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2016-07-13 18:30:13 -0600 commented answer compiling gzweb with gazebo 7.3

@chapulina Thanks a lot.. That worked great ..

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2016-07-12 21:40:11 -0600 asked a question compiling gzweb with gazebo 7.3

I tried compiling gzweb for the latest version of gazebo..

Gazebo multi-robot simulator, version 7.3.0 Copyright (C) 2012-2016 Open Source Robotics Foundation. Released under the Apache 2 License.

Node version v4.2.6

But I am unable to compile as it throws errors like

gzweb/tools/gzcoarse.cc:113:28: error: ‘const class gazebo::common::SubMesh’ has no member named ‘GetVertex’
     inVertex = _inSubMesh->GetVertex(i);

and this seems to be true as there doesn't seem to be any GetVertex in the Submesh? Does gzweb work with gazebo7 or should I downgrade?

2016-07-03 17:04:10 -0600 asked a question is soft_cfm and soft_erp utilized by ODE

I have been trying to add some softness for my grasping ball experiment and I have been struggling to get anywhere. I have been fiddling around with soft_cfm and soft_erp values.

But if you look at physics/ode/ODEPhysics.cc, you can see that the values for soft_cfm is calculated using the kp and kd, so does the value of soft_cfm and soft_erp have any affect?

// Compute the CFM and ERP by assuming the two bodies form a
  // spring-damper system.
  double kp = 1.0 / (1.0 / surf1->kp + 1.0 / surf2->kp);
  double kd = surf1->kd + surf2->kd;

  contact.surface.soft_erp = (this->maxStepSize * kp) /
                             (this->maxStepSize * kp + kd);

  contact.surface.soft_cfm = 1.0 / (this->maxStepSize * kp + kd);

  // contact.surface.soft_erp = 0.5*(_collision1->surface->softERP +
  //                                _collision2->surface->softERP);
  // contact.surface.soft_cfm = 0.5*(_collision1->surface->softCFM +
  //                                _collision2->surface->softCFM);
2016-06-29 03:41:29 -0600 asked a question Fixed joint moving when grasping

I have fixed joint in my arm joining the shoulder to world, but this joint moves around when I am trying to grasp an object. The entire urdf is here.

The important part is

<!-- Left arm -->
<link name="left_base"/>
<!-- First element of the arm fixed to the parent -->
<joint name="left_base_leftarm__base_joint" type="fixed">
    <origin rpy="-1.570796327 -1.570796327 0" xyz="0.045 0.1665 1.526"/>
    <parent link="left_base"/>
    <child link="leftarm_shoulder_link"/>
</joint>

<link name="world"/>
<joint name="world_left" type="fixed">
    <parent link="world"/>
    <child link="left_base"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
</joint>
<joint name="world_right" type="fixed">
    <parent link="world"/>
    <child link="right_base"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
</joint>
<joint name="world_stand" type="fixed">
    <parent link="world"/>
    <child link="base_link"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
</joint>

Joint Error

2016-06-27 16:06:34 -0600 commented question Picking up a soft ball using dual arm

@hsu Do you have any thoughts on how I could accomplish this.. thanks

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2016-06-22 14:40:36 -0600 commented question Mud plugin with non static models

@hsu Do you mean using the softcfm and softerp params? I tried that and was unable to get it working as mentioned in the link to the other question, so I thought that using mud plugin would be another of approaching this problem.

2016-06-22 14:37:13 -0600 commented question Picking up a soft ball using dual arm

@hsu I modeled the fingers as a box and set the inertia of the diagonal to `Ixx=0.0008125 Iyy=Izz=0.001125`. But that did not help. I am not sure about the cfm and kp values. I used random set of values. Few that I tried are `kd=1, kp=1000, cfm=erp=1`. But then the ball goes through the cylinder.

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2016-06-21 14:44:58 -0600 commented question Mud plugin with non static models

@chapulina I am trying to throw a ball using two arms, but I don't read too much into to the size of the ball as such. Therefore during the process the ball is squeezed a lot (this is how it happens in the real world), I wanted to do the same in gazebo. So just modelling the ball using a sphere doesn't work as it jumps around, so I thought that using the mud plugin would help achieve the process.

