Uuv_simulator: <neutrally_buoyant> tag does nothing.

Hi,

thanks for reporting, I'll check that. Meanwhile, you can have your vehicle positively buoyant if you set the neutrally_buoyant flag to zero and set the volume instead, like in the rexrov model https://github.com/uuvsimulator/uuv_simulator/blob/master/uuv_descriptions/models/rexrov/urdf/rexrov.gazebo.xacro#L32.
The volume is then used to compute the buoyancy force vector.

Hello,

I tried to set the volume to be quite large. Not as large as the rexrov, and it was still sinking. I will try that and get back to you, but I tried to shift my volume up and my mass down to force it to float. I'll get back to you with results in a second though.

So I set my volume to 3.1093918 m3 and my mass to 0.123497, and my vehicle still sank. I may try to set it to exactly what you have the rexrov set for it's volume, and even set the <box> tag to what the rexrov had as well as it's hydrodynamic model. So I don't know where to check for an issue.

Did you set <neutrally_buoyant>0</neutrally_buoyant>?

@musamarcusso I tried setting <neutrally_buoyant> to 0 and 1. No real change.

Hi @atomoclast, is this the vehicle your want to model?

http://www.videoray.com/images/specsheets/2016/2016_P4STANDARDBASE_FINAL.pdf

I will try to replace these parameters here to reproduce this.

@musamarcusso Yes, this is the vehicle I'm trying to model.

I have a mesh file if you need it.

I just tried to launch a test box with what I understand is the buoyancy plugin and attempted it with both the neutrally_buoyant tag set to 0 as well as 1, and the box still sank both times. It was also printing the [Wrn] [UnderwaterObjectPlugin.cc:207] Relative angular acceleration is invalid -nan error over and over.

I have both files below for you to review. Not sure what the issue is. I added the .txt extension so I can upload in the comment.

box.urdf.txt
upload_box.launch.txt

As soon as you see the error Relative angular acceleration is invalid our UnderwaterObjectPlugin will not apply any forces or torques anymore, since this is a clear indicator of the physics engine is broken.

I had a look at your box definition:

<inertia ixx="0" ixy="0" ixz="0" iyy="0" iyz="0" izz="0" />

This is the culprit. No rigid body should have moments of inertia nor a mass of zero. Because of the way Gazebo computes accelerations from forces/torques, this will result in a division by zero.

Let us know if this solves your issue.

@sebastianscherer That makes perfect sense. I just used a basic ellipsoid to estimate my inertia for my vehicle, and it's floating now.

On to figuring out the Thruster plugin! I'm getting some issues there too.

In the gazebo terminal I see:

[Msg] Thruster #0 initialized
[Msg]   - Link: videoray_pro4/thruster_0
[Msg]   - Robot model: videoray_pro4
[Msg]   - Input command Gazebo topic: /videoray_pro4/thrusters/0/input
[Msg]   - Thrust output Gazebo topic: /videoray_pro4/thrusters/0/thrust
[Msg] Thruster #1 initialized
[Msg]   - Link: videoray_pro4/thruster_1
[Msg]   - Robot model: videoray_pro4
[Msg]   - Input command Gazebo topic: /videoray_pro4/thrusters/1/input
[Msg]   - Thrust output Gazebo topic: /videoray_pro4/thrusters/1/thrust
[Msg] Thruster #2 initialized
[Msg]   - Link: videoray_pro4/thruster_2
[Msg]   - Robot model: videoray_pro4
[Msg]   - Input command Gazebo topic: /videoray_pro4/thrusters/2/input
[Msg]   - Thrust output Gazebo topic: /videoray_pro4/thrusters/2/thrust
[Msg] JointStatePublisher::robotNamespace=videoray_pro4

In the thruster terminal, I see:

process[videoray_pro4/thruster_allocator-1]: started with pid [26422]
[INFO] [1500390755.909692, 0.000000]: ThrusterManager::update_rate=50
output_dir= /home/andrew/Development/ underwater_ws/install/share/videoray_description/config/videoray_pro4
ThrusterManager: updating thruster poses
conversion_fcn= proportional
conversion_fcn_params= {'gain': 0.00031}
transform: /videoray_pro4/base_link -> /videoray_pro4/thruster_0
could not get transform from: /videoray_pro4/base_link
to: /videoray_pro4/thruster_0
[]

