dynamixel-api

Table of Contents

1. Introduction
2. Getting Started
   1. Prerequisites
   2. Hardware Setup
   3. Installation
3. Usage
   1. Increase Baud Rate
   2. Reduce Latency
   3. Control the Dynamixel Motor
   4. Custom Motor Support
4. Contribution
5. License

Introduction

dynamixel-api is a Python wrapper for the Dynamixel SDK library, designed to control various Dynamixel motors. This library provides a high-level API that simplifies motor control through a DynamixelConnector class, which establishes and manages serial connections, and a Motor class that offers direct access to frequently used control parameters. Users can read and write motor control fields easily, enabling quick setup for common robotic manipulation tasks. The library's modular design can accommodate multiple types of Dynamixel motors, making it versatile for various robotics applications.

Getting Started

Prerequisites

Make sure you have a working Python 3 installation. If not, follow the instructions on the Python 3 download page.

Hardware Setup

To use the dynamixel-api library, you need to have a Dynamixel motor and the appropriate hardware to connect it to your computer. The motors are controlled via a U2D2 Power Hub Board, which connects to the motor with a 4-pin JST EH cable. The U2D2 Power Hub Board is connected to a computer via a USB cable, allowing the user to send commands to the motor using the Dynamixel SDK library.

Installation

To install the dynamixel-api library, simply run the following command:

pip install dynamixel-api

or clone the repository and install the package locally:

pip install git+https://github.com/TimSchneider42/dynamixel-api.git

Usage

The dynamixel-api library provides out-of-the-box support for the following hardware:

• ROBOTIS RH-P12-RN and RH-P12-RN(A) Grippers: These are advanced robotic grippers powered by Dynamixel motors.
• DYNAMIXEL XL430-W250-T Motor: The motor used to control the actuated-UMI gripper.

Increase Baud Rate

To increase the baud rate of your Dynamixel motor, first download the Dynamixel Wizard 2.0. Select the Baud Rate tab and set the baud rate to the desired value. The default baud rate for the XL-430-W-250-T motor is 57600, but you can set it to a higher value (e.g. 2000000) for faster communication. Make sure to set the same baud rate in your code when creating the Connector instance.

Reduce Latency

If you encounter latency issues when using the dynamixel-api library, you can try reducing the latency by running the reduce_latency.sh script. This script sets the Ubuntu latency_timer to 1. Run the script with the following command:

bash reduce_latency.sh

Control the Dynamixel Motor

First, create a Connector instance of your motor and call the connect() function to establish a serial connection to the motor. For example, to connect to an XL430-W250-T motor:

from dynamixel_api import XL430W250TConnector

connector = XL430W250TConnector(device="/dev/ttyUSB0", baud_rate=57600, dynamixel_id=1)
connector.connect()
...
connector.disconnect()

Connector instances can also be used as context managers:

with XL430W250TConnector(device="/dev/ttyUSB0", baud_rate=57600, dynamixel_id=1) as connector:
    ...

The connector object allows reading and writing of arbitrary addresses of the motor's control table:

print(connector.read_field("torque_enable"))
connector.write_field("torque_enable", 1)
print(connector.read_field("torque_enable"))

For a comprehensive list of its entries, refer to the docs of your motor. Alternatively for this example, all entries are listed in dynamixel_api/models/xl430w250t.py. Note that the motors have to be disabled ("torque_enabled" has to be set to 0) for EEPROM values to be written, while RAM values can be written at any time.

For convenience, the Motor class provides direct access to the most commonly used fields:

import time
from dynamixel_api import Motor

motor = Motor(connector)
motor.torque_enabled = True
motor.goal_position = 1.0
time.sleep(3.0)
motor.torque_enabled = False

For a full example of the usage of this package, refer to example/xl430w250t_open_close.py.

Custom Motor Support

To use a custom motor, define its control table (EEPROM and RAM Fields) and implement a Connector class based on the motor's documentation. Refer to the dynamixel_api/models folder for examples and templates.

After defining the Connector class, you can use the Motor class to control the motor as shown above. If you want to have additional control over the motor, you can create a child class of the Motor class and add custom methods.

Finding the correct baud rate and Dynamixel ID

If the baud rate and/or Dynamixel ID is unknown, the find_grippers(dynamixel_api/sweep.py) method can be used to find those parameters by performing a full sweep. It can be invoked as follows from the command line after installing the package:

dynamixel-sweep

You can pass following arguments to the command:

• --device: The device path to the serial port (default: /dev/ttyUSB0)
• --baud-rate: The baud rate to use for the sweep (default: 9_600 57_600 115_200 1_000_000 2_000_000 3_000_000 4_000_000 4_500_000 10_500_000)

Contribution

We welcome contributions to this repository. If you would like to contribute, please fork this repository and submit a pull request with your changes.

License

This project is licensed under the MIT License - see the LICENSE file for details.