The issue you are running into is not one of whether the simulation works, but whether the simulations have been released as debian (ie:
.deb) packages for a specific OS and ROS release.
Seeing as you tagged this
melodic, I'm going to assume you are running Ubuntu Bionic.
On a Bionic machine you cannot install packages built for ROS Indigo -- that version of ROS just isn't supported on Ubuntu Bionic (see REP-3).
fetch_gazebo_demo (the ROS package) has not been released for Melodic, trying to install it using
apt-get will also not work: the debian package simply doesn't exist (see status_page/ros_melodic_default.html?q=fetch_).
Now as to the question of whether simulations (and I'm assuming Gazebo simulations here) created for ROS Indigo will work on ROS Melodic: the question is more subtle than that. ROS Indigo installed Gazebo 2.2 by default (see
REP-3 again). ROS Melodic comes with Gazebo 9 (see REP-3).
There are quite a few changes between these two versions of Gazebo (and about 6 major versions), both in terms of the API and ABI as well as the dynamic behaviour of the simulator and the things that are simulated (Gazebo 9 has become a lot more realistic in its simulation than Gazebo 2 ever was).
So even while things (ie: plugins or Gazebo models) may work (ie: load) perhaps after fixing some incompatible things, the behaviour they exhibit in Gazebo 9 vs Gazebo 2 may be so different that we can no longer state that they "work".
Note that I'm not referring to the Fetch packages that you mention -- I don't know whether they work -- but wanted to address your question in general.
Originally posted by gvdhoorn with karma: 86574 on 2018-10-12
This answer was ACCEPTED on the original site
Post score: 1
Comment by JerelVelarde on 2018-10-13:
Thanks, had a hint that thsi would be the issue. however I'm having issues with models for melodic; for example the fetch robot, I found this bot under the melodic robots category but in the documentations the instructions are all for indigo :(
Comment by gvdhoorn on 2018-10-14:
That would be something to "complain" about to Fetch. They are the ones who release those packages. I don't own one of those robots, so I don't know, but you could look around to see whether someone forked their pkgs to make them compatible with Melodic.