[ros-users] Fuerte SIG 2.10: Efficient Simulation/Control of Articulated Robots

[Mike Stilman]

> Indeed. But rather, it is not about "extending", but integrating two (or
> more) different sets of functionalities.

This may prove to be a difficult challenge indeed. The two libraries have 
significant difference in representation. I would love to discuss it with 
you and Karen together - though I'm really not sure that this whole 
conversation needs to continue to spam the ros-users list - unless folks 
are really that interested.

> Have you ever asked about it? Or made suggestions? That's how open source
> projects work :-)

I think part of open source is that "how it works" is open to 
interpretation :0}

Honestly, at the time I was looking ~08-09 there were no concrete plans 
to add dynamics to KDL. There was this confusing comment chain:
http://www.orocos.org/node/735
which I now find to be even more confusing.

More recently, I checked again on the KDL page and documentation and there 
was no mention of any forward/inverse dynamics. Even now dynamics are 
not mentioned and all the examples are purely kinematic.

At the same time, working with Karen we have a complete dynamic solver 
with lots of examples (just not releasing until we complete the contact 
handling) - i.e. have a full open source dynamic simulator with both 
dynamic solvers in generalized coordinates and contact resolution. It will 
be accompanied by documentation and fully BSD.

> I react to your posting, and the same thing could/should happen for you
> with things KDL might or might not provide in the future.

Basically there was intermittent discussion about dynamics in KDL on 
the web and it did not appear that there was a final solution in place 
after a couple years of development. Mostly "experiental." I'm aware of 
those discussions - but I was looking for a tested dynamics solution that 
we could use directly and hence now we have one.

> If you have unit test cases, and want to share them with others, that
> would be a nice contribution to the community.

Abslutely we will have lots of test cases to share. The library should 
definitely be entirely open with lots of examples.

> These are _integration_ issues, which should not be done by extending one
> single library. Otherwise, we end up where we have ended up for decades
> already: huge monolithic libraries that are not interoperable.

I really do think this is a longer discussion. Maybe even one to have in 
person. Will you be at IROS?

> I'm looking forward to these things. Within KDL we are now trying to use
> Collada the standard data format to represent kinematic chains. (And to
> couple it to other functionalities such as controllers.)

Yup, same here. Collada and URDF actually to support multi-resolution 
meshes and sensors. Probably starting with Collada first.

>> Exactly, so I would consider a force/impedance controller to be a tool
>> that may benefit from the dynamics of the library or the collision
>> checking library or neither or both. I see no reason to force the tools
>> (algorithms) built on top of the basic solvers to be constrained in any
>> particular way.
> Agreed!

Great!

> What does "join the SIG means"? Yet another mailinglist?

At the moment it means go to this wiki:
http://www.ros.org/wiki/fuerte/Planning
And add your name to Section 2.10

------------------------ Here's a forward of what this means from Sachin

The signup period will last until September 14th.

After the signup period, any SIG that has at least two people signed
up for it will be considered valid.  If you are proposing a SIG, we
urge you to recruit authors/maintainers of the relevant software --
the authority of what goes in/out of a library remains with the
maintainer/author, so their buy-in is crucial.  Similarly, we
encourage authors/maintainers to signup for SIGs that are relevant to
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The follow-up process is also very simple:

  1. Each SIG designates a SIG Coordinator.  If an SIG cannot agree on
a coordinator, one will be chosen for you.
  2. The coordinator will organize planning meeting(s) for the SIG.
This can be over IRC, video chat, at IROS, or whatever medium bests
fits the composition of your SIG. The deadline for these meetings is
September 28th.
  3. Each SIG group will post their planning notes as a sub-page of
http://ros.org/wiki/fuerte/Planning/<SIG-NAME>.  The deadline for
posting these notes is September 30th.  SIGs can have followup
meetings, but this initial deadline is to ensure that the SIG is
activated.

The plans are just that -- plans.  It is up to the members of each SIG
to achieve as much of that plan as possible in time for the freeze
dates of ROS Fuerte (remember, there's always Groovy Galapagos).

As always, we appreciate your participation.  We hope this more
distributed process will better match the distributed nature of ROS
development.