need help in quadruped limb setup


#1

hi guys,

i need help in setting up a rig for a quadruped (sheep to be specific). i have problem especially in the limb setup. I think 6 joints is sufficient to setup a limb. But i’m confused with what Iks should i use, how many and where to put them. i tried different combinations of IKs but i’m not able to get all poses required for animation. :banghead:

can anyone help me solve it??


#2

What software are u using? The back legs are pretty straight forward but the front are more difficult as you have to lock and unlock the lower leg. Also your never gunna get a rig, which will do all the poses.

You may need two rigs, this is what i do which overlap each other via constraint, this means you can use ik when you need it and break into fk when you want.

Tell me what soft your using and post a pic.

eek


#3

thanks for the response eek.

sorry that i forgot to mention the software i’m using. anyways i’m using maya 6.

i worked on it yesterday n found something that’s working almost fine but i was just wondering if i could do a simpler setup. As u can see in the picture, i’ve used 6 bones and 4 ikRPsolvers for each limb. i’ll explain u w.r.t the front limb. i’ve named the joints as follows (from top to bottom) : clavicle, shoulder, elbow, carpal, fetlock and pedal.
one ik from shoulder to carpal, second from elbow to fetlock, third from fetlock to pedal and forthe from pedal to the end joint (hoof). The first two iks r overlapping (is there any problem wid overlapping iks?). For the foot roll, i’ve setup something like a reverse foot. Three joints that run from the hoof to fetlock (rev_hoof,rev_pedal and rev_fetlock) . i’ve parented the ik at the fetlock to the rev_fetlock, ik at pedal to rev_pedal and ik at hoof to rev_hoof.
Finally i’ve aim constrained the shoulder joint to the foot control (the oval shape) so that it automatically follows the control when it is moved.

that’s 'bout the rig … so i would like to know whether my idea is right :slight_smile: or any improvements :hmm: or it’s all crap and i need to start over again :cry:


#4

Ok first of, cant see your pic.

I used to have complex setups but found it way to problematic, slow, and buggy. 4 ik chains wow! Remember though you gunna have to control every swivel angle of each bone. As for the overlap method yep i used it a while back and works quite well, but i found i had to break the rig when i wanted fk as i find that you really need to tweak the shoulder in place.

Genrally i have a simple setup at the back, for the front its much more complex and i have a floating rig, which allows the locking and unlock of the lower leg in motion - this is key! The shoulders are fk to.

Heres a pic:

And a movie in action: >>play<<

The crucial thing to say to yourself is " is this exactly what i want the character to do?" only put in what you you need. Be very optimized, as yourll find out yourll need more constraints, expression and ik chains. Remember if 1 ik chain can do the work of 4, use that!

eek


#5

thanx again … that was a good ref video and a simple rig too.

i have a few clarifications on ur rig.

  1. as per the anatomy of sheep or most quadrupeds, in the front limb, the joint just below the shoulder joint (in ur case, the joint from which the ik starts) is not a rotational joint and it’s just there to hold some muscles. all other joints rotate. So in ur setup, that joint is rotating too much causing odd deformation in that part of the limb.

  2. if i leave the toe joints without putting iks (in maya), they don’t stay anchored to ground. so the joint on which the end affector stays is anchored. This makes it bad for animation. but how r the toe joints in ur animation anchored even though there r no iks on them?

  3. In one of the scene, the sheep walks for a distance n sits down. i think is not possible to achieve this shift from walking to sitting pose using iks alone. For this shot i think there should be a very good system for ik-fk switch. any ideas regarding this?

cheers


#6

first, the image you posted is blablabla.JPG, and not blablabla.jpg, that’s why it’s not showing. It’s case sensitive.

I’m animating a sheep character at the moment, it’s much more cartoonish than yours and much more simple, but I’ll post you an image of my rig, at least it wont do any bad.
it’s made in max and not in maya, and it will have lots of mistakes, because I just self-teached myself on how to do it, reading some tutorials… but, for the moment, it works.

  1. as per the anatomy of sheep or most quadrupeds, in the front limb, the joint just below the shoulder joint (in ur case, the joint from which the ik starts) is not a rotational joint and it’s just there to hold some muscles. all other joints rotate. So in ur setup, that joint is rotating too much causing odd deformation in that part of the limb.
    …maybe I’m wrong, but it seems to me that you have a lot of bones, if for example you are not going to move the shoulder, remove the bone, or just fix its position so it never moves

I agree that you will need iks in the toes
I hope it helped…that were my two cents…I’m one of those who believe that the simpler way is usually the better way


#7

ok,

  1. as per the anatomy of sheep or most quadrupeds, in the front limb, the joint just below the shoulder joint (in ur case, the joint from which the ik starts) is not a rotational joint and it’s just there to hold some muscles. all other joints rotate. So in ur setup, that joint is rotating too much causing odd deformation in that part of the limb.
    This setup is not for a sheep, but i am not allowed to disclose the creature due to NDA. Its based on anatomical research, reference material and muscle study.
  1. if i leave the toe joints without putting iks (in maya), they don’t stay anchored to ground. so the joint on which the end affector stays is anchored. This makes it bad for animation. but how r the toe joints in ur animation anchored even though there r no iks on them?
    You dont need to always rely on reverse foot for rig. This is just your basic setup. An ik control and fk toes.

if i leave the toe joints without putting iks (in maya), they don’t stay anchored to ground.
Umm ok?, this is wierd, where are you deriving your ikhandle, i have an ik handle at the ankle then i just positionally constrain it to a locator/point. And constrain the orientation of the foot to this locator - its very very basic stuff. You dont need ik to lock a bone, many of the best setup rely on expressions and constraints. Remember to every ik chain you need a pole vector or your likely to get flipping at some stage.

