sdf2usd: all revolute joints have an angular drive that prevents joint motion by default

[scpeters]

Environment

• OS Version: macOS 14.7 (Sonoma)
• Source or binary build? source build of main branch (178e136) with Gazebo Ionic

Description

I used the sdf2usd command to convert the
mimic_fast_slow_pendulums_world.sdf
gz-sim example world from SDFormat to USD and then simulated it in IsaacSim.

• Expected behavior: When simulating this world in Gazebo, the pendulums swing when simulation is started. Some of the pendulums are coupled by mimic constraints, though mimic constraints are not the focus of this issue.
• Actual behavior: When simulating this in Isaac Sim, none of the pendulums move. This is because all the revolute joints have an angular drive that prevents joint motion by default (see src/sdf_parser/Joint.cc:240-254).

Steps to reproduce

1. Build gz-usd
2. Download the mimic_fast_slow_pendulums_world.sdf example world into the gz-usd build folder
3. From the gz-usd build folder, convert to USD with the following command:

./bin/sdf2usd mimic_fast_slow_pendulums_world.sdf mimic_fast_slow_pendulums_world.usda

4. Load the USD file in Isaac Sim and start the simulation, observing that pendulums do not swing.

Output

Download the generated mimic_fast_slow_pendulums_world.usda file.