• This tutorial shows you how to read data from a Dynamixel using the Dynamixel Easy SDK.

NOTE: It assumes that you have already installed and built the SDK.

Make cpp file

• Create a new C++ source file Open it with your editor.

  $ touch tutorial_step2.cpp
  

Check the Port Names

• Before running the code, check the port name of the connected Dynamixel.
• For General
  • OpenRB-150: ttyACM0: USB ACM device
  • U2D2: FTDI USB Serial Device converter now attached to ttyUSB0

    $ sudo dmesg | grep tty
    

Source Code Description

#include "dynamixel_easy_sdk/dynamixel_easy_sdk.hpp"

int main(){

  dynamixel::Connector connector("/dev/ttyACM0", 57600);
  std::unique_ptr<dynamixel::Motor> motor1 = connector.createMotor(1);

  auto result_int32_t = motor1->getPresentPosition();
  int present_position = result_int32_t.value();
  std::cout << "Present Position: " << present_position << std::endl;
}

Add Header Files

• Add dynamixel_easy_sdk/dynamixel_easy_sdk.hpp to the top of your CPP file. This class is included in the Dynamixel SDK package.

  #include "dynamixel_easy_sdk/dynamixel_easy_sdk.hpp"
  

Create Connector and Motor Object

• Create a Connector object with port name, baud rate, and protocol version to manage the communication.(Only protocol 2.0 is supported)

  int main(){
    dynamixel::Connector connector("/dev/ttyACM0", 57600);
  

• Create a Motor object for each Dynamixel servo you want to control, using the createMotor method of the Connector class.
• This method takes the motor ID as an argument and returns a unique pointer to a Motor instance. (shared_ptr is also available)

    std::unique_ptr<dynamixel::Motor> motor1 = connector.createMotor(1);
  

• This process throws a DxlRuntimeError if the object creation fails.

Get Present Position

• You can read the present position of the motor using the getPresentPosition method.
• Return type of this method is Result<int32_t, Error>. You can get the actual position value using the value() method of the Result object.

    auto result_int32_t = motor1->getPresentPosition();
    int present_position = result_int32_t.value();
    std::cout << "Present Position: " << present_position << std::endl;
  

Error Handling

• To ensure your code is robust, every method that sends a command to the motor returns a Result object that encapsulates values and errors.
• This object lets you safely check for any communication or device errors before proceeding.
• You can check for communication errors and device(dynamixel) errors using the Result object.

• If you use value() when error occurred without checking for errors, it may throw an exception.

  Example

    auto result_int32_t = motor1->getPresentPosition();
    if (!result_int32_t.isSuccess()) {
      std::cerr << dynamixel::getErrorMessage(result_int32_t.error()) << std::endl;
      return 1;
    }
    int present_position = result_int32_t.value();
  

Compile and Run

• You can compile and run the code using the following commands

  $ g++ tutorial_step2.cpp -o tutorial_step2 -l dxl_x64_cpp
  $ ./tutorial_step2
  

Full Source Code With Error Handling

#include "dynamixel_easy_sdk/dynamixel_easy_sdk.hpp"

int main(){
  dynamixel::Connector connector("/dev/ttyUSB0", 2.0, 57600);
  std::unique_ptr<dynamixel::Motor> motor1 = connector.createMotor(1);

  auto result_int32_t = motor1->getPresentPosition();
  if (!result_int32_t.isSuccess()) {
    std::cerr << dynamixel::getErrorMessage(result_int32_t.error()) << std::endl;
    return 1;
  }
  int present_position = result_int32_t.value();
  std::cout << "Present Position: " << present_position << std::endl;
  }
}