Hi again,

Is it possible to perform a classical inverse dynamic analysis on the model?

I would like to calculate joint torques and reaction forces at the joints

required to perform a certain motion. In the tutorial this step is skipped,

saying: “Since we have no muscles so far, kinematic analysis is really all

that makes sense”. But in my case there is some relevant information I’d

like to extract from this.

I tried using an AnyForceMomentMeasure and including all muscles that act on

the joint, but it seems that these muscles are not considered to be applied

directly (am I right?), so I get a zero moment vector.

I also tried looking at the Constraints.Reaction, but those are just, as the

name says, the constrained reaction, and therefore do not provide the

torques in the non-constrained degrees of freedom.

How can I get the joint torque in the non-constrained degrees of freedom of

a joint?

Thanks you,

Jean-Olivier

From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf

Of AnyBody Support

Sent: 21 avril 2007 15:12

To: anyscript@yahoogroups.com

Subject: [anyscript] Re: Contraints.Reaction.Fout

Hello Jean-Olivier,

Contraints.Reaction.Fout is a menber of any constraint. It is the

force(s) in the constraint. If the constraint is a joint then

Contraints.Reaction.Fout contains the joint reactions just as you

anticipate.

But here is the point of the story: Joint reactions are very

different depending on whether you have muscles in the model or not.

Joint reaction forces in models relying only on joint torques, i.e.

classical inverse dynamics, are hugely under estimated. If you only

have joint torque providers in the model, then the joint reactions

are only what the external forces produce. When you include the

muscles, their contribution to the joint reaction is added and it is

often larger than what the xternal forces provide. A muscle can only

produce torque in a force couple with a joint reaction, so the real

joint reactions are much larger than what you get from a model with

pure joint torques.

In other words, it is correct that you get different joint reactions

depending on whether you include muscles in the model or not.

Best regards,

John

— In anyscript@yahoogrou <mailto:anyscript%40yahoogroups.com> ps.com,

Jean-Olivier Racine <jean-

olivier.racine.1@…> wrote:

>

> Hello all,

>

>

>

> I am wondering what are the Contraints.Reaction.Fout values. As I

run my

> model with and without muscles, I get different values for those.

Therefore,

> I conclude that these are not the Reaction Forces, as defined when

doing

> classical inverse dynamics (reaction forces and moments passed from

one

> joint to the other), since they should not change with or without

muscles.

> So my questions:

>

>

>

> 1. What are these Constraint.Reaction.Fout value?

> 2. How can I get those reaction forces that come directly from

the

> classic inverse dynamics analysis?

>

>

>

> Thanks!

>

> Jean-Olivier

>

>

>

> [Non-text portions of this message have been removed]

>

[Non-text portions of this message have been removed]