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This repository showcases how to use the DynamixelSDK C++ and Python APIs to control an Interbotix XSeries Arm.
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Welcome to the dynamixelsdk_xsarm_examples repository! This repo contains example code written in both C++ and Python which can be used to control any Interbotix XSeries Arm. To accomplish this, the DynamixelSDK C++ and Python APIs were used. Additionally, the C++ code was loosely based on the read_write.cpp and sync_read_write.cpp examples provided by Robotis in the DynamixelSDK repository. Similarly, the Python code was loosely based on the read_write.py and sync_read_write.py examples as well.
The examples are based on the Protocol 2.0 communication protocol, so any arm made with Protocol 2.0 compatible Dynamixel servos can be used. Note that while the examples are specific to the WidowX 200 arm, it can be easily modified to work with any of the XSeries arms shown below.
Below is a list of the hardware you will need to get started.
There is not much required to get the robot ready to work as most of the setup is done for you. Just make sure to do the following steps:
To get all the code setup, refer to Robotis's documentation here to download the various APIs, and the instructions here to install them (click the appropriate library on the left-hand side). Then download a zip file with the code or clone this repository wherever you'd like on your computer by typing...
$ git clone https://github.com/Interbotix/dynamixelsdk_xsarm_examples.git
If you're going the 'cpp' route (at least in Linux), navigate to the directory that contains the Makefile and type make. An executable file should pop up called 'interbotix_arm'. To run it, just type ./interbotix_arm.
Both the 'Cpp' and 'Python' examples in this repo do the exact same thing so that you can get a feel for which language you prefer to use. Also, the code in this repo is pretty 'lightweight' in that all code is kept to just a single file. This is to make it easier for you to see how to implement the DynamixelSDK without jumping all over the place to view Python modules or Cpp header files. In that sense, the code shown here is meant to act as a starting point for your own development.
The structure for both files is pretty straightforward and contains two parts. The first part is the largest and just contains many helper functions that can be used to work with the motors. This includes functions that allow you to read/write from/to a single motor or many motors sequentially. It also includes functions to allow you to read/write to multiple motors simultaneously (using the 'sync read/write' feature of the Dynamixel SDK). Note that the main benefit of communicating simultaneously with the motors is that it takes much less time than communicating sequentially, and all data has the same 'time stamp'. For example, if you command the arm motors to move to your desired goal positions simultaneously (and specify each one to take 1.5 seconds), all motors will start and stop at the same time. However, if you were to command the arm motors to move to your desired goal positions sequentially in the same manner, the motors will each start at different times and finish their motions at different times.
Another helper function defined in the first part of both files is called 'CalibrateDualJoint'. This function can be used to calibrate a joint that is composed from two motors (like the shoulder joint in our WidowX 200 arm, or the elbow joint in our WidowX 250 arm). Essentially, the issue that can arise is that the encoder on each motor can show slightly different positions despite having their horns physically aligned during robot assembly. As a result, if a goal position is commanded to that joint, one motor might reach the goal position and stop moving. However, the other motor's encoder might show that the goal position hasn't been reached yet and exert more effort to reach it. As a result, the first motor will exert more effort to keep holding its position. This leads to a vicious cycle that can ultimately lead to one or both motors overloading and torquing off. To prevent that from happening, the 'calibrateDualJoint' function sets the Homing Offset register of the second motor in a dual joint setup so that the second motor's encoder shows the same value as the first motor's encoder.
The second part of both files is the 'main' function where you write code to interact with the robot. It consists of defining vectors/lists of the IDs that make up the arm as well as initial values that should be sent to those motors' registers. It also entails the writing of those initial values to the motors. This portion of the code should be modified depending on which robot arm is being used. Following that 'initial setup part', the code shows how to move the arm, open/close the gripper, and get data like current temperatures and PWMs or currents.
As an FYI, the code does not contain any IK Solvers or higher level APIs. It is only meant to showcase how to implement the DynamixelSDK API so that you don't have to try figuring it out on your own.
For help using the examples, feel free to submit an Issue. Just please include your operating system, any applicable error messages, and the commands you ran as well. You can also contact us directly at trsupport@trossenrobotics.com, but we recommend submitting an Issue so that other people who may be facing the same difficulty can benefit. Note that this repository is actively maintained and any open Issues will be addressed as soon as possible.
Feel free to send PRs to add features (like demos in other languages) or bug fixes. All PRs should follow the same type of organizational structure and documentation as shown in this repo.