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digartisan
01-10-2005, 09:07 AM
I'm trying to do an elephant walking in Lightwave and because I have to rock and sway the body, the feet keep moving and I have to keep adding frames to keep them still.

Is there a way to stick them to the ground when I need to like in Maya?

- Lor

Dodgy
01-10-2005, 09:36 AM
Use IK?

For each bone in the leg, in the Motion options panel (press M) go to the controller tab and select which channels you want to be controlled by IK, then for the foot object, in the Motion options panel again, select an object (usually a Null) as the IK goal and turn Full time IK on :)

digartisan
01-10-2005, 06:46 PM
Thanks Dodgy,

Yeah I'm already using IK and using Nulls to control the feet but what I need is a means to lock or 'stick' a Null to a spot so if you pick up the elephant that foot just sticks there.

It's an extremely useful tool and I used it years ago - even before Maya was Maya.

Cheers,

Lor.

Dodgy
01-11-2005, 04:13 AM
My nulls don't move about if I don't want them to, could you be a little more precise?

mjanson
01-11-2005, 08:35 AM
Maybe what you want is a detached foot setup. This would give you the option to move the body of your beast away and the actual geometry of the foot would remain where it was placed. The polys inbetween would of course stretch like mad. If this sounds about right, then read on...

The bone chain in your legs should be broken by the foot (the foot bone is not parented to the shin bone but is parented to the pelvis). NOTE: Haven't done this setup in ages so I might be missing or screwing something up.

I would suggest making a very small ankle bone at the tip of your shin bone as part of the chain (or end of it). This bone would have a null, let's call it Foot Null, as its goal and the preceding IK Chain would be setup normally. With expressions, tie the placement (world coordinates) of the Foot Bone to the position of the null. E.g. Foot_Null.wpos(Time).x for placement on the Foot Bone's x channel. This can probably be done with follower as well...

After this is done, any movement of the null would translate the IK Chain and the foot will follow along. The foot, however, would only follow along and would not experience any automatic roll-off or similar effects. The foot would have to be setup as well in order to animated with ease and the animation will most likely have to be keyframed (no IK). Maybe there is an ingenious way of setting this up... who knows...

Hope this helped...

/Magnus

DigiLusionist
01-11-2005, 09:03 AM
I not sure if I'm just repeating what mjansen is suggesting.

I would do a reverse leg IK set up. This is where the leg bones are parented in the following order (from parent to descendant):

Heel bone (parent)
Toe bone
Foot bone
Shin bone
Thigh bone
Hip bone (descendent)

The Goal in this chain would be at the Hip area. The Goal would be parented to the character's pelvis bone, so the Hip bone would reach for the goal.

The feet will remain plastered to the floor. Of course, if you pull the body too far from the leg, the character will stretch in an unrealistic manner.

UnCommonGrafx
01-11-2005, 12:03 PM
Same thing. Still worthy.

Should make for a cool addition to the walk of the Elepant and really does give one a better sense of weight. Particularly when you stretch the skin, which I think you would with your present steps.

Try it and let us see your results. The firsts were real nice.

SplineGod
01-11-2005, 10:26 PM
It really depends on how the foot is rigged. In its simplest form youll have an IK chain with a goal object on the end. Turn on match goal for the bone thats linked to a goal object. Also turn up the goal strength to around 50 or so.
The IK goal PINS the ankle but doesnt prevent if from turning. Match goal locks the orientation of the ankle/foot to the goal object and keeps the foot locked in place.
If you use constraints make sure you dont overdrive them or the leg may push away from the goal. Match goal is basically a quick 'n dirty orient constraint. :)

digartisan
01-12-2005, 05:42 AM
Thanks guys for your help.

Basically all the feet (with Nulls attached and IK) are linked to the Body Master bone and Null which controls the roll and tilt of the body. Because of this, when I move that master, the feet go out of whack. I did not make this rig but it works really well except for that problem so I dare not muck about with it too much at this stage. All feet bones are using the Matched Goal Orientation function and I did try Spline God's idea but it didn't work. I understand that it could work in other situations though so thanks SG!

I think if Lightwave had a 'Sticky Feet' plugin it may have helped, but maybe not. It's a great idea in any case.

Here's my latest version of the elephant walk (with extra frames added to stop moving feet)

http://www.digitalartisan.com.au/elephant

Cheers,

Lor.

Castius
01-12-2005, 07:01 AM
The animation looks very nice.

Hard to say whats wrong since you said you added the extra keys already. I'm guessing they are not sticking when the body of the elephant is moveing away from the feet to much.

Getting a solid stable foot with LWs IK can be a difficult but not impossible.

Can you replace the elephant with a null and post the scene?

SplineGod
01-12-2005, 09:39 AM
Thanks guys for your help.

Basically all the feet (with Nulls attached and IK) are linked to the Body Master bone and Null which controls the roll and tilt of the body. Because of this, when I move that master, the feet go out of whack. I did not make this rig but it works really well except for that problem so I dare not muck about with it too much at this stage. All feet bones are using the Matched Goal Orientation function and I did try Spline God's idea but it didn't work. I understand that it could work in other situations though so thanks SG!

I think if Lightwave had a 'Sticky Feet' plugin it may have helped, but maybe not. It's a great idea in any case.



Ive rigged and animated all kinds of stuff including quadrupeds though for something like an elephant the rig would be very simple. Off hand Id say that its not rigged properly especially if you need a plugin to make the feet stick. I never have a problem making feet stick with any rigs Ive done.

The feet goals should not be parented to the root bone because it defeats the whole purpose of using IK. Generally you have a Global Postion Null that the body of hte elephant and IK Goals are parented to which you ONLY use to place the whole rig in a scene. After that you should be able to move or rotate the root bone and the feet should stick (because the IK goals are NOT parented to it). You should also be able to pose eachy leg with its own IK Goal and not affect any other pose of each leg or the body..

Heres a basic walk cycle using a quadruped rig I have. Its super easy to animate and youll notice that the feet stay exactly where I plant them when the body is moved and/or rotated.
http://www.3dtrainingonline.com/examples/quadruped_ikb_test.avi
http://www.3dtrainingonline.com/examples/quadruped_ikb_test2.avi

digartisan
01-14-2005, 07:57 PM
Thanks Spline God.

I see your point. The feet/leg chain should be parented to the Null at the base which moves the whole elephant, not to the Null that controls tilt/roll. I would not have rigged it that way if my job was to rig the thing.

I had trouble changing it earlier without upsetting the animation but I'll have a fiddle with it again because I'm working on the front shoulders, head and adding more weight to the movement.

- Lor.

SplineGod
01-14-2005, 10:26 PM
Cool! Well it should work better after changing that :)