can you get nice arcs with IK

[jadamburke]

If you want arcs in your legs, set more keyframes, use less interpolation. If you want arcs in your arms, don't use IK, just delete it and animate in FK.

IK is only necessary if the limb needs to plant solid somewhere. If it doesn't do that consider not using it.

[Jacob]

Forward and Inverse Kinematics have nothing to do with arcs. They are just heirarchy orders.

Arcs are a principle of animation that needs to be incorporated during your inbetweening stage.

Remember...as 3D animators we have the luxury of seperating our animation into proceedures and steps. (unlike 2D where everything has to be encapsulated in one drawing).

The best way to do arcs is to key them, or adjust the key frames in your Graph Editor to substitute fro them.




"Arcs"- Every organic object moves in a circular motion. From the lightest smile, to the biggest take.

Have fun!:thumbsup:

[jschleifer]

something to be careful of however is using too MUCH of an arc..

you don't need huge arcs.. otherwise things can look swoopy and strange. Remember there are rules, and there are times when you need to break the rules.

-jas

[Ripley]

I generally use FK on the arms and IK on the legs. Unless I need to lock down the arm onto a table or whatever.. but for acting I'm an FK animator. It's a big challenge to give IK arms, follow through and overlapping actions.

What program are you using? I know XSI has parameters on the upper arm bone that let you key/blend between IK and FK. I'm not sure if Maya has a similar tool.

[loked]

I think Maya 5 has a similar option, where you can blend freely between FK and IK. 4.5 has the same option, it just never worked very well. Well, thats not entirely true; If you owned Jason's fast animation rigs DVD, you could get it to work nicely with his handy little scripts:)

I would just go with FK for nice arm movement and if you need the hand to be stuck in one place while the rest of the body moves, then use IK.

Later:wavey:
loked

[Andy741]

I think I would just add a key where I would want the curve to be and then look at the f-curve to see if it's smooth looking. I think "Inspired 3d Character Animation" talks about this if you have a copy laying around.

[Pete2003]

Hi,

Dunno if this is feasible or not, with not having done an awful lot of character animation in the past. I also use Maya so I dont know how this might translate to other packages.

What if you created a curve for each IK, and then constrained the IK Handle to the curve. You could then animate the curve into different positions for the ranges of arcs you need and just animate the IK constraint up and down the curve using a slider or whatever

Again, don't know how feasible this would be and I suppose it would be a different way of thinking for a character animator. But with practice I suppose it could be like using traditional animation techniques (drawing in motion lines etc).

Anyhow, not having tried this personally Im sure someone will shout if this is completely unfeasible :)

Pete

[loked]

Funnily enough, I tried this same technique, but I built an 8 curve and used it for the hand swinging motion while a character was walking. I tried it once and it gave decent results, but I'm sure some animation expert will find something wrong with this.

I basically create a locator that followed the path of the curve and used constraints to get the arm to follow to locator when needed.

later:wavey:
loked

[Pete2003]

Yeah, Im sure with a little scripting knowledge someone could make a pretty useful tool using this technique with maybe a little interface allowing you to create a curve for each of your selected IK handles with a user-input for the number of control points for each one etc. Then the constraint process could be handled by the tool to save time.

Hmm, might try this out some time, could be pretty useful for say animating the swinging motion of arms for a walk cycle without having to use FK. :thumbsup:

Pete.

[safakoner]

Hi everyone

Loked, what is "Jason's fast animation rigs DVD" ? and where can I find that.

I am working on a complex setup for advanced character animation in Maya ( for my flying character like spiderman) . I finished IK/FK blending for leg and "Hand Stoper".

[loked]

Jason basically did 2 masterclasses at Siggraph I think in 2001 and 2002. Alias|Wavefront then made instructional DVD's out of it and you can buy them online. Just go to www.alias.com and look in the store. They are quite expensive, but definitely worth it if you're serious about rigging.

later:wavey:
loked

[adavies]

What I've found:

If I had a choice I would definitely go with FK for the arms. I have found IK REALLY hard to use for anything other than planting the hand. One of the horrible things I have to worry about is the wrist - you can always tell when an arm has been animated IK by the horrible wrist! If you start setting too many keys to get an arc the animation just gets jerky. I've also found it quite hard to get overlapping motion between the different segments of the arms with IK - that's not to say that all this isn't possible, you CAN do it if you spend the time, but why play around when you can do it much quicker with FK.

Of course, you have to way up the pros and the cons - figure out what you want your character to do. If you can't set up an IK/FK rig you are going to have to choose between them.

If we get given a rig with just FK arms and you need to place the hand on the ground, or pick something up you can get round it by quickly adding IK to the rig, animating away with the IK and, when you're done, select all the joints in the FK arm and use 'Bake Simulation' in Maya (have a look in the help - F1 key!!). you can now delete the IK chain and you will have an FK arm doing all the IK stuff

[Ripley]

I think the 'built arc' idea would work on a one jointed arm. But the problem is, on a 2 jointed arm (like a human), both joints don't move at the same time. The upper arm drives the lower arm in a reactionary way. First motivation (thought), then action (move upper arm up), then reaction (lower arm lags behind, then swings up and overlaps when the upper arm changes direction or stops).

In short: drag and overlapping action.

That, and the wrist thing, is why I find it easy to spot an IK animated arm.

[safakoner]

sometimes ik usage very diffucult for arms. I use both IK / FK for arms.

But I created complex setup for IK FK blending for legs. Click here (www.safakoner.com/temporary/ikfkleg.avi) to watch the playblast

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