How to use restraints

Ok. These pics are not quite in the order I wanted, but…
This is the model I am trying to animate. Don’t laugh, it’s only my 6th model using Blender and my first animated one. When complete, there will be four different animations: Idle, Running, Attacking, Dying.
Right now, I am just trying to tackle what I think should be the easiest: Idle, where the spider just sort of bounces a little bit, twitches legs at random, and works its mandible. Sort of like a wolf spider might do when it is not running. (though this is not an attempt to replicate a wolf spider.)
The central bone in its thorax (is that right?) is the parent of all the other bones and all are connected to it directly or indirectly. Each leg has 4 bones: a base which does not move, but provides a pivit point for the next bone; the two “in between” bones; and the bone at the end of the leg, the “foot” if you will. The mandibles I don’t really need to describe as they are not an issue, nor is the tail.
I doubt you can tell from the screen shots, but as the spider bobs up and down, his legs have to adjust to maintain a zero z-axis movement at the tips where they touch the ground. Of course. To make the spider bob up and down, I use the only meathod I know, which is to grab the main body bone and move it along the z-axis. Consequently, all the other bones move with it. So… I am having to one-at-a-time, reposition the bones in each leg so that the tips appear to stay one the ground. This is tedious and does not work well. The are 40 bones in my armature and it is alot of adjustment.
I tried using a floor restrait (I am using 2.56 btw and this is weight-painted) and use the “sticky” option, but it does not do what I expected it to do. I obviously do not know how to properly apply/use it. I click on a “foot” bone, choose restraints, for target I put “armature” (which happens to be the name of my armature! ha ha) and then it asks me which bone. I type in the name of the bone I have highlighted. This I do in Pose Mode (I think). So… I said all this to ask these questions: How can I make the tips of the “foot” bones stay in place regardless of what all the rest of the armature is doing (unless I actually decide to move a foot, which I do). How can I delete the settings for one bone in particular from a keyframe without deleteing the entire keyframe? And how can I make the animation, after the last keyframe, smoothly return to what it was in the first frame to form a looping effect? (I have been copy/pasting frame #2 to the last frame to achieve this, but there is a better way I am sure.)
Thank you for reading this very lengthy and wordy post… I wanted to make sure that I gave enough info. I am such a noob that I do not even know WHAT to ask or how to ask it!


What you’re looking for is inverse kinematics (IK). Blender has an IK constraint and it would be well-worth your time to read up (manuals, tutorials, videos… whatever your preferred learning flavor) on how to use it. For a basic setup, you’ll need one IK constraint per leg… and an extra bone that’s not part of the chain to be you IK target.

See this .blend file and hopefully it should give you a more clear idea.