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asked 2013-04-08 04:13:56 -0600

Kirill_Sokolov gravatar image

updated 2014-01-28 17:16:05 -0600

ngrennan gravatar image

Hi, I'm beginner in ROS, and don't know where to start my task. I'm studied beginner tutorials and want to build robot. My robot is tricycle with two drive wheels and one slave respectively. Drivers are control by two servo, and servo must controled by ROS via modbus protocol. For a start I want moving it (forward, backward, left, right) from keyboard. And dont know what nodes me need.

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answered 2013-04-08 06:08:50 -0600

Hi Kirill,

I suggest you write a "driver" node for your robot. It should subscribe to a topic called "cmd_vel" (although you can rename it if you want) of type geometry_msgs/Twist. The Twist messages tell you how fast the robot should move forward (msg.linear.x) and how fast it should turn (msg.angular.z); you can ignore all other fields of the message. You can have a look at the turtlebot_node to get an idea how to calculate individual speeds for the two motors from this info. Then you "only" have to send this speed to the servos. :-)

As a publisher, you can use the keyboard teleop node from the turtlebot_teleop package (don't be confused by the name turtlebot, it works with all robots).

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O good, it is what I need, thanks Martin=). So at node "driver" i have only implementation of the protocol modbus. And so turtlebot_teleop publishing messages of type Twist?

Kirill_Sokolov gravatar image Kirill_Sokolov  ( 2013-04-09 09:09:27 -0600 )edit

Exactly, that's how it works. Glad I could help. :-)

Martin Günther gravatar image Martin Günther  ( 2013-04-10 01:20:17 -0600 )edit

answered 2013-04-08 05:37:29 -0600

davinci gravatar image

The industrial stack has some modbus programs but they are for a gripper. Perhaps you can modify them for your servo drivers. But that is not easy for a beginner.

The Robotiq package

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I think I do not need to use this stack, because it is realy dificult for me now=)

Kirill_Sokolov gravatar image Kirill_Sokolov  ( 2013-04-09 09:12:39 -0600 )edit

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Asked: 2013-04-08 04:13:56 -0600

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Last updated: Apr 08 '13