Use Generic (Pedal) Force

[Andrea Morelli]

I need help to import pedal force into OS for ID.
I have right and left pedal force, tangential and radial crank component.
How i need to define the .mot file ?
I'm becaming crazy with this...

Having only 2 component I leave "O" the vz component ?
After that I did not understand how to reference the COP... i can use a virtual point for "force application" ? (for example pedal axis center or I need to apply to a "body" ?

Please help me, I really appreciate it.
Kinematics data are collected @ 250Hz., both scaling and IK is working fine.

Excuse me for the silly question.

Here an example of the mot file i created



ergo_test1.mot
version=1
nRows=1501
nColumns=7
inDegrees=yes
endheader
time RightPedal_force_vx RightPedal_force_vy RightPedal_force_vz RightPedal_force_px RightPedal_force_py RightPedal_force_pz
0 -26.521 -84.478 0 0 0 0
0.02 -58.362 -90.648 0 0 0 0
0.04 -85.732 -62.79 0 0 0 0
0.06 -89.971 -16.568 0 0 0 0
0.08 -75.439 25.595 0 0 0 0
0.1 -55.202 50.089 0 0 0 0
0.12 -38.284 54.234 0 0 0 0
0.14 -28.057 43.143 0 0 0 0


Thank you
Andrea

[Ayman Habib]

Hi Andrea,

Do you have a model of the pedal included in your OS model (with contact or constraint to connect the feet with it)? If so then you can apply the measured forces to the pedal directly. If not do you have data for the trajectory of the point of force application? What frame is it in? The latest refactoring of External Forces allows for specifying both the point of application and the force vector in arbitrary segment frames and does the transformations for you.

Please let me know if that helps. You may find the post below on this forum also useful in this regard.

https://simtk.org/forums/viewtopic.php?f=91&t=3203

Best of luck and please let me know if you have any questions,
-Ayman

[Andrea Morelli]

Hi Aymanh,
unfortunately I not have a model of the pedal in my model. I'm using the lower limb model. And really I not have the knowledge to add it to the model
In this case if someone can help me or is interested to study cycling is welcome.
I have the trajectory of the point of application (calculated from markers applied on the pedal spindle). The trajectory is "lab" reference like the coordinates I use for the markers for model IK and they are working well. Pedal forces are tangential and radial on the crank and so I need to understand how they are referenced compared to my "point of application".

I've attached a pics of my 3D software (BTS) and you see the trajectory of the point of application of the force with the 2 components (I'm using powered pedals). Naturally my LAB axis are inverted x/z and so when I import kinematics data and force data I transform it using the preview utility.

I read the post you link me and I unserstanf how to choose the setup file and set it up for body or point of application.....
I not have torque data so I leave "torque" deactivated.

Thank you a lot for your help

Pedal force (radial and tangential) for right pedal with trajectory of a calculated point of application.

Andrea

[Andrea Morelli]

Good morning Ayman

I reach to orient the force and import the data into Opensim (now with preview they are working correctly!).
Now my problem is.. I apply the force to a "point of force" (toes and ltoes) set force/point x/y/z (z is all zero for force because is a 2D force) but I received this error:

WARNING: Storage forze.mot could not locate data for identifier Unassigned.
WARNING: Storage forze.mot could not locate data for identifier Unassigned.
WARNING: Storage forze.mot_transformedP could not locate data for identifier Unassigned.
WARNING: Storage forze.mot_transformedP could not locate data for identifier Unassigned.

My question is point of force trajectory is a virtual point that has nothing to do with trajectory of the toes.... is that correct ? If yes is correct to load this coordinates for the point of force and apply the force to the toes ?

How i can fix this problem ?

Thank you
Andrea

[Ayman Habib]

Hi Andrea,

I came across a similar issue while helping another user recently that was caused by missing Torque data. I didn't get around to investigate it further but as a workaround you should be able to add 3 columns of 0 torque (adjust headers accordingly) and specify these in the ExternalForce definition dialog.

The point you specify is in a specific frame (ground by default I believe) so you need to set it according to how your data is collected (likely raw data would be in ground frame since mocap doesn't have info about the model or segments unless the measuring device is attached to a moving segment).

For the segment of application, you can use the toes, but you also need to think about the mass properties of it and how it's connected to the rest of the model.

Please let me know how it goes and best of luck,
-Ayman

[Andrea Morelli]

Good morning Hayman.
I try to add some masses to the body segments, insert column for torque

no in the file I have 19 columns and torque name are defined like that...

Dxpedal_torque_x Dxpedal_torque_y Dxpedal_torque_z Sxpedal_torque_x Sxpedal_torque_y Sxpedal_torque_z
(in the torque data i use 0.0001)

Now I received the message:
"Tool execution failed
Messages windows for details."

I click ok and message appear
"Tools execution failed or canceled by the user. Output files were not written."

But in the messages windows no details are available....

Thank you
Andrea