[Robotics] Force/torque/collision sensor

[Fernando Garcia Bermudez]

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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