[GSOC-52] Migration of rexov model

[rakeshv24]

This PR introduces the migration of rexrov model. The following changes have been made:

1. Removed all uuv_simulator plugins.
2. Converted xacro and urdf model files to sdf.
3. Added buoyancy, thruster, and hydrodynamic plugins.
4. Tested in dave_ocean_waves.world

Note: The added mass values for the model do not seem correct and cause the simulation to crash. Therefore, we have used values of LRAUV in their place for the hydrodynamics plugin.

[woensug-choi]

Initial position

• for empty.world
  • Rexrov starts half-way into the ground plane. setting initial z to 2.0 will spawn the rexrov in air and will drop due to the gravity
• for ocean_waves
  • Could we initiate at z=-5 to be able to see it from the beginning.

tag warning in joints

• Multiple warning of unrecognized tag in the joints.

  Warning [Utils.cc:132] [/sdf/model[@name="rexrov"]/joint[@name="thruster6_joint"]/limits:<data-string>:L465]: XML Element[limits], child of element[joint], not defined in SDF. Copying[limits] as children of [joint].

• It seems, it should be <limit> instead of <limits> and should be included within <axis> tag

  • https://github.com/gazebosim/gz-sim/blob/5641ef2cc7bed13e06892d29ffd3663b2f172e76/examples/worlds/sensors.sdf#L257-L267

Imu sensor plugin not included model.sdf

Warning [Utils.cc:132] [/sdf/model[@name="rexrov"]/sensor[@name="imu_sensor"]:<data-string>:L595]: XML Element[sensor], child of element[model], not defined in SDF. Copying[sensor] as children of [model].

to Fix, add below to model.sdf

 <plugin
   filename="gz-sim-imu-system"
   name="gz::sim::systems::Imu">
 </plugin>

Added Mass

• Just to avoid using 0 values, let's use this (from LRAUV)

   <xDotU>-4.876161</xDotU>
   <yDotV>-126.324739</yDotV>
   <zDotW>-126.324739</zDotW>
   <kDotP>0</kDotP>
   <mDotQ>-33.46</mDotQ>
   <nDotR>-33.46</nDotR>

Rexrov in dave_ocean_waves flip upside down when surfaced.

• As the center of gravity is too high to keep it straight, let's add values to bring it down

  # in model.sdf
   <link name="base_link">
      <inertial>
        <pose>0 0 -0.59 0 0 0</pose> # z value changed to -0.6

Collision model

• Collision model doesn't seem to match with visual? was it this way on original dave too? Could we adjust little to match with the visual?
  • It especially looked strange since the collision model at the bottom is extended further out of the vehicle so that the rexrov would not touch ground.

[rakeshv24]

@woensug-choi Thank you for the review! I have addressed all the comments.

Imu sensor plugin not included model.sdf

The issue was not actually with the plugin as it already existed. Rather, I had to move the following snippet inside the link for base_link:

<sensor name="imu_sensor" type="imu">
  <always_on>true</always_on>
  <update_rate>1000.0</update_rate>
  <topic>imu</topic>
</sensor>

Collision model

Yes, it was also defined this way on the original dave repo. However, after fixing the tag warnings, the collision model looks much better!

[woensug-choi]

Thank you! It all look good to me! Go ahead and merge!