Chtrain_pendulum

[Marco Zanichelli]

Dear all,

I am new to project chrono, I have installed pychrono via anaconda  on windows and I have been running some tests. 

My goal for the moment would be to run a MB simulation of an inverted pendulum, with the later goal of producing a simulation of an inverted pendulum on a cart.

I have seen that at the path "demos\chrono-tensorflow\envs" there is already available a script that should already do the latter.

The problem I'm having is that the demo does not seem to run on the version of pychrono I am using (the latest build for win). I will now refer to the files env_test.py and chtrain_pendulum.py .

The first issue I face is with:

      self.body_rod_shape = chrono.ChVisualShapeCylinder()

      self.body_rod_shape.GetCylinderGeometry().p1= self.cyl_base1

      self.body_rod_shape.GetCylinderGeometry().p2= self.cyl_base2

      self.body_rod_shape.GetCylinderGeometry().rad= self.radius_rod

For which I get the error telling me that the ChVisualShapeCylinder has no attribute GetCylinderGeometry.

I have worked around this problem by just assigning a radius and height to the first of those 4 lines and discarding the other 3, not sure if that is a good solution.

The problem that I have not be able to fix is related to ImposeAbsoluteTransform

which I found in rows 143 and 147 of the chtrain_pendulum.py file. By looking at the documentation for the C++ version, that method is supposed to take as argument a ChFrame, whereas in the demo the argument given is a ChCoordsysd built with a ChVector3d.

 ImposeAbsoluteTransform(chrono.ChCoordsysd(chrono.ChVector3d(0,0,0)))

This gives an error so I tried to build a chframe as follows:

ImposeAbsoluteTransform(chrono.ChFrame(chrono.ChCoordsysd(chrono.ChVector3d(0,0,0))))

but the error is telling me that ChFrame does not exist in pychrono.

How can I fix this issue? Is there anywhere a specific documentation for pychrono or should I switch to the C++ version?

I am sorry if I was unclear and I am of course available to give more information about this. Thank you in advance.

Best regards,

Marco

[Radu Serban]

Marco,

 

You do not indicate what version of the PyChrono conda package you are using. 

From your message, I infer that this is likely a package corresponding to the current main development code. However, that doesn’t seem to be consistent with some line numbers you refer to.  Please make sure you look at the right demo for whatever PyChrono distribution you are using!  Please see the notice (marked in red) at the top of https://api.projectchrono.org/tutorial_table_of_content_pychrono.html

 

Having said that, the scripts in src/demos/python/chrono-tensorflow/envs/ were out-of-date.  I pushed a fix to update them to the latest Chrono API.  Keep in mind that these are not included in any PyChrono conda package yet!

 

My suggestion would be to:

1. Use the C++ API if possible.
2. If you must stick with Python, build your own PyChrono from the C++ sources instead of using a conda package.

In either case, use the latest Chrono code, in the ‘main’ branch of the GitHub repository.

 

(As a side note, to answer your question about ChFrame, in Python you should be using ChFramed – look for other uses of this in the very same script).

 

--Radu

--
You received this message because you are subscribed to the Google Groups "ProjectChrono" group.
To unsubscribe from this group and stop receiving emails from it, send an email to projectchron...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/9c38cb0a-d450-4c42-90bd-13833456c537n%40googlegroups.com.

[Marco Zanichelli]

Thanks, I am now looking into the c++ version