Gazebo: Q&A Forum - RSS feedhttp://answers.gazebosim.org/questions/Open source question and answer forum for GazeboenCopyright Askbot, 2010-2011.Wed, 22 May 2019 02:59:36 -0500How to know the vector of force when my model collides a wallhttp://answers.gazebosim.org/question/22612/how-to-know-the-vector-of-force-when-my-model-collides-a-wall/ I want to make a simulation in Gazebo about what will happen when a satellite hit an irregular objection like a comet in space. I used the "spacedyn" in MATLAB to calculate the dynamics of satellite. But "spacedyn" needs to know the force when satellite hit the objection. I don't know how to get the force from Gazebo. However, it seems like that Gazebo won't return the collision force. FORGRESSWed, 22 May 2019 02:59:36 -0500http://answers.gazebosim.org/question/22612/Changing the relative pose of a link in simulationhttp://answers.gazebosim.org/question/21271/changing-the-relative-pose-of-a-link-in-simulation/Hello,
I'd like to write a plugin that could change the relative position of a link to its parent. For now I can get the pointer of the link and use "SetRelativePose()" or "UpdateParameters()" to change the relative position. However, right after the position shift, the link immediately shifts back to its original position. I'd like it to stay. It's kinda like the changing the geometry of the model without relaunching the simulation or respawn the entire model. But so far I haven't been able to find a way to do it. Can anyone help? Tao_GazeboMon, 03 Dec 2018 15:55:04 -0600http://answers.gazebosim.org/question/21271/Can Gazebo simulate turbulence?http://answers.gazebosim.org/question/19602/can-gazebo-simulate-turbulence/ When a fixed wing plane flies, its propeller will produce wind to the airspace behind the plane, and the wings of the plane will produce cavitation. This is mentioned in the tutorial http://gazebosim.org/tutorials?tut=aerodynamics&cat=plugins
So, if I simulate 2 planes in Gazebo, and plane B is following plane A airborne. So will plane B being affected by plane A's propeller and cavitation?ekaradonTue, 05 Jun 2018 03:44:46 -0500http://answers.gazebosim.org/question/19602/Unusual dynamic in graspinghttp://answers.gazebosim.org/question/19020/unusual-dynamic-in-grasping/ Hi all,
I was using gazebo to simulate planned grasping. I had observed some unusual dynamics going on with the robot gripper and the box items I created as target objects. in particular, it seems like the gripper is constantly colliding with the object. More details are included in the video I attached to this post: please jump to 0:30 to see what exactly is going on.
https://drive.google.com/file/d/1a1OAXSpzOiCBsFtk1g6C2Pv-MHVMG3fe/view?usp=sharingJekyll1021Sun, 15 Apr 2018 16:56:51 -0500http://answers.gazebosim.org/question/19020/Getting forward dynamics of a modelhttp://answers.gazebosim.org/question/17182/getting-forward-dynamics-of-a-model/I have a robot model in the form of an sdf file (relatively simple). Now, I have a certain control policy which manipulates torques applied to robot joints, but the real system is set up in a way that it receives position setpoints.
So what I would like to get is the bare minimum forward dynamics functionality that would allow me to input the robot pose and joint states and output the positions.
Is that possible with Gazebo, and if so, how?
Also, it is probably worth mentioning that the real system is real-time and that it is a control policy (i.e. adaptive to the environment) we are talking about, so simply generating the trajectory in Gazebo would not work.hamzamerzicThu, 07 Sep 2017 08:18:48 -0500http://answers.gazebosim.org/question/17182/How to accurately simulate motor reduction effect on inertiahttp://answers.gazebosim.org/question/17113/how-to-accurately-simulate-motor-reduction-effect-on-inertia/I am researching humanoid robot walking and I am trying to use Gazebo to accurately simulate the DARwIn-OP robot in terms of dynamics. To have a accurate dynamic model, I am trying to accurately simulate the MX-28 servomotors dynamics. However, I have doubts about how I should include the motor reduction effect on inertia. I tried to simply add N^2 * Jmotor to the inertia of each driven link in the axis rotation direction. Despite not perfect, I have found that this is an approximation usually done in manipulator dynamics simulation. For a discussion about this, see: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900020545.pdf
However, since I do not know how exactly Gazebo simulates dynamics, I am not sure that I have implemented this correctly in Gazebo. Which is the correct way of implementing motor reduction effect on inertia in Gazebo?Marcos MaximoSat, 26 Aug 2017 16:18:17 -0500http://answers.gazebosim.org/question/17113/I want to do dynamical modelling of a spherical robot and simulate it. How do I go about it? what software/libraries do I use?http://answers.gazebosim.org/question/16590/i-want-to-do-dynamical-modelling-of-a-spherical-robot-and-simulate-it-how-do-i-go-about-it-what-softwarelibraries-do-i-use/ How do I model it? I will be using dynamixel AX-12A inside it for forward and rear motion. For turning, I will use a pendulum actuated with a servo motor/Syed Adnan AkhtarSat, 01 Jul 2017 06:01:11 -0500http://answers.gazebosim.org/question/16590/How does ODE determine contact points in Gazebo?http://answers.gazebosim.org/question/13714/how-does-ode-determine-contact-points-in-gazebo/
I was looking at the contact points for the Atlas in the DRCsim package. Each foot has 4 contact points at each vertex of the rectangle. I'd like to know how these points are determined. I've tried looking at the ODE code, but C++ isn't my strong suit so I had some difficulty figuring out what was going on. What I understand is that ODE compares the geometries one by one however it's not possible to compare all points so it only compare a select few points. What I'm trying to understand is what basis are those particular points selected? Why does the Atlas have the 4 contacts set up the way they are, and not some additional points on the heel? Can I add them myself?
