Servo Torque Explained for Large Elevons on FPV Wings

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Understanding Servo Torque for FPV Wings

If you’re building or flying FPV wings, especially larger models with elevons, having the right servo torque is crucial. Elevons combine the functions of elevators and ailerons, controlling pitch and roll by moving up and down. Because these control surfaces are often larger and need to move quickly and precisely, selecting servos with adequate torque ensures smooth and accurate flight control.

What Is Servo Torque?

Servo torque is the amount of rotational force a servo can apply to move or hold its control surface against aerodynamic forces. It’s usually measured in kilogram-centimeters (kg·cm) or ounce-inches (oz-in). For example, a servo with 10 kg·cm torque can exert a force equivalent to 10 kilograms acting one centimetre from the servo shaft.

In simple terms, higher torque means the servo can handle bigger or more resistant control surfaces without struggling or stalling.

Why Servo Torque Matters for Large Elevons

Large elevons on FPV wings face more air pressure, especially at higher speeds or during aggressive manoeuvres. Insufficient torque can cause:

  • Sluggish response: The servo can’t move the elevon quickly enough.
  • Positioning errors: The elevon may not reach the desired angle, affecting control.
  • Servo strain: Overloading can cause overheating or damage.

Choosing the right torque helps maintain control accuracy and prolongs servo life.

Calculating Required Servo Torque for Elevons

To estimate the torque needed, consider:

  • Elevon size: Larger surfaces require more force.
  • Hinge length: The distance from the servo arm to the elevon’s control horn affects leverage.
  • Flight speed: Higher speeds increase aerodynamic load.
  • Material stiffness: Flexible surfaces may need more torque to avoid flutter.

A rough formula to estimate torque is:

Required Torque (kg·cm) = Aerodynamic Load (kg) × Distance from Servo Shaft (cm)

Since aerodynamic load depends on many variables, it’s wise to add a safety margin—usually 20–30% more torque than your calculation suggests.

Choosing the Right Servo

When selecting servos for large elevons on FPV wings, look for:

  • High torque rating: Aim for at least 10–15 kg·cm for medium to large wings.
  • Metal gears: Metal gears offer better durability under load.
  • Fast response times: Speed helps with quick manoeuvres.
  • Quality brand: Reliable manufacturers ensure consistent performance.

Popular servo models among UK FPV pilots include the Savox SC-1256TG or the Hitec HS-7955TG, both known for solid torque and durability.

Installation Tips

Proper installation also affects how well your servo performs:

  • Use the shortest possible servo arm to increase torque (leverage).
  • Ensure the control horn is securely fastened and aligned.
  • Check for smooth hinge movement without binding.
  • Test the elevon deflections at different speeds on the ground before flying.

Final Thoughts

Selecting the correct servo torque for your large elevons is key to achieving responsive, reliable control in your FPV wing. By understanding the forces involved and picking servos with sufficient torque and quality build, you’ll enjoy smoother flights and longer-lasting components. Happy flying!

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