I want to simulate pouring objects into a cup

[miyukin73]

Hello,
I'd like to simulate pouring objects into a cup.

So, I created the STL file of the cup in CAD.

However, I found the following text at the URL site below.

" if you want to model a non-convex shape, you have to decompose it into a union of convex geoms and attach all of them to the same body. "
https://mujoco.readthedocs.io/en/latest/overview.html

In fact, using the STL file of the created cup (black object), the object (green sphere) did not fit into the cup as shown in the attached photo.

I saw the answer to question "hollow cynlinder geom #19",
but as a beginner, I don't know how to convert from concave to convex and would like to know.

Thank you!
pouring objects.zip

[kevinzakka]

Hi @miyukin73, you can use V-HACD to decompose the mesh into approximate convex submeshes. I've made a tool to simplify this process here. Run the bash script to install V-HACD and then you can run the V-HACD executable on your mesh. Note you'll want to convert the STL to an OBJ file to use it with V-HACD, you can do that with either Blender or trimesh.

[kevinzakka]

You can either include the cup file in the jaco file or copy paste the relevant meshes / textures / geoms into the jaco file. Whatever works for your current workflow.

[miyukin73]

Thank you very much @kevinzakka

I transcribed the contents of cup.xml into jaco.xml.

However, when I run it, I get the following error

Is there any solution to this problem?

I would appreciate it if you could reply when you have time.
Thank you.

[kevinzakka]

Not 100% but looks like you're using mujoco_py? Unclear what MuJoCo version it uses, but OBJ support was only added in 2.1.2.

[miyukin73]

I used mujoco-2.1.5 and was able to run the simulation successfully!

Thank you very much for your very kind support!!

[miyukin73]

Hello, @kevinzakka

I am very sorry for asking the same question.
I have been away for a little while, but I tried to run the following program that you taught me before to convert from stl to obj files again.

import trimesh

mesh = trimesh.load("cup.stl")
mesh.export("cup.obj", file_type="obj")

However, the following error occurred.

Data not utf-8! Trying ISO-8859-1 (confidence 0.73)

I feel that it is not a problem with the stl file because the same error occurred with the file that worked before.
What is the problem?
I would appreciate it if you could tell me.
Thank you in advance.

[miyukin73]

Hello @kevinzakka

I am sorry for the frequent interruptions...

I was successful if I just run the XML file using mujoco-2.1.5.
However, when I run the same XML file using mujoco_py, I get the error below.

As far as I confirm, mujoco_py was updated in November 2021 and MuJoCo was updated in May 2022,
so maybe mujoco_py has not kept up with updates...?

Anyway, I would like to ask if you know of any solution to this problem.

Thank you.

[yuvaltassa]

Hi,

I made you an example model. Copy this file into models/mug/ and load it

mug with balls

<mujoco model="mug with balls">
  <include file="mug.xml"/>
  <size nconmax="1000" njmax="3000"/>
  <worldbody>
    <light pos="0 0 1" diffuse=".3 .3 .3"/>
    <composite type="particle" count="5 5 5" spacing="0.011" offset=".005 .003 .15">
      <geom size=".005" rgba=".8 .2 .1 1" solref=".005 1"/>
    </composite>
  </worldbody>
</mujoco>

This is what it look like:

mug_with_balls.mp4

[miyukin73]

Hello @yuvaltassa

Thank you so much for taking time out of your busy schedule to create the example model!
I wanted to create a simulation environment just like the one in the movie...!!!

However, I also got the error below when using mujoco-2.1.5.

I am really sorry to trouble you with something so basic, but I am new to mujoco and don't know how to deal with it,
so I would like to know.
Thank you very much.

[yuvaltassa]

It says FILE_NOT_FOUND, your file is not where you think it is...

[miyukin73]

Hello @yuvaltassa

Sorry... I didn't activate the conda...
Thank you very much for your advice.

However, when I tried to run the XML file in the environment again, I got the following error.

Do you know what the cause is...?
Thank you.

[yuvaltassa]

Can you try reducing shadowsize (line 4 in mug.xml)? Try 1024 and let me know what happens.

[miyukin73]

Thank you very much for your advice, @yuvaltassa !

I reduced shadowsize, and the XML file is successfully executed!!

However, I have two additional questions.

The first question is regarding the video you sent me, in the video it looked like you were clicking and knocking over the cup,
how can that be done...?

The second question is regarding mujoco_py,
I still get the error below when I use mujoco_py. is it a problem with the version of mujoco_py that it cannot read obj files?

I am sorry to keep repeating this, but I would like to know.
Thank you in advance.

[yuvaltassa]

in the video it looked like you were clicking and knocking over the cup, how can that be done...?

I'm using simulate, the built-in native viewer. Hit 'F1' for basic help and take it from there. I think specifically for this you want double-click to select the cup, then control-drag to apply a torque.

I still get the error below when I use mujoco_py. is it a problem with the version of mujoco_py that it cannot read obj files?

Sorry, we don't support mujoco-py. It is an unmaintained package. Please switch to the native bindings and/or dm_control.

[miyukin73]

Thanks for letting me know, @yuvaltassa .
could over the cup using simulate!

I understand.
I would like to ask you if you know anything about dm_control.
I want to use python code to display a Jaco2 arm robot and the mug in the simulation environment,
and then Jaco2 grabs the mug and tilts it.

Is this possible with dm_control?

[miyukin73]

Hi @yuvaltassa
I’m sorry for repeating myself.

Or, I would like to do something like rotating a mug at a constant angular acceleration, like I did simulate.
Are there any sample programs?