Hello,

I am trying to implement a landing motion on the full body model so I can see the effect on the ACL and other ligaments. For this to happen, I have constrained the metatarsal right (i am only using the right leg for this, I turned off the left one) on X,Y,Z translation and X,Y rotation, and I have turned off some other drivers which were turned on before so I have the proper constraints. I have left the Z rotation Off so the model can rotate about the metatarsal.

I first tried to implement a simple driver using the already existent `AnyKinEqSimpleDriver PelvisGroundDriverPosY`

to see if the drivers I chose are correctly turned On or Off. For this, it is working perfectly.

Now my problem starts when I try to implement a `AnyKinEqFourierDriver`

. I thought this might be a good driver since I want an oscillating motion to be made starting from an upright position to a flexed one, and back up again. Although maybe this can be switched with a polynomial driver so I can control the accelerations for different phases, but first I would like to make this one work since they are similar and it is easy to check if the model is working with this motion.

So when I switch the `AnyKinEqSimpleDriver`

with `AnyKinEqFourierDriver`

, then suddenly my model tells me that `ERROR(OBJ.MCH.KIN3) : InverseDynamicsMoSyn.any(136) : InverseDynamicStudy.InitialConditions : Kinematic analysis failed in time step 0 : Failed to solve position constriants`

. I undestand what the error is saying, so I tried to give the model different initial positions to start so it can solve the constraints, but the result is the same. Now my question is: why does one work and the other not since I only switched the driver type and how can I solve this?

Here is my code where I made the changes for the driver (the numbers inside the A and B coeff. are random, I just placed them there so I see if it works):

```
#if MANNEQUIN_DRIVER_PELVIS_POS_Y
/// Default mannequin driver. Control with:
/// #define BM_MANNEQUIN_DRIVER_PELVIS_POS_Y ON/OFF
///
AnyKinLinear lin = {
#if GLOBAL_REFERENCE_FRAME_SWITCH == 0
AnyFixedRefFrame &ref1 =.GenericGRF;
#else
AnyFixedRefFrame &ref1 = GLOBAL_REFERENCE_FRAME;
#endif
AnyRefFrame &ref2 =..BODYMODEL_FOLDER.Trunk.SegmentsLumbar.PelvisSeg.AnatomicalFrame;
};
AnyKinEqFourierDriver PelvisGroundDriverPosY ={
AnyKinLinear &Jnt = .lin;
MeasureOrganizer = {1};
Type = Cos;
Freq = 2;
A = {{0.5}};
B = {{0}};
Reaction = {#var Type={Off};};
#if MANNEQUIN_DRIVER_WEAK_SWITCH == 1
#var AnyVar WeakDriverWeight = .DefaultWeakDriverWeight;
AnyFolder Weights =
{
AnyFunConst Fun = {
#var Value = {..WeakDriverWeight};
};
};
#var WeightFun = {&Weights.Fun};
#var CType = {Soft};
#endif
};
#endif
```

Thanks in advance,

Diana