KST MS320 6.5kg Torque Swashplate Servo: Compact HV Digital Servo for RC Helicopters and UAV Applications

Posted By levi@uavmodel.comLevi on September 2026

KST MS320 6.5kg Torque Swashplate Servo: Compact HV Digital Servo for RC Helicopters and UAV Applications

The KST MS320 6.5kg Torque Swashplate Servo is a compact high-voltage digital servo designed for applications where limited installation space, fast response, accurate positioning, and reliable mechanical transmission are important. With its compact 23 × 12 × 27.5 mm form factor, approximately 20 g weight, hardened steel gear train, coreless DC motor, and contactless position sensor, the MS320 provides a practical combination of size and control performance for RC helicopters, aircraft models, and other precision-controlled mechanisms.

KST positions the MS320 as a micro servo solution, while the current technical documentation identifies a DC 6.0–8.4V operating range, 5.5 kgf·cm torque at 7.4V, and a response speed of 0.08 sec/60° at 7.4V. The servo uses a 25T, 5 mm output shaft spline and supports PWM control.

For RC helicopter builders and UAV engineers, servo selection is not simply about maximum torque. The servo must also fit the available mounting space, provide predictable positioning, tolerate repeated control cycles, and work correctly with the aircraft's power and flight-control system. The KST MS320 addresses these requirements with a compact metal construction and contactless feedback system.

KST MS320 Servo Overview

The KST MS320 is a high-voltage digital micro servo developed for compact control applications. Its small footprint makes it particularly useful where conventional standard-size servos are too large or unnecessarily heavy.

The aluminum-alloy case provides a rigid mechanical housing while helping manage heat generated during operation. Inside the servo, a coreless DC motor drives a hardened-steel gear train. Position feedback is provided through a contactless sensor, allowing the servo electronics to continuously determine the output position without relying on a conventional mechanical contact sensor.

The result is a servo that can be integrated into compact mechanical systems while still providing the response and positioning characteristics expected from a modern digital servo.

Key Product Highlights

KST MS320 high-voltage digital servo
Compact micro-servo dimensions
Designed for swashplate and precision control applications
DC 6.0–8.4V operating voltage range
5.5 kgf·cm torque at 7.4V
0.08 sec/60° speed at 7.4V
Coreless DC motor
Hardened steel gear set
Contactless position sensor
Aluminum-alloy case
Approximately 20 g weight
23 × 12 × 27.5 mm dimensions
25T / 5 mm output shaft spline
PWM command interface
Programmable soft-start function
Up to ±100° default travel range with the specified pulse range

Why Choose a Compact Swashplate Servo?

In RC helicopter systems, the swashplate is a particularly important control mechanism. Servo movements are translated through the swashplate linkage into changes in rotor control geometry. Because several servos can work together, consistency between the servos is important for predictable cyclic and collective control.

A servo used in this type of application needs to combine several characteristics:

Compact physical dimensions
Adequate torque
Fast response
Accurate position feedback
Reliable gears
Appropriate operating voltage
Low overall weight

The MS320's compact dimensions make it suitable for installations where space is limited. Its 20 g-class weight can also help reduce unnecessary mass in small RC helicopter and aircraft configurations.

For builders, the advantage is not simply that the servo is small. Its small size allows the servo to be positioned close to the mechanical control system without requiring a large mounting area.

Core Technology of the KST MS320

1. Coreless DC Motor

The KST MS320 uses a coreless DC motor.

A coreless motor design is commonly used in compact servo systems where low rotating mass and responsive operation are desirable. Because the motor structure is optimized for a compact package, it can provide the quick response required by RC control applications.

The MS320 achieves a specified speed of 0.09 sec/60° at 6.0V and 0.08 sec/60° at 7.4V.

This response time makes the MS320 suitable for applications requiring frequent and relatively rapid control corrections.

2. Hardened Steel Gear Train

Mechanical transmission is one of the most important parts of a servo.

