Too few kinematic constraints. Why?

Archive Old Self-Supported Forum
1

Hello support,

I am trying to analyse the muscular forces of a lizard’s jaws for a scientific work at university. I’ve programmed the attached file but it always says “too few kinematic constraints” when I reload it. I do not know what I’ve missed because I’ve used the AnyBody tutorials as a guide.

Maybe one of you sees where the problem is located.

Thank you in advance and regards,

Christian

PS: There are two versions attached. The file called “sicherheitskopie” may be easier to read and understand because i tried to rearrange some parts of the code in order to see if it has any effect.

2

Hi Christian,

The problem is the AnySeg oberkiefer, it is not fixed. It can float in the global ref frame and needs to be driven to a certain point:

include a ANyKinLinear and a AnyKinRotational and drive both to 0.

Advice for the start, try to do less at once.

  1. Create one segment and drive it to zero;
  2. Add another segment and drive to to a certain position
  3. Add the Muscle nodes
  4. add the muscles…

I hope that helps

3

Thanks for the fast answer. I already assumed that this would be the problem, but how do I implent the AnyKinLinear and AnyKinRotational? And how can I set them to 0? The AnyScript Reference did not really help me.

4

Hi Christian,

They are the same as a 6 DOF joint, you can also use a Joint and a Driver…

A AnyKinLinear and AnyKinRotational are measures that make a connection between two nodes:

  1. Linear: 3 translations
  2. Rotational: 3 rotations

that you can “fix” with a SimpleDriver, here form the Refmanual:
AnyKinEqSimpleDriver Motion = {

  AnyKinLinear lin = {
    AnyRefFrame &Ref0 = Main.Model.Ref0;
    AnyRefFrame &Ref1 = Main.Model.Ref1;
  };
  
  AnyKinRotational rot = {
    AnyRefFrame &Ref0 = Main.Model.Ref0;
    AnyRefFrame &Ref1 = Main.Model.Ref1;
    Type = RotAxesAngles;
  };
  
  DriverPos = {1,1,1,0,0,0};
  DriverVel = {0,0,0,2*pi,0,0};
  DriverAcc = {0,0,0,0,0,0};
};
5

Thank you, Amir, but I still did not manage to run it with AnyKinLinear/Rotational.

I used the structure of demo lesson 6 in order to make the kinematics work.

My next problem is the inverse dynamics.
AnyBody keeps telling me “The muscles in the model are not loaded due to kinetically over-constrained mechanical system.[SIZE=2]”[/SIZE]

[SIZE=2]But why and especially where is it over-constrained now?[/SIZE]
[SIZE=2][/SIZE]
[SIZE=2][/SIZE]
[SIZE=2]EDIT: I works now. I had to set the reaction type to off.
[/SIZE]