  1. In one of the scene, the sheep walks for a distance n sits down. i think is not possible to achieve this shift from walking to sitting pose using iks alone. For this shot i think there should be a very good system for ik-fk switch. any ideas regarding this?
    Hehe a lot of people have asked me this question, And yes it can be done, i have a rig just for this purpose, which allows the knees to be manually tweaked for when sitting. I also have and fk-ik system.These currently not for release.

elmasfeo,

…maybe I’m wrong, but it seems to me that you have a lot of bones, if for example you are not going to move the shoulder, remove the bone, or just fix its position so it never moves
That rig is based on anatomical sketches, as before i cant disclose the mesh due to NDA, the animation for it is pretty complex and has to be able to do real world movements. Its based on sketches, muscles research, reference video etc etc.

I agree that you will need iks in the toes
You dont, you can if you want. Ive done about 30 or so quad rigs and in everyone one none of them used reverse feet, or ik.


Ok elmasfeo,

Ok a little about me, ive used max for 7 years, maya 2, soft 7.9 7 months and a little xsi.

your rig looks fine, what looks slightly odd is the front legs, how will you lock them straight when the foot meets the ground? They only bend like that through the passing postion, then lock.

Personally i would make the neck fk, currently you can only hinge it upwards, what if it needs to look between its feet say?

Btw,

Ive posted a quadraped rig on this forum,

http://www.cgtalk.com/showthread.php?t=49073&page=4&pp=15

It uses all the same techniques described here, and by is no means the definative rig but might give you some ideas.

eek


#8

yeah … think i’m getting close to the solution

i tried this and it indeed works well… but with one drawback! the pivot for the limb is at the ankle. so when animating “kickback” part of the walk (just before any limb takes off from ground), the animator has to play around with the rotation of the toe and the position of the pivot so that the front tip of the toe stays on ground till the last moment. So its something that the animator won’t find so friendly.

so when is the deadline for the current project??? :twisted:

i checked out your quadruped rig and its very cool and informative. think u r more of a max freak than of maya. well i too agree on the fact that there r many good features in max that that need to be dug out and exploited to create unbelievable things. but sad thing is only a few people r patient diggers!!!

Thanks elmasfeo for ur reply and info.

i still think there is a need for a shoulder bone since the deformation of the leg starts way up from the upper part of the body. the shoulder blade’s effect won’t be visible if u put the first bone at the base of the body. And what eek told 'bout the neck part is also what u’ve to work on.

thanks again guys. i’ll get back to u soon. :cool:


#9

Hi Guys!!

I’m back! just to thank u for ur help in setting up the rig for my quadruped. Its finally done and approved by my supervisor. so i’m currently skinnin it and will be doing test animations to check the rig. So hope the current setup gives no problem during animation. If it does, i always know where to learn something i dont know.

thanks again
cheers
Venu


#10

Hi,
I’m about to build a dog-leg rig, and I’m curious about your foot setup, eek. I always saw other riggers using a reverse foot IK setup on humans to lock the toe contact point, and thought that was the way to go. However, I recently saw a human rig that simply uses a single IK goal at the ankle, and keyframed FK for the rotations of the ball of the foot and the toe when they touch the ground. The sample animation that came with it looked good and played blazingly fast on my old machine. (Multiple IK chains slow it down to a crawl.) I think the example movie of your quad limb rig showed good toe contact and foot motion. I was wondering if you felt FK animation was enough to keep the toes from looking like they were “slipping” at the moment of contact (on humans as well as animals), or if this was a special case and a reverse foot IK would be in more common use. If FK is enough, I’m getting the idea that simpler is better. :slight_smile:


#11

michaelb: Many times simpler is better…and this case is no different. If the FK system works for you and you are comfortable animating with it then I would say go for it. Often times animators want the extra control on the toe anyway, and would prefer to animate it manually. The bottom line is one set-up really isn’t any better than the other in the grand scheme of things…at least in my opinion…it has more to do with the animators preference and the animtion requirements.


#12

I was wondering if you felt FK animation was enough to keep the toes from looking like they were “slipping” at the moment of contact (on humans as well as animals), or if this was a special case and a reverse foot IK would be in more common use. If FK is enough, I’m getting the idea that simpler is better. :slight_smile:

Simply yes, Michaelb, Harvey,

Simple i find is always best. Every quad rig ive done has fk for the feet, no reverse foot or ik. And ive done really complex animations: rearing, falling over, getting up, turning. And they all hold up well. Ive even dont sitting down stuff etc, etc.

