Reaction Forces

Main Forum
1

Hi all,

This might seem a bit simple but I have one more small question about the model I’m designing.

If I am designing a human body model which is connected to the ground then which reaction forces do I need to specify?

I attempted to include additional AnyReacForce for the left and right feet but it came up saying that the model contains redundant constraint reactions since I have already specified drivers at the toe. Additionally I am assuming it is not required to have a reaction force at the pelvis if reaction forces are already specified at the ground, is this correct?

Many thanks in advance for any help,
Lewis

2

Hi Lewis,

The error indicates that whatever you used to connect your model to ground already contains reaction forces. Joints by default contain active reaction forces, so if you add additional reactions by means of AnyReacForce, they become redundant.

You are not writing how you model is connected to ground, but if it is standing and the feet are connected to ground by means of joints, and these joints together provide reactions in all six rigid body DoFs of the body, then you do not need additional reactions in the pelvis.

Cheers,
John

3

thanks for information.

4

Hi John,

Thanks once again for your help. My feet are connected to a platform which I have designed via drivers. For this connection I have set as Reaction.Type Off.

In order to provide ground reaction forces I have then subsequently defined reaction forces at each feet, e.g. for the right foot.

AnyReacForce RightFootReaction =
{
AnyKinRotational rot =
{
AnySeg &ref1= Main.HumanModel.BodyModel.Right.Leg.Seg.Foot;
AnySeg &ref2= Main.Model.Environment.Origin.Plate;
//AnyFixedRefFrame &ref2 = Main.Model.Environment.Origin;
Type = RotVector;
AngVelOnOff = On;
};

  AnyKinLinear RightFootLinMeasure = 
  {
    AnySeg &ref1= Main.HumanModel.BodyModel.Right.Leg.Seg.Foot;
    AnySeg &ref2= Main.Model.Environment.Origin.Plate;
    //AnyFixedRefFrame &ref2 = Main.Model.Environment.Origin;  
  };
};

Where the second reference frame is the reference frame of the segment which is that platform the feet are connected to. Is this the correct way to set this up?

Many thanks,
Lewis

5

Hi Lewis,

Sorry for the slow answer,

I would write
AnyKinLinear RightFootLinMeasure =
{
Ref=0;
AnySeg &ref1= Main.HumanModel.BodyModel.Right.Leg.Seg.Foot;
AnySeg &ref2= Main.Model.Environment.Origin.Plate;
//AnyFixedRefFrame &ref2 = Main.Model.Environment.Origin;
};
};

To ensure it is using the foot coordinate system, i am not 100% sure though if this will make a difference for the loads on the human though in this case, since all six reactions on.

Best regards
Søren

6