Real-Time Physics Simulation Forum 2020-01-21T05:48:55+00:00 https://pybullet.org/Bullet/phpBB3/app.php/feed/topic/12848 2020-01-21T05:48:55+00:00 2020-01-21T05:48:55+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=42585#p42585 <![CDATA[Re: Robot Joints stiff despite no damping and deactivated motors]]> Statistics: Posted by LocknutBushing — Tue Jan 21, 2020 5:48 am

]]> 2020-01-20T00:25:39+00:00 2020-01-20T00:25:39+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=42583#p42583 <![CDATA[Re: Robot Joints stiff despite no damping and deactivated motors]]> Statistics: Posted by LocknutBushing — Mon Jan 20, 2020 12:25 am

]]> 2020-01-19T20:54:26+00:00 2020-01-19T20:54:26+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=42581#p42581 <![CDATA[Re: Robot Joints stiff despite no damping and deactivated motors]]> Statistics: Posted by LocknutBushing — Sun Jan 19, 2020 8:54 pm

]]> 2020-01-19T04:56:05+00:00 2020-01-19T04:56:05+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=42576#p42576 <![CDATA[Re: Robot Joints stiff despite no damping and deactivated motors]]> Statistics: Posted by LocknutBushing — Sun Jan 19, 2020 4:56 am

]]> 2020-01-19T00:07:10+00:00 2020-01-19T00:07:10+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=42575#p42575 <![CDATA[Robot Joints stiff despite no damping and deactivated motors]]>
I'm new to PyBullet, so I wouldn't be surprised if the answer to my question is something fairly obvious.

I used the SolidWorks to URDF exporter to export my bipedal robot design to PyBullet. When the model loads in and I run the simulation in real time, the robot can fall over on its side but the joints can't move.

POSITION_CONTROL has no effect. I also tried velocity control and torque control with force=0, expecting the robot to collapse like a ragdoll, but it continues to act like a figurine. When I load other models in (e.g. biped2d_pybullet.urdf), they collapse like ragdolls.

The robot has 8 revolute joints, and there is no damping specified in the URDF (so it should default to zero).

Strangely enough, the following command just causes the robot to vibrate without moving its joints:

Code: 

for joint in range(p.getNumJoints(robot)):   p.setJointMotorControl2(robot, joint, p.VELOCITY_CONTROL, targetVelocity=50, force=500)
Here is the URDF for reference...

Code: 

