Mujoco-py: Touch Sensors

Created on 18 Jan 2017 · 4Comments · Source: openai/mujoco-py

Are touch sensors supported by mujoco-py? I am trying to create one using this xml-file:

<worldbody>
        <camera name="maincam" mode= "fixed" fovy="75" euler="0 0 0" pos="0 0 .75"/>
        <body name="particle" pos="0 0 0.03">
            <inertial pos="0 0 0" mass="5" diaginertia="166.667 166.667 166.667"/>
            <geom name="particle_geom" type="capsule" fromto="-0.01 0 0 0.01 0 0" size="0.05" rgba="0.9 0 0.1 0.6" />
            <joint name="ball_x" type="slide" pos="0 0 0" axis="1 0 0" />
            <joint name="ball_y" type="slide" pos="0 0 0" axis="0 1 0" />

            <sensor>
                <site name="sensorsurf" pos="0 0 0.035" size="0.05" type="ellipsoid" rgba="0.3 0.2 0.1 0.3"/>
                <touch name="touchsensor" site="sensorsurf" />
            </sensor>

        </body>

</worldbody>

However I'm getting the following error:

/site-packages/mujoco_py/mjcore.py", line 37, in __init__
    raise MjError(buf.value)
mujoco_py.mjcore.MjError: XML Error: Schema violation: unrecognized element

Element 'sensor', line 19, column 13

Do you have an example xml-file of how to define touch sensors?

If touch sensors are not yet supported what would need to be done to integrate them?
As an alternative to touch sensors, is there a straightforward way to obtain contact forces from mujoco-py?

Source

febert

Most helpful comment

Any idea how to access sensory data in mujoco_py/gym?

MahanFathi on 6 Dec 2017

👍5

All 4 comments

It is working now, the bindings indeed support touch sensors. I had to modify the xml to have the sensor defined outside the body.

Here is xml which works:

<worldbody>
    <camera name="maincam" mode= "fixed" fovy="75" euler="0 0 0" pos="0 0 .75"/>
    <body name="particle" pos="0 0 0.03">
        <inertial pos="0 0 0" mass="5" diaginertia="166.667 166.667 166.667"/>
        <geom name="particle_geom" type="capsule" fromto="-0.01 0 0 0.01 0 0" size="0.05" rgba="0.9 0 0.1 0.6" />
        <joint name="ball_x" type="slide" pos="0 0 0" axis="1 0 0" />
        <joint name="ball_y" type="slide" pos="0 0 0" axis="0 1 0" />
        <site name="sensorsurf" pos="0 0.045 0" size=".03 .03 .03" type="ellipsoid" rgba="0.3 0.2 0.1 0.3"/>

    </body>

</worldbody>

 <sensor>
     <touch name="touchsensor" site="sensorsurf" />
 </sensor>

febert on 19 Jan 2017

Any idea how to access sensory data in mujoco_py/gym?

MahanFathi on 6 Dec 2017

👍5

Find the file with the simulation data, for example gym/gym/envs/mujoco/humanoid.py
There you can find the sensor data with (in this issue case):

self.sim.data.get_sensor('touchsensor') # Gives one value
self.sim.data.sensordata # Gives array of all sensorvalues

Michielskilian on 11 Dec 2018

👍4

It is working now, the bindings indeed support touch sensors. I had to modify the xml to have the sensor defined _outside_ the body.

Here is xml which works:

<worldbody>
    <camera name="maincam" mode= "fixed" fovy="75" euler="0 0 0" pos="0 0 .75"/>
    <body name="particle" pos="0 0 0.03">
        <inertial pos="0 0 0" mass="5" diaginertia="166.667 166.667 166.667"/>
        <geom name="particle_geom" type="capsule" fromto="-0.01 0 0 0.01 0 0" size="0.05" rgba="0.9 0 0.1 0.6" />
        <joint name="ball_x" type="slide" pos="0 0 0" axis="1 0 0" />
        <joint name="ball_y" type="slide" pos="0 0 0" axis="0 1 0" />
        <site name="sensorsurf" pos="0 0.045 0" size=".03 .03 .03" type="ellipsoid" rgba="0.3 0.2 0.1 0.3"/>

    </body>

</worldbody>

 <sensor>
     <touch name="touchsensor" site="sensorsurf" />
 </sensor>

Hey,
I want to add torque sensors in joints of my robotic arm but when I add it and read data, it changes in 3 axis. I think it should change only in one axis (z on frame in joint). Am I wrong?

I use 'site name="lumi_torque3" zaxis="0 0 1"/' in body and 'torque name="lumi_joint3_torque" site="lumi_torque3" /' in sensor tag.