• 9g Servos: Very small and lightweight servos, commonly used in park flyers, small foam models, and lightweight control surfaces such as ailerons and elevators on small aircraft.
  

• 17g Servos: Slightly larger and stronger than 9g servos, suitable for small to medium foam or balsa models where a little extra torque is required without adding much weight.
  

• Micro Servos: Compact servos offering a good balance of size and power. Commonly used in small to medium models for ailerons, elevators, and rudders.
  

• Mini Servos: Mid-sized servos used in medium aircraft. Ideal for primary control surfaces where more torque is needed but space is still limited.
  

• Standard Servos: The most common servo size, used in many sport, scale, and aerobatic models. Suitable for larger control surfaces and higher-load applications.
  

• Low-Profile Servos: Designed with reduced height for thin wings and tight fuselage spaces. Commonly used in wing installations on aerobatic and scale models.

• Wing Servos: Slim, purpose-designed servos for direct wing mounting, often used for ailerons and flaps. They provide a neat installation with minimal wing modification.

• Jumbo Servos: Large, high-torque servos primarily used in RC cars and trucks, especially for steering in large-scale models. They are designed to handle high loads and harsh conditions.
  
  

Servo speed affects how quickly the control surface responds to your inputs. Faster servos are ideal when frequent corrections are required or where instantaneous response is important, such as aerobatic flying or precise throttle control.

Slower servos can provide a smoother, more relaxed feel, particularly for scale or sport models. The speed of the servo will directly influence the “feel” of the model in flight, similar to using positive or negative exponential settings on your transmitter.

Choosing the right servo speed helps balance responsiveness, smoothness, and overall control.

When selecting a servo gear train, ask yourself two key questions: Is this a large or powerful model? and Will it be flown aggressively or experience sudden high-impact or high-energy loads?

If the answer is yes, metal gears should be used.

Metal Gears (Recommended for High Demand Applications):

Metal gear servos are designed for strength, durability, and precision under load. Servo manufactures utilize premium materials to match different performance needs:

• Titanium: Maximum strength with reduced weight, ideal for top-tier aerobatic and jet models
  
• Unique Steel / Hardened Steel: Exceptional durability for extreme loads and aggressive flying
  
• Aluminium: A lightweight metal option suitable for mid-power applications
  

Use metal gears for large aircraft, high-power electric or gasoline models, jets, giant-scale aircraft, and any application involving aggressive manoeuvres or high control loads.

• Plastic (Industrial Composite) Gears: Plastic gears are best suited for lower-power, less aggressive models or applications where super-lightweight construction is critical. They provide smooth operation and weight savings for trainers, small electric aircraft, and light sport models with modest control surface loads.

Key Rule to Remember:
If you are unsure which gear type to choose, always select metal gears. They offer greater reliability, longer service life, and better protection against unexpected loads or impacts.

Bearings in a servo determine longevity, control accuracy, and resolution, especially in models exposed to high vibration or heavy loads.

• Single Ball Bearing – Suitable for lightweight, low-vibration, or smaller models. Provides smooth operation and decent durability.
  

• Double (Twin) Ball Bearing – Ideal for larger, more powerful models or those exposed to high vibration. Offers improved accuracy, control resolution, and longer life.
  

• High-End Servos (ChaServos) – Can use up to 6 bearings, giving maximum precision and durability for extreme performance models.
  

Choosing the right bearing setup ensures your servo can handle the demands of your model while maintaining precise and reliable control.

The weight of a servo can affect the balance, performance, and handling of your model, depending on where it is mounted.

• Consider Placement: Mounting a heavy servo in a critical location (like the wing tip or nose) can impact flight characteristics.
  

• Choose Lightweight Servos: Use the lightest servo that meets your torque and speed requirements to minimize negative effects.
  

• Save Weight Elsewhere: Combine lightweight servos with aluminium servo arms and titanium turnbuckles to further reduce overall weight without compromising strength.
  

Proper weight management ensures your model remains nimble, balanced, and performs as intended.

A servo spline is the toothed shaft on top of a servo that the servo arm (horn) fits onto. The spline transfers the servo’s movement to the control linkage.

Spline tooth count and shaft size must match the servo arm for a secure, slip-free fit.

Common servo spline types

• 23-tooth spline: Common on some JR and older servos. Used mainly on standard-size aircraft servos.
  
• 24-tooth spline: Often found on Hitec servos. Widely used across many aircraft and car applications.
  
• 25-tooth spline: Very common on Futaba-style and many modern servos. One of the most popular spline standards.
  

Spline shaft widths

• 5 mm: Typically used on smaller servos where loads are lower.
  
• 6 mm: Common on standard-size servos for aircraft and cars.
  
• 8 mm: Found on large or high-torque servos, usually in large-scale aircraft or RC cars.
  

Why spline choice matters

Using the wrong spline type can result in:

• Poor fit or stripped splines
  
• Slipping under load
  
• Loss of control
  

Always check your servo’s tooth count and shaft width before selecting a servo arm or horn to ensure safe and reliable operation.

Servo arms (horns) transfer movement from the servo to the control surface. The type you choose has a big impact on strength, precision, and reliability.

Plastic Servo Arms

• Lightweight and inexpensive
  
• Suitable for small models and low-load applications
  
• Can flex under load and may strip in a crash
  
• Best for park flyers, trainers, and lightweight control surfaces
  

Metal Servo Arms

• Much stronger than plastic
  
• Reduced flex improves control accuracy
  
• Better suited to larger or higher-performance models
  
• Can still slip on the spline if not fitted perfectly
  

Metal Locking Servo Arms ⭐ Best Choice

• Clamp tightly onto the servo spline using a locking screw
  
• No spline slip, even under high load or vibration
  
• Maximum precision and reliability
  
• Ideal for large-scale, fast, high-torque, or aggressive flying
  
• Slightly heavier, but the strength and security far outweigh this
  

Summary

• Plastic: light, cheap, low load
  
• Metal: strong, good for higher loads
  
• Metal locking: best overall for strength, precision, and safety
  

For any model where control reliability matters, metal locking servo arms are the preferred option.

Pushback is a type of servo behavior where the servo resists or pushes against the control input instead of moving smoothly. It usually occurs when the servo is under high load, moving a heavy control surface, or the linkage is too stiff.

Common causes of pushback:

• Control surfaces are too large or heavy for the servo torque
  
• Stiff or binding linkages and pushrods
  
• Inadequate servo speed or power
  
• High friction in hinges or mechanical components
  

How to fix pushback:

• Use a higher-torque servo to handle the load.
• Check linkages so the servo can move freely.
• Lubricate or reduce friction at hinges and control surfaces.
  
• Shorten servo arms if possible to reduce leverage strain.

Pushback can reduce control precision and may cause flutter or servo strain, so it’s important to address for reliable and safe model operation.