<?xml version="1.0" encoding="utf-8"?><!-- This URDF was automatically created by SolidWorks to URDF Exporter! Originally created by Stephen Brawner (brawner@gmail.com)      Commit Version: 1.5.1-0-g916b5db  Build Version: 1.5.7152.31018     For more information, please see http://wiki.ros.org/sw_urdf_exporter --><robot  name="spryped rev02">  <link    name="body">    <inertial>      <origin        xyz="0.00146683164005432 -0.0471884402468711 0.076169520744687"        rpy="0 0 0" />      <mass        value="3.70313889840838" />      <inertia        ixx="0.00429570716761128"        ixy="3.03278167284736E-09"        ixz="-2.3332902790982E-06"        iyy="0.00335471620497785"        iyz="-8.32059718979089E-06"        izz="0.00591264443127761" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/body.STL" />      </geometry>      <material        name="">        <color          rgba="0.752941176470588 0.752941176470588 0.752941176470588 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/body.STL" />      </geometry>    </collision>  </link>  <link    name="left femur">    <inertial>      <origin        xyz="0.0014637 0.050952 -0.056842"        rpy="0 0 0" />      <mass        value="0.30999" />      <inertia        ixx="0.00069104"        ixy="-9.483E-08"        ixz="3.5642E-05"        iyy="0.00070116"        iyz="3.5726E-05"        izz="0.00059024" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left femur.STL" />      </geometry>      <material        name="">        <color          rgba="1 1 1 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left femur.STL" />      </geometry>    </collision>  </link>  <joint    name="1"    type="revolute">    <origin      xyz="0.14547 -0.10347 0.055904"      rpy="0 0 0" />    <parent      link="body" />    <child      link="left femur" />    <axis      xyz="0 -1 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="left tibiotarsus">    <inertial>      <origin        xyz="0.0492126930232007 0.0535384623347315 -0.0842779052215516"        rpy="0 0 0" />      <mass        value="2.87772219223662" />      <inertia        ixx="0.00533528507057087"        ixy="7.37273330855451E-08"        ixz="-1.09674863027954E-07"        iyy="0.0034959774077804"        iyz="0.00148266889917068"        izz="0.00225851284239546" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left tibiotarsus.STL" />      </geometry>      <material        name="">        <color          rgba="0.752941176470588 0.752941176470588 0.752941176470588 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left tibiotarsus.STL" />      </geometry>    </collision>  </link>  <joint    name="2"    type="revolute">    <origin      xyz="-0.04965 0.05165 -0.114"      rpy="0 0 0" />    <parent      link="left femur" />    <child      link="left tibiotarsus" />    <axis      xyz="-1 0 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="left tarsometatarsus">    <inertial>      <origin        xyz="0.0653386529323088 0.00410211529259828 -0.10795430435685"        rpy="0 0 0" />      <mass        value="0.386426569747224" />      <inertia        ixx="0.00159650766426425"        ixy="3.44828011287871E-05"        ixz="-3.16861898281007E-05"        iyy="0.00150999755658726"        iyz="-0.000310806569340194"        izz="0.000553884465795286" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left tarsometatarsus.STL" />      </geometry>      <material        name="">        <color          rgba="1 1 1 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left tarsometatarsus.STL" />      </geometry>    </collision>  </link>  <joint    name="3"    type="revolute">    <origin      xyz="-0.0005 0.10545 -0.16876"      rpy="0 0 0" />    <parent      link="left tibiotarsus" />    <child      link="left tarsometatarsus" />    <axis      xyz="-1 0 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="left toe">    <inertial>      <origin        xyz="0.00549999991446565 0.0246536250465857 -0.0376986621147014"        rpy="0 0 0" />      <mass        value="0.111889664829208" />      <inertia        ixx="0.000217562035776632"        ixy="-7.62138636248417E-13"        ixz="8.82511593906485E-14"        iyy="3.26048621480854E-05"        iyz="-1.99012084230601E-06"        izz="0.00019521205650501" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left toe.STL" />      </geometry>      <material        name="">        <color          rgba="1 1 1 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/left toe.STL" />      </geometry>    </collision>  </link>  <joint    name="4"    type="revolute">    <origin      xyz="0.0444 -0.12296 -0.48273"      rpy="0 0 0" />    <parent      link="left tarsometatarsus" />    <child      link="left toe" />    <axis      xyz="-1 0 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="right femur">    <inertial>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <mass        value="0" />      <inertia        ixx="0"        ixy="0"        ixz="0"        iyy="0"        iyz="0"        izz="0" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right femur.STL" />      </geometry>      <material        name="">        <color          rgba="1 1 1 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right femur.STL" />      </geometry>    </collision>  </link>  <joint    name="5"    type="revolute">    <origin      xyz="-0.14253 -0.10347 0.055904"      rpy="0 0 0" />    <parent      link="body" />    <child      link="right femur" />    <axis      xyz="0 -1 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="right tibiotarsus">    <inertial>      <origin        xyz="-0.0492495047620073 0.053501663392721 -0.0842309932012287"        rpy="0 0 0" />      <mass        value="2.87581042362099" />      <inertia        ixx="0.00533529391220343"        ixy="-7.07923527083726E-08"        ixz="1.22239241571791E-07"        iyy="0.00349593182338153"        iyz="0.00148267255132337"        izz="0.00225848427762363" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right tibiotarsus.STL" />      </geometry>      <material        name="">        <color          rgba="0.776470588235294 0.756862745098039 0.737254901960784 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right tibiotarsus.STL" />      </geometry>    </collision>  </link>  <joint    name="6"    type="revolute">    <origin      xyz="0.04965 0.05165 -0.114"      rpy="0 0 0" />    <parent      link="right femur" />    <child      link="right tibiotarsus" />    <axis      xyz="1 0 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="right tarsometatarsus">    <inertial>      <origin        xyz="-0.0654870852390804 0.00442186689390905 -0.107335066340509"        rpy="0 0 0" />      <mass        value="0.388385413325526" />      <inertia        ixx="0.0015965161251087"        ixy="-3.45791013100941E-05"        ixz="3.15809364112141E-05"        iyy="0.00151198241193131"        iyz="-0.000307831493495565"        izz="0.000551992188290932" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right tarsometatarsus.STL" />      </geometry>      <material        name="">        <color          rgba="1 1 1 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right tarsometatarsus.STL" />      </geometry>    </collision>  </link>  <joint    name="7"    type="revolute">    <origin      xyz="0.0005 0.10545 -0.16876"      rpy="0 0 0" />    <parent      link="right tibiotarsus" />    <child      link="right tarsometatarsus" />    <axis      xyz="1 0 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint>  <link    name="right toe">    <inertial>      <origin        xyz="-0.0160000000855337 0.00863889472199542 -0.0319952935808615"        rpy="0 0 0" />      <mass        value="0.111889664829208" />      <inertia        ixx="0.000217562035776632"        ixy="-7.62138591136326E-13"        ixz="8.82511158185202E-14"        iyy="3.26048621484914E-05"        iyz="-1.99012084072618E-06"        izz="0.000195212056504604" />    </inertial>    <visual>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right toe.STL" />      </geometry>      <material        name="">        <color          rgba="1 1 1 1" />      </material>    </visual>    <collision>      <origin        xyz="0 0 0"        rpy="0 0 0" />      <geometry>        <mesh          filename="package://spryped rev02/meshes/right toe.STL" />      </geometry>    </collision>  </link>  <joint    name="8"    type="revolute">    <origin      xyz="-0.0339 -0.10545 -0.48875"      rpy="0 0 0" />    <parent      link="right tarsometatarsus" />    <child      link="right toe" />    <axis      xyz="-1 0 0" />    <limit      lower="0"      upper="0"      effort="0"      velocity="0" />  </joint></robot>
And here is the .py:

Code: 

import pybullet as pimport timeimport pybullet_dataGRAVITY = -9.81dt = 1e-3iters = 2000physicsClient = p.connect(p.GUI)p.setAdditionalSearchPath(pybullet_data.getDataPath())p.resetSimulation()planeID = p.loadURDF("plane.urdf")robot = p.loadURDF("Desktop/spryped rev02/urdf/spryped rev02.urdf", [0,0,0.8], useFixedBase=0)p.setGravity(0,0, GRAVITY)p.setTimeStep(dt)jointFrictionForce = 0for joint in range(p.getNumJoints(robot)):   p.setJointMotorControl2(robot, joint, p.VELOCITY_CONTROL, targetVelocity=50, force=20)p.setRealTimeSimulation(1)time.sleep(10000)

Statistics: Posted by LocknutBushing — Sun Jan 19, 2020 12:07 am

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