Step 4: OMX Teleoperation Example

This tutorial shows an example of OMX teleoperation using the Dynamixel Easy SDK.
With an OMX leader and follower, you can create your own teleoperation system in just a few lines of code.

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_step4.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_leader("/dev/ttyACM1", 1000000);
  dynamixel::Connector connector_follower("/dev/ttyACM0", 1000000);

  std::unique_ptr<dynamixel::Motor> leader_motor1 = connector_leader.createMotor(1);
  std::unique_ptr<dynamixel::Motor> leader_motor2 = connector_leader.createMotor(2);
  std::unique_ptr<dynamixel::Motor> leader_motor3 = connector_leader.createMotor(3);
  std::unique_ptr<dynamixel::Motor> leader_motor4 = connector_leader.createMotor(4);
  std::unique_ptr<dynamixel::Motor> leader_motor5 = connector_leader.createMotor(5);
  std::unique_ptr<dynamixel::Motor> leader_motor_gripper = connector_leader.createMotor(6);

  std::unique_ptr<dynamixel::Motor> follower_motor1 = connector_follower.createMotor(11);
  std::unique_ptr<dynamixel::Motor> follower_motor2 = connector_follower.createMotor(12);
  std::unique_ptr<dynamixel::Motor> follower_motor3 = connector_follower.createMotor(13);
  std::unique_ptr<dynamixel::Motor> follower_motor4 = connector_follower.createMotor(14);
  std::unique_ptr<dynamixel::Motor> follower_motor5 = connector_follower.createMotor(15);
  std::unique_ptr<dynamixel::Motor> follower_motor_gripper = connector_follower.createMotor(16);

  follower_motor1->enableTorque();
  follower_motor2->enableTorque();
  follower_motor3->enableTorque();
  follower_motor4->enableTorque();
  follower_motor5->enableTorque();
  follower_motor_gripper->enableTorque();

  while (true) {
    int present_position1 = leader_motor1->getPresentPosition().value();
    int present_position2 = leader_motor2->getPresentPosition().value();
    int present_position3 = leader_motor3->getPresentPosition().value();
    int present_position4 = leader_motor4->getPresentPosition().value();
    int present_position5 = leader_motor5->getPresentPosition().value();
    int present_position_gripper = leader_motor_gripper->getPresentPosition().value();

    follower_motor1->setGoalPosition(present_position1);
    follower_motor2->setGoalPosition(present_position2);
    follower_motor3->setGoalPosition(present_position3);
    follower_motor4->setGoalPosition(present_position4);
    follower_motor5->setGoalPosition(present_position5);
    follower_motor_gripper->setGoalPosition(present_position_gripper);
  }
}

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.
In OMX, two separate OpenRB adapters are used for the leader and follower motors, so create two Connector objects with different port names.
On OMX, the default baud rate is 1,000,000.

Port names may vary depending on your system configuration.

int main(){
  dynamixel::Connector connector_leader("/dev/ttyACM1", 1000000);
  dynamixel::Connector connector_follower("/dev/ttyACM0", 1000000);

Create a Motor objects for each Dynamixels, using the createMotor method of the Connector class.

In OMX, the leader motors have IDs 1 to 6, and the follower motors have IDs 11 to 16.

  std::unique_ptr<dynamixel::Motor> leader_motor1 = connector_leader.createMotor(1);
  std::unique_ptr<dynamixel::Motor> leader_motor2 = connector_leader.createMotor(2);
  std::unique_ptr<dynamixel::Motor> leader_motor3 = connector_leader.createMotor(3);
  std::unique_ptr<dynamixel::Motor> leader_motor4 = connector_leader.createMotor(4);
  std::unique_ptr<dynamixel::Motor> leader_motor5 = connector_leader.createMotor(5);
  std::unique_ptr<dynamixel::Motor> leader_motor_gripper = connector_leader.createMotor(6);

  std::unique_ptr<dynamixel::Motor> follower_motor1 = connector_follower.createMotor(11);
  std::unique_ptr<dynamixel::Motor> follower_motor2 = connector_follower.createMotor(12);
  std::unique_ptr<dynamixel::Motor> follower_motor3 = connector_follower.createMotor(13);
  std::unique_ptr<dynamixel::Motor> follower_motor4 = connector_follower.createMotor(14);
  std::unique_ptr<dynamixel::Motor> follower_motor5 = connector_follower.createMotor(15);
  std::unique_ptr<dynamixel::Motor> follower_motor_gripper = connector_follower.createMotor(16);

Enable Follower Torque

Enable the torque of the follower motors for teleoperation.

  follower_motor1->enableTorque();
  follower_motor2->enableTorque();
  follower_motor3->enableTorque();
  follower_motor4->enableTorque();
  follower_motor5->enableTorque();
  follower_motor_gripper->enableTorque();

Leader and Follower Control Loop

In a loop, read the present position of the leader motors using the getPresentPosition method and set the goal position of the follower motors to the same value using the setGoalPosition method.

  while (true) {
    int present_position1 = leader_motor1->getPresentPosition().value();
    int present_position2 = leader_motor2->getPresentPosition().value();
    int present_position3 = leader_motor3->getPresentPosition().value();
    int present_position4 = leader_motor4->getPresentPosition().value();
    int present_position5 = leader_motor5->getPresentPosition().value();
    int present_position_gripper = leader_motor_gripper->getPresentPosition().value();

    follower_motor1->setGoalPosition(present_position1);
    follower_motor2->setGoalPosition(present_position2);
    follower_motor3->setGoalPosition(present_position3);
    follower_motor4->setGoalPosition(present_position4);
    follower_motor5->setGoalPosition(present_position5);
    follower_motor_gripper->setGoalPosition(present_position_gripper);
  }
}

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 = leader_motor->getPresentPosition();
  if (!result_int32.isSuccess()) {
    std::cerr << dynamixel::getErrorMessage(result_int32.error()) << std::endl;
    return 1;
  }
  int present_position = result_int32.value();

Compile and Run

You can compile and run the code using the following commands

$ g++ dxl_tutorial_4.cpp -o dxl_tutorial_4 -l dxl_x64_cpp
$ ./dxl_tutorial_4