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2012-03-28 01:12:52 -0600 answered a question Choosing the right coefficients for Gazebo simulation

Here is the output from Solidworks for the chassis:

Output  coordinate System: -- default --

Mass = 489.90 grams

Volume = 181445.50 cubic millimeters

Surface area = 189380.73 millimeters^2

Center of mass: ( millimeters )
       X = 41.53
       Y = 93.76
       Z = 131.23

Principal axes of inertia and principal moments of inertia: ( grams *
square millimeters )
Taken at the center of mass.
        Ix = (0.00, 0.01, 1.00)        Px = 4157521.05
        Iy = (1.00, 0.00, 0.00)        Py = 5704820.80
        Iz = (0.00, 1.00, -0.01)       Pz = 9356042.65

Moments of inertia: ( grams * square millimeters )
Taken at the center of mass and aligned with the output coordinate system.
       Lxx = 5704820.80        Lxy = 0.00      Lxz = -0.00
       Lyx = 0.00      Lyy = 9355391.53        Lyz = 58176.21
       Lzx = -0.00     Lzy = 58176.21  Lzz = 4158172.18

Moments of inertia: ( grams * square millimeters )
Taken at the output coordinate system.
       Ixx = 18448329.91       Ixy = 1907623.47        Ixz = 2669963.78
       Iyx = 1907623.47        Iyy = 18637105.26       Iyz = 6086030.51
       Izx = 2669963.78        Izy = 6086030.51        Izz = 9309884.18

And here is how I've put it in URDF:

<link name="base_link">
    <inertial>
        <mass value="${chassis_mass}" />
        <origin xyz="0.04153 0.09376 0.13123" />
        <inertia ixx="0.00415752105" ixy="0.0" ixz="0.0"
                 iyy="0.0057048208" iyz="0.0"
                 izz="0.00935604265" />
    </inertial>

Is this correct? I guess this is only correct if my model has the coordinate system aligned with the representation from Gazebo, right?

2012-03-27 01:25:16 -0600 received badge  Editor (source)
2012-03-27 01:24:10 -0600 asked a question Choosing the right coefficients for Gazebo simulation

Hello, I am trying to create an URDF and simulate it in Gazebo for a 4WD Skid steering robot. The chasis is actually a box with the following properties:

  • body_width (base_size_y) : 22 cm
  • body_length (base_size_x) : 27 cm
  • body_height (base_size_z) : 5 cm
  • body_mass : 5 kg

    and wheels:

  • wheel_diameter : 0.12065 m
  • wheel_width : 0.060325 m
  • wheel_mass 0.181436948 kg

    I have created the URDF and a differential drive plugin for gazebo to simulate the model but I have no idea how to choose appropriate values for torque, mu1, mu2, kp, kd and inertia matrix. The values that I am currently using are taken/combined from the erratic/guardian/turtlebot stacks.

    By publishing the odometry (calculated in the plugin) and comparing the robot's position in Gazebo and RViz I can see that the model slips a lot while performing turns.

    Relevant files: myrobot.urdf.xacro myrobot_constants.xacro myrobot_wheel.xacro myrobot_materials.xacro

    Any help is appreciated.

    Thanks in advance.

    Update:

    Here is the output from Solidworks for the chassis:

    Output  coordinate System: -- default --
    
    Mass = 489.90 grams
    
    Volume = 181445.50 cubic millimeters
    
    Surface area = 189380.73 millimeters^2
    
    Center of mass: ( millimeters )
           X = 41.53
           Y = 93.76
           Z = 131.23
    
    Principal axes of inertia and principal moments of inertia: ( grams *
    square millimeters )
    Taken at the center of mass.
            Ix = (0.00, 0.01, 1.00)        Px = 4157521.05
            Iy = (1.00, 0.00, 0.00)        Py = 5704820.80
            Iz = (0.00, 1.00, -0.01)       Pz = 9356042.65
    
    Moments of inertia: ( grams * square millimeters )
    Taken at the center of mass and aligned with the output coordinate system.
           Lxx = 5704820.80        Lxy = 0.00      Lxz = -0.00
           Lyx = 0.00      Lyy = 9355391.53        Lyz = 58176.21
           Lzx = -0.00     Lzy = 58176.21  Lzz = 4158172.18
    
    Moments of inertia: ( grams * square millimeters )
    Taken at the output coordinate system.
           Ixx = 18448329.91       Ixy = 1907623.47        Ixz = 2669963.78
           Iyx = 1907623.47        Iyy = 18637105.26       Iyz = 6086030.51
           Izx = 2669963.78        Izy = 6086030.51        Izz = 9309884.18
    

    And here is how I've put it in URDF:

    <link name="base_link">
        <inertial>
            <mass value="${chassis_mass}" />
            <origin xyz="0.04153 0.09376 0.13123" />
            <inertia ixx="0.00415752105" ixy="0.0" ixz="0.0"
                     iyy="0.0057048208" iyz="0.0"
                     izz="0.00935604265" />
        </inertial>
    

    Is this correct? I guess this is only correct if my model has the coordinate system aligned with the representation from Gazebo, right?

  • 2012-02-16 02:42:53 -0600 received badge  Student (source)
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    2011-12-04 06:33:29 -0600 asked a question RGBDSLAM Ubuntu 11.10

    Hello, I'm trying to build RGBDSLAM on a Ubuntu 11.10 32bit and ROS Electric. The build fails with the following output: http://pastebin.com/1SNcy0pR

    2011-12-03 00:23:17 -0600 asked a question usb_cam low FPS from webcam

    Hello, I found out I can use usb_cam to publish images from my webcam. I tested it with my laptop's webcam and it performs poorly, only 7 FPS.

    OS: Ubuntu 11.10 Oneric

    ROS: Electric (installed via apt-get)

    dmesg output regarding webcam:

    [ 7209.629430] usb 2-1: USB disconnect, device number 3 [ 7211.188071] usb 2-1: new high speed USB device number 6 using ehci_hcd [ 7211.383400] uvcvideo: Found UVC 1.00 device CNF7231 (04f2:b073) [ 7211.395092] input: CNF7231 as /devices/pci0000:00/0000:00:1d.7/usb2/2-1/2-1:1.0/input/input11

    I downloaded http://www.ros.org/wiki/usb_cam and compiled it using rosmake. Compilation log: http://pastebin.com/rJYMR0Bw

    As you can see it complains about libswscale (although I have it installed) but it managed to compile it.

    Starting usb_cam gives the following output: http://pastebin.com/6JQ2CSpP

    Any ideas?

    Thanks in advance.