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2018-08-08 01:40:15 -0500 marked best answer Building URDF from scratch, how to calculate inertial values?

I've been stuck on this for a while. Most resources online point to complex equations even for the simplest of shapes. Surely there is some sort of software in which I can just build my robot and have it generate inertial values?

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2018-01-11 19:55:36 -0500 marked best answer Could use some guidance on how to navigate while avoiding obstacles

I have a physical robot that needs to navigate from its current location A to some point B defined by a GPS coord while avoiding all physical obstacles.

The robot is equipped with a GPS of its own and has a LIDAR. Just not sure how to approach this.

The LIDAR has limited range so the robot can't see very far, this can cause it to get stuck in certain situations. If the robot was making a map of the environment as it went along, something like SLAM, then this could be avoided.

I'm just not sure how I can do SLAM while also navigating to a specific goal while also doing obstacle avoidance.

I looked at this tutorial: http://wiki.ros.org/cob_tutorials/Tut... but didn't learn from it.

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2017-10-27 18:10:53 -0500 asked a question Could use some guidance on how to navigate while avoiding obstacles

Could use some guidance on how to navigate while avoiding obstacles I have a physical robot that needs to navigate from

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2017-09-07 05:41:24 -0500 edited question how to play bag files from c++ or python class

how to play bag files from c++ or python class At the moment I'm reading bag files and publishing back the results: bag

2017-09-07 05:40:44 -0500 commented answer how to play bag files from c++ or python class

Updated with explanation of what I'm trying to do. Again not sure if it's the best way to go about it but don't know of

2017-09-07 05:38:37 -0500 edited question how to play bag files from c++ or python class

how to play bag files from c++ or python class At the moment I'm reading bag files and publishing back the results: bag

2017-09-07 05:12:30 -0500 commented answer how to play bag files from c++ or python class

Thanks, that saves me a lot of trouble. However I've noticed that the playbag is fairly inconsistent. I'm playing back a

2017-09-07 05:10:00 -0500 marked best answer how to play bag files from c++ or python class

At the moment I'm reading bag files and publishing back the results:

bag = rosbag.Bag('2017-09-04-16-11-56.bag')
rospy.init_node('talker', anonymous=True)
rate = rospy.Rate(0.5) # Not sure what this should be set to  
pub = rospy.Publisher('cmd_vel', Twist, queue_size=10)
for topic, msg, t in bag.read_messages(topics=['cmd_vel']): 
    pub.publish(msg)
    rate.sleep()

But this is not the same as playing back the data since it does not take into account the time difference between each message.

In this answer ( https://answers.ros.org/question/1446... ) the poster included their solution which as far as I can tell, just publishes all the messages to a topic.

So now the only thing I can think of is to go look through the source code of the player.cpp and see how they are publishing rosbag messages at the same rate at which they were recorded ( https://github.com/ros/ros_comm/blob/... )

Is there a better way?

EDIT:

I'm trying to build a model of a real life differential drive robot in gazebo. I created a URDF which is just some simple shapes but think it should be accurate enough.

However it's difficult to figure out the right parameters that the URDF should have. For example, I don't know what the weight of the caster wheels are or how much torque is being applied to the front wheels. I can't take the robot apart and measure each component.

So my plan was to take the real robot outside for a test run and use rosbag to record all the commands being sent to it. Then use rosbag to playback all those commands on various different URDF models until I find one that accurately matches the behavior of the real robot (was hoping to use a genetic algorithm to find the best parameters).

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2017-09-04 19:49:03 -0500 asked a question how to play bag files from c++ or python class

how to play bag files from c++ or python class At the moment I'm reading bag files and publishing back the results: bag

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2017-07-12 09:19:49 -0500 edited question How does GZSDF handle the URDF transmission tags?

How does GZSDF handle the URDF transmission tags? Trying to understand how exactly the transmission tags are handled whe

2017-07-12 08:26:51 -0500 asked a question How does GZSDF handle the URDF transmission tags?

How does GZSDF handle the URDF transmission tags? Trying to understand how exactly the transmission tags are handled whe

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2017-04-28 03:45:07 -0500 asked a question Building URDF from scratch, how to calculate inertial values?

Building URDF from scratch, how to calculate inertial values? I've been stuck on this for a while. Most resources online

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2017-02-20 02:50:46 -0500 asked a question gazebo - issues with caster wheels and inertial values

Just imported a simple differential drive with 2 motor controlled big wheels at the front and 2 small caster wheels in the rear.

Have found 2 issues which have me stumped.

1.) After increasing the weight of the motor, the robot slowly slides across the floor when still.

2.) The rear caster wheels always turn perpendicular to the direction of movement. When the robot stops moving the rear wheels turn to align with the front wheels.

below is the code for one of the caster wheels

  <link name="rrw">
<visual>
  <geometry>
    <cylinder length="0.03175" radius="0.0635"/>
  </geometry>
  <material name="black">
    <color rgba="0 0 0 1"/>
  </material>
</visual>    

    <collision>
 <geometry>
    <cylinder length="0.03175" radius="0.0635"/>
 </geometry>
</collision>

   <inertial>
  <mass value="1"/>
  <inertia ixx="5.1458e-5" iyy="5.1458e-5" izz="6.125e-5"
           ixy="0" ixz="0" iyz="0"/>
</inertial>

</link>

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2017-01-28 15:35:24 -0500 asked a question Connecting a motor controller to ROS

I have installed a driver to connect ROS with the AX2550 motor controller ( https://github.com/wjwwood/ax2550 ).

After connecting the motor controller and enabling permissions, I get this error.

rosrun ax2550 ax2550_node

(info): AX2550 connecting to port /dev/ttyUSB0

(error): Failed to connect to the AX2550: x{o??

[(info): Will try to reconnect to the AX2550 in 5 seconds.

I get this error regardless of what device is connected to the USB port.

2017-01-22 01:43:45 -0500 marked best answer Migration from hydro to kinetic

I need to find a kinetic kame driver for a motor controller (Roboteq AX2550) but the closest thing I found was a driver from hydro ( https://github.com/wjwwood/ax2550 ). After copying it from github, I can't figure out how to convert it over to kinetic kame.

In CMakeLists.txt, I changed

find_package(catkin REQUIRED COMPONENTS geometry_msgs nav_msgs roscpp serial serial_utils tf )

to

find_package(catkin REQUIRED NO_MODULE)

as per instructions on http://wiki.ros.org/kinetic/Migration

but then it says

"If you were using the exported dependency list to pass a CMake module name that will not work anymore. You will need to find the CMake module manually in your CMake extra file. "

I have no idea what this means. How do I find those CMake modules manually? What/where is that CMake extra file?

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