Does BushingForce have bug?

[Sina Porsa]

Hi,
I am not sure if this is a bug or not.
This is my OSIM file to define a BushingForce in Arm26.osim
.
.
<BushingForce name = "DirectionY">
<isDisabled> False </isDisabled>
<body_1> ground </body_1>
<body_2> r_ulna_radius_hand </body_2>
<location_body_1> (0 0 0) </location_body_1>
<orientation_body_1> (0 0 0) </orientation_body_1>
<location_body_2>(-0.00110000 -0.23559000 0.09430000)</location_body_2>
<orientation_body_2>(0 0 0)</orientation_body_2>
<rotational_stiffness>(0 0 0)</rotational_stiffness>
<translational_stiffness>(0 100 0)</translational_stiffness>
<rotational_damping>(0 0 0)</rotational_damping> <translational_damping>(0 0 0)</translational_damping>
</BushingForce>
.
.
so it has only transitional stiffness in Y direction. But When I use "property viewer"in GUI it shows this as transitional stiffness (100 0 0). in puts 100 in X direction in stead of Y. It also changes the location on body 2.
I am not sure if it is a bug, or I do not know how to use bushing force.
Regards,
Sina

[Ayman Habib]

Hi Sina,

I would take out the extra "()" around various quantities, and just to be extra safe, use decimal points where needed. Please try that and let me know how it goes.

Best,
-Ayman

[Sina Porsa]

Hi Ayman,
Thanks, your suggestions solved the issue,
I used "()" as it was mentioned in ( help --> available objects ) in GUI.
Thanks for your help
Regards,
Sina

[Gregory Philips]

Hi Sina.

I am trying to create a new force the upper extremity model and I am using your BushingForce as the template. I wanted to confirm a couple of things with you about it.

1) When you enter the line name=DirectionY are you specifying the axis on which the force acts?
2) Are the location and orientation parameters you have used the same as the joint in the model?
3) You specified the stiffness and the damping parameters for the force but not the magnitude. Do you have the magnitude at everytime instant stored in a .mot file?

Thanks.

Regards,
Gregory Philips.

[Sina Porsa]

Hi Gregory,
1- no, directionY is the name of the bushing force which appears in the GUI. this linespecifies the stiffness of spring in each direction: <translational_stiffness> 0 100 0 </translational_stiffness>

2- No, I used a random location. I just wanted to check how "BushingForce" works.

3- I cannot understand your question, The bushing force acts like spring force. So the magnitude of force would be (stiffness*distance between frames)

[Gregory Philips]

I see. I wanted to create parameters for the force and wanted to know what kind of parameters can be added.