Rigging A Mechanical Robot With Tentacles

[rowan-e]

Hi all, my first post here, begging for help already...

I'm trying to rig and animate a robot, think the sentinel from the matrix, to move around the base of a chasm. Currently using IK Splines on the tentacles, but I don't know how to get the grab at the end of the tentacle to stay attached to the rock when the main body moves. I'm guessing there's some sort of constraint to use, but I can't work out how. Any help is very much appreciated.

Rowan

[gmask]

Yea that's a tricky one.. that's not helped by using spline IK's since the IK's can slip on the length of the spline. I guess I'd probably go with using an FK solution. If it were a tentacle where you only see the one end with the claw then I'd just place the root at that end.

[rowan-e]

Problem is you see it all... if it's too tricky I'll probably ditch the idea and come up with another idea. File this one away for when I know more Maya.

[visualfx]

if you allowed the IK spline joints to stretch and compress a little you should be able to lock the end of your chain (or tentacle) as you described.
if you don't want your joints to scale at all, you could maybe try the fixedLengthCurve plugin. the only problem with that is you will likely need to compile (or have some one else compile) it for any recent version of maya (5.0 or later).

[joojaa]

maya knows how to fix the length of a curve!

[visualfx]

Joojaa, are you referring to the Modify Curves -> Lock Length menu option (aka. LockCurveLength cmd)?

This does lock the length of a curve, but I have not found this to be very useful for rigging. It breaks as soon as you attach a cluster to the curve. It does seem to still work if you connect into the contolPoints attribute of the curve, but the behaviour is unpredictable at best. It is practically impossible to return the curve back to its original shape (similar to the multi-chain IK handle).
I have found the fixedLengthCurve plugin to return a much more desirable result, as it uses the full length curve (original) as a target.

If you know of a better method, I would really like to hear about it.

[joojaa]

Well its still not going to fix underlying problems of the rig. If the user cannot see in his minds eye whats going to happen hes not going to be able to use the rig anyway despite any other support tool.

In general i rig is so that the user has free control of the curve length then just let thet drive a second curve that claps the length, one way to do thsi is to use a dynamic curve for this.

PS: does anybody else find the maxxon add on this forum a bit thick. I what 3d application DOES NOT have direct export to ae, finalcut, shake.-

[visualfx]

QUOTE(Joojaa @ 12/05/07, 05:32 PM) [snapback]277593[/snapback]
In general i rig is so that the user has free control of the curve length then just let thet drive a second curve that claps the length, one way to do thsi is to use a dynamic curve for this

This is exactly what the fixedLengthCurve node allows you to do...except without the need for dynamics.

[rowan-e]

I'm afraid this is all going over my head... I'm teaching myself all of this stuff, since it's way beyond 1st year coursework... The curve length isn't a problem, since then tentacles won't stretch. What I really need is a way to lock the CVs on the curve to dummy objects. Then the end will stay fixed whilst the body moves (well at least until then body gets too far away). Is there a way of doing this?

[gmask]

You could create clusters for each CV in the curve and then parent the clusters to a bones in a skeleton.

Then you might also consider using attach to motion path to position each segment in the tentacle but detacht eh aniamtion curves.

If you have ten segments then the motionpath node for each one would be incremented ..0, .1 , .2 ,.3, .4 etc...

[rowan-e]

I tried using clusters, but the clusters took the IK Spline deformer movement before the constraint, so that didn't work. Is there no way to force a CV to remain in one place? Or is there a way to rig the character so that it's possible to? I could do it using a non-spline solver, but that would loose the control over the curve of the tentacle, unless there's a way to bind bones to a CV curve, then use that in combination with an IK solver. Just clutching at straws now...

EDIT: Would it be possible to link the CVs EXCEPT the last one to the main body, so instead of the Curve itself being moved, only those CVs are. Going to have a mess around but would appreciate expert help

[joojaa]

Then reorder your history.

QUOTE
EDIT: Would it be possible to link the CVs EXCEPT the last one to the main body, so instead of the Curve itself being moved, only those CVs are. Going to have a mess around but would appreciate expert help

yes this all is exactky whgat your clusters are there for.

PS: take a empty file and start with the minimum amount of distraction t work yourself up. THEN bind the real deal.

[rowan-e]

The history is that way because that's how I wanted the curves to deform... I think I have a solution. I'm selecting the first CV in the curve (CV 0), freezing transformations, then linking its X,Y,Z (maybe rotation, not looked into that yet) to the body X,Y,Z etc, with the net result that it's effectively linked. Hopefully this will work.

EDIT: For some reason I can't freeze the transformations of the individual CVs.. is there a trick to this? Or some way of creating them as such?

I've used a cluster to link the 1st CV to the body, all works fine, but I need some way to keep the end of the bone chain in place, as it currently moves along the path.

[joojaa]

QUOTE
The history is that way because that's how I wanted the curves to deform...

so you want it not to work out for you. Dont just fix something that is broken make it anew its easier.

Just because something is almost there does not mean you are on path that right. I mean it almost works to send people food when they are strawing in Africa. But this just ensures theres going to be a next time. Because it solves nothing.

QUOTE(Rowan_E @ 12/07/07, 03:47 PM) [snapback]277731[/snapback]
EDIT: For some reason I can't freeze the transformations of the individual CVs.. is there a trick to this? Or some way of creating them as such?

ARGH Freeze makes the transformations matrix identity. The shape has no matrix functionality. It is quite safe to say you should steer clear of freeze for while. Freeze is one of the most likely tool cause you major toruble if you dont know what it really does.

TRUST me this si exactly what you want clusters for they do EXACTLY all you need here. You just need to rethink your ordering, and parent relationships.

Maybe this helps you straighten your mind:

make a ball, make a curve then make one cluster for all but the last points of the curve then one for the last point then parent the first cluster to the ball nw move ball see what happens. THEN build the tentacke rig on that curve.

Im not sayting id use this but it atlest does what you ask.

PS: its not that i cant calculate this as if you'd frozen it but its a bit pointless as it unworks stuff you shouldnt be doing in first place.

[gmask]

I agree.. it would be best if you started a new file to figure this out and then apply what you learned to the real deal. I don't quite understand why you history on the curve either.

[rowan-e]

I am working from a new file. Just looking at a body (a cube) the bones and the curve. I solved the freeze thing by using clusters. Tried putting the IK the other way round, but no joy. I don't think Spline IK will work for this, since I can't find a way to fix the end and start of the curves. Going to have to leave this idea now, as the deadline is getting too close, and I still need to light and texture the scene. Going to go for the 'monster at the bottom of the pit' idea I think. I will come back to this however, and you've all taught me lots, so a BIG thanks for that