Too few kinematic constraints. Why?

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,


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.

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

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.

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};

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]EDIT: I works now. I had to set the reaction type to off.