasing the amount of thrust.

  ●Key Insight: Doubling the diameter increases thrust by 16 times, making diameter the most influential factor in the formula.

4. Pitch

  ●Impact: Pitch determines how far the propeller moves air forward per revolution, affecting thrust efficiency and airspeed.

  ●Role: Higher pitch increases the speed of the displaced air, improving thrust at higher RPMs, but requires more torque to maintain speed.

  ●Key Insight: High-pitch propellers are ideal for applications requiring speed, while low-pitch propellers are better for applications requiring stability and lift.

How to choose the right motor and propeller?

Selecting the best combination of a motor and propeller depends on your thrust (lifting force) and speed (airflow velocity) requirements. To simplify, think of it like choosing a bicycle: different gears (propeller sizes and pitches) and muscle strengths (motor torque and RPM) are suited for different terrains (applications).

1. High Thrust, Low Speed (Lifting Heavy Loads)

Example Applications:

  ●Agricultural drones (spraying pesticides)

  ●Delivery drones carrying heavy packages

Optimal Combination:

  ●Motor: Low KV motor (60-800 KV) with high torque.

 Analogy: Like a strong cyclist in a low gear—great for steep hills, not for speed.

  ●Propeller: Large diameter (e.g., 15-30 inches), low pitch (e.g., 4-6 inches).

Why? Large propellers move a lot of air, generating high thrust at low speeds.

2. Moderate Thrust, Moderate Speed (General Use)

Example Applications:

  ●Photography drones

  ●Mapping or survey drones

Optimal Combination:

  ●Motor: Mid-range KV motor (800-1200 KV).

Analogy: A cyclist in medium gear, balancing strength and speed for efficiency.

  ●Propeller: Medium diameter (e.g., 8-14 inches), medium pitch (e.g., 4.5-7 inches).

Why? Balances lifting power with reasonable speed for stable, smooth operation.

3. Low Thrust, High Speed (Racing or Aerobatics)

Example Applications:

  ●Racing drones

  ●FPV (First-Person View) drones for stunts

Optimal Combination:

  ●Motor: High KV motor (1600-2600 KV).

Analogy: A sprinter on a bike—fast and nimble but not built for carrying weight.

  ●Propeller: Small diameter (e.g., 4-7 inches), high pitch (e.g., 5-7 inches).

Why? Smaller propellers spin faster, and higher pitch creates more forward speed.

Tips for Matching Motor and Propeller

1.Motor KV and Propeller Size:

  ●Lower KV motors pair with larger, slower-turning propellers.

  ●Higher KV motors pair with smaller, faster-turning propellers.

2.Voltage and Current Limits:

  ●Ensure the motor can handle the voltage and current required to drive the selected propeller.

3.Test and Tune:

  ●Theoretical matching is a starting point, but real-world performance often requires fine-tuning for optimal results.

In summary, understanding the balance between a drone's payload and the thrust produced by its motors is essential for designing drones that can perform specific tasks efficiently. Whether you need a drone to carry heavy loads, fly at high speeds, or hover with stability, the right combination of motor power, propeller size, and design is key. By considering factors such as thrust-to-weight ratio, propeller specifications, and motor torque, drone operators can optimize their setups for maximum performance, ensuring that the drone meets both lifting and maneuverability needs. As a global leading lipo battery manufacturer, Grepow offers high-energy-density semi-solid state batteries and UAV batteries which are compatible with drones equipped with diverse motor and propeller setups. If you have any questions or needs, please feel free to contact us at info@grepow.com.