# force plate related data of "GaitLowerExtremity"

Hello,

I got a question when running “GaitLowerExtremity”, I found that in “GaitNormal0003-processed.c3d”, the maximum of Fz is about 50N, but when I load and run the model, I found the maximum of force in force plate in z direction, it is like 600N.

So I am confused that in .c3d what is the Fx, Fy, Fz? they are real forces in force plate with the units of N? what about Mx, My, Mz? the units are N.m?

Hi,

The force plates of this example are of type 4, so they have a calibration matrix that must be applied to the raw force and moment data in order to get it in N and N.m (this is done in the script).

So most probably the value 50 you read directly from the c3d file was not in N.

Please look at the web page c3d.org for more details on the plate type and calibration matrix.

Best regards, Sylvain.

Thank you Sylvain.

I got the calibration matrix for my force plate which is also the type 4.

I was wondering that the Fx, Fy, Fz, Mx, My, Mz in the c3d should be the electric signal getting from the force plate? AnyBody will calculate the force through considering matrix?
But I found the in example “GaitLowerExtremity”, file “GaitNormal0003-processed.c3d” the units of Fx, Fy, Fz, Mx, My, Mz are all N.
I am confused.

I also find a problem, I already loaded the data in my model with the similar method in “GaitLowerExtremity”, there are numbers in PlateFootReaction FzTotal but it is zero in Force Fin and Fout.

Hi,

The Fx, Fy, Fz, Mx, My, Mz in the c3d file is indeed the electric signal, the unit is mV i think (but it doesn’t really matter for us).
Then AnyBody uses the calibration matrix to convert the electric signal in Newtons like this:
Data=.Cal’*{Fx,Fy,Fz,Mx,My,Mz};

In anybody if you llok at the value “Main.ModelSetup.C3DFileData.Analog.DataFiltered.Fz1” this is the electric signal. And “Main.Studies.InverseDynamicStudy.Output.EnvironmentModel.Plate1.Force.Flocal” is the force in newtons.

I hope it is clear now.

I am not sure i understand very well you second question, could you precise it a little more?

Best regards, Sylvain.

Thank you very much. I think I have got it. Another question I want to know that in AnyBody the units of F and M are N and Nm respectively?

Yes they are. Forces in N, and moments in Nm.