bullet-featherstone: Add Kinematic feature

[iche033]

🎉 New feature

Summary

Note: bullet version >=3.07 is need for this feature. On Jammy, the version is 3.06 so you'll need to build bullet from source. Noble should come with 3.24

Initial support for kinematic mode in bullet-featherstone implementation.

• Adds a new Kinematic feature
  • Looking for feedback - In the physics plugin, I added the implementation in a new KinematicFeatures class. However, there is already a class with very similar name, KinematicsFeatures (note the extra s) for handling frame semantics. This may create confusion in the future so I'm open to renaming the feature.
• Reads the <kinematic> SDF value sets a link to kinematic if true.
  • sdformat support added in https://github.com/gazebosim/sdformat/pull/1390

Not supported yet - setting velocity to a kinematic link or to a joint connecting kinematic links.

Test it

Added tests to make sure we can make base and non-base links kinematic.

You can also test with gz-sim. Example: the base and upper_link links are set to kinematic in the pendulum_links.sdf.

patch

diff --git a/examples/worlds/pendulum_links.sdf b/examples/worlds/pendulum_links.sdf
index 5eecd1893..bd5ec53d5 100644
--- a/examples/worlds/pendulum_links.sdf
+++ b/examples/worlds/pendulum_links.sdf
@@ -71,6 +71,7 @@
 
     <model name="double_pendulum_with_base">
       <link name="base">
+        <kinematic>true</kinematic>
         <inertial>
           <pose>-0.188749 0 0.75813399999999997 -0.13567899999999999 0 1.5708</pose>
           <mass>256.42500000000001</mass>
@@ -130,6 +131,7 @@
       </link>
       <!-- upper link, length 1, IC -90 degrees -->
       <link name="upper_link">
+        <kinematic>true</kinematic>
         <pose>0 0 2.1 -1.5708 0 0</pose>
         <self_collide>0</self_collide>
         <inertial>

Launch the world with bullet-featherstone plugin:

gz sim -v 4 <path_to_pendulum_links.sdf> --physics-engine gz-physics-bullet-featherstone-plugin

Checklist

• [ ] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 78.36%. Comparing base (492b124) to head (d175730). Report is 16 commits behind head on main.

:exclamation: Current head d175730 differs from pull request most recent head 894645d. Consider uploading reports for the commit 894645d to get more accurate results

Files	Patch %	Lines
include/gz/physics/detail/Kinematic.hh	0.00%	4 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #618      +/-   ##
==========================================
+ Coverage   78.32%   78.36%   +0.04%     
==========================================
  Files         140      141       +1     
  Lines        8069     8136      +67     
==========================================
+ Hits         6320     6376      +56     
- Misses       1749     1760      +11     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[scpeters]

I think we need more documentation on what it means for a Link to be Kinematic, including the documenation for the SDFormat //link/kinematic tag:

• http://sdformat.org/spec?ver=1.11&elem=link#link_kinematic

I'm currently looking at the documentation for ODE and bullet for inspiration:

• https://ode.org/wiki/index.php/Manual#Kinematic_State
• page 19: https://github.com/bulletphysics/bullet3/blob/master/docs/Bullet_User_Manual.pdf

[scpeters]

I think we need more documentation on what it means for a Link to be Kinematic, including the documenation for the SDFormat //link/kinematic tag:

• http://sdformat.org/spec?ver=1.11&elem=link#link_kinematic

I'm currently looking at the documentation for ODE and bullet for inspiration:

• https://ode.org/wiki/index.php/Manual#Kinematic_State
• page 19: https://github.com/bulletphysics/bullet3/blob/master/docs/Bullet_User_Manual.pdf

also for dart: https://github.com/dartsim/dart/blob/main/dart/dynamics/Joint.hpp#L178-L187

[iche033]

I think we need more documentation on what it means for a Link to be Kinematic, including the documenation for the SDFormat //link/kinematic tag:

I expanded the SDF description in https://github.com/gazebosim/sdformat/pull/1462 and updated the Link SetKinematic API doc in c2e2f40