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Nangleator
12-15-2010, 09:57 AM
What's the difference between a goal and a target, when setting up IK?

Why would you use one rather than the other? It seems like you can set up two, for the same object or bone.

I'm confused.

RebelHill
12-15-2010, 10:45 AM
target item is to point the controlled item at another, ala aim constraint, nothing really to do with IK, whereas goal is what the IK chain will reach for.

Unless Im missing what you're getting at.

Nangleator
12-15-2010, 11:16 AM
Just working on a steam locomotive rig. I'm trying to point the items at parented nulls, and I have the choice of using Target and Point at Target, which gives me a 180 pop in another axis, or I can use Goal and Point at Goal, which doesn't fully work. It mostly works, but not quite.

Perhaps I should post one of my 'negative tutorial' videos, wherein I point out something isn't working as it should, and we all get a little stupider watching it.

Otterman
12-15-2010, 12:20 PM
Sounds like Gimbal lock to me. Baine of my life. I'd love to know Rebelhills tips on avoiding/remedying it

Dexter2999
12-15-2010, 12:31 PM
Perhaps I should post one of my 'negative tutorial' videos, wherein I point out something isn't working as it should, and we all get a little stupider watching it.

Great!, it'll be just like us watching DANCING WITH STARS, AMERICAN IDOL, or KEEPING UP WITH THE KARDASHIANS!

I swear I can feel the IQ points draining away when one of those shows is on.

dandeentremont
12-15-2010, 01:47 PM
Just working on a steam locomotive rig. I'm trying to point the items at parented nulls, and I have the choice of using Target and Point at Target, which gives me a 180 pop in another axis, or I can use Goal and Point at Goal, which doesn't fully work. It mostly works, but not quite.

Perhaps I should post one of my 'negative tutorial' videos, wherein I point out something isn't working as it should, and we all get a little stupider watching it.

Hmm, just curious, what goes wrong when you use Point at Goal? Are you making a train coupling rod rig by any chance?

Personally, I use IK's "Point at Goal" when I need something to target, but also blend to FK when I need. Same thing goes for YZ "Plane Through Goal," which is a fancy way of saying Pole Item.

Nangleator
12-15-2010, 01:57 PM
Here's a quick video. (http://www.youtube.com/watch?v=Yfy45sEqhRk)

See that the bar isn't always pointed at its goal? There's some vertical drift. Z+ is to the right, here.

dandeentremont
12-15-2010, 02:26 PM
I made a really quick scene trying to mimic yours. That's really frustrating; I'm not having a problem with the vertical position of the tip, but I am getting an big IK jitter on the rod...

If I use Goal to Goal IK I can get it to work fine, but it sees like it should be unnecessary :[

Nangleator
12-15-2010, 02:35 PM
The bar on the left uses a goal of the null at the end of the piston, and Point at Goal. Heading and Bank are locked off, and Pitch is set to IK.

The piston is set with a goal of the null at the right end of the bar, and Go to Goal. Z position is set to IK.

Hell, I just realized something. The bar is always pointed at the start position of the piston's null! Like, it doesn't see the motion of the right side of this rig. Did I do stuff in the wrong order?

dandeentremont
12-15-2010, 02:37 PM
Ok here's something else that seems to work, though I don't know what the future repercussions will be:

-Make the rod's Pole Item be your target null
-Make ONLY the Pitch controller Align to Pole. Everything else set to keyframe.
-????
-Profit!

Edit: is it possible to provide a scene, cuz I think I'm not getting the whole picture.

Nangleator
12-15-2010, 02:46 PM
Success!

Fiddling around in the Motion Options panel is frustrating. All sorts of things are getting flipped on each time I change something. I got excited when I saw a choice that said, "Base on First Keyframe/Base on Current Time" but that choice... it did nothing.

But this worked. Thank you!

dandeentremont
12-15-2010, 02:50 PM
Good to hear!

By the way, if you haven't seen it already, I've found this GIF extremely useful in the past.
http://i294.photobucket.com/albums/mm109/papalive/Walschaerts_motion.gif

Nangleator
12-15-2010, 02:53 PM
Holy smokes.

I ran a saddlestitch binder for a few years that had impressive wheels and cams and rocker arms like that. Brings me back. Awesome and scary to see such things working faster and faster and faster...