Joint Reaction and Contact Forces

[Adam Henderson]

I have recently downloaded OpenSim and after completing the tutorials and reading up in the forums, I have not found a way of viewing or plotting the joint reaction forces or joint contact forces with OpenSim. Is this possible? Or am I missing something that is obvious to others?

[Ayman Habib]

Dear Adam,

As of now there isn't a way for OpenSim to report/plot joint contact forces to users. We understand it's an important functionality and we hope to implement this feature in the near future.

Best regards,
-Ayman

[GRANT LACK]

Has the ability to build joint reaction force data been addressed in the more recent build? If so, a) how would one go about it and b) what general algorithm is the program utilizing to approximate? Any update on this topic would be greatly appreciated.

Thank you,
Grant

[Dan Qiu]

Also looking for update information on this issue.

Thanks,
Dan

[Ayman Habib]

Hi Dan,

Version 2.0 of OpenSim, now posted, does support the computation of Joint Reaction forces. You can get an example model and setup file from the Wiki page:
http://wiki.simtk.org/opensim/
under "Additional Notes"/"Joint Reaction Analysis Example".

Hope this helps,
-Ayman

[Hossein Mokhtarzadeh]

Hi Ayman,
I actually tried to do "Joint Reaction Analysis Example" from http://wiki.simtk.org/opensim/ but I could not do it. is there any manual for that?
I also made an XML file and applied to my model to get reaction forces but the forces were too much.
I also did the same analysis(joint reaction) on Gait2354 example for walking. the results were so big e.g. knee_r_on_tibia_r_in_ground_FY was in the order of 10e5. by the way, my simulation is so fast.

Has anyone used "JointReaction" analysis and got good results? I can also attach my XML that was made by opensim GUI if it is needed.

Cheers,
Hossein

[Ayman Habib]

Hi Hussein,

Just to make sure that you include all forces and actuators used/calculated in you original simulation/calculation. If it's a cmc or forward solution you can just give it the external forces and states files. If you want to study a static optimization solution just provide the kinematics mot file, external forces, and a forces file (by name) containing the time history of actuator forces solved during SO. All this is provided in the analysis comments, so if you save a setup file you'll get an explanation of usage.

Hope this helps,
-Ayman

[Tim Dorn]

Hi Ayman,

I am also getting abnormally high JR outputs from my analysis of normal gait (I am using a <forces_file> input from static optimization and have set all the relevant tags). After a little bit of playing around, I realized that the JR results stay the same regardless of whether I supply an <external_loads_file> xml file or not (its as if the analysis is not applying the external forces at all, even though it is recognizing the <external_loads_file> as a valid one). Could there be a bug there?

Cheers,

Tim

[Rahul Goel]

Hi
Is there a way to get the Joint Reaction forces and moments in joint coordinates rather than global coordinates?
Rahul

[Roger Mathys]

Hi,

I want to calculate Joint Reactions based on calculations obtained by Static Optimization.

As Ayman described I have to chose the original motion file under motions and a force file under additional force set, that should be appended to the model.

My question is, where do I get this force set file from? It should be a xml file. I get a force file from Static Optimization but this is a .sto file and it does not work.

Thanks,

Roger