[Robotics] Force/torque/collision sensor

Fri Jun 10 11:56:35 CEST 2011

Ciao Fernando,
I've been playing around with this for a while, and I think I got the hang
of it, thank you :-)
I just had to change the script a little because the mathutils.Matrix api
has changed in Blender 2.56 (namely: I had to copy() and then .transpose()
the beam rotation Matrix), but it works very well.

I'm working on the linear springs now, and I'm planning to transform this in
a Morse-style sensor, even though a few peculiarities will apply.

Thank you again for your kind help

Anna Chiara Bellini

On 7 June 2011 17:40, Fernando Garcia Bermudez <fgb at eecs.berkeley.edu>wrote:

> Since the e-mail below was being held due to a large attachment, I
> decided to re-post without it. You can grab the attachment from:
>
> http://github.com/fgb/passive_compliant_joint
>
> Thanks,
>
> -- Fernando
>
> On Mon, Jun 6, 2011 at 12:05, Fernando Garcia Bermudez
> <fgb at eecs.berkeley.edu> wrote:
> > Anna,
> >
> > I've constructed passive compliant joints in the past using a mixture
> > of rigid body joints and a python script controller, since there are
> > no generic spring constraints in Blender that I know of.
> >
> > In a nutshell, I create a generic 6 DoF rigid body joint between two
> > bodies, disabling collisions between them. I then proceed to allow
> > only the rotations that the spring joint I'm envisioning has. I setup
> > rigid body physics for both bodies and then add some parameters to the
> > game property editor (spring constant, damping constant, and resting
> > position for the joint). Finally, I add an always sensor connected to
> > a python script which effectively controls the passive compliant
> > joint. The script implements torque feedback based on the game
> > property parameters. You could easily implement force feedback for a
> > linear spring joint in a similar way. For clarity, I'm including a
> > demonstration blend file.
> >
> > As you can see, the forces/torques are available to you as part of the
> > simulation, but as Gilberto notes, they might not be very precise due
> > to Bullet's limitations.
> >
> > I hope this helps you solve your issue. Let me know if you have any
> questions,
> >
> > -- Fernando
> >
> >
> > On Mon, Jun 6, 2011 at 11:09, Anna Chiara Bellini
> > <annachiara.bellini at gmail.com> wrote:
> >> Hello Gilberto,
> >>
> >> I'll try to explain it better... I need to detect forces for two
> reasons:
> >>
> >> 1 - our robot is an UAV, and as it flies, it will get in touch with
> objects
> >> and environment. On the robot I need to have a few force/torque sensors,
> >> that will tell me the force/torque applied in that spot, and then we
> combine
> >> the different values to get a resulting force that will get back to the
> user
> >> using a force-feedback device.
> >>
> >> 2 - the robot features a grasp/manipulate tool, and I need to read the
> force
> >> applied on it.
> >>
> >> Now, my first idea is this: if I model the sensor as a small pivoting
> >> damper, then I could read the position and pose of the damper to
> calculate
> >> force and torque... but this is just a very basic idea, I don't know if
> it's
> >> correct or if there are better ways. (Ideally, this should end up being
> a
> >> MORSE sensor, but that would be a second step, hence why I posted the
> >> question here instead on the morse mailing list)
> >>
> >> I have also found this on the Bullet forum:
> >> http://www.bulletphysics.org/Bullet/phpBB3/viewtopic.php?p=&f=9&t=3637,
> but
> >> I'm not understanding it completely, for instance I do not know what a
> >> "proxy" object is and how to set it up.
> >>
> >> Hope this is clear enough :-)
> >>
> >> You are saying that the Bullet engine is not extremely precise... can
> you
> >> tell me what are the limitations, or point me to a place where I can get
> >> more information?
> >>
> >> Thank you again
> >>
> >> Anna Chiara Bellini
> >>
> >>
> >> On 6 June 2011 18:09, Gilberto Echeverria <gilberto.echeverria at laas.fr>
> >> wrote:
> >>>
> >>> Hello Anna Chiara,
> >>>
> >>> For the moment, MORSE does not include this sort of force sensors in
> >>> joints. So far, the main developers of MORSE have not approached this
> sort
> >>> of simulation, so it remains an open area for development. However,
> maybe
> >>> other people in the Blender community may have worked on similar
> problems.
> >>>
> >>> It should be possible to measure forces in Blender, but the physics
> engine
> >>> used by default (Bullet) is not extremely precise. It will depend on
> what
> >>> exactly you want to model.
> >>> If you can provide more details, we can give you a better insight on
> how
> >>> to deal with this kind of sensors.
> >>>
> >>> Best regards,
> >>> Gilberto Echeverria
> >>>
> >>> On 06/06/2011 04:16 PM, Anna Chiara Bellini wrote:
> >>>
> >>> Dear all,
> >>>
> >>> I am working on a robot simulation project ( http://www.airobots.eu/ )
> >>> with Blender and I am trying to do something which I'm sure someone
> else has
> >>> already done, so I'm asking for directions: I need to model passive
> >>> compliant joints and detect the forces acting on them. I guess that the
> way
> >>> is through Blender's rigid body joint constraint , possibly the
> >>> 6DofSpringConstraint, but I'm not really sure about it and I really
> don't
> >>> know which would be the best solution.
> >>>
> >>> In our project, we are using MORSE for sensors/actuators/middleware, so
> if
> >>> anyone had a MORSE-specific solution or suggestion, that would be
> great.
> >>>
> >>> Any ideas?
> >>>
> >>> Thank you in advance
> >>>
> >>> Anna Chiara Bellini
> >>>
> >>> _______________________________________________
> >>> Robotics mailing list
> >>> Robotics at blender.org
> >>> http://lists.blender.org/mailman/listinfo/robotics
> >>>
> >>>
> >>> --
> >>> Gilberto Echeverria
> >>> Research Engineer
> >>> Robotics and Interactions Group (RIS)
> >>> LAAS/CNRS, Toulouse
> >>> +33 (0)5 61 33 78 95
> >>>
> >>> _______________________________________________
> >>> Robotics mailing list
> >>> Robotics at blender.org
> >>> http://lists.blender.org/mailman/listinfo/robotics
> >>>
> >>
> >>
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