ROStips

Recommended Practices for ROS development on Aqua

Command line fun

To be able to interact with AQUA through ROS, a little familiarity with [| ROS will go a along way. Once ROS nodes are running, one can interact with AQUA either using programs written in [| Python], [| CPP], or [| Lisp]; or simply using the command line. \\ Here are some examples. Note that these could be run either on the ocu or vision stack.

• Calibrate robot legs and put it in underwater swimmer mode. This is the fiurst thing we must do after turning the robot on.

->[@$ rosservice call /aqua/calibrate @]

• Swim forward for a few seconds

->[@$ rostopic pub -1 /aqua/command aquacore/Command -- 0.5 0 0 0 0 @] ->The last 5 numbers are : linear speed, yaw, pitch, roll, heave. all values are between -1 and 1

• Print state variables (depth)

->[@$ rostopic echo /aqua/state@]

• Set gait

->[@$ rosservice call /aqua/set_gait <gaitname> @] ->Where [@<gaitname> = midoff | hover | hover-midoff | alternate | sine | leftright | sinalt@]

• OLED Display

->[@$ rostopic pub -1 /aqua/display std_msgs/String "Hello World"@]

• Health status: battery voltage, current etc..

->[@$ rostopic echo /aqua/health@]

Autopilot and Depth control

Once calibrated, the robot enters underwater swimmer mode, and can be in one of the three states: Manual, Autopilot, or Autopilot+DepthControl. In manual mode, all commands are interpreted directly. In autopilot mode, the roll and pitch of the robot is automatically stablized. In autopilot+depthcontrol mode the robot also tries to maintain the desired depth by changing the pitch angle of the robot.

• Toggle autopilot (controls pitch and roll to keep robot level)

->[@$ rosservice call /aqua/enable_autopilot [true|false] @]

• Toggle automatic depth control(maintains current depth)

->[@$ rosservice call /aqua/enable_depthcontrol [true|false] @]

• Set Target Depth(depth control must be on)

->[@$ rosservice call /aqua/set_targetdepth xx@]

• To list all autpilot parameters:

->[@$ rosservice call /aqua/get_autopilot_params@]

• To set a param by:

->[@$ rosservice call /aqua/set_autopilot_params -- <K1> ... <K9>@]

• Extra notes:
  • it is possible to disable the connection of the GuiParam to the Autopilot by setting the parameter DisableAutopilotParamGui to 1 in the appropriate .rc file.

Joystick control

• To use the joystick, plug it into the ocu, and run the following command

->[@$ roslaunch aquajoy joy.launch@]

Note that joystick control requires the autopilot to be running and the gait to be set to 'hover-midoff'.

Stop/Go

After you turn on the robot, and have calibrated (by making the service call /aqua/calibrate), the robot is by default in "GO" state. i.e., it will respond to commands given by the user and the autopilot. Even if you have given the robot 0 command (speed=0, yaw=0, roll=0, pitch=0, heave=0), the robot still might move because of the autopilot giving it commands. If you want to stop the robot completely, you must call the [@/aqua/stop@] service.

• [@$ rosservice call /aqua/stop@]

Once this is done, robot will not respond to any command from autopilot or the user. You must call [@/aqua/go@] service to resume operation.

• [@$ rosservice call /aqua/go@]

Cameras

images from the 3 cameras are available on the following topics:

[@<prefix>/image_raw @]: raw bayer encoded images

[@<prefix>/image_mono @]: bayer decoded mono image

[@<prefix>/image_color @]: bayer decoded RGB images

[@<prefix>/image_rect @]: rectified mono image (calibration file must be present)

[@<prefix>/image_rect_color @]: rectified RGB images (calibration file must be present)

Here [@<prefix> = /aqua/back | /aqua/front/left | /aqua/front/right@] To get a live view, we can use the image_view node which comes with ROS imaging pipeline.\\ [@$ rosrun image_view image_view image:=/aqua/back/image_color @]

Tags

Several families of marker/tag have been used. Here we refer to AR tags, but this also applies to other kinds of marker. ARTags can be used to interact with users.

• [@$ rosservice call /aqua/ui/ask "start?"@]

->This will show a prompt with string "start?" on the display, and return the user's AR tag response. If the user canceled the question, then the service call fails, otherwise a boolean response is received.

• [@$ rostopic echo /aqua/tags ar_recog/Tags @]

->show the detected tag id(s), its distance and orientation.

Gazebo Simulator

To launch the gazebo simulator:

• [@$ roslaunch aqua_gazebo aqua.launch @]

An example launch file for joystick control in the simulator

• [@$ roslaunch aqualaunch sim_AP_joy.launch @]

Autostart Process on the vision stack.

• on bootup the Upstart script in /etc/init/aqua-ros.conf calls ~aqua/aqua/init/start_ros.sh
• Overall Process is: [@ boot -> networking started -> /etc/init/aqua-ros.conf -> ~aqua/aqua/init/start_ros.sh -> roslaunch aqualaunch aqua.launch@]

Other ROS pages and resources

See also ROS_stopstart and ROS_packages