Troubleshooting¶

Import errors with ROS 2 sourced¶

When ROS 2 is sourced, PYTHONPATH points at ROS’s own Python packages, which can shadow numpy, matplotlib or other packages of your environment and break imports. Unset it for the commands that install or run the library:

env -u PYTHONPATH ~/venvs/vmc/bin/python -c "import virtualmodelcontrol"

For a conda environment, Installation shows how to do it once and for all.

No virtual environment on Ubuntu¶

python3 -m venv fails with “ensurepip is not available” until the python3-venv package is installed:

sudo apt install python3-venv

CasADi does not import¶

pip installs CasADi from a prebuilt wheel. If pip starts building CasADi from source, or import casadi fails, there is no wheel for your Python version or platform. Create the environment with a Python version that CasADi has a wheel for. The file names on its PyPI page show them: cp312 means Python 3.12.

Compiling takes long¶

Compiling a controller takes a fraction of a second for the robots in this library, and a control step about 20 µs. A large model compiles slower. Compile once, and change gains and goals while running with controller.set, which needs no new compile. Only Params that are not live (geometry, masses, attachment points) need a new compile after a change; see parameters.

Figures and LaTeX¶

viz.use_style() sets text with LaTeX when latex and dvipng are installed. If LaTeX then fails on a missing package, install the fonts and packages matplotlib needs, or use the style without LaTeX, which keeps the Computer Modern look:

sudo apt install texlive-latex-extra texlive-fonts-recommended cm-super dvipng

from virtualmodelcontrol import viz

viz.use_style(usetex=False)

matplotlib 3.11 drops minus signs from figures saved as PDF with LaTeX; use matplotlib 3.10 for those until it is fixed.

Saving videos¶

viz.animate writes MP4 with the ffmpeg that pip installs with imageio-ffmpeg. On a platform without that wheel, install ffmpeg with your package manager, or save a .gif or .webp instead.