External Load with known Normal Force but no CoP

[Maud Hendriksen]

Hi all,

I have a question regarding the application of external loads. I have force data that only consists of the normal force without a direction. The CoP is unknown, but I want to assume that the force is applied perpendicular to the CoM of the hand. I want to make a .mot file to be able to make the external loads file, but I dont know how and I dont know if this is even possible to apply in OpenSim.
Is there anyone that knows how to do this or if it is possible?

Any help is very much appreciated.

Kind regards,
Maud

[Dimitar Stanev]

Hi Maud,

I am not sure if this will give you good results. However, you could experiment with this in the GUI and the check the pelvis residuals afterwards. When you apply an external force in the inverse dynamics tool for example, you can edit how forces are applied. There is an option to apply the force on a body instead of a point force. Also, you can disable/enable the torque component.

https://simtk-confluence.stanford.edu/d ... ernalLoads

[Maud Hendriksen]

Thank you, I forgot about the option of applying the force to a body. One more question, is it possible if I have just one force column and not in the x,y and z direction?

Why are you not sure if this will give me good results? because of my assumptions?

Thank you

[Dimitar Stanev]

You can populate the .mot file with values = 0 for x, z. Joint moments and pelvis residuals are very sensitive to the ground reaction forces. Please keep in mind that when you evaluate your approach, you should also consider the pelvis residuals. This is typically ignored by a lot of people, however it shows how much modeling/measurement mismatch exists for the specific input.

[krishna raj]

Hi

am new to opensim, stuck on the load part.

I have a force file in single column value in newtons ,how can i transform the single value to x,y,z axis values for open sim, and i have to apply that force in the skull body part ,the osim is a half body (hyoid model)

what parameters should i provide in the point forces(x,y,z),and body forces(x,y,z)

and ground forces are required or not.

in the excel i have filled the point force x,y,z from (x axis* value in Newtons),(y axis * value in newtons),(z axis * value in newtons)- is it the right way or not.

the location of force -(green arrow ) not visible

any one ,plz suggest.

regards
krishnaraj gr