Waveshare ST3215 Serial Bus Servo (7.4V, 19.5kg·cm, 360° Encoder)
Precision motion for serious robots
The Waveshare ST3215 (7.4V version) is a smart serial bus servo built for projects where a regular hobby servo runs out of strength or accuracy. It delivers up to 19.5 kg·cm of stall torque at 7.4V, turns a full 360°, and knows its exact shaft angle thanks to a contactless 12-bit magnetic encoder. It runs straight from a 2S LiPo or 7.4V Li-ion pack, so it suits battery-powered robots. Because every servo has its own ID on a shared serial bus, you can wire dozens of joints with a single cable chain and read back live position, speed, load and voltage from each one.
What it is for
Use the ST3215 wherever you need strong, repeatable, closed-loop motion: robot arm joints, walking-robot legs, camera gimbals and animatronic mechanisms. It works as a precise position servo, or can be switched to motor mode for continuous rotation with speed control, so one part covers both jobs.
Key features
High torque: 19.5 kg·cm at 7.4V for strong joints and long lever arms.
Battery friendly: 4 to 7.4V operation, ideal for 2S LiPo and Li-ion powered robots.
360° magnetic encoder: 4096 steps per turn (about 0.088° each). No wiper to wear out, unlike potentiometer servos.
Serial bus control: Up to 253 servos on one UART line, each with a unique ID.
Two-way feedback: Read position, speed, load and input voltage in real time.
Two modes: Angle (servo) mode or continuous-rotation (motor) mode, switchable by command.
Smooth motion: Programmable speed and acceleration for soft starts and stops.
Easy setup: One-button mid-point calibration lets you mount the horn at any angle.
Rugged build: High-precision metal gears, glass-fibre-reinforced nylon case, aluminium horns, dual-shaft design.
Technical specifications
Model: Waveshare ST3215 (7.4V version)
Operating voltage: 4 to 7.4V DC (7.4V recommended)
Stall torque: 19.5 kg·cm at 7.4V
No-load speed: 0.192 s/60° (about 52 RPM) at 7.4V
No-load current: about 150 mA
Stall current: 2.5 A
Rotation range: 360°, no mechanical limit
Position sensor: 12-bit magnetic encoder, 4096 steps (0 to 4095)
Gear ratio: 1:345
Gear material: high-precision copper and steel metal gears
Feedback: position, speed, load, input voltage
Communication: half-duplex UART serial bus, TTL level
Baud rate: 38.4 kbps to 1 Mbps (default 1 Mbps)
Servo ID range: 0 to 253
Control modes: servo (position) and motor (continuous rotation)
Dimensions: about 45.2 × 24.7 × 35 mm
Weight: about 55 g
Projects you can build
Desktop robotic arm: 4 to 6 DOF arms for pick-and-place, drawing or teaching kinematics.
Quadruped robot dog: 8 or 12 servos running from one 2S battery for walking and trotting gaits.
Hexapod walker: chain 18 servos on one bus and coordinate them from a single controller.
Pan-tilt camera and AI vision: face or object tracking with a Raspberry Pi, Jetson or ESP32-CAM.
Humanoid robots and animatronics: heads, arms and puppets that move smoothly and hold position.
Wheeled rovers and turntables: use motor mode for drive wheels, rotating displays or 3D-scanner platforms.
ROS and STEM lab projects: real joint feedback makes it ideal for learning closed-loop control.
Getting started
The ST3215 needs a serial bus servo driver board (for example a Waveshare Bus Servo Adapter or a general driver board) and a 7.4V supply or 2S battery that can handle the combined current of all servos. Do not power this version from 12V. Control it from Arduino, ESP32, Raspberry Pi or a PC using the open-source libraries and examples. The driver board and power supply are sold separately.
In the box
1 × Waveshare ST3215 serial bus servo (7.4V)
1 × servo horn and screw accessory set
1 × 3-pin servo cable