Thanks.
Mav14Wed, 22 Jun 2016 14:33:27 -0500http://answers.gazebosim.org/question/13714/Symbolic jacobian of an armhttp://answers.gazebosim.org/question/13542/symbolic-jacobian-of-an-arm/ Hi all,
I've a 7 DOF arm described in .xacro format and I would like to extrapolate its jacobian in symbolic form (not numerical angle values in the matrix ).
I tried to use KDL for this scope, and I was able to obtain the jacobian of this arm but in a numerical form. That is, during a gazebo simulation, I could read the values of each angles, insert them in the jacobian matrix with a specific kdl command, and obtain the jacobian matrix on every gazebo step time.
That's ok, but if I have another target in which I need the symbolic for of this jacobian from which extrapolate other matrix (inertial, coriolis ecc..), I'm not able to do this. (For example if I want to control my arm in a particular way in which I need the dynamic expression of the system).
Has anyone every have this problem? Is there a method with kdl or another software that I can use?
Thank you!gabri89Sun, 05 Jun 2016 05:52:15 -0500http://answers.gazebosim.org/question/13542/Videos that show Gazebo doing hard dynamics?http://answers.gazebosim.org/question/3563/videos-that-show-gazebo-doing-hard-dynamics/Are there any videos that show Gazebo doing any moderately hard robot dynamics problems? Running? Hopping? Jumping? Catching? Sliding? The most "dynamic" examples I can find just show mostly-kinematic situations, such as slow walking with a bit of ZMP to keep the effective CG over the feet. The DRC videos show the Atlas robot doing a lot less than the videos of the real Atlas robot. John NagleFri, 12 Jul 2013 11:38:00 -0500http://answers.gazebosim.org/question/3563/Changes to model behavior when converting between Gazebo 1.0 and Gazebo 1.8http://answers.gazebosim.org/question/3237/changes-to-model-behavior-when-converting-between-gazebo-10-and-gazebo-18/Hi All,
I've been modelling an arm which uses a plugin that models hydraulic actuators and valves. The model is a state representation that uses actuator velocity and acceleration as states and outputs force.
to link to gazebo model I get my velocity state from the joints using joint::GetVelocity() in the model and apply my actuator force to the joints via joint::SetForce().
These are both done on the plugin's OnUpdate()
This works fine with Gazebo 1.0 and the model was controllable.
I recently converted over standalone Gazebo 1.7, and the joint response was no longer sufficient to defeat gravity and my actuators that previously responded correctly now can no longer lift the links of my manipulator.
My gravity vector is (0, 0, -9.8)
Additionally my model's joints jerk around quite a bit without input from any controller to the plugin.
I'm just wondering if there have been any changes that may be causing this behavior in the new Gazebo. I haven't significantly modified my models or plugins other than to convert them for Gazebo 1.7. As a result the plugin did have to be outside ROS as per the Tutorials1.5/ros_plugin. but was functionally unchanged.
Any suggestions as to what may be wrong?PMilaniSun, 16 Jun 2013 21:49:52 -0500http://answers.gazebosim.org/question/3237/DRCSIM: Loss of dynamics parameters accuracyhttp://answers.gazebosim.org/question/405/drcsim-loss-of-dynamics-parameters-accuracy/In general the conversion from drc_skeleton.cfg to model.sdf is dropping
bits. For example:
ltorso:
moi_xx = 0.0039092029372626179
moi_xy = -5.0449050133996959e-08
moi_xz = -0.00034215713173324773
moi_yy = 0.0034169356417788309
moi_yz = 4.8711939124200493e-07
moi_zz = 0.0017449235428106818
com_x = -0.01129844
com_y = -3.1536621e-006
com_z = 0.074683465
becomes
inertia ixx="0.0039092" ixy="-5.04491e-08" ixz="-0.000342157" iyy="0.00341694" iyz="4.87119e-07" izz="0.00174492"
Although this is probably negligible, it is not wise to let the dynamics
model parameter "resolution" be determined by how "%g" works, and raises
the question of which is the "true" model.
cgaTue, 04 Dec 2012 20:54:52 -0600http://answers.gazebosim.org/question/405/