Subscriber to Joy Topic in ROS

Question

I want to integrate my XBOX Gamepad in ROS.

The idea is to write a Subscriber to the topic "/joy" and get the data of each Button and each Axes so that I can use them in controlling my robot.

I followed this Tutorial : " http://wiki.ros.org/joy/Tutorials/WritingTeleopNode " and i wanted to edit it. But they took information only from the Axis. I want to get from the Buttons too.

In addition, I don't want to publish these messages as Twist Messages to the turtle node. I want to send them to a new topic.

Can i have some help or maybe a link to package already done for this type of problems ?

I assume this is a continuation of [this SO](https://stackoverflow.com/a/62397914/6069586) — JWCS, Jul 08 '20 at 17:45
Hello, Yes it is. Thanks for the last tip ! But I need later to connect in REAL TIME and I don't want to use ROS-Simulink connection because it doesn't feature Real Time. So I'll manage to have it all in ROS. — Slachcrash, Jul 08 '20 at 18:51

JWCS · Accepted Answer · 2020-07-13T19:31:23.657

When you subscribe to the sensor_msgs/joy msg, you have a float32[] axes, and a int32[] buttons. In your callback for the topic in your node, you can access the members of the msg as such. Arrays are lists in python and vectors in C++. The classic two paradigms are either to publish your new msg from the callback, doing transformations in the callback, and/or store the data from the callback as a global variable, to be used in another msg callback or a timer/periodic callback.

You still have to figure out which buttons map to which number element in the array, however. See the normal numberings in the joy_node docs or jstest/jstest-gtk for help on this; store the mappings as an enum somewhere relevant.

Minimum example:

// joy_to_something_node.cpp

// ROS
#include <ros/ros.h>
#include <sensor_msgs/Joy.h>
#include <std_msgs/Bool.h>
#include <geometry_msgs/Vector3Stamped.h>

// Std Libs
#include <vector>
#include <stdint.h>

// Subscribers
//   joy_sub (sensor_msgs/Joy): "joy"

// Publishers
//   estop_pub (std_msgs/Bool): "estop"
//   btn_dir_pub (geometry_msgs/Vector3Stamped): "joy/btn_dir"

// Parameters
//   frequency (double): 10 Hz
//   lag (double): 0.25 %
//   // could have the mappings as params

enum {
  JOY_BTN_A = 0,
  JOY_BTN_B = 1,
  JOY_BTN_X = 2,
  JOY_BTN_Y = 3,
  JOY_BTN_LB = 4,
  JOY_BTN_RB = 5,
};

// ROS Nodehandles and Publishers
ros::NodeHandle *nh;
ros::NodeHandle *pnh;
ros::Publisher estop_pub;
ros::Publisher btn_dir_pub;

// ROS Callbacks
void joy_cb(const sensor_msgs::Joy::ConstPtr& msg);
void timer_cb(const ros::TimerEvent&);

// ROS Params
double frequency = 10.0;
double lag = 0.25;

// Globals (ex)
std::vector<int32_t> btn_dir_data;
geometry_msgs::Vector3Stamped btn_dir_msg;

int main(int argc, char** argv){
  // Init
  ros::init(argc, argv, "joy_to_something_node");
  nh = new ros::NodeHandle();
  pnh = new ros::NodeHandle("~");

  pnh->getParam("frequency", frequency);
  pnh->getParam("lag", lag);

  btn_dir_msg.header.frame_id = "base_link";

  // Subs
  ros::Subscriber joy_sub = nh->subscribe("joy", 1, joy_cb);
  ros::Timer timer = nh->createTimer(ros::Duration(1.0/frequency), timer_cb);

  // Pubs
  estop_pub = nh->advertise<std_msgs::Bool>("estop", 1);
  btn_dir_pub = nh->advertise<geometry_msgs::Vector3Stamped>("joy/btn_dir", 1);

  // Exec
  ros::spin();
  return 0;
}

void joy_cb(const sensor_msgs::Joy::ConstPtr& msg){
  std_msgs::Bool estop_msg;
  estop_msg.data = msg->buttons[JOY_BTN_LB] > 0; // Should be 1 or zero
  estop_pub.publish(estop_msg);

  btn_dir_data = msg->buttons;
}

void timer_cb(const ros::TimerEvent&){
  btn_dir_msg.header.seq++;
  btn_dir_msg.header.stamp = ros::Time::now();
  // X is fwd, Y is right
  btn_dir_msg.vector.x *= lag;
  btn_dir_msg.vector.x += (1.0 - lag) * (btn_dir_data[JOY_BTN_Y] - btn_dir_data[JOY_BTN_A]);
  btn_dir_msg.vector.y *= lag;
  btn_dir_msg.vector.y += (1.0 - lag) * (btn_dir_data[JOY_BTN_B] - btn_dir_data[JOY_BTN_X]);
  btn_dir_pub.publish(btn_dir_msg);
}

I usually have my CMakeLists.txt have these:

find_package(catkin REQUIRED
    roscpp
    cmake_modules
    std_msgs
    geometry_msgs
)

catkin_package(
  INCLUDE_DIRS include 
#  LIBRARIES [custom libs]
  CATKIN_DEPENDS
    roscpp
    std_msgs
    nav_msgs
#  DEPENDS [sys libs]
)

include_directories(
  include
  ${catkin_INCLUDE_DIRS}
)

add_executable(my_node src/my_node.cpp)
target_link_libraries(my_node ${catkin_LIBRARIES})
set_target_properties(my_node PROPERTIES COMPILE_FLAGS "${CPP_DEVEL_FLAGS}")

Likewise, your package.xml depends can just be the ones you also put in CMakeLists.txt, and don't need multiple declarations if you're using the (modern) format=2.

<buildtool_depend>catkin</buildtool_depend>
<depend>roscpp</depend>
<depend>geometry_msgs</depend>
<depend>std_msgs</depend>

Edit: Added clarifications & the cmake/package.xml.

It works but i changed `ros::now()` to `ros::Time::now()`. There was an error with `btn_dir_msg.header.frame` I changed it to `btn_dir_msg.header.frame_id` and at the end `ros::spin()` needs a `;`. And then everything works perfectly. Thank you very much. The solution worked. — Slachcrash, Jul 13 '20 at 18:58

Subscriber to Joy Topic in ROS

1 Answers1