# 2D model: Computation of resultant hip force

Hi everybody,

I’m a novice at Anybody and would really appreciate someone’s help.

I went through the tutorials to get an overview, but yet do not know how to start exactly.

Well, I would like to compute the resultant hip force “R”, composed of the weight force “G5”, which can be simplified as a simple force acting on the center of gravity, and a resultant of all muscle forces “M” balancing the pelvis on the femoral head (please see attachment). The line of action of the resultant of muscle forces originates at a point somewhere at the pelvis and is inserted at the trochanter major, it can be simplified as a “simple muscle”.

The model can be simplified as a 2D model standing on one leg. S6 (please see attachment) should always meet the vertical line going through the ankle joint.

I would like to simulate three different postures of the pelvis: a) horizontal, b) inclination of 10 degrees and c) declination of 10 degrees (also please see attachment).

I know there is already a body model “PelvisRightLeg” existing in the Repository and I went through the application “KneeLoad” as it’s a similiar task I guess, but even though I couldn’t get started with my project…
It’s not so easy haven’t done anything with this software.

Steffi

Hi Steffi,

The KneeLoad application can be a good starting point. However in this application a moving force is applied on the feet and as i understand you only want static postures loaded by gravity.
So you will have to remove the force and applied a ground support as can be found in the StandingModel application.

An other solution is to start directly from the StandingModel and remove the non-used body parts (left leg, arms) as the application use a full body model.

After that you can modify the drivers in the JointsAndDrivers file to set the inclination of the pelvis. You can also set the ankle to be exactly below the S6 point by driving a linear measure between the two points.

I hope this helps you starting. If you need more explanations please write again.

Best regards, Sylvain.

Hi Sylvain,

Yes, I only want static postures loaded by gravity.

So far I created a “New Main” and included the “PelvisRightLeg\BodyModel.any”. I also drew the global reference frame and noticed that the pelvis is shifted only in y-direction (x- and z- coordinates are zero). That’s the position I want it to be, too.
But I would like to have the ankle fixed in the origin of the global reference frame. Where and how can I set this? I don’t find the nodes.

Steffi

Hi Sylvain,

Now I started with the “KneeLoad”, removed the moving force which was applied to the feet and fixed the ankle joint to the global reference frame. I don’t need apply an extra ground support, do I?

I also added some nodes, for example “r5”, where I applied the weight force “G5”. I tried to make this force visible (as an arrow), but it doesn’t work and I don’t know why (there is no error message). I did it in the same way as it was shown in the tutorials.
Maybe you can have a short look, I put the following in the “Environment.any” file:

AnyForce3D Gewichtskraft=
{
F = {0, -588.6, 0};
AnyRefFrame &PointOfAttack= Main.HumanModel.BodyModel.Trunk.SegmentsLumbar.PelvisSeg.r5;
AnyDrawVector drF = {
Vec = .Fout/200; // Scale the length down
Line = {
Style = Line3DStyleFull;
Thickness = 0.01;
RGB = {1, 0, 0};
End = {
Style = Line3DCapStyleArrow; // This specifies the end to be an arrowhead
RGB ={149/256,51/256,55/256};
Thickness = 0.02; // The head begins with twice the thickness of the shaft
Length = 0.05;
};
};
// attach the arrow to G5
AnyRefFrame &g5 = Main.HumanModel.BodyModel.Trunk.SegmentsLumbar.PelvisSeg.r5 ;
};

};

Is there a mistake?

Thank you very much.

Best regards, Steffi

Hi Steffi,

It is a good choice to strat with the KneeLoad instead of a making a new application bottom up. Reusing existing applications is easier in general.

About the support please take in account the following: the KneeLoad model originaly has the pelvis fixed to the ground and supported by a standard joint. In your case the support should be on the feet as the force is applied to the pelvis. So make sure this is done. The suport can be done by a joint or a reaction force or the more complex but realistic support of the standing model.

And for the AnyDrawVertor probaly the length is too short ( Fout/200) so you can’t see anything. Try to make it longer.

Best regards, Sylvain.