Pin a bone in place?

Support Animation and Rigging
#1

Hi
I am trying to animate a character walking down a ramp…
Using the pose mode and action editor I have set the whole armature to move from the start position to the end position of the animation.
I am now trying animate the legs to walk down the ramp…

Trouble is as the character walks down the ramp the whole armature moves and its very hard to keep the foot currently in contact with the ground exactly in a fixed place until its time for that foot to leave the ground as it takes its next step. The results I get have the foot sliding about unless I set an i at every frame and its still too easy to have the foot jumping about

Is there a way of pinning a bone in space so it will stay there whatever the rest of the armature is doing and it will not move until released - which would make my job a lot easier?

#2

That is called inverse kinematic.
And yes you can set up a IK chain with blender.
There are several rigs around here that can do FK IK switching.

Read the fantastic manual.
http://wiki.blender.org/index.php/Manual
http://wiki.blender.org/index.php/Manual/Inverse_Kinematics

in this thread the animation gurus bassam and cessen are giving deep insight to IK/FK switching
http://blenderartists.org/forum/showthread.php?t=130777

For a first animation i think you might stick to IK for the legs. It is harder to get nice arcs that way, but since your goal is simple walk cycle and not an artistic soccer player that might do.

BM

#3

Sorry I think I didn’t explained what I wanted properly
I’ve set up my simple armature with the “foot bone” as an IK that effects the “lower leg” and “upper leg” bone.
what I want is the ability to I place my foot where I want it on the “floor” and lock or pin it in place
Then move the armature a bit by its root and (if its physicaly possible) the foot bone to remain pinned in place and the Lower leg bone and Upper leg bone to bend and move the leg to keep joining the body to the foot
I don’t even know if this is possible but it would be very useful.
My problem is that I am trying to animate a character moving over uneven terrain and its very hard to keep the foot thats on the ground from moving as I move the rest of the armature

#4

go into pose mode, select the foot bone, in edit buttons add a constraint of type IK. see the field that says ‘target’? add an empty, then type the name of the empty in that field. now the foot will stick to the empty, and you can key the influence of the constraint.

1 Like
#5

You got slip foot problem? Why not using walk.o.matic
Walk.o.matic you will get here http://www.blender.org/download/python-scripts/
My Walk.o.matic Samles
http://video.google.com/videoplay?docid=5263202606268216316
http://video.google.com/videoplay?docid=-7806625525700767930
http://video.google.com/videoplay?docid=-1688324515100159992
Or you can use BVH
http://video.google.com/videoplay?docid=-5864723441469612271

#6

Eh. The fact that your feet slide means that you’re rig is incorrect. Grab any of the free biped rigs available on these forums and try to animate them briefly. You will see that you don’t have a slipping problem then.

#7

Hum, i guess your foot bone is child of another animated bone.
I usually have a “root” or “socket” bone that rests during the entire animation.
Most of the IK targets have this as a parent.
BM

#8

Thanks for all your tips
I think i’ll have to go away and work out how to do a better rig!

1 Like
#9

try this (similar to what is suggested above)

  • add root bone below character (if none already)
  • add floating IK target bone which is separate from the foot and has root as its parent. Constrain the shin bone to have this as an IK solver. This means the leg will always try to point towards this bone (you can hand-animate the foot)
  • have the main body bone (usually a spine bone) which currently moves the whole rig as a child of the root bone too

This will mean that you can move your root bone and everything will move. You can move your foot IK target and the leg will move towards it. You can move the current main body bone and the body will move but the leg will still point towards the IK target. Duplicate for the other leg and play around and you will find it is very easy to animate as you want to.

There are much more complex rigs to do beyond this but this is a good start.

1 Like
#10

It took a while but doncuan’s tip worked for me!!
I made a new ROOT bone with the spine a child off it
I made a floating IK target LEFT bone - constrained the SHIN to it - selected LEFTshift selected SHIN - Ctrl I
I got a bit stuck at this point as the whole armature went a bit mad if I moved the LEFT bone
After a bit of experimenting I found I needed to make the Chain len of the Shins new constraint = 2 otherwise if you leave it at 0 and you move the floating Left bone then the whole armature moves rather than just the leg - noob error I know
thanks every one for your tips

#11

omg, thank