The MS320 uses a hardened steel gear set rather than relying on lightweight plastic gears. The metal gear train provides a durable mechanical interface between the motor and output shaft and is appropriate for applications where the servo repeatedly transmits mechanical loads.

For helicopter swashplate systems, the output gear can experience repeated load changes as the flight controller or transmitter commands cyclic and collective movements. A hardened-steel gear train helps provide the mechanical robustness needed for this type of repeated operation.

3. Contactless Position Sensor

One of the key features of the MS320 is its contactless position sensor.

The technical specification identifies the position sensor as contactless.

Unlike a traditional contact-based position sensor, a contactless sensing system does not require the position-detection element to physically rub against another component during normal operation. This design is particularly relevant for precision servo applications because position feedback is a critical part of closed-loop servo control.

The sensor allows the servo electronics to determine the output position and adjust motor operation accordingly.

For users operating an RC helicopter or aircraft for extended periods, consistent feedback is important because even small variations in servo positioning can affect the overall control geometry.

Compact Aluminum-Alloy Housing

The MS320 uses an aluminum-alloy case.

The housing provides a rigid enclosure for the motor, gears, electronics, and feedback components. Compared with a purely plastic enclosure, an aluminum case can also provide a more substantial mechanical mounting structure.

The complete servo measures approximately:

23 mm × 12 mm × 27.5 mm

with a specified weight of approximately:

20 g ±10%.

This compact configuration is one of the major reasons the MS320 is useful for small and medium-sized RC control installations.

KST MS320 Electrical Performance

The MS320 is designed as a high-voltage servo with a rated voltage of 7.4V and an operating range of 6.0–8.4V.

The voltage range gives builders flexibility when designing an RC power system, but the actual power supply should always remain within the manufacturer's specified limits.

Torque and Speed

According to the current technical specification:

Operating Voltage	Torque	Speed
6.0V	4.5 kgf·cm	0.09 sec/60°
7.4V	5.5 kgf·cm	0.08 sec/60°

The manufacturer's current specification identifies 7.4V as the rated voltage.

The UAVSSS product title uses the 6.5kg torque designation, while the available KST V2 technical sheet currently specifies 5.5 kgf·cm at 7.4V. For engineering applications, users should refer to the latest KST specification corresponding to their exact MS320 version before designing around a specific maximum torque value.

PWM Control Interface

The MS320 uses a PWM command interface.

The current specification lists:

Working frequency: 1520 μs / 333 Hz
Pulse length: 500–2500 μs
Position reference points: 500 μs / 1500 μs / 2500 μs
Signal voltage: HIGH 3.3–5.0V; LOW 0.0–1.5V

This makes the servo compatible with conventional PWM-based RC control architectures when the flight controller, receiver, or servo controller provides a compatible signal.

Before installation, users should confirm the PWM output configuration of the flight controller or receiver and ensure that the selected frequency and pulse range are supported.

Travel Angle and Servo Setup

The MS320's default travel specification is approximately ±100°, or 200° total, when using the specified 500–2500 μs pulse range.

Actual usable mechanical travel should be determined by the requirements of the model and linkage system.

For a swashplate application, excessive servo travel can create mechanical interference, excessive linkage angles, or unnecessary servo load. Therefore, the servo endpoints should be configured according to the helicopter manufacturer's setup procedure rather than simply using the maximum available travel.

Correct endpoint adjustment is especially important when multiple servos operate the same swashplate.

KST MS320 for RC Helicopter Swashplate Applications

The KST MS320 swashplate servo is well suited to compact RC helicopter installations where servo dimensions and response characteristics are important.

A helicopter swashplate converts servo movement into changes in rotor blade pitch. Depending on the helicopter's mechanical design, multiple servos may work together to control cyclic and collective pitch.

In such a system, the servos should be:

Mechanically matched
Properly centered
Configured with consistent travel
Installed without linkage binding
Powered within their specified voltage range
Connected to a compatible receiver or flight controller

The MS320's compact dimensions can make it easier to integrate into a tightly packaged helicopter frame.

