SG90 Servo Horn Size: A Comprehensive Guide to Choosing the Right Attachment

The SG90 servo motor is a staple in robotics, RC vehicles, and DIY electronics due to its compact size, affordability, and versatility. But one often overlooked component that plays a critical role in its performance is the servo horn. This small plastic or metal attachment acts as the bridge between the servo’s rotating shaft and your project’s mechanics. Choosing the right servo horn size isn’t just about compatibility—it’s about unlocking precision, torque efficiency, and creative potential.

What Is a Servo Horn?

A servo horn is a mounting accessory that connects the servo motor’s output shaft to external components like wheels, arms, or linkages. It translates the servo’s rotational motion into linear or angular movement, making it indispensable for tasks like steering a robot, adjusting a camera angle, or animating a model. The SG90 typically comes with multiple horns in its package, each designed for specific use cases.

Why Horn Size Matters

The size and shape of the servo horn directly influence:

Torque and Speed: Longer horns increase leverage but reduce speed, while shorter horns prioritize speed at the expense of torque. Precision: Smaller horns offer finer control, ideal for delicate movements. Mechanical Compatibility: The horn must align with your project’s spatial constraints and mounting points.

Common SG90 Servo Horn Types and Sizes

Most SG90 servos include a set of plastic horns, though metal upgrades are available for heavy-duty applications. Let’s break down the standard options:

1. Standard 4-Arm Horn

Size: ~22–25 mm in diameter. Design: Four arms at 90-degree intervals with pre-drilled holes. Use Case: Ideal for multi-point linkages, such as robotic grippers or pan-tilt mechanisms. The symmetrical design distributes force evenly.

2. Circular Horn

Size: ~20–22 mm in diameter. Design: A single disc with multiple holes arranged in a circular pattern. Use Case: Perfect for applications requiring adjustable linkage positions, like RC car steering. The circular layout allows fine-tuning the pivot point.

3. Star Horn

Size: ~25–28 mm (arm-to-arm). Design: Six arms radiating outward, resembling a star. Use Case: Best for projects needing multiple attachment points, such as animatronic face movements or complex mechanical arms.

4. Custom 3D-Printed Horns

Size: Variable. Design: Tailored to specific projects, from ultra-long arms to irregular shapes. Use Case: Advanced DIY projects where off-the-shelf horns don’t fit.

How Horn Size Affects Performance

Imagine using a 30mm horn for a robotic arm joint. The longer arm provides greater leverage, reducing the strain on the servo when lifting heavier loads. However, the trade-off is slower movement. Conversely, a 15mm horn on the same servo would enable quicker rotations but struggle with weight.

Example: In an RC airplane’s flap control system, a 20mm circular horn allows precise adjustments of the flap angle without overloading the servo.

Applications of Different Horn Sizes

Robotics: Shorter horns for quick, precise joint movements. RC Vehicles: Medium-length horns balance speed and torque for steering. Camera Gimbals: Small horns ensure smooth, incremental adjustments.

In Part 2, we’ll dive into selecting the perfect horn for your project, installation tips, and creative hacks to maximize your SG90’s potential.

How to Choose the Right SG90 Servo Horn

Selecting the optimal horn involves three key considerations:

1. Project Requirements

Load and Torque: Heavy loads demand shorter horns to minimize stress. Range of Motion: Longer horns provide wider angular movement. Space Constraints: Compact designs may require smaller horns.

2. Material Matters

Plastic Horns: Lightweight and sufficient for most hobby projects. Metal Horns: Essential for high-stress applications like drone rudders.

3. Mounting Style

Screw Holes: Ensure the horn’s hole spacing matches your linkages. Shaft Fit: The horn must snugly fit the servo’s splined shaft (25T for SG90).

Step-by-Step Installation Guide

Detach Existing Horn: Unplug the servo, then gently pry off the current horn. Align New Horn: Match the horn’s splines to the servo shaft. Secure with Screws: Use the included screws to fasten the horn. Avoid over-tightening. Calibrate: Center the servo using a controller before attaching linkages.

Common Mistakes to Avoid

Ignoring Spline Count: Using a 23T or 24T horn on an SG90 (25T) causes slippage. Overloading: Long horns paired with heavy loads can strip gears. Poor Alignment: Misaligned linkages strain the servo and reduce accuracy.

Creative Uses for SG90 Horns

Smart Home Automation: Attach a 25mm horn to a micro servo to create automatic window openers. Interactive Art: Use star horns to drive kinetic sculptures with multiple moving parts. Pet Feeders: Circular horns can rotate a dispenser plate for timed feeding.

Pro Tips for Maximizing Performance

Lubricate Joints: A drop of silicone grease reduces friction in moving parts. Reinforce Attachments: Use locknuts or threadlocker to prevent screws from loosening. Test Iteratively: Run the servo at low power first to check for binding or misalignment.

Conclusion

The SG90 servo horn size is a small detail with a massive impact on your project’s success. By understanding the types, applications, and selection criteria, you can transform this humble component into a powerhouse of precision and reliability. Whether you’re building a nimble robot or a responsive RC car, the right horn ensures your servo works smarter—not harder. Now, go experiment and let your creativity take the wheel!