Relative movements of bones ?


again I got stuck… :slight_smile:

I am currently experimenting with IPOs/Actions/NLAs. Is there any way
to accomplish this:

Suppose there is one bone to move from point A in space to point B in
space. This movement shall result in one stripe in the NLA editor and will
be part of a “greater movement” :wink:

The movement is done based on an already modified armature in POSE

The problem: This bone has one child (parent->child relationship, not
connected like in a spinal chord). This child normally follows the parent
bone, but in this case the child should only move its root (which is
located in near of the parent) but its tip (which has a greater distance
to the parent) should stay in its place and the child bones rotation
should be conserved as much as possible. As well the child as its parent
are located “free in space” – no axis is in parallel to any global axis.
Rearranging the child manually after the parent has been moved to its
destination is too difficult and not accurate enough.

Is there any way to perform this trick ?

Thank you very much for any help in advance!

Keep blendering !

I know fore sure when you want to the root to move and not the tip, there is IK constraint and Track to constraint. It let you move the root and always pointing at the same place. Or just invert the bone position. If rotation mustn’t change, just use a bone as a pointer(this one will rotate) but put a copy location constraint on the good one copying the pointer, it’s like a offset parent, but without rotation.

How about activating the hinge button on the Armature Bones panel? The tip of the child bones would not keep the exact position if you moved the parent bone, but the disturbance to the child bone is kept to a minimum…

Hi Gabio, Hi grafix,

thank you very much for your replies !

I see that I havn’t explained the situation completly…for the description I
gave your replies solved the problem absolutely perfect.

Now “The Story of my problems PART XXIV: The rest of truth” :wink:

I am not at frame 1 – I am at the middle of the animation…sigh…

The consequences:
“Mother Bone” has already (and intentionally) moved her child.
This already altered position of the child is wanted and the starting point
of the problem described previously.

When I push the “Hinge” button now, Grafix, – in the middle of the
animation – the child totally gets uncontrolled by its mother and all
previous wantend influence gets lost and nullified.
The armature jumps off control partially.

With your solution, Gabio, there is another problem I can not solve:
I need to put an empty at the tips current position as a target for
contraints. To get the position of the bone’s tip I need to go to EDIT
mode – and the armature jumps back into rest position and all previous
arrangement is lost.

Is there a trick to circumvent this ?

Have a nice weekend and thanks a lot for your given freindly support! :slight_smile:

Added later:
How can I copy a rotation/location from a posed bone to anything
else, which I later can use as a target for a contraint for that bone?

Sadly you can’t. If you need to modify the armature you must come back to rest pose, however it should not be of a real problem because as soon as you get out of editmode all bone will get back to the last pose (except the new stuff). If I understand what you say, you just want something to hold position. in this case Add it in editmode, come back and place it in posemode with 1 key pose. This way it will always stay put.
Now if your situation is more complicated than that. please post a damn screenshot so I can stop scratching my head on the carpet.
you can use

How can I copy a rotation/location from a posed bone to anything
else, which I later can use as a target for a contraint for that bone?

does it have to be automatic? I think you can easily do a copy-paste (button in header of 3Dview) on a single bone to hold the info and then use a constraint to get back to this position later by playing with influence slider. Or even simpler, just copy (shift-d) the damn Key in action window when you need to come back to this position.

The “Hinge” button doesn’t make a joint into a hinge, with only one degree of freedom. You can still bend the joint in two axes. Its tooltip (in 2.41) says “Don’t inherit rotation or scaling from parent bone”. That seems a wierd function to attach to the name “hinge”.

How do you get a hinge joint, like a knee, in an armature?