# static indeterminacy and constraint forces

Hello!
I have a statically indeterminate system, when looking at the mechanical system as “one unit”. The problem is described (in general) rather well in the anyscript wiki FAQ, see link,
http://wiki.anyscript.org/index.php/FAQ#How_is_it_possible_that_the_model_will_calculate_automatically_the_reaction_forces_with_the_environment.3F
or this one,
http://en.wikipedia.org/wiki/Statically_indeterminate#Static_indeterminacy
I was thinking of “enforcing” symmetry of the reactions (3 forces and 3 moments at each foot in my case) to reduce the ratio of unknowns versus equations, ie (“Reaction force in X for right foot” = “Reaction force in X for left foot”) , (“Reaction force in Z for right foot” = “Reaction force in Z for left foot” times -1) and so forth. Whether this would help the optimization routine in finding a better load distribution between the muscles and more realistic reaction forces I don’t know. However, I have not been able to figure out how to do this. I fear that such an implementation would require fiddling with a part of code that is not accessible via anyscript.
Any ideas?
/jokke

Hi,

This kind of constraints (linear combination) is not available for the forces in genral, that means not for the reaction forces either.

However it is available for muscle activity. So if you realy need to constrain reaction forces, what you can do is replace them by strong muscles and use the AnyActivityConstraint (using the strength of the muscle as coefficient you end up controling directly the force of the muscle).

Now in your case (foot-floor contact) such a setup is probably not strictly necessary. Using the conditional contact of the tool box like in the StandingLift model will give good results.

Best regards, Sylvain.