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cant assign the value to 'cmd_msg.data' in runtime.

asked 2018-01-10 00:49:34 -0500

updated 2018-01-10 05:51:46 -0500

I am doing a stepper motor programming.what i want is "when i enter an angle on command line,then stepper should rotate that angle". but i cant assign the value in runtime. help me please.

#include <ros.h>
#include <std_msgs/Empty.h>
#include <std_msgs/UInt16.h>
signed int angle;
int enable2 = 13;
const int stepPin = 9; 
const int dirPin = 8;
int x;

ros::NodeHandle  nh;
void pwm( const std_msgs::UInt16& cmd_msg)
{

 analogWrite(enable2, cmd_msg.data);
angle=analogRead(enable2);


}


ros::Subscriber<std_msgs::UInt16> sub("servo", pwm);

void setup(){
 // pinMode(angle, OUTPUT); 
 pinMode(enable2, OUTPUT);   
 pinMode(stepPin,OUTPUT); 
  pinMode(dirPin,OUTPUT);
  nh.initNode();
  nh.subscribe(sub);

 // servo.attach(9); //attach it to pin 9
}

void loop()
{

   if (angle<0)
     {
       cw();
       delay(100);
      }
 else
   {
    ccw();
    delay(100);
   }
delay(10000);
nh.spinOnce();
  delay(1);
}
void cw()
{
  digitalWrite(dirPin,LOW); 
  for(x = 0; x < 17.77*(angle*-1); x++) {
    digitalWrite(stepPin,HIGH); 
    delayMicroseconds(500); 
    digitalWrite(stepPin,LOW); 
    delayMicroseconds(500); 
  }}
  void ccw()
{
  digitalWrite(dirPin,HIGH); 
  for(x = 0; x < 17.77*angle; x++) {
    digitalWrite(stepPin,HIGH); 
    delayMicroseconds(500); 
    digitalWrite(stepPin,LOW); 
    delayMicroseconds(500); 
  }}
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2 Answers

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answered 2018-01-10 05:07:34 -0500

gvdhoorn is right. You are setting up a subscriber with a callback function called cmd_msg, but cmd_msg has not been defined, further more you seem to have coded your callback function into the loop function so it would run continuously.

You'll need to define a function called cmd_msg and access the angle that the message contains as shown below:

void cmd_msg(const std_msgs::UInt16::ConstPtr& msg)
{
  int angle = msg.data;
  ...
  ...
}

Then add the rest of the code you have inside loop into this callback function.

Have a look at the publisher and subscriber example for some pointers.

Hope this helps.

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Comments

Note that the OP is using rosserial. The tutorial may help, but could also confuse.

gvdhoorn gravatar imagegvdhoorn ( 2018-01-10 05:31:57 -0500 )edit

brothers, can you check the question once more ? i just edited my code.thats why.

and now the problem is i csnt assign the value in runtime . and it shows lost the sync with device.

sudo_melvinyesudas gravatar imagesudo_melvinyesudas ( 2018-01-10 05:48:25 -0500 )edit
2

I'm not your brother, but:

void loop(){
  ..
  delay(10000);
}

you cannot delay the loop() for 10 seconds like that.

gvdhoorn gravatar imagegvdhoorn ( 2018-01-10 05:53:08 -0500 )edit

ok sorry. but still it wont make any difference.

analogWrite(enable2, cmd_msg.data);
    angle=analogRead(enable2);

is it right ?thus can i pass the value which i enter in cammandline to variable angle ?

sudo_melvinyesudas gravatar imagesudo_melvinyesudas ( 2018-01-10 06:20:39 -0500 )edit
0

answered 2018-01-10 02:14:47 -0500

gvdhoorn gravatar image

updated 2018-01-10 02:16:00 -0500

This does not appear to be a ROS problem, but a C/C++ programming one.

So where do you declare / define cmd_msg?

ros::Subscriber<std_msgs::UInt16> sub("servo", &cmd_msg);

According to this, cmd_msg is a function.

angle=cmd_msg.data;

According to this, it should be some kind of structure or object.

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Asked: 2018-01-10 00:49:34 -0500

Seen: 92 times

Last updated: Jan 10 '18