I just ran rosrun tf view_frames and this was the output. I see the TF tree show a transform between the base_link and the thruster...
frames.pdf

The frames between world and the vehicle's base_link are generated by the message_to_tf node, which is part of the hector_localization package. The RexROV model's launch file example is this

https://github.com/uuvsimulator/uuv_simulator/blob/master/uuv_descriptions/models/rexrov/launch/upload_rexrov_default.launch#L31

How did you state this in the launch file?

@musamarcusso As per the wiki tutorial, I called out the transform as follows:

<!-- Publish state and tf for in relation to the world frame -->
            <group ns="$(arg namespace)">
                <node name="ground_truth_to_tf" pkg="message_to_tf" type="message_to_tf" output="screen">
                    <param name="odometry_topic" value="/$(arg namespace)/pose_gt" />
                    <param name="frame_id" value="/$(arg world_frame)" />
                    <param name="tf_prefix" value="$(arg namespace)" />
                </node>
            </group>

It seems different than the line you called out above. I will try that now.

Can you try replacing the block you sent me by this

<include file="$(find uuv_descriptions)/models/common/launch/message_to_tf.launch">
    <arg name="namespace" value="$(arg namespace)"/>
</include>

If this fix works, I will correct the tutorial right away.

I tried to replace my block with your block, but it wouldn't work. Only way it worked was will both blocks called together.

VelocityControllerNode: initializing node Thruster #0 - proportional - thrusters/0/input transform: /videoray_pro4/base_link -> /videoray_pro4/thruster_1 Thruster #1 - proportional - thrusters/1/input transform: /videoray_pro4/base_link -> /videoray_pro4/thruster_2 Thruster #2 - proportional - thrusters/2/input transform: /videoray_pro4/base_link -> /videoray_pro4/thruster_3 could not get transform from: /videoray_pro4/base_link to: /videoray_pro4/thruster_3 [<uuv_thrusters.models.thruster_proportional.ThrusterProportional object at 0x7efc4bdb8a50>, <uuv_thrusters.models.thruster_proportional.ThrusterProportional object at 0x7efc4bdb8c10>, <uuv_thrusters.models.thruster_proportional.ThrusterProportional object at 0x7efc4bd4c190>] TAM= [[ 1. 0. 0. ] [ 0. 0. 0. ] [ 0. 0.99999968 0.99999968] [ 0. 0.09999997 -0.09999997] [ 0.1 0.15249995 0.15249995] [ 0. 0. 0. ]] ThrusterManager: ready ThrusterManager: ready
Now I need to see why it can't get the TF from thruster 3.

I'm able to launch my version of the joy_velocity.launch, but I'm un able to control the vehicle with my controller.

I've been trying to debug things, and I'm comparing the outputs of the rqt_graph visualization of the nodes. These are the two networks I'm seeing. Not sure why it isn't working exactly.

Another update I just realized:

Wiki calls out: <xacro:property name="prop_mesh_file" value="file://$(find uuv_descriptions_example)/models/rov_example/mesh/propeller.dae"/>

Should be: <xacro:property name="prop_mesh_file" value="file://$(find uuv_descriptions)/models/rexrov/mesh/prop.dae"/>

Hi @atomoclast,

no, it is correct in the tutorial. The example in the tutorial is not a funcional example, that's why I put this README.md in the mesh folder, so this prop_mesh_file has to be edited by the person making the new vehicle model.
The joy_velocity is defined per default for the XBox controller mapping. What is the model of the controller that you have?
Do you have your files somewhere in Github? I could try running it and give you a feedback.

@musamarcusso I have uploaded the repo here: https://github.com/atomoclast/videoray_description/tree/feature/DEEP-291

Hello @musamarcusso, have you had a chance to look through this repo yet?

Yes, I cloned it. I will give a feedback later today.