Arjo/experimental/multidrone drag

[aaronchongth]

This PR continues @arjo129's work for lifting and dragging objects using multiple UAVs, and is based on #108.

Few things that this PR does:

• adds a new world for testing dragging overweight objects, mbzirc_ign/worlds/test/multi_drone_drag.sdf. This adds the Large * Handles models mentioned in Update large objects and vessels geometry #130 into the world
• modifies the original examples/multi_uav_demo.py script to allow users to specify each velocity of the twist command
• adds a demo launch script, multi_uav_drag_demo.launch.py: spawns 2 UAVs with suction above the Large Crate Handles model at the front of the vessel
• adds a demo launch script, multi_uav_drag_with_handles_demo.launch.py, spawns 2 UAVs with suction above the Large Dry Box Handles model at the top of the vessel

Instructions on running,

First terminal,

cd ~/mbzirc_ws/src/mbzirc/mbzirc_ign/worlds/test
ign gazebo multi_drone_drag.sdf

Second terminal,

source ~/mbzirc_ws/install/setup.bash
ros2 launch mbzirc_ign multi_uav_drag_demo.launch.py

# or
# ros2 launch mbzirc_ign multi_uav_drag_with_handles_demo.launch.py

Start the simulation,

Third terminal,

source ~/mbzirc_ws/install/setup.bash
ros2 run mbzirc_ign multi_uav_demo.py -z 10 -y -40 -x 0

The UAVs should start dragging Large Crate Handles to the side of the vessel. The process is much slower since the vessel's surface there is curved, it should be much faster if the drones were maneuvered properly too.

drag_demo.mp4

[iche033]

works for me! I made some style fixes in #141 which should help to make CI green.

The default inertial values may be be the best but seem to be helping the drones drag the objects. See if it's possible to give them them with proper values and that dragging still works.

[iche033]

#143 should fix the detach topic issue when there are multiple drones with grippers. I think there are still more detach issues remaining as mentioned in gazebosim/gz-physics#352 (comment)

[iche033]

updated all Large * Handles models on Fuel. Dragging is now working well for me. We still need the detachable joint fix in gazebosim/gz-physics#352 (comment) but that shouldn't block this PR

[aaronchongth]

@iche033 Should we be concerned that the tests have timed out?

[iche033]

I thought it's flaky but I restarted the test a few times and it's still failing. I'm also seeing the test failure locally. There could be an issue. I'll take a closer look tomorrow.

[aaronchongth]

Thanks for the fix! I'll merge this so we can move onto the next PR, #108