For users replacing existing servos, mounting dimensions, output spline compatibility, linkage geometry, and electrical requirements should all be checked before installation.

KST MS320 for RC Aircraft

Although the MS320 is strongly associated with compact helicopter control applications, its characteristics can also make it useful for other RC aircraft mechanisms.

Potential applications include:

Control surfaces on compact aircraft
Rudder mechanisms
Elevator systems
Aileron linkages
Compact mechanical actuators
Experimental UAV mechanisms
Model aircraft requiring small metal-gear servos

The correct application depends on the required torque, speed, travel, installation dimensions, and duty cycle.

For large UAV control surfaces or high-load industrial mechanisms, users should select a servo with sufficient torque margin rather than choosing a servo solely because it fits physically.

Advantages of a Metal Gear Micro Servo

A compact servo can save installation space, but the gear system remains critical.

The MS320's hardened steel gears provide several practical advantages for mechanical control systems.

Mechanical Durability

Steel gears are well suited to repeated mechanical loading and can provide greater resistance to tooth deformation than many lightweight plastic gear systems.

Compact Power Transmission

The servo combines a small overall package with a metal gear transmission, allowing builders to retain a compact installation while using a mechanically robust output system.

Suitable for Repeated Control

RC helicopters and aircraft continuously adjust control surfaces during operation. The metal gear system is therefore useful for applications involving repeated servo movements.

Contactless Feedback and Position Accuracy

Servo accuracy depends on the interaction between the motor, gear train, electronics, and position sensor.

The MS320 uses a contactless position sensor to provide output-position feedback.

This is particularly relevant in applications where precise mechanical positioning matters.

For a helicopter swashplate, consistent servo positioning helps maintain the intended relationship between transmitter commands, servo movement, linkage movement, and rotor pitch.

For aircraft control surfaces, accurate servo positioning helps the control surface follow the commanded position without requiring an unnecessarily large servo body.

Installation Considerations

Before installing a KST MS320, check the following specifications of the target model.

1. Physical Dimensions

The MS320 measures approximately:

23 × 12 × 27.5 mm

Allow sufficient space for the servo case, mounting hardware, cable routing, and servo arm movement.

2. Mounting Compatibility

Do not assume that every micro servo has identical mounting geometry. Check the mounting tabs, hole spacing, frame clearance, and servo orientation before installation.

3. Output Spline

The MS320 uses a 25T, 5 mm output shaft spline.

The servo horn or swashplate linkage component should be compatible with this spline configuration.

4. Voltage

The specified operating voltage range is 6.0–8.4V.

Never connect the servo directly to a battery or power source that exceeds its maximum specified voltage.

5. Servo Travel

Configure the endpoints before applying full mechanical load. Check that the servo arm and linkage can move through the required range without binding.

Recommended Setup for RC Helicopter Builders

When installing multiple MS320 servos in a swashplate system, consistency is important.

A recommended setup process is:

Step 1: Center the Servo

Connect the servo to the receiver or appropriate controller and establish the neutral position before installing the servo arm.

Step 2: Install the Servo Arm

Install the servo arm as close as possible to the intended neutral angle required by the helicopter's mechanical design.

Step 3: Adjust Linkage Length

Set the linkage lengths according to the helicopter manufacturer's setup specifications.

Step 4: Configure Endpoints

Use the transmitter or flight controller to establish the required travel limits.

Step 5: Check for Binding

Move the swashplate through the full control range and verify that no linkage contacts the frame or other mechanical components.

Step 6: Check Servo Synchronization

For systems using multiple servos, verify that the servos move consistently and reach the required positions together.

Step 7: Perform a Final Power Check

Verify the servo power supply and confirm that the voltage remains inside the specified 6.0–8.4V range.

KST MS320 Servo for UAV and Robotics Projects

The compact form factor of the MS320 can also be useful outside conventional RC helicopter applications.

