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Old 06-05-2008, 01:18 PM   #1
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Question Four legged walk cycle

I im trying to make a four legged spider like robot walk using IK. I am having troubles with figuring out exactly how the walk cycle should be, and have trouble getting the legs to bend how I want them, they want to twist not quite right. I have set up limits for each piece. The legs are to be snake like and are made up of about 30 seperate pieces. I have attached the scene file and object to look at and tell me what I am doing wrong. using LW9.3

Please help!
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File Type: zip spider.zip (102.7 KB, 3 views)
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Old 07-05-2008, 02:55 AM   #2
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Do NOT parent the Goals to the IK chain.

Ok, that took me the most to figure out. Cause the goals simply wouldn't move.
Anyway, set the Heading, Pitch and Bank Controlers (under the Motion tab, shortcut M) to Inverse Kinematics, and set a corresponding stiffness so the motion has some resistance.
Ok, now, for the last bone/piece of the chain, the one closest to the goal object. Hit M, chose Goal object( in your case Null (1-4)) and mark the Full-time IK and Keep Goal in reach, set a goal strength of 100 to 10000000000, depending on what you'd like.

Now, a few notes on IK. It's not always easy to control, when you cross over the original position it tends to jump. You'll see what I mean. Also, I would recommend first posing your robot, then set the IK, cause it's a lot easier for the computer to calculate the IK based on preexisting bends, it also gives fewer errors. So bend the legs into position before you set the IK up.

Watch some IK tutorials. The Zombie one is really good, down at KurvStudios I think.
You'll learn how to better create and control your IK chains, add secondary goals and a lot more.

Here's your scene with an IK leg to show you how to do it.

Others could have more valuable advice, or you could find out stuff for yourself. Just keep playing.

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File Type: zip ik_leg.zip (113.7 KB, 8 views)
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Old 08-05-2008, 11:18 AM   #3
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Thanks for the help, and the work on the file. Yes, I defiantly need to earn more about IK. And I also appreciate web sites like this for being there to find help.
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Old 12-05-2008, 11:48 PM   #4
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When it comes to animation, you need to remember to first brebend your character and get the bones bent to match, LW needs to find out which way the joint is supposed to bend.

set up a rest pose, by first selecting all (bones) (select one bone, then click the middle mouse button and drag over the skeleton then hit the r key. Hit enter and set your key frame to >for all items. Set the frame for something like frame negative 10, then hit enter again and reset the keyframe to only selected, and also back to frame 0, to reset everything and prevent needless keyframes.

When posing, if you notice LW has the rotational translation set as Heading, Pitch, Bank. It's done that way for a reason - the rotations are Hierarchical, always set your heading first, then the pitch, then the bank. You will get good movement that way without the "IK pop" that is a common problem.

There are many good tutes out there that explain the process in much greater detail > Jonny Gorden's book "Cartoon Charcter animation Volume two" is a great book, Timothy albee has another video that's great, Larry Schultz has a great set of tutes also
Good Luck :beer:
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