Lock for servomotor SG90

Transmission & Fixation System

The mechanism is designed to be as simple and robust as possible, prioritizing reliability over unnecessary complexity.

The motion is achieved through a rack and pinion system, where the pinion is directly driven by an SG90 servo motor. Instead of using additional mechanical couplings (such as screw-mounted servo horns or inserts), I opted for a more direct approach: structural bonding of the pinion to the servo shaft.

This approach offers several advantages:

• Eliminates tolerance stack-up from intermediate parts

• Reduces backlash in the system

• Simplifies assembly and maintenance

• Ensures more efficient direct torque transfer

For bonding the pinion to the servo shaft, I recommend using a high-strength adhesive such as:

• Cyanoacrylate (super glue) for quick setups

• Two-part epoxy for a more structural and durable bond

Proper alignment during bonding is critical, as it directly affects motion efficiency and overall system longevity.

Servo Mounting

The SG90 servo is also fixed to the base using adhesive. While alternatives like screws or snap-fit features are possible, this design is optimized for rigid adhesive mounting, which provides:

• Reduced vibrations

• Minimal play in the assembly

• A more compact overall system

Recommended adhesives:

• Epoxy for maximum structural rigidity

• Cyanoacrylate for faster assembly

Before bonding, make sure to clean the surfaces thoroughly and, if possible, lightly roughen them to improve adhesion.

Design Considerations

This system is intended for low-load applications such as a door stopper, where the SG90 operates within its optimal range. The gear and rack geometry are designed to ensure:

• Smooth motion

• Low wear

• Reliable positional response

The simplicity of the mechanism is intentional: fewer parts result in fewer points of failure.