This doesnt mean its hard to do, as you wont it to work simply for the animators and simply for the rig. Remember animators also like to change the rig add there own touches etc etc.

We have 2 setups at work for bipeds feet, fk and reverse foot. Most of the time i.e 90% we use the fk setup- rotate foot-rotate toe. We occasionally add a bit of finesse with the reverse foot i.e jumping up, waving etc. Really for a time issue as animations have to be done fairly quick.

Remember ik chains are like expressions,constraints - the more you have the more data it has to chomp through. Even if there history independant it doesnt matter.

I always go back to the analogy of Geppetto. His puppets are just the right amount of sting, joints, screw etc. If he used 3 times the amount of strings for every part of the puppet theyd all get in the way, tangle up and probably break.

He only adds what he needs. If it can be done with fk then use fk. Because your bound to need more stuff, more iterations. You have to be effeciant.

eek


#13

Thanks for your input; I appreciate all I can get. It helps me to get the perspective of people with more experience… saves me work and headaches too. :slight_smile:
I was also a bit curious what you would think about a rig that features what I describe as “multi-chain” IK. Anything and everything would be connected by IK; for example, pulling on the wrist goal pulls the elbow, which pulls the shoulder, which pulls the collarbone, which pulls the chest, which pulls the neck, etc. Theoretically it would seem good for producing some more subtle secondary motions, like weight shifts. I wasn’t sure about how well that type of setup would work in a production environment, though. Multi-goal IK chains seem a bit touchy to work with. If a simpler rig with FK and limited IK chains gives faster feedback and is more system responsive, wouldn’t that almost be easier to work with than one with full-on IK?
And since I’m really curious now, are you partial to an IK spine setup for animals? Or perhaps an IK spine with the controls under FK? Or maybe… a straight FK spine, since “simpler is better?” :slight_smile:


#14

Hi Michaelb,

Ive tried a few approaches to the mulitchain/overlap rig i.e you pull an arm and it pull everything subtly in that area. Funnily enough most of my rigs do thatto a degree just by pulling the controls further than the reach.

Ive looked it doing a full setup like that, it can be done but its pretty complex as you have to start using expression, which tell distance between extents of ik chains and there handles. I got into problems as to where do you give the control, do you want full control or kinda procedural control?- it becomes a headache to the animator as there always counter animating.

As for spine setups, we have two techniques. 3 bone setup and 6/8bone setup. They dont use IkSpline, there a hybrid custom setup combining ik and fk in one. Not like a ik/fk arm but more like a medium between the two. Very simple to setup but pretty powerful.

Our 6/8 bone setup is pretty much the same, slightly more complex, but also has the added affect of stretch and compression.

eek


#15

Have a look on my site and you can see a movie of a quad rig in action. I have used two, two bone IK solvers not over laping and I control the top one in the leg by having it stay about half way between the shoulder and the foot. I then also have an over ride for it. This allows for always having a bit of action in the upper leg when positioning the body.

http://paulneale.com and go to the technical section of the site.


#16

Howdy,

Would it be possible for you to give a more detailed explanation of this type of spine rig? I’ve used either Spline IK setups or hierarchal rotation (FK) set ups for a spine rig, but I’ve always wondered how to combine both IK and FK in one set up.

I saw the image of your dog rig (nice), but I’m on a Mac so I couldn’t check out your 3DS Max file. Did you use that kind of spine setup for the dog rig?

Adios,
Cactus Dan


#17

Yes i did Cactus,

All our rigs at work use that setup for both biped and quadraped. Its based on a spine called the Isner spine with a few modifactions. We have two main controls torso and upper torso, then a three finite controls: Hips and chest and head.

Torso controls:
hips
upper torso

Upper torso controls:
chest
head

Rotations drive fk, where as tranlations drive ik.

There where many Isner spine variations, it was first developed under softimage then SpineIK replaced it in a way on Maya and Max. But my setup goes back to the true isner setup which wasnt reliant on a curve but used expressions. Its a hybrid setup combining the feel of both ik and fk in one. My setup does exactly the same thing but uses constraints and ik handles.

http://www.isner.com/isnerspine/spine_introduction.htm

eek

eek


#18

Howdy,

eek:
Thanks for the info and the link. Now let’s see if this old dog can learn a new trick. :smiley:

Adios,
Cactus Dan


#19

Eek, that is one that I have looked at but not tried myself as I have had a working system using a spline since before spline IK. I don’t know my way around XSI very well at all so it would be hard for me to pull that apart. Can you discribe it a bit more in Max or Maya terms, or just general math terms?


#20

I forgot to mention that I added another movie to my site showing the IK solvers working in quadrapeds leg. You can see it on my site in the tech section or here…

http://paulneale.com/technical/quadrapedOutline/[u]QuadLeg.wmv[/u]