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Re: [PlayerStage-Gazebo] Omni-wheel model for Gazebo
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From: chgans <ch...@gn...> - 2008-02-19 11:38:20
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Hendrik Skubch wrote: > I modeled an Omni wheel in gazebo using friction coefs. It works quiet > well. I don't think it's feasible to model the wheel using geoms, due to > the number of geoms and the high rotational velocities involved (For our > wheels I'd need 26 geoms per wheel per robot). > > The trick lies in two modifications to gazebo: > 1) The CollisionCallback function in ODEPyhsics needs to compute the > primary friction direction based on the surface description of the > colliding objects and their rotation. > 2) The same function needs to query the colliding geoms for surface > parameters depending on the contact point and normal, since an Omni > Wheel (and other physical elements) have different friction parameters > depending on whether the collision was on the wheel's shell or side. > > In order to implement this, I added a <surface>-tag to the XML > description of geoms, holding collision parameters and a positional flag. > If you are interested, I can try and make a patch out of the modifications. > Indeed, yes, i'm very interested by your patch. Chris > cheers, > hendrik. > > > Sawyer wrote: > >> Chris, >> The ability to adjust the ODE parameters for the friction coefs (esp axis >> specific) is not currently implemented in Gazebo world files. I was wondering >> how you would go about modeling an omni-wheel when this question was first >> proposed and I think you are onto an elegant solution. >> >> Jordi, Nate, >> Where in the svn code base are the ODE parameters for wheels adjusted? Where >> are the XML parameters read? I am trying to give Chris an idea of where the >> current system would need to be patched to allow this behavior. >> >> Sawyer >> >> (Sorry I can't be of more help, I'm currently still working with the older >> Gazebo platform) >> >> On Monday 18 February 2008 1:57:09 pm chgans wrote: >> >>> Hi all, >>> >>> Sorry not to reply in the thread, but i've just subscribed, and so i >>> don't have the original email. >>> >>> I'm very interesting as well in modeling omni-directional wheel and >>> holonomous robot in Gazebo. >>> I used to work on an open source project which try to develop such a >>> platform[1] (as well as an ODE-based simulator). >>> At that time we used a "normal" wheel model, but the simple trick was to >>> define the ODE friction coef along the wheel axis to be very small >>> compared to the one along the wheel path, I'm not sure gazebo allow to >>> access these type of parameters from the xml file. >>> >>> I'm really new to player/stage/gazebo, I start having a look on >>> Saturday! Did a few build, trys (and errors), and finally get everything >>> running (last player/stage (pre-)release, and a fresh svn for gazebo). >>> Try playercam, joystick, laser, sonar, i am still exploring... and i >>> enjoy! Thank's to you all! >>> >>> I'm so enthusiastic, that i would like to resuscitate the WISIRC project >>> that i start with some of my friends in 2004, but actually what i >>> realized is that all we wanted to do is something like >>> player/stage/gazebo, but the main difference is p/s/g do it for real! :-) >>> Having all this framework running, will allow me to concentrate more on >>> HW, meca, drivers, sensors, etc of the robot (i'm actually more on HW, >>> low-level SW side). >>> For this holonomic platform we developped a specific PC104 motor control >>> board[2], based on 3 HCTL1100 ICs(z filter), each of these was accessed >>> from userspace by the "motion control" daemon, which in turn was >>> accessed by the path planner. The goal was to implement the same "motion >>> control" interface within the simulator, and we almost did, almost... >>> Then we decide to start working with a DSP running the motion control >>> algorithm (2 PIDs, one for controlling the linear position/velocity, the >>> second one for controlling angular position/velocity), which has >>> odometry directly connected (wheel encoder + laser motion sensors, such >>> has found in laser mouse for gamer), and then the project start slowing >>> down and down and ... dies. (snif! ;)) >>> Ah, and i didn't tell you about our plan for having DSP-based (TI C6711) >>> camera imagery , etc... ;) >>> Well, the big difference between p/s/g and wisirc, is that our goal was >>> to build completely from scratch (HW, Meca, SW) an 99.99% open-source >>> holonomic platform. As hobbyist, the fun is in the do-it-youself! (And i >>> don't have the money to buy all these very expensives ready-to-uses >>> sensors) >>> >>> I'm really happy to see all the features that p/s/g offers, very >>> exciting. So for now, i have to create these configuration/model files >>> for my bot, and start digging into the player's drivers/interfaces model. >>> >>> Have fun! >>> Chris. >>> >>> >>> [1] http://home.gna.org/wisirc/images/wizbot1-20040901/ >>> http://download.gna.org/wisirc/MecaWiz/wizbot-20060819/chassis_1.png >>> >>> http://download.gna.org/wisirc/MecaWiz/wizbot-20060819/new_wheel_1.png [2] >>> http://home.gna.org/wisirc/projects/WizHard >>> PS: this site is really out of date, unfortunately our newer wisirc.org >>> web site disapeared recently... >>> >>> ------------------------------------------------------------------------- >>> This SF.net email is sponsored by: Microsoft >>> Defy all challenges. Microsoft(R) Visual Studio 2008. >>> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >>> _______________________________________________ >>> Playerstage-gazebo mailing list >>> Pla...@li... >>> https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo >>> >> >> ------------------------------------------------------------------------- >> This SF.net email is sponsored by: Microsoft >> Defy all challenges. Microsoft(R) Visual Studio 2008. >> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ >> _______________________________________________ >> Playerstage-gazebo mailing list >> Pla...@li... >> https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo >> > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Playerstage-gazebo mailing list > Pla...@li... > https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo > |
