Can this be done?

[michaeljortiz]

hey everyone im new here, hope to hear from all of you =)

my question is can i use fk for one half of my animation and have ik for the later half?? is there a way to key a constraint so i can have ik when i need it?? i know this might sound confusing so leave me a msg if you want me to elaborate..thanks everyone

[mtmorrione]

Yes. Please elaborate.

I'm a character setup TD. I'm pretty sure I can help you.

Are you working with a particular body part?

-Rafe

[michaeljortiz]

ok what I'm trying to do is animate my arms, I've done some animation using fk but then realized i need to constraint my character's hands to a object that is weighted to his own body (the object is stuck onto his body and he is going to try and pull it off). Is there a way i can key a constraint so ik will kick in on a certain frame? I need that hands to stay with the object that is stuck on his body as he is moving around trying to pull it off. It wouldn't be so hard if i animated from the start using ik, but I have already animated using fk, now in the middle of the shot i need to convert to ik for his hands to stick to that object. This might still sound confusing so please bare with me =) thanks

[mtmorrione]

It is probably my fault I don't fully understand. The elbows and the knees are pretty much the only joints on your character that should be IK. Do you have a two bone chain for your arm, with the effector positionally constrained to a controller of some type, and an upvector? If so you should have your animation on the controller. Then it is farly simple to constrain the controller to an object for a part of your animation. If you aren't set up this way, I can help you set it up without loosing you animation (Hopefully). I have a trick to do this.

-Rafe

Edited by RafeSacks on 02/24/01 08:03:06 PM.

[michaeljortiz]

Right now i dont have a controller for the effector, as well as a up vector because I lose my aniamtion when i put one in, but if you have a trick so i dont lose my animation and still have the same affect as I had before I'm all ears!!
What Im really looking for is a way to keep the fk i have already and have ik come in when neccessary, but that might not be possible, anyways your help is truly appreciated =)

[mtmorrione]

This has to be done on a new null, because you need the outcome to be in global space. So get a new null, and position constrain it to the effector in the chain. Leave the new null without a parent (global and local are the same). Then plot the animation of the new null. Now set up the rig the way you want it and transfer the new null's animation to the controller.

You may have a problem with the placement of the elbow. Unfortunately this is little more manual, but, I think, still worth it. Before doing anything with the plotted null, repeat the same procedure with another null at the elbow. There a several ways to use this new null at the elbow:

1) As a reference. When you get your setup to be the proper way(with an upvector), animate the upvector control to put the elbow in the right place and create keys at desired frames, until the elbow closely matches the plotted null. Of course you would do this after you had the controller for the arm moving.

2) A little messy, but quicker...Just this time to save your work. Put a controller at the elbow used only to save your old animation. Position constrain the controller to the plotted null for the duration of the animation. Plot keys for the controller at desired frames and then delete the plotted null. this leaves you with an animated controller at the elbow. Now you can toggle the constraint off at the right time for the IK to take over, and just never use that controller again.

This sounds like a lot of work, but it isn't. And it's good practice.

Hope this helps,
-Rafe

[michaeljortiz]

ok since im just a student, I dont fully understand the proceedure. Are you saying I shoud get a null and have it copy the position of the effector from the animation i had. Then constraint the effector to the null. After that I should get a up vector and key it so the position of the elbow is also the same as the animation i had before? Therefore i will have roughly the same animation but with ik. Is this what you are saying??

[fredc]

I highly recommend you complete your skeleton entirely before you attach envelopes and animate. Test it to be sure it gives you all the control you need.

Trying to get it fixed after you start animating, usually plagues your work forever. Softimage is a very forgiving product and XSI even more so, however I would reserve these abilities to save your butt, don't assume there is always going to be an easy solution when changing your mind on setup.

Hope this helps,
Urp

[fredc]

The animation document gives details on combining FK and IK. However, to answer you question:

1. Determine the frames where you want the FK to take over.
2. Then open a DopeSheet (same place as you select Schematic).
3. Select the Effector that is controlling the IK you want to stop.
4. In the dope sheet, select the frames you need for FK to take over.
5. At the top of the dope sheet select deactivate.

Now your FK should be functional during the frames you deactivate the effector.

Although, this might solve your immediate problem, what I think you are intending to do is use Local Effectors versus Global. I think this what the others are trying to describe to you. This method is much more beneficial. Although FK has it

[mtmorrione]

I aggree. Start over. you can use you old anim as reference (like rotoscoped animation). This is a highly technical area of character animation. Hence the title Character Setup Technical Director. It requires knowledge of animation, movement, math, scripting(in some cases), and planning. The Idea is to do all your animation on just a few "controllers". I use cubes and spheres that are non-renderable. In XSI these are call implicit objects.

A simple example:
1) create a two bone chain.
2) Get 2 cubes.
3) positional constrain one cube to the effector and one to the chain root.
4) relax both constraints (killing both constraints leaves you with the cubes in the right place so you can do the next step without destroying the current position of the skeleton.)
5) now constrain the effector to the cube that now lies on the effector, and do the same for the chain root (to the cube near the chain root.)

now you have a simple controll rig. There is so much more, but it would take a week to explain it in this way.

(TIP: you can make an implicit cube by getting a regular cube, turning on snap to points, and drawing a linear curve to all points on the cube. The final look is a wireframe cube created by a spline, which won't render.)

Good Luck
-Rafe

[michaeljortiz]

Thanks for the help! Just one more question, I swiched from fk to ik by having the effector activate on a certain frame and that works just fine, but how do I get the up vector to deactivate too. The up vector is still controlling my arm when I'm using fk. I cant deactivate the arm because then I will lose the rotation animation I already had. Thanks
Edited by SiR6 on 02/26/01 08:50:23 PM.

[fredc]

Did you try to deactivate the Null for the up vector too? I'm not at a workstation with Soft right now, but it should work.
Urp

[michaeljortiz]

Oops I wasn't looking in the right place =) thanks Rafesacks and Urp for all your help. Now I can finally do some work!!
Edited by SiR6 on 02/27/01 09:07:20 PM.