Testing IK solvers, I create a leg armature chain composed of Leg.R, Shin.R and Foot.R. In the heel (edit mode), I add a separate bone, not parented to anything - IK_Leg.R
In pose mode, I select Foot.R, then add an IK_solver constraint to it. As soon as I type in ‘Armature’, the leg collapses in on itself. This collapse is still apparent in object mode but the leg looks fine in edit mode. If I remove the constraint or decrease the IK solver influence to 0, the leg regains its natural form.
The manual (manual/user/htmlI/x7174.html) makes mention of something like this when teaching how to add an IK_solver to a wrist:
“Choose “Hand.R” and add an IK solver constraint to it in the Constraints Panel. In the OB field type the object name: “Armature”. The bone went to the centre of the armature, but we’ll fix this now. In the new BO field, that appeared in the constraint window, type the bone name “IK_arm.R”.”
But the “we’ll fix this now” doesn’t seem to occur.
I’ve figured it out. I’d created an armature then deleted it then recreated. However, since I deleted the bones in edit mode, then created a new armature in object mode, I thought I was still working with my original armature - ‘Armature’ - whereas I was really working with ‘Armature.001’. Hence, constraining the foot of Armature.001 to target OB:Armature (which still existed as an object but has no bones) caused all sorts of problems.
The moral of the story is, always display and pay attention to the name of your object in the 3D window.