Differential drive control

[zweistein]

Is there an easy way to use the robot driver on the turtulebot3 burger such that the motion control is differential drive rather than operation space control (ROS cmd_vel)?

In order to control the wheel velocity directly, do I need to use the dynamixel drivers from dynamixel_workbench controller?

[routiful]

Hi :)

Dynamixel in TB3 is controlled by Dynamixel SDK that is included in turtlebot3_core.ino (firmware).

You can make other subscriber to control it with writeVelocity() function

[zweistein]

Thanks for the advice, I would like to use a service with a custom message type (or similar topic) like:

float32 left
float32 right
---
bool success

Can I also create a service server in the tb3.core? Can I use custom .srv or .msg in the core? Are there any examples regarding this feature extension?

[routiful]

rosserial has not supported ros service. Visiting website for rosservice tutorial might be help you

[zweistein]

Thanks for the help, I managed to build in the Arduino IDE a new firmware that includes my message type. Before downloading this new firmware to the board, is there a way to upload form the board to the PC the current firmware to keep it as a backup?

[routiful]

I'm sorry,unfortunately, there is no way to backup it after downloaded.

[zweistein]

I uploaded the new firmware with my_DiffDrive massage. But somehow I have made an arduino ros_lib that does not match the one that is on the RPi because when I launch the driver turtlebot3_robot.launch I get an error:

process[master]: started with pid [5291]
ROS_MASTER_URI=http://192.168.0.1:11311/

setting /run_id to a63083e0-d0df-11e5-9b67-b827ebcfff6c
WARNING: Package name "melodyPlayer" does not follow the naming conventions. It should start witha lower case letter and only contain lower case letters, digits, underscores, and dashes.
process[rosout-1]: started with pid [5304]
started core service [/rosout]
process[turtlebot3_core-2]: started with pid [5315]
process[turtlebot3_lds-3]: started with pid [5322]
process[turtlebot3_diagnostics-4]: started with pid [5323]
[INFO] [1455209472.125106]: ROS Serial Python Node
[INFO] [1455209472.147911]: Connecting to /dev/ttyACM0 at 115200 baud

[ERROR] [1455209474.303776]: Creation of publisher failed: Checksum does not match: d537ed7b8d95065b6c83830430b93911,427f77f85da38bc1aa3f65ffb673c94c

This seems to be located in the: SensorState msg The new firmware of the opencr was built on a PC and not on the RPi but the turtulebot3_msgs pkg has the same version number on bot machines (v 0.1.5)

How can I fix this issue? Where is the mismatch between the two massages?

It looks like the first checksum is from the opencr developer folder while the other is from my ROS libraries:

elod@rbo:~/Arduino$ grep -rl d537ed7b8d95065b6c83830430b93911
OpenCR/arduino/opencr_arduino/opencr/libraries/turtlebot3_ros_lib/turtlebot3_msgs/SensorState.h
OpenCR/arduino/opencr_develop/opencr_ld_shell/opencr_update/waffle.opencr
OpenCR/arduino/opencr_develop/opencr_ld_shell/opencr_update/waffle_turtlebot3_core.ino.bin
OpenCR/arduino/opencr_develop/opencr_ld_shell/opencr_update/burger_turtlebot3_core.ino.bin
OpenCR/arduino/opencr_develop/opencr_ld_shell/opencr_update/burger.opencr
elod@rbo:~/Arduino$ grep -rl 427f77f85da38bc1aa3f65ffb673c94c
libraries/turtlebot3_ros_lib/turtlebot3_msgs/SensorState.h
OpenCR/arduino/opencr_develop/opencr_fw_template/opencr_fw_arduino/src/arduino/libraries/turtlebot3_ros_lib/turtlebot3_msgs/SensorState.h

[routiful]

Hi :)

If you want to add your own msg in Arduino. You have to make new ros_lib

First, make msgs package in your remote PC like turtlebot3_msgs You should concern CMakeLists to build properly.

Second, make new ros_lib. Below link would be help you http://wiki.ros.org/rosserial_arduino/Tutorials/Arduino%20IDE%20Setup

Third, replace [turtlebot_ros_lib](https://github.com/ROBOTIS-GIT/OpenCR/tree/master/arduino/opencr_arduino/opencr/libraries/turtlebot3_ros_lib) to all files you made before

Fourth, build it by Arduino IDE and upload to OpenCR

Fifth, copy and paste msgs package in your RPI and cmake it.

Good luck!

[zweistein]

Thank you for your help. I managed to fix the message issue by following your instructions and regenerating the ROS_lib.

Now, the new driver is working flawlessly :)