Your ik test looks fine.
I set it up with out any joints and got perfect results.
I placed “front” in a null. I put that nulls axis where i wanted the pivot, in the is case directly on the hinge. Then I created a new null(controller) and added user data slider. i added an expresso tag to the controller null and dragged both controller and the front null into the expresso. Then in the controllers red box i selected user data: front null. then i attached that to the front nulls blue box: coordinates:global rotaion:P
and then you have a controller and can easly set up a walk cycle. you can add a slider to ik the same way but this is the simplest way.
If you are going to be rigging things up you need to set up the higharchy and connect more pieces. The way the model is now is too much to try to rig.
/randy