Waveshare
40kg.cm Metal Serial Bus Servo, High Precision And Large Torque, With Programmable 360 Degrees Magnetic Encoder and Brushless Motor
The Waveshare ST3025 is a high-performance metal serial bus servo featuring a brushless motor, steel gearbox, and 360° programmable magnetic encoder. With up...
The Waveshare ST3025 is a high-performance metal serial bus servo featuring a brushless motor, steel gearbox, and 360° programmable magnetic encoder. With up to 40 kg·cm of torque at 12V, it is built for demanding robotics applications requiring precise position and speed control.
Controllable via UART serial bus, up to 253 servos can be daisy-chained on a single channel. The servo provides real-time feedback on position, load, speed, input voltage, current, and temperature — ideal for closed-loop control systems. Three operating modes (angle servo, speed closed-loop motor, and step mode) make it versatile for a wide range of projects.
Key Features
- 40 kg·cm Torque – High torque output at 12V, suitable for heavy-duty robotic joints
- Brushless Motor – Longer lifespan and quieter operation compared to brushed alternatives
- 360° Magnetic Encoder – 12-bit precision (0.088° resolution, 4096 steps) with no mechanical wear
- UART Serial Bus – Daisy-chain up to 253 servos on one channel, 38400 bps to 1 Mbps baud rate
- Three Operating Modes – Angle servo (0–360°), speed closed-loop motor (continuous rotation), and step mode (relative positioning)
- Two-Way Feedback – Real-time reporting of position, load, speed, voltage, current, and temperature
- Acceleration Control – Configurable speed and acceleration for smooth start/stop motion
- Multi-Loop Position Control – Up to 7 full rotations of position tracking in both directions (default precision)
- One-Button Middle Calibration – Set any position as the centre point for easy installation
- Wide Voltage Input – 6.0–12.6V DC, directly compatible with 3S LiPo batteries
- All-Aluminium Alloy Case – Excellent heat dissipation and mechanical rigidity
- High-Strength Steel Gears – Low noise, high durability under load
- T6061 Aluminium Servo Horns – Corrosion-resistant, included with the servo
- Flat-Shaft Flange Compatible – Mount wheels, timing pulleys, gears, and 6 mm shaft couplings (sold separately)
Specifications
- Model: ST3025
- Input Voltage: 6.0–12.6V DC (typical 12V)
- Stall Torque: 40 kg·cm at 12V
- Torque Constant: 9 kg·cm/A
- No-Load Speed: 0.117 sec/60° (85 RPM) at 12V
- Position Resolution: 0.088° (4096 steps over 360°)
- Static Current: 6 mA
- No-Load Current: 380 mA
- Rated Current: 1.5A
- Stall Current: 4.4A
- Baud Rate: 38400 bps – 1 Mbps (default 1 Mbps)
- ID Range: 0–253
- Gear Type: High-precision steel
- Dimensions: 40 × 20 × 40 mm
Ideal For
- Quadruped and hexapod walking robots
- Robotic arms and grippers
- Pan-tilt camera mounts
- Industrial automation requiring closed-loop control
- Any project needing high-torque, precise servo positioning
Package Contents
- 1× ST3025 Serial Bus Servo
Resources
- Waveshare ST3025 Wiki – Documentation, software, and 3D models
Jargon buster
Plain-language definitions for the technical terms used above.
- baud
- Baud is the signalling rate of a serial connection, often used as the speed setting for UART communication. Matching the baud rate matters because both connected devices must use the same setting for readable data.
- closed-loop control
- Closed-loop control means the system uses feedback, such as motor position or speed, to adjust its output automatically. This matters because it can keep a motor moving accurately even when the load changes, unlike simple open-loop control.
- encoder
- A device attached to a motor or shaft that reports movement, such as rotation steps or position. In a pump system, an encoder can help measure or control how much the motor has turned, which affects how repeatable the watering amount can be.
- ESP32
- ESP32 is a family of microcontroller modules with built-in wireless features such as Bluetooth and WiFi. Knowing this product uses an ESP32-based module helps explain how it provides wireless serial communication and firmware update features.
- kg·cm
- A torque unit often used for hobby servos, meaning how many kilograms of force the servo can hold at a 1 cm arm length. A higher kg·cm rating means the servo can move or hold heavier loads, but power supply current needs may also increase.
- LiPo
- A lithium polymer rechargeable battery commonly used in portable electronics projects. It matters because LiPo batteries need correct charging circuitry and care, and this board includes hardware intended for that battery type.
- servo
- A servo is a motor with built-in position control, usually told to move to a specific angle by a control signal. It matters when you need repeatable movement, such as steering, arms, flaps, or linkages, rather than continuous spinning.
- Stall torque
- The maximum twisting force a servo can produce when its output is held still and cannot move. It helps you judge whether the servo is strong enough for a robot joint, steering linkage, or other load.
- Torque
- A twisting force that causes something to rotate, usually measured in newton-metres or kilogram-centimetres. It matters when choosing motors, servos, gears, and tools because higher torque is needed to lift heavier loads, turn larger wheels, or move mechanisms without stalling.
- UART
- UART is a simple serial connection that sends data over separate transmit and receive wires, often labelled TX and RX. It matters because this module is designed to replace a wired UART cable with a wireless link while keeping the same serial data format.
Find this product in
Robotics & Motion