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2016-06-20 21:38:23 -0600 asked a question Mud plugin with non static models

With regards to this question where I am tying to pick a soft ball, I tried to use the mud plugin for the entire ball. But mud plugin seems to work only for static objects. If static is false, then the object just falls through the ground plane, is there way of making the plugin work with non static models?

ball.sdf

<model>
  <link>
    .....
    <geometry>
      <sphere>
        <radius>0.13</radius>
      </sphere>
    </geometry>
    <collision name='collision'>
      <geometry>
        <sphere>
          <radius>0.13</radius>
        </sphere>
      </geometry>
      <surface>
        <contact>
          <collide_without_contact>true</collide_without_contact>
          <!-- <collide_without_contact_bitmask>3</collide_without_contact_bitmask> -->
        </contact>
      </surface>
    </collision>
    <sensor name="mud_contact" type="contact">
      <always_on>true</always_on>
      <update_rate>1000</update_rate>
      <contact>
        <collision>collision</collision>
      </contact>
    </sensor>
  </link>
  <plugin name="gazebo_mud" filename="libMudPlugin.so">
    <contact_sensor_name>ball/mud_contact</contact_sensor_name>
    <!-- <contact_surface_bitmask>3</contact_surface_bitmask> -->
    <stiffness>0.8</stiffness>
    <damping>100000.0</damping>
    <link_name>finger::finger_link</link_name>
  </plugin>
</model>
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2016-06-19 23:44:14 -0600 asked a question Picking up a soft ball using dual arm

I am trying to pick a soft ball using two arms and then throw it. I am using a soft ball because I want to be able to throw the ball even when it is slightly crushed by the fingers.

But when I try to run it using gazebo, the ball jumps around on contact. I tried making the object soft using different values of kp, kd, soft_cfm and soft_erp with no success. Any suggestions on how I can achieve this.

ball.sdf

<model name="basketball">
    <static>false</static>
    <link name="ball">
      <inertial>
        <mass>0.25</mass>
        <!-- inertia based on solid sphere 2/5 mr^2 -->
        <inertia>
          <ixx>0.00169</ixx>
          <iyy>0.00169</iyy>
          <izz>0.00169</izz>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyz>0</iyz>
        </inertia>
      </inertial>
      <visual name="visual">
        <geometry>
          <sphere>
            <!-- <radius>0.1172</radius> -->
            <radius>0.13</radius>
          </sphere>
        </geometry>
      </visual>
      <collision name="collision">
        <geometry>
          <sphere>
           <radius>0.13</radius>
          </sphere>
        </geometry>
      </collision>
    </link>
  </model>

finger.sdf

<model name="finger">
  <joint name="asdf" type="fixed">
    <parent link="world"/>
    <child link="finger_link"/>
    <pose frame="">0 0 0 0 1.5707963267948966 0</pose>
  </joint>
  <link name="finger_link">
    <visual name='visual'>
      <pose frame="">0 0 0 1.5707963267948966 0 0</pose>
      <geometry>
        <mesh><uri>model://finger/finger.stl</uri></mesh>
      </geometry>
      <material name="white"/>
    </visual>
    <inertial>
      <pose frame="">0 0 0 0 0 0</pose>
      <mass value="0.250"/>
      <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.0"/>
    </inertial>
  </link>
</model>

image description

Just before the contact between the fingers and the ball image description

Collision model

image description

2016-06-17 21:30:48 -0600 asked a question Models vibrate or fall down

I have a dual armed robot that I am using with ros_control - PositionJointInterface. The problem I am facing is that the one of the arm continuously vibrates when I use the controller without any PID. But the other arm remains fine.

image description

However if I set PID's for the gazebo ros control then the arms just fall down to the ground.

The files are here..

https://github.com/nikhilkalige/baske...

https://github.com/nikhilkalige/robot...