Not being able to work with gmapping node

[iandresolares]

Hello,
I am working with summit-xl-steel robot platform which has built in two LiDARs and so I am using this the merge node to use both laser data for the navigation stack. My problem is the following:
The merge_node works well but if it is launched at the same time as the hole robot, the node doesn't subscribe to the original laser topics (As reported in this issue: #5), I tried with the answer there to solve this problem but it didn't work for me. What did work tho was to use the timed_roslaunch package, which allows to delay the start of a launch file from another launch file, so by delaying the merge node this works fine.
The problem is when I also use the gmapping node and want it to subscribe to the new /merge_lasers topic instead of the original ones.:
– If I don’t use the delay for the merge node the gmapping node doesn’t work because nothing it’s published in the new /merge_lasers topic since the node it is not subscribing to the original laser topics.
– If I do use the delay (above 3 seconds to work in my case) then the gmapping crashes because it starts before the merge_node and requests a topic which has not been created yet (/merge_lasers).
I have tried also to delay the gmapping node even more so that the topic /merge_lasers has the time to be published but even thought it does, the gmapping node doesn't work.
Any help is apreciated. Cheers,

Andrés

[antoszy]

I have similar problem on ROS noetic. On ROS melodic it works fine.