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Old 20-11-2002, 09:51 AM   #1
dkouts
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Question Mechanical Arm with IK

Hi all...

I'm creating an articulated mechanical arm that I want to
control with an IK skeleton/bone chain.


eg from this...

o-------o-------D



to this...

o
/ \
/ \
o D <--


(Just by pulling that rightmost IK end effector leftward)


Now since the skeleton wont actually be DEFORMING any CVs
or geometry, I was wondering if the only way to achieve this
is to parent the various segment lengths of geometry to their
respective bones, with the hinges lining up with the IKjoints, or
is there a way in Maya to replace the tetrahedron display of
bones with the actual geometry itself, thereby animating the
geometry directly with IK?


Dan
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Old 20-11-2002, 09:53 AM   #2
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Default by the way...

Seems my second little ascii drawing has come out a bit skewed!

Should be a simple triangular peak, like an upside down V.

Dan
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Old 20-11-2002, 09:56 AM   #3
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how about attachin' a pic m8.. would make us understand better.. :p
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Old 20-11-2002, 11:02 AM   #4
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I get the impression that you want to make an arm that flexes without the geometry near the joints moving at all. If this is the case, rigid binding might work. You would probably have to tweak the setting to get exactly what you wanted, though. What will work is this: Each segment of the arm would have to be a seperate object. You make the skeleton.

|------------||-------------|
|+++++++++<>++++++++++|
|------------||-------------|

Consider that as two cubes side by side. The +'s are the skeleton, while the <> is the middle joint. The skeleton was created from LEFT to RIGHT. Click the skeleton portion on the left. It highlites both the portion you clicked on as well as the right skeleton due to the hierarchy (sp) of it all. Anyway, after you select the left skeleton, select the left box. Go to Skin>Bind>Smooth or Rigid Bind. Now select the rightmost skeleton. Select the right box. Choose Skin>Bind>whatever. Now both segments of geometry move independantly with the skeleton part it was attached to. This won't work unless the segments are two different objects, though, unless you can select individual faces to bind to skins.

If it is all one big piece of geometry, look into rigid binding.

Anyone else have a take on this?
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Old 20-11-2002, 11:29 AM   #5
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Post OK, check this (rough) diagram

OK, Roman see on this pic - The top image represents the final effect;

the middle part represents the IK chain with bones, joints in place etc;

And the bottom image I guess illustrates my question - Is the only way
to animate my mechanical arm with IK to parent my various modelled
segments to the bone objects,

OR!!!

Is there a way in Maya to replace the tetrahedral bone "objects" with
modelled polygon/nurbs geometry?

Does this make sense?

: - )
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Old 20-11-2002, 12:20 PM   #6
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Thumbs up

Hey Darkware - thanks a million for the reply - That gives me a place to start!

I'll go and R&D your suggestions now!

Dan
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Old 20-11-2002, 08:40 PM   #7
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One thing I forgot to add - make sure you SHIFT select the boxes after you select the skeletons. It must be selected in that order, too for bind skin to work. Yeah, yeah, you know all that probably...
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Old 20-11-2002, 09:18 PM   #8
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cool.. nice goin' Darkware.. :p
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Old 21-11-2002, 07:08 PM   #9
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I just parent the the geometry to the joints, should work with or with out IK's. Have go try it.
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Old 21-11-2002, 07:58 PM   #10
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Ok think I figured it out!!! I used my comic guy as the example. I also didn't have to bind anything its all parented.


Steps

1) make your skeleton

2) go to the elbow and rotate it 90 degree's than set perfered angle.

3) Add ik from shoulder to wrist (I used ikSCsolver)

4) Parent the Geometery to the joints you want them to stick too

It should work, thats how I did mine.

Post a picture if it dosent work, so I can take a look see.


Hope this helps
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Last edited by Kurt : 21-11-2002 at 08:01 PM.
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Old 21-11-2002, 11:44 PM   #11
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Hey Kurt, thanks a lot for that reply - a BIG help.

And thanks Darkware & Roman too! What a great community
this is.

Dan
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Old 21-11-2002, 11:51 PM   #12
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Glad it helped bud
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