For experimental UAVs, robotics projects, and compact electromechanical systems, a servo can provide a simple method of converting a PWM control signal into mechanical movement.

Potential applications include:

Compact UAV actuators
Camera mechanisms
Mechanical positioning systems
Small robotic joints
Antenna positioning mechanisms
Flight-control prototypes
RC model aircraft
Laboratory and educational projects

However, the servo should always be selected according to the actual mechanical load rather than the physical size of the application.

Why Servo Weight Matters in UAV Applications

For aircraft and UAV systems, every component contributes to total aircraft weight.

At approximately 20 g, the MS320 is designed as a compact servo rather than a large standard-size actuator.

When several servos are installed, the total weight difference can become significant.

For example, a helicopter or aircraft may use multiple servos for different control functions. Reducing unnecessary servo mass can help designers maintain the intended aircraft weight budget.

Nevertheless, weight should never be reduced at the expense of insufficient torque or mechanical reliability.

KST MS320 vs. Standard-Size Servo Applications

The MS320 occupies a different design category from large standard-size servos.

A standard servo may provide substantially higher torque but also require considerably more installation space and add more weight.

The MS320 is intended for situations where the designer needs a compact servo with adequate torque and fast response.

It can therefore be considered when the design priorities include:

Compact installation
Low component weight
Fast servo response
Metal gears
High-voltage operation
Contactless position sensing
PWM compatibility

For applications requiring very high torque, large control surfaces, or heavy mechanical loads, a larger servo may be more appropriate.

Technical Specifications

Specification	KST MS320
Product Type	Digital Micro Servo
Application	Swashplate / RC Control
Rated Voltage	DC 7.4V
Operating Voltage	DC 6.0–8.4V
Torque at 6.0V	4.5 kgf·cm
Torque at 7.4V	5.5 kgf·cm
Speed at 6.0V	0.09 sec/60°
Speed at 7.4V	0.08 sec/60°
Command Interface	PWM
Working Frequency	1520 μs / 333 Hz
Default Travel	±100° / 200° total
Pulse Length	500–2500 μs
Motor	Coreless DC Motor
Gear Material	Hardened Steel
Position Sensor	Contactless
Case Material	Aluminum Alloy
Dimensions	23 × 12 × 27.5 mm ±0.2 mm
Weight	20 g ±10%
Output Spline	25T / 5 mm
Temperature Range	-10°C to +65°C
Soft Start	Programmable
Programmable	Yes

Specifications are based primarily on the current KST MS320 technical documentation.

Important Notes About Torque Ratings

Servo torque figures should always be interpreted together with operating voltage.

The MS320's documented torque increases from 4.5 kgf·cm at 6.0V to 5.5 kgf·cm at 7.4V.

This means that a designer should not treat the torque rating as a single universal value independent of the power supply.

When calculating the required servo capacity, consider:

Actual operating voltage
Control-surface size
Mechanical linkage ratio
Aerodynamic load
Servo arm length
Required control speed
Expected operating temperature
Safety margin

A servo should not normally be selected to operate continuously at its maximum rated capability.

Maintenance and Long-Term Use

Although the MS320 is designed for demanding RC applications, proper installation and maintenance remain important.

Avoid Mechanical Binding

Binding can significantly increase servo load. If the linkage is difficult to move manually, the servo may experience unnecessary stress.

Keep the Servo Clean

Dust, dirt, moisture, and debris can affect mechanical components and connectors. Keep the servo and surrounding installation area clean.

Check the Gear Train

After a hard landing or crash, inspect the servo arm, output shaft, and gear system for damage.

Check the Mounting

Loose mounting screws can introduce unwanted movement and reduce the accuracy of the control system.

Inspect Cables and Connectors

A reliable electrical connection is essential for any flight-control servo. Check cables for damage before operation.

Frequently Asked Questions

Is the KST MS320 a digital servo?

Yes. The MS320 is specified as a digital servo and uses a