gazebo_ros_wheel_slip plugin

[scpeters]

Uses dynamic_reconfigure to set wheel slip parameters and publishes wheel slip in JointState message.
Requires gazebo 9.5.

I marked this as WIP since it's a bit weird to use JointState to publish the wheel slip. We should consider a different / custom message.

This inherits from gazebo's WheelSlipPlugin added in the following pull requests:

• https://bitbucket.org/osrf/gazebo/pull-requests/2950/adding-wheelslipplugin-for-adding-wheel/diff
• https://bitbucket.org/osrf/gazebo/pull-requests/2976/wheelslipplugin-add-test-with/diff

Description copied from those pull requests:

This adds a new plugin for tuning the amount of wheel slip experienced by a wheeled robot. It dynamically adjusts the ODE slip1 and slip2 parameters (see Force-dependent slip parameters in ODE user guide). This parameter has units like an inverse damper (velocity / effort). It is often preferred to use normalized parameters, so this plugin accepts unitless longitudinal_slip_compliance and lateral_slip_compliance parameters. The slip1 and slip2 parameters are then dynamically updated by multiplying the normalized slip compliance by the linear wheel spin velocity (radius * angular spin rate) and dividing by a wheel_normal_force parameter supplied to the plugin.

Here's some ASCII art and documentation pasted from the plugin header file:

A graphical interpretation of these parameters is provided below for a positive value of slip compliance. The horizontal axis corresponds to the slip ratio at the wheel, and the vertical axis corresponds to the tangential force ratio (tangential / normal force). As wheel slip increases, the tangential force increases until it reaches the maximum set by the friction coefficient. The slip compliance corresponds to the inverse of the slope of the force before it reaches the maximum value. A slip compliance of 0 corresponds to a completely vertical portion of the plot below. As slip compliance increases, the slope decreases.

+        |                                            .
+        |      _________ friction coefficient        .
+        |     /                                      .
+        |    /|                                      .
+        |   /-┘ slope is inverse of                  .
+        |  /    slip compliance                      .
+        | /                                          .
+        |/                                           .
+      --+-------------------------- slipRatio
+        |

cc: @azeey @jacobperron

[jacobperron]

Friendly ping. Let me know if there's something I can do to help move this forward.

I can help with a ROS 2 port once this lands.

[scpeters]

the reason it's WIP is because it feels weird to publish wheel slip data in a JointStates message. we can remove that publisher for now and merge the rest of it, which allows dynamically updating the wheel slip parameters

or we could make a custom message for wheel slip data. I'm not sure if people are planning to use that or not

[jacobperron]

Although the published wheel slip data sounds useful, I don't think it's necessary on my end. So, I'd be okay removing the publisher for now, with a TODO to add it back once a new message type is defined.

[scpeters]

Although the published wheel slip data sounds useful, I don't think it's necessary on my end. So, I'd be okay removing the publisher for now, with a TODO to add it back once a new message type is defined.

are you up for removing the publisher and pushing to this branch? I'll give you permissions on my fork if so

[jacobperron]

are you up for removing the publisher and pushing to this branch?

I probably don't have time to get to it any time soon, but I'll poke you if that changes.

[jacobperron]

LGTM

[azeey]

Looks good. I tested in gazebo and seems to work great. Left a comment about cleaning up memory.

[scpeters]

I've added a test world:

roslaunch gazebo_ros empty_world.launch \
  verbose:=true \
  world_name:=<REPO_PATH>/gazebo_plugins/test/test_worlds/trisphere_cycle_wheel_slip.world ~~~

then you can use the dynamic reconfigure gui to change the wheel slip parameters for different groups of wheels

[scpeters]

the build.ros.org job is parsing some console error messages from a test as compiler warnings:

• http://build.ros.org/job/Mpr__gazebo_ros_pkgs__ubuntu_bionic_amd64/36/gcc/

19:32:40 [ROSUNIT] Outputting test results to /tmp/ws/test_results/gazebo_plugins/rostest-test_set_model_state_test_set_model_state_test.xml
19:32:41 Gazebo multi-robot simulator, version 9.0.0
19:32:41 Copyright (C) 2012 Open Source Robotics Foundation.
19:32:41 Released under the Apache 2 License.
19:32:41 http://gazebosim.org
19:32:41 
19:32:41 �[0m[ INFO] [1586399561.369891224]: Finished loading Gazebo ROS API Plugin.�[0m
19:32:41 �[0m[ INFO] [1586399561.371208450]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...�[0m
19:32:41 �[1;32m[Msg] �[0m�[1;32mWaiting for master.�[0m�[1;32m
19:32:41 �[0m�[1;32m�[0m�[1;32m[Msg] �[0m�[1;32mConnected to gazebo master @ �[0m�[1;32mhttp://127.0.0.1:11345�[0m�[1;32m
19:32:41 �[0m�[1;32m�[0m�[1;32m[Msg] �[0m�[1;32mPublicized address: �[0m�[1;32m172.17.0.2�[0m�[1;32m
19:32:41 �[0m�[1;32m�[0m�[1;31m[Err] [RenderEngine.cc:725] �[0m�[1;31mCan't open display: �[0m�[1;31m�[0m�[1;31m
19:32:41 �[0m�[1;33m[Wrn] [RenderEngine.cc:93] �[0m�[1;33mUnable to create X window. Rendering will be disabled
19:32:41 �[0m�[1;33m[Wrn] [RenderEngine.cc:293] �[0m�[1;33mCannot initialize render engine since �[0m�[1;33mrender path type is NONE. Ignore this warning if�[0m�[1;33mrendering has been turned off on purpose.
19:32:41 �[0mALSA lib confmisc.c:767:(parse_card) cannot find card '0'
19:32:41 ALSA lib conf.c:4528:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory
19:32:41 ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
19:32:41 ALSA lib conf.c:4528:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory
19:32:41 ALSA lib confmisc.c:1246:(snd_func_refer) error evaluating name
19:32:41 ALSA lib conf.c:4528:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
19:32:41 ALSA lib conf.c:5007:(snd_config_expand) Evaluate error: No such file or directory
19:32:41 ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM default
19:32:41 AL lib: (EE) ALCplaybackAlsa_open: Could not open playback device 'default': No such file or directory
19:32:41 �[1;31m[Err] [OpenAL.cc:84] �[0m�[1;31mUnable to open audio device[�[0m�[1;31mdefault�[0m�[1;31m]
19:32:41  Audio will be disabled.
19:32:41 �[0m�[0m[ INFO] [1586399561.660409081]: waitForService: Service [/gazebo/set_physics_properties] is now available.�[0m
19:32:54 �[0m[ INFO] [1586399561.696777220, 350.334000000]: Physics dynamic reconfigure ready.�[0m
19:32:55 �[1;33m�[0m�[1;36m�[0m�[1;31m�[0m�[1;32m�[0m[Testcase: testset_model_state_test] ... ok
19:32:55 
19:32:55 [ROSTEST]-----------------------------------------------------------------------
19:32:55 
19:32:55 [gazebo_plugins.rosunit-set_model_state_test/FrameTest][passed]

http://build.ros.org/job/Mpr__gazebo_ros_pkgs__ubuntu_bionic_amd64/36/

[scpeters]

@ros-pull-request-builder retest this please

[scpeters]

the build.ros.org issue persists, but I think it's not blocking

[scpeters]

indeed, those false positive compiler warnings are tracked by ros2/ci#316

I believe I've addressed your comments @azeey