Gazebo: Q&A Forum - RSS feedhttp://answers.gazebosim.org/questions/Open source question and answer forum for GazeboenCopyright Askbot, 2010-2011.Wed, 10 Jan 2018 16:32:15 -0600Standalone gzserver executablehttp://answers.gazebosim.org/question/18268/standalone-gzserver-executable/Is it possible to create a Standalone gzserver executable. In other words if the executable is build on a certain PC , can it be used on another PC with the same specs without any installations? If possible what are the steps that must be performed? If not why?
pchidambWed, 10 Jan 2018 16:32:15 -0600http://answers.gazebosim.org/question/18268/Best Setup or Solver for soft contacthttp://answers.gazebosim.org/question/17098/best-setup-or-solver-for-soft-contact/ I am simulating a caged drone in contact/collision with surfaces. The cage allows deformation, and the spring/damper coefficients are studied and available.
In my test I fly horizontally at same speed (1.5m/s) with additional vertical speed against a vertical wall. My parameter setup:
Solver step: 0.001 s, ODE
Collision parameters: Kp=20000 N/m, Kd =1, and mu = 1, max_vel = 5.0m/s, min_depth = 0.001
I am trying to compare the deformation of the cage(or intersection), and pitch forward disturbances in the simulation with real life. So far it has been really hard. The disturbance from the simulation is half as big as in real life, and the disturbance is strongly dependent on Kp and step size. Smaller step size (even 0.01ms) leads to stronger disturbance, instead of converge to same results. I know this comes from CFM and ERP definition, but this still troubles me.
Currently I am using the RotorS framework from ETH. I wonder if anybody has experience with modeling collision or contact behavior? Is there anything wrong with my setup or is ODE not the right solver for this?
Best,JDJDThu, 24 Aug 2017 10:47:06 -0500http://answers.gazebosim.org/question/17098/Gazebo physics : max_step_size, real_time_update_rate, solver etchttp://answers.gazebosim.org/question/16170/gazebo-physics-max_step_size-real_time_update_rate-solver-etc/Hi everyone. I am working with Gazebo and ODE and I have a question about physics parameters. I read ODE and Gazebo documentation but still don't understand differences between max_step_size/real_time_update_rate combination and solver iters parameter.
Does someone here could explain me ?
Thanks a lot :) blevesqueTue, 16 May 2017 09:00:09 -0500http://answers.gazebosim.org/question/16170/ODE with solver type "world" crasheshttp://answers.gazebosim.org/question/6237/ode-with-solver-type-world-crashes/Hi all,
With the following:
<physics type="ode">
<gravity>0 0 -9.8</gravity>
<ode>
<solver>
<type>world</type>
<min_step_size>0.001</min_step_size>
<iters>50</iters>
<sor>1.3</sor>
</solver>
</ode>
</physics>
Gazebo 1.9 crashes when a simple box is placed on the ground plane.
Reducing the number of iterations did not solve the problem.
[link](http://answers.gazebosim.org/question/107/ode-world-vs-quick-method-in-gazebo-ros-fuerte/) explains a similar problem but does not answer the question fully.
Any help would be appreciated.
Thank youpeshalaTue, 20 May 2014 00:13:36 -0500http://answers.gazebosim.org/question/6237/Physics solver parameters and BDI behavior controllerhttp://answers.gazebosim.org/question/1747/physics-solver-parameters-and-bdi-behavior-controller/I just installed the latest DRCSim (had to compile from source because although Gazebo 1.5 was added to the repository, DRCSim 2.2 wasn't). As we work mainly on getting the robot to walk, the first thing we tried is the BDI behavior controller which produces a fine walking gait.
It was clear from the tutorial that this runs with different solver parameters so we got curious about what happens with normal parameters and found out that a small change in any of the parameters will cause the controller to fail (the robot joints don't behave as expected causing the robot to fall).
The question is: what will the solver parameters be during the qualifications and the VRC?
Which approach would you recommend for developing a walking algorithm if the behavior changes so drastically depending on the solver parameters?EricSidorovTue, 12 Mar 2013 09:17:09 -0500http://answers.gazebosim.org/question/1747/Gazebo Physics Solver Type: quick vs. worldhttp://answers.gazebosim.org/question/232/gazebo-physics-solver-type-quick-vs-world/Can anyone expand upon the quantitative/qualitative differences between running with the "quick" or "world" solver settings in Gazebo?
My understand is the quick solver is faster than world, but at what expense? Is one or the other quantitatively more accurate?
Is the world solver currently supported? In the latest DRCsim release changing the solver type to "world" makes the sim fail.
Many thanksRoboUserThu, 15 Nov 2012 09:45:58 -0600http://answers.gazebosim.org/question/232/Effect of Stiffness and Mass on Gazebo Simulation stabilityhttp://answers.gazebosim.org/question/553/effect-of-stiffness-and-mass-on-gazebo-simulation-stability/Hi All,
I've been developing a model that has hydraulic actuators that are as a result very stiff in that a small change to either the load on the actuator or on the valve spool will result in a relatively instant and relatively large change in the states of the actuator. These motors are represented by a class hydmotor;
//Hydraulic motor models
private:
hydmotor motor_joint1, motor_joint2, motor_joint3, motor_joint4, motor_joint5, motor_joint6, motor_joint7, motor_gripper;
during the update of the plugin the motors are run through a simulation step of their own based on their own states for pressureload using Gazebo provided dt (from get sim time) and GetVelocity(), returning the result (the force on the joint) via SetForce(axis, value):
motor_joint1.dt=dt;
//motor_joint1.u = 0.5;
motor_joint1.thetaspeed =joint1->GetVelocity(0)*motor_joint1.gearratio;
//Calculate the Motor Dynamics
motor_joint1.updateinput();
joint1->SetForce(0, (motor_joint1.getTorque()*motor_joint1.gearratio));
dt is calculated from sim_Time. the method:
motor_joint1.updateinput();
Is basically where the next state iteration is calculated for the motor (where the states are pressureload, and rotationalspeed and the input is the valve position.
These have been incorporated into a Gazebo model via a plugin so that it can talk to ROS. To get it to work required a dt value of around 0.1 ms in the solver. Anything larger and the model ( a serial robot made of a number of links) would end up as a jumbled heap. I tried increasing the iter value about 100 times and can see that the model works for a short time before becomming unstable and flying apart.
**My question is why would stability be affected if I only add an additional variable of type hydmotor?**
I would expect it to run slower sure, but not to affect the overall stability.
The stability issue can be corrected by making the solver timestep even slower. at the moment it sits at about dt = 0.000044 with iters = 95.
CheersPMilaniThu, 20 Dec 2012 22:01:48 -0600http://answers.gazebosim.org/question/553/