DuoDMXL Code Overview

General idea for communication between microcontroller and Dynamixel servos

Communication is done through a specific protocol for communication which is embedded in the Dynamixel servomotors. The detailed description can be found in ROBOTIS manual. Specifically, to the Communication 1.0 protocol. The idea is that the microcontroller has to send a package with a specific structure (in the Robotis manual they call this instruction packet). Then the servo responds back with another series of bytes, structured in a similar manner. The response (or status packet in Robotis documentation) contains an error report and additional data if it was requested (e.g., we asked for the angle of the servo).

The package sent to the servo and the response obtained must have the following structure:

Overview of the communication protocol.

Both the package and response always have two bytes as header which must be 0xFF (or 255 as base 10 integer). The instruction byte refers to the action to perform (write, read, etc.). Params is a series of bytes including the address that will be accessed on the servomotor and additional information. Do not worry, DuoDMXL takes care of parsing the package correctly and sending it.

The minimal response obtained for each exchange with the servo will be of six bytes (no data requested). Although the response can be disabled altogether, DuoDMXL assumes that this response is enabled always. In other words, do not turn it off unless you are willing to tweak the source code.

How to use the library

First, copy the source files into your Arduino libraries folder. You can find more instructions on the web. Your folder structure should look similar to this:

../Arduino/
    libraries/
        ..
        DuoDMXL/
            examples/
                ..
            copying.lesser.txt
            DuoDMXL.cpp
            DuoDMXL.h
            keywords.txt
            library.properties
            license.txt
        ..

If your folder structure is correct, you can find the library in the Arduino IDE in the section Sketch->Include Library-> DuoDMXL:

and you can find the examples in File->Examples->DuoDMXL

The DuoDMXL library has to be included in your code:

#include <DuoDMXL.h>

which defines the DynamixelClass() class. However, an instance called Dynamixel is available already. For example, to call the function begin() defined in DuoDMXL.h you can use:

Dynamixel.begin(baud, dataPin);