vassar-feetech-servo-sdk 0.2.3

Vassar Robotics' Python SDK for Feetech servo control and position reading

Vassar Feetech Servo SDK

A comprehensive Python SDK and command-line tool for controlling Feetech servos (STS/HLS series).

Features

• 🔌 Auto-detection of serial ports
• 🎯 Support for STS and HLS servos (HLS includes torque control)
• 📖 Read positions from single or multiple servos
• 🎯 Set middle position - Calibrate servos to position 2048
• ✍️ Write position targets (coming soon)
• 💪 Write torque targets (coming soon)
• 🚀 High-performance group sync operations
• 📊 Real-time monitoring with configurable update rates
• 🐍 Clean Python API with servo configuration at initialization
• 💻 Command-line interface for all operations
• 🔧 Context manager support for clean resource management

Installation

From PyPI

pip install vassar-feetech-servo-sdk

From Source

git clone https://github.com/vassar-robotics/feetech-servo-sdk.git
cd feetech-servo-sdk
pip install -e .

Dependencies

• Python >= 3.7
• pyserial >= 3.5

Note: The scservo_sdk is bundled with this package, so no separate installation is needed.

Quick Start

Command Line Usage

# Read from motors 1-6 continuously at 30Hz
vassar-servo

# Set all servos to middle position
vassar-servo --set-middle

# Read from specific motors at 60Hz
vassar-servo --motor-ids 1,3,5 --hz 60

# Use HLS servos (default is STS)
vassar-servo --servo-type hls

# Read once and exit
vassar-servo --once

# Output JSON format (useful for scripting)
vassar-servo --once --json

Python API Usage

from vassar_feetech_servo_sdk import ServoController

# Initialize controller with your servo configuration
servo_ids = [1, 2, 3, 4, 5, 6]
controller = ServoController(servo_ids=servo_ids, servo_type="sts")  # or "hls"
controller.connect()

# Read all configured servos
positions = controller.read_all_positions()
for motor_id, pos in positions.items():
    print(f"Motor {motor_id}: {pos} ({pos/4095*100:.1f}%)")

# Set servos to middle position
success = controller.set_middle_position()
if success:
    print("All servos calibrated to middle position!")

controller.disconnect()

# Using context manager
with ServoController([1, 2, 3], "sts") as controller:
    positions = controller.read_all_positions()
    print(positions)

# Continuous reading with callback
def my_callback(positions):
    print(f"Got positions: {positions}")

with ServoController([1, 2, 3], "hls") as controller:
    controller.read_positions_continuous(
        callback=my_callback,
        frequency=50.0
    )

Advanced Usage

# Initialize with specific configuration
controller = ServoController(
    servo_ids=[1, 2, 3, 4, 5, 6],
    servo_type="hls",  # 'sts' or 'hls'
    port="/dev/ttyUSB0",
    baudrate=1000000
)

# Error handling
from vassar_feetech_servo_sdk import ServoReaderError, PortNotFoundError

try:
    controller = ServoController([1, 2, 3], "sts")
    controller.connect()
    positions = controller.read_all_positions()
except PortNotFoundError:
    print("No servo port found!")
except ServoReaderError as e:
    print(f"Error: {e}")

API Reference

ServoController Class

Constructor

ServoController(servo_ids, servo_type="sts", port=None, baudrate=1000000)

• servo_ids: List of servo IDs to control (e.g., [1, 2, 3, 4, 5, 6])
• servo_type: Type of servo - 'sts' or 'hls' (default: 'sts')
• port: Serial port path (auto-detect if None)
• baudrate: Communication speed (default: 1000000)

Methods

• connect(): Establish connection to servos
• disconnect(): Close connection
• read_position(motor_id): Read single motor position
• read_positions(motor_ids=None): Read multiple motor positions
• read_all_positions(): Read all configured servo positions
• set_middle_position(motor_ids=None): Calibrate servos to middle position (2048)
• read_positions_continuous(motor_ids=None, callback=None, frequency=30.0): Continuously read positions

Utility Functions

• find_servo_port(): Auto-detect servo serial port

Servo Types

• STS: Standard Feetech servos (default) - position and speed control
  • Middle position calibration uses torque=128 method
• HLS: High-end servos with additional torque control capabilities
  • Middle position calibration uses offset calibration (reOfsCal) method

Troubleshooting

Port Not Found

If auto-detection fails, specify the port manually:

# Linux
vassar-servo --port /dev/ttyUSB0

# macOS
vassar-servo --port /dev/tty.usbserial-*

# Windows
vassar-servo --port COM3

Permission Denied (Linux)

Add your user to the dialout group:

sudo usermod -a -G dialout $USER
# Log out and back in for changes to take effect

Connection Failed

1. Check servo power supply
2. Verify baudrate matches servo configuration (default: 1000000)
3. Ensure proper wiring (TX/RX not swapped)

Examples

The package includes several example scripts in the examples/ directory:

• basic_usage.py - Simple example showing how to connect and read servo positions
• continuous_reading.py - Real-time monitoring with custom callbacks
• servo_types.py - Demonstrates differences between STS and HLS servos
• set_middle_position.py - Shows how to calibrate servos to middle position

Acknowledgments

Built on top of the excellent scservo_sdk library for Feetech servo communication.