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Simulation of a Barometric Tactile Sensor Array

Prerequisites

  • MuJoCo 2.3.6
  • Drake (tested with 1.12.0 - 1.22.0)

Installing and Running

  1. Create catkin workspace (mkdir -p mj_ros_demo_ws/src && cd mj_ros_demo_ws && catkin init)
  2. Clone the demo repository into the workspace with git clone https://github.com/ubi-agni/mujoco_ros_demos src/mujoco_ros_demos
  3. Download ros package dependencies into catkin workspace src folder with vcs import src < src/mujoco_ros_demos/hydroelastic_contacts/baro_5x5/baro.deps
  4. Install MuJoCo and Drake by extracting the tar container and setting the following environment variables:
export MUJOCO_DIR=PATH_TO_EXTRACTED_MUJOCO_DIR
export DRAKE_DIR=PATH_TO_EXTRACTED_DRAKE_DIR

export LD_LIBRARY_PATH=$MUJOCO_DIR/lib:$DRAKE_DIR/lib:$LD_LIBRARY_PATH
export CPATH=$MUJOCO_DIR/include:$CPATH
export LIBRARY_PATH=$MUJOCO_HOME/lib:$LIBRARY_PATH
  1. Build catkin workspace with catkin b baro_demo and source the devel workspace.
  2. Run roslaunch baro_demo baro_demo.launch use_sim_time:=true.

sensor readings can be fetched on the /baro topic, e.g. in the terminal with rostopic echo /baro.

Play around with the launchfile arguments, if you like.

Explanaition

This demo spawns a simulated 5x5 barometric sensor array and a measure device which can be used to penetrate the sensor surface. The following section in the model file provides the config for the hydroelastic contact properties of geoms:

<custom>
    <!-- All custom parameters related to contact surfaces have the prefix cs:: -->
    <!-- Options are traingles or plygons, though currently only triangles are supported -->
    <text name="cs::HydroelasticContactRepresentation" data="kTriangle"/>
    <!-- If this option is enabled, the contact surface will be rendered in sim -->
    <numeric name="cs::VisualizeSurfaces" data="1"/>
    <!-- If cs::ApplyContactSurfaceForces is 0 Contact Surfaces are only computed for tactile sensors and standard mujoco contacts are used to compute physics -->
    <numeric name="cs::ApplyContactSurfaceForces" data="1"/>
    <!-- Contact properties for each geom: hydroelasticModulus, dissipation, resolutionHint.
    A rigid object has hydroelasticModulus of 0 and dissipation of 1. 
    A soft box with a resolution hint of 0 uses a resolution automatically computed by drake. -->
    <numeric name="cs::measure_tip" data="0 1.0 0.01 0.3 0.3"/>
    <numeric name="cs::baro_silicone" data="5e4 5.0 0 0.3 0.3"/>
</custom>

This next part defines a mocap body -- a body which is not affected by physics -- and attaches the body of the measure instrument to it with a weld constraint. This allows us to send target positions for the mocap body which controls the position of the measure.

    <body name="mocap" mocap="true" pos="0. 0.0 2.2">
        <geom type="box" size="0.05 0.05 0.05" rgba="1.0 0 0 1." contype="0" conaffinity="0" />
        <site name="mocap_site" type="box" size="0.25 0.25 0.25" rgba="1.0 0 0 0" group="0" />
    </body>

</worldbody>

<equality>
    <weld body1="mocap" body2="measure_body" active="true" solref="0.1 1" solimp=".3 .4 0.01"/>
</equality>

target positions can be sent with a ros service call to /mujoco_server/set_mocap_state, e.g.

rosservice call /mujoco_server/set_mocap_state "mocap_state:
  name:
  - 'mocap'
  pose:
  - header:
      seq: 0
      stamp:
        secs: 0
        nsecs: 0
      frame_id: 'world'
    pose:
      position:
        x: 0.0
        y: 0.0
        z: 1.6
      orientation:
        x: 0.0
        y: 0.0
        z: 0.0
        w: 1.0"

Alternatively, the measure or the mocap body (the red box) can be dragged around by double-clicking and ctrl + right mouse button. Note that if a mocap position command has been sent before, the mocap body will jump between the sent position and the one it is being dragged to.

In the simulation window, clicking t will toggle transparency of bodies, which makes inspection of the collisions easier. Pressing w toggles wireframe mode, making the rendered contact surface better visible.