ds4_twist_node crashes on foxy-devel

[3mrrrx]

I am having trouble running the "ds4_twist_node.py " on the "foxy-devel" branch.

the python script crashes on line 73:

val = eval(expr, {}, input_vals)

as the expr is allways of type None!

thanks for the support

[naoki-mizuno]

Thanks for reporting! ds4_twist_node.py seems to be working in my environment. Could you elaborate more about your environment and what you tried so far?

[3mrrrx]

thank you for the quick reply.

I just setup every thing two days ago, so i might have newer versions of some code. but i am not sure about this.

but everything is pretty much standard. i am using the "foxy-devel" branch.

when i echo the /status topic, and the output seams normal.

i also check if the ds4_twist.py is subscribing to the topic and getting the data, which seam to be the case.

i think the error happens in the part where the data from the /status topic is beaing mapped to the twist topic.

this is the error:

`
ros2 run ds4_driver ds4_twist_node.py

Traceback (most recent call last):
File "/home/ubuntu/ros2_example_ws/install/ds4_driver/lib/ds4_driver/ds4_twist_node.py", line 101, in
main()
File "/home/ubuntu/ros2_example_ws/install/ds4_driver/lib/ds4_driver/ds4_twist_node.py", line 95, in main
rclpy.spin(node)
File "/opt/ros/foxy/lib/python3.8/site-packages/rclpy/init.py", line 191, in spin
executor.spin_once()
File "/opt/ros/foxy/lib/python3.8/site-packages/rclpy/executors.py", line 714, in spin_once
raise handler.exception()
File "/opt/ros/foxy/lib/python3.8/site-packages/rclpy/task.py", line 239, in call
self._handler.send(None)
File "/opt/ros/foxy/lib/python3.8/site-packages/rclpy/executors.py", line 429, in handler
await call_coroutine(entity, arg)
File "/opt/ros/foxy/lib/python3.8/site-packages/rclpy/executors.py", line 354, in _execute_subscription
await await_or_execute(sub.callback, msg)
File "/opt/ros/foxy/lib/python3.8/site-packages/rclpy/executors.py", line 118, in await_or_execute
return callback(*args)
File "/home/ubuntu/ros2_example_ws/install/ds4_driver/lib/ds4_driver/ds4_twist_node.py", line 80, in cb_status
val = eval(expr, None, input_vals)
TypeError: eval() arg 1 must be a string, bytes or code object
`

[naoki-mizuno]

Okay, I was able to reproduce the problem. It happens when you don't have the inputs parameter defined. You must either specify it via command line arguments or use ros2 launch ds4_driver ds4_twist.launch.xml.

Although, I did update the code so it doesn't crash when no parameter is defined, so please try out the latest commit.

[3mrrrx]

great!!! thank you....

i am still in the early stages of my project... that is why i was starting the nodes directly....

would be great to add the start/launch cmd to the read me!

[naoki-mizuno]

No problem! The README was indeed outdated so I updated it with the correct instructions.

[3mrrrx]

Hallo Again,

so basically to get the ds4_twist node to work with turtlesim i had to fix another bug.

the basic turtelsim node required a "none-stamped" type for the /cmd_vel topic, but the stamped argument is not passed when set in the launch.xml file.

furthermore the line 74 of ds4_twist.py gives an error:

'AttributeError: 'Twist' object has no attribute 'twist''

and thus has to be changed to something like :

twist = to_pub #.twist

with this quick fix i was able to get turtlesim to work with this node.

the bigger picture.... what i am trying to do with this node is to map the /status topic of this ds4_node to an arbitrary topic. thus making it possilble to control motors and other functions in ros2 using the ds4 controler.

how difficult would it be to add an arbitrary confi.yaml file that would do this kind of mapping?

thank you for the support!

[naoki-mizuno]

The stamped parameter in ds4_twist node controls whether it should output a Twist or a TwistStamped.

[naoki-mizuno]

Not quite sure what you mean by "mapping to an arbitrary topic."

[3mrrrx]

The stamped parameter in ds4_twist node controls whether it should output a Twist or a TwistStamped.

yes... think I am a aware of this part.. but when using the "Twist" output the code using in the library didn't work for two reasons:

1. the Stamped Var is not read from the python code...
2. In case of a "Twist" output the "to_pub" variable does not need to be appended with a "twist" as it is it's self a Twist object. in the current implantation of the code this results in the error:

AttributeError: 'Twist' object has no attribute 'twist'

and thus has to be changed to something like :

twist = to_pub #.twist

[3mrrrx]

Not quite sure what you mean by "mapping to an arbitrary topic."

the idea is to have generic topic that can be mapped with the input of the DS4 for example for topic:

/set_velocity
"id: 1, velocity: axis_left_y "