## page was renamed from ax12_controller_core/Tutorials/CreatingJointController
## page was renamed from ax12_controller_core/Tutorials/Creating a joint controller
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## note.0= [[dynamixel_controllers/Tutorials/ConnectingToDynamixelBus|connecting to Dynamixel bus]]
## descriptive title for the tutorial
## title =Creating a joint controller
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## description = This tutorial describes how to create a joint controller with one or more Robotis Dynamixel motors.
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<<IncludeCSTemplate(TutorialCSHeaderTemplate)>>

<<TableOfContents(4)>>

All files that are created in this tutorial should be saved into my_dynamixel_tutorial package which we have created in [[dynamixel_controllers/Tutorials/ConnectingToDynamixelBus|previous tutorial]].

{{{
roscd my_dynamixel_tutorial
}}}

== Step1: Specify controller parameters ==

<<Anchor(ControllerParameters)>>

First we need to create a configuration file that will contain all parameters that are necessary for our controller. Paste the text below following into tilt.yaml file:

{{{
tilt_controller:
    controller:
        package: dynamixel_controllers
        module: joint_position_controller
        type: JointPositionController
    joint_name: tilt_joint
    joint_speed: 1.17
    motor:
        id: 4
        init: 512
        min: 0
        max: 1023
}}}

'''Note:''' Make sure that the motor id matches the id assigned to your dynamixel actuator.

Now, let's understand the .yaml file. Realize that in the section "motor" there are four parameters: "id", "init", "min" and "max". 
 * The id parameter is arbitrary, you can choose whatever number you like it, except if you are using other dynamixels, then the dynamixel id must be unique.
 * The init parameter has 4096 values, so it varies from 0 to 4095. This parameter is related to the joint initial position, hence init. Since a full rotation is 360 degrees, setting init: 1365 would leave the initial state of the motor 120 degrees from the original reference 0.
 * The min parameter is the minimum rotation the motor can do, it follows the same rule as the init parameter.
 * The max parameter is the maximum rotation the motor can do, it also follows the same rule as the previous parameters.

== Step 2: Create a launch file ==

Next we need to create a launch file that will load controller parameters to the parameter server and start up the controller. Paste the following text into start_tilt_controller.launch file:

{{{
<launch>
    <!-- Start tilt joint controller -->
    <rosparam file="$(find my_dynamixel_tutorial)/tilt.yaml" command="load"/>
    <node name="tilt_controller_spawner" pkg="dynamixel_controllers" type="controller_spawner.py"
          args="--manager=dxl_manager
                --port pan_tilt_port
                tilt_controller"
          output="screen"/>
</launch>
}}}

== Step 3: Start the controller ==

We need to start up the controller manager node first. Please refer to the [[dynamixel_controllers/Tutorials/ConnectingToDynamixelBus|previous tutorial]] on how to do that.

After the controller manager is up and running we finally load our controller:

{{{
roslaunch my_dynamixel_tutorial start_tilt_controller.launch
}}}

This node will load the controller and then exit, the output will look similar to the one below:

{{{
process[tilt_controller_spawner-1]: started with pid [4567]
[INFO] 1295304638.205076: ttyUSB0 controller_spawner: waiting for controller_manager to startup in global namespace...
[INFO] 1295304638.217088: ttyUSB0 controller_spawner: All services are up, spawning controllers...
[INFO] 1295304638.345325: Controller tilt_controller successfully started.
[tilt_controller_spawner-1] process has finished cleanly.
}}}

If everything started up cleanly, you should see "Controller tilt_controller successfully started." message printed to the terminal.

Next, let's list the topics and services that the Dynamixel controller provides:

{{{
rostopic list
}}}

Relevant topics:
{{{
/motor_states/ttyUSB0
/tilt_controller/command
/tilt_controller/state
}}}

/tilt_controller/command topic expects a message of type <<MsgLink(std_msgs/Float64)>> which sets the angle of the joint.

/tilt_controller/state topic provides the current status of the motor, the message type used is <<MsgLink(dynamixel_msgs/JointState)>>.

Relevant services:
{{{
/restart_controller/ttyUSB0
/start_controller/ttyUSB0
/stop_controller/ttyUSB0
/tilt_controller/set_compliance_margin
/tilt_controller/set_compliance_punch
/tilt_controller/set_compliance_slope
/tilt_controller/set_speed
/tilt_controller/set_torque_limit
/tilt_controller/torque_enable
}}}

A few services are provided that change the parameters of the joint, like speed, motor torque limit, compliance margin and slope, etc.

== Step 4: Moving the motor ==
To actually move the motor we need to publish a desired angle to /tilt_controller/command topic, like so:

{{{
rostopic pub -1 /tilt_controller/command std_msgs/Float64 -- 1.5
}}} 

That's it, see the motor move!
Want to control two motors in position mode? Learn how to do it in the [[dynamixel_controllers/Tutorials/Creating a dual joint position|next tutorial]].
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