This tutorial will show you how to configure the controller for controlling multiple dynamixels simulataneously through different serial ports. Note that this tutorial requires additional hardware in the form of a second USB2Dynamixel or equivalent TTL or RS-485 device. Tutorial Level: Beginner Previous Tutorial: Using the controller
This tutorial assumes that you have a package setup according to the previous tutorial: Using the controller. Open the controller_config.yaml file in my_dynamixel_project, it should look similar to this:
# GLOBAL OPERATION PARAMETERS
loop_rate: 100 # desired rate for joint state updates. actual rate may be less depending on number
# of dynamixels on each port
control_mode: position # control mode, either 'position', 'velocity', or 'effort'
disable_torque_on_shutdown: true # with this enabled the motors will switch off when the controller closes
ignore_input_velocity: false # ignore input velocity commands in position mode (no profile velocity)
diagnostics_rate: 1 # rate to publish diagnostic information
dataport_rate: 1 # rate to read from dynamixel external dataports
# The below values are used as global defaults and are applied for each servo unless overridden in the entry for the servo below
global_max_vel: 5.0 # maximum joint speed (rad/s) (in position or velocity control)
global_torque_limit: 1.0 # maximum motor torque for all modes, given as a fraction of rated max (0-1)
# PORT AND SERVO CONFIGURATIONS
ports:
# PORT LIST
- name: Port_1 # name for this port in config
device: /dev/ttyUSB0 # serial device this port will communicate on
baudrate: 1000000 # baudrate in use
use_legacy_protocol: false # wether to use new 2.0 protocol (false) or legacy 1.0 protocol (true)
group_read_enabled: true # specify whether to use group comms for reading
group_write_enabled: true # specify whether to use group comms for writing
servos:
# SERVO LIST FOR THIS PORT
- id: 1 # (ID set in servo eeprom, must be unique on this port)
joint_name: joint_1 # (MUST BE UNIQUE ACROSS ALL PORTS)
#
# The three values below are mandatory, they define the orientation and zeroing of the dynamixel:
#
zero_pos: 2048 # initial (0 rad) servo position (in raw encoder count)
min_pos: 0 # minimum servo position (in raw encoder count)
max_pos: 4095 # maximum servo position, Note when MIN > MAX ROTATION IS REVERSED
#
# The below arguments are all optional and override the global values:
#
max_vel: 5.0 # maximum joint speed (rad/s) (in position or velocity control)
torque_limit: 1.0 # maximum motor torque for all modes, given as a fraction of rated max (0-1)
- id: 2
joint_name: joint_2
zero_pos: 2048
min_pos: 0
max_pos: 4095
#
# This servo doesn't have any optional values defined, the global defaults will be used
#
Adding a second serial port is very very easy, simply paste in the following at the end of the file:
- name: Port_2
device: /dev/ttyUSB1
baudrate: 3000000
use_legacy_protocol: false
group_read_enabled: true
group_write_enabled: true
servos:
- id: 1 # id only needs to be unique for each port and so id 1 can be reused here
joint_name: joint_3 # name DOES have to be unique though, so we continue the naming scheme
zero_pos: 1000
min_pos: 1000
max: 3000
- id: 2
joint_name: joint_4
zero_pos: 2048
min_pos: 0
max_pos: 4095
Here we can see we have defined a second serial port. this serial port can be configured differently to the first one, with different baudrate and even motor series. It is also important to note that as this is an entirely separate serial bus, the ID's on it can be configured independently from the first port. The only thing that must remain globally unique is the joint name, as this is used to identify the servo when sending and receiving commands. For something different this time, go ahead and change the control_mode to Velocity mode by editing the control_mode parameter at the top of the file. You may also have to change the configuration of motors to suit the hardware you have available. Once that is done, save and close the file.
That is all the changes we needed to make to define new motors, ports and switch the control mode. The controller is designed so that, through this file, it can be quickly configured to whatever application you need. We also do not need to edit the launch file.
Launch the controller the same way we did in the first tutorial:
roslaunch my_dynamixel_project dynamixel_interface_controller.launch
Now, as before, there will be the same topics available to us. Go ahead and run
rostopic echo -w 5 -c /joint_states
You should see, if your configuration matches the one above, the following output:
header:
seq: 84
stamp:
secs: 1485821873
nsecs: 625054383
frame_id: ''
name: ['joint_1', 'joint_2', 'joint_3', 'joint_4']
position: [0.0000, 0.0000, 0.0000, 0.0000]
velocity: [0.0000, 0.0000, 0.0000, 0.0000]
effort: [0.0000, 0.0000, 0.0000, 0.0000]
And to publish a command, we can do the following:
rostopic pub /desired_joint_state sensor_msgs/JointState '{name: ['joint_1', 'joint_2', 'joint_3', 'joint_4'], velocity: [1.0, 1.0, 1.0, 1.0]}' --once
This will command all the motors to move at a velocity of 1 rad/s. As you can see, all joint state information from all servos across all ports is published into the one message simultaneously, this makes it very easy to control any configuration of motors as you never need to worry about which motors are on which port, as long as you send the right value to the right joint_name, the controller takes care of the rest!
That's it! From here it should be straightforward to configure this controller for whatever application you need.