simtk.org

Hi,
I'm working on a simulation to determine joint reaction forces in a knee.
For that purpose I'm currently using the gait2354 modell from the examples folder.
I have completed every step of the way (according to the user guide) until the RRA. When I use the Setup-files specified in this chapter, and try to simulate it, the programm suggests that I'm missing constraints.
After completion of the analysis the motion it creates looks realy wierd. All body parts seem to rotate randomly around their respective joints with no simularity to the previous kinematic analysis.

My first question would be, where can I specify the missing constraints (the part of the chapter in RRA where the constraints-file should be explained seems to be missing)?
And secondly. Am I on the right path to getting joint reaction forces out of my analysis? (IK->ID->RRA->CMC->Analysis of JRF)

Andy

HI Andreas, I thought if you are using 2.0.2 or any version newer than 1.9.1, the examples of gait2354 would fail by no reason, and the same example in version 1.9.1 could succeed at least.

So, just keep in 1.9.1 until they could run their example in their directory successfully.

When they released the v2.0.2, i thought they could fix the example in the gait2354 directory and run it though RRA step, but they didn't, that's why I'm still using v1.9.1 whose examples could at least run properly.

My mail is tinyvane@gmail.com and I'm also working on knee issues, and I hope to get touch with you. Thanks.

University of Utah
Ergonomics & Safety program

Hi Yi,

The examples in the distribution folder (gait2354_simbody) do run without problem (I just tried that again using the 2.0.2 distribution which was posted a few days ago). If you can not run these then please file a bug report and include your specific model, data, setup, and environment.
Bugs need to be reported in order that they can be fixed. Not reporting bugs and hoping that somebody else will run into them and they get fixed in the future does not help.

Andreas, can you please give the Chapter/Section in the user guide that you believe is incomplete? What was the specific message you got trying to run RRA? You maybe able to get JointReactions from StaticOptimization rather than having to do CMC depending on how bad/high are your RRA residuals.

-Ayman

Hi Ayman,

What is the criteria for defining RRA residuals are bad or good?
I got values as follows.

Average Residuals:

FX average = -12.0391
FY average = 76.2288
FZ average = -24.047
MX average = -72.8873
MY average = 33.0188
MZ average = 27.9293

Should they be considered as really bad?

Thanks.

Kang

Hi Kang,

If you think residual are kind of big, how do you manage to decrease them? I mean the specific progress?

Thanks in advance.
Yi.