SDFormat to MJCF: Add support for force/torque sensors

[azeey]

🎉 New feature

Toward #16

Summary

The handling of //force_torque/frame is a little tricky. My interpretation of the SDFormat spec is that the reported torque is always about the joint origin, so I'm setting the pos of the mjcf site for the sensor to the joint origin regardless of the value in //force_torque/frame. For the rotation, I'm setting the rotation of the mjcf site for the sensor to the rotation of the body indicated by //force_torque/frame.

Test it

test_add_sensor.py test_add_joint.py

Checklist

• [x] Signed all commits for DCO
• [x] 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)
• [x] codecheck passed (See contributing)
• [x] All tests passed (See test coverage)
• [x] 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

Merging #50 (88bc827) into main (7900a5a) will increase coverage by 0.10%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #50      +/-   ##
==========================================
+ Coverage   97.62%   97.73%   +0.10%     
==========================================
  Files          16       16              
  Lines         589      617      +28     
==========================================
+ Hits          575      603      +28     
  Misses         14       14              

Impacted Files	Coverage Δ
...ormat_to_mjcf/sdformat_to_mjcf/converters/joint.py	97.43% <100.00%> (+0.51%)	:arrow_up:
...rmat_to_mjcf/sdformat_to_mjcf/converters/sensor.py	100.00% <100.00%> (ø)
...format_to_mjcf/sdformat_to_mjcf/sformat_to_mjcf.py	100.00% <100.00%> (ø)

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[traversaro]

The handling of //force_torque/frame is a little tricky. My interpretation of the SDFormat spec is that the reported torque is always about the joint origin, so I'm setting the pos of the mjcf site for the sensor to the joint origin regardless of the value in //force_torque/frame. For the rotation, I'm setting the rotation of the mjcf site for the sensor to the rotation of the body indicated by //force_torque/frame.

Cross-link to a related sdformat issue: https://github.com/gazebosim/sdformat/issues/130 .