Link Wrench Estimation

[jeljaik]

Still pending for Version 0.2

[jeljaik]

Any update on this @traversaro? Can I maybe help somehow?

[jeljaik]

c.c. @rbonghi This is the issue I was telling you about. We have to wait for @traversaro to fix/add this in the yarp-WholeBodyInterface.

[traversaro]

Sorry guys, at the moment is a bit difficult to find the time to implement this, unless it is a top priority.
However if someone wants to tackle this issue, the necessary steps are to mplement a new estimate in yarpWholeBodyState, namely ESTIMATE_EXTERNAL_FORCE_TORQUE. The necessary information are already published in the contacts:o port of wholeBodyDynamicsTree, it is just necessary to parse them and translate them in the right frames.

[traversaro]

All stakeholders interested in this feature (cc @rbonghi @DanielePucci ) can provide a description of what they would expect from this block (considering frame of expression issues and other technicalities)?
P.s. consider also this : robotology-legacy/codyco-modules#39

[DanielePucci]

So, as you mentioned in robotology-legacy/codyco-modules#39, the method

get(ESTIMATE_EXTERNAL_FORCE_TORQUE, fake_link)

should return the force/torque expressed w.r.t. the fake_link, that is, point = origin of the fake_link, orientation = orientation of the fake_link. In the case "fake_link" is a "real link", the method should return the force/torque expressed w.r.t. it. What do you think @traversaro ?

[traversaro]

So do you like the ESTIMATE_EXTERNAL_FORCE_TORQUE to return the force oriented as the local frame? Take into account that this could be an inconsistency with the velocity estimates and their jacobians , that are expressed with the orientation of the world frame and with the point of the "fake_link" frame.

[DanielePucci]

No sorry, I confused fake_frame with a sort of additional frame. I think that the method should be something like

get(ESTIMATE_EXTERNAL_FORCE_TORQUE, frame)

and then it returns the force/torque expressed w.r.t. "frame". Probably, in most control applications, the orientation of this frame is going to be kept equal to that of the world frame, thus being consistent with velocities.

[traversaro]

Sorry, how the get(ESTIMATE_EXTERNAL_FORCE_TORQUE, frame) is able to get the link of which you want the external wrench?

[francesco-romano]

get(ESTIMATE_EXTERNAL_FORCE_TORQUE, linkID, frame) returns the wrench on link linkID w.r.t. frame specified in frame. Optionally If frame is null it returns the wrench w.r.t the link frame.

?

[jeljaik]

Sorry guys I can start working on this just tomorrow... you know why.

[traversaro]

@francesco-romano The getEstimate signature is fixed in the wholeBodyStates, and it just accepts one numeric index. We can certainly change it, but it would adding a new non generic method to the wholeBodyStates interface. On the short term I would prefer to have something working with the existing interface.

[francesco-romano]

@traversaro from the simulink point of view:
We can get the estimate of the wrench in the link reference frame and the frame transformation from the link frame to the required (user input) frame and apply it to get the final result

[traversaro]

+1 .

Actually the frame of expression is quite prone to misunderstanding: when you mean wrench expressed in a frame (for example the world frame) you refer to both the point of expression and the orientation. For now (for example the jacobians and the velocities estimates) we are assuming (and the user can't change this, for now, at least at the WBI/WBI-Toolbox level) that the point of expression is the one of the frame, while the orientation is the one of the world/inertial. For this reason it may be more useful to specify both the point of expression and the orientation of the requested estimate.

[azadm]

any update on this? This block seems to be necessary for dealing with compliant contacts.

[traversaro]

Hi @azadm , reading the estimate of the external wrench is definitely important at the moment.
I will provide you with an estimate on when this will be ready Thursday (tomorrow is holiday here in Italy).