# Force plate measurement calculation

Hi, my name is Yi hwan.

In the “ForcePlateType2.any” there is COP and Tz calculation code.

that code is this

``````  AnyVar Vx= my/fzz;
AnyVar Vy= -mx/fzz;
AnyVar Vz= 0;
AnyVar T_twist = mz-Vx*fy+Vy*fx;
``````

but my question is that equation is different with amti force_plate manual

that manual explained that

Mx = FzY
My = - Fz
X
Mz = - FxY + FyX + Tz

therefore COP and Tz equations to be
X = -My/Fz
Y = Mx/Fz
Tz = Mz+FxY-FyX

both models are using same equation for Tz but different equation for COP

I want to know reason of two models are using different method.

Hi YiHwan

Let’s see some piece of ‘ForcePlateType2AutoDetection.any’ file in AMMR V1.3.

``````    AnyDrawVector vector =   {
AnyVar time=..ForcePlateDriver.t;

//AnyVar lx=..ForcePlate.ydist;
//AnyVar ly=..ForcePlate.xdist;
//AnyVar lz=..ForcePlate.zdist;

AnyVar fzz =iffun(gtfun(  (fz^2)^0.5,0),fz,fz+1000000);

AnyVar Vx= my/fzz;
AnyVar Vy= -mx/fzz;
AnyVar Vz= 0;

[b]Vec = -..OnOff*{ Vx,Vy,Vz    };[/b]
GlobalCoord=Off;
PointAway = On;
DrawCoord = Off;
Line.Style=Line3DStyleFull;
Line.RGB = {0,1,0};
Line.Thickness = 0.000001;

Line.End.Thickness = 2*0.015;
Line.End.Length = 4*0.015;
Line.End.Style=Line3DCapStyleEllipsoid;
//
Line.Start.Thickness = 0*0.015;
Line.Start.Length = 0*0.015;
Line.Start.Style=Line3DCapStyleEllipsoid;

AnyRefFrame &ref = ..ForcePlate;
};
``````

So when this class template draws the center of pressure,
there is a minus sign.
So basically, we are using the same equation as you referenced.

Best regards,
Moonki