View Full Version : Run/Walk Cycles in C4D: Do you prefer IK or FK? Mind if I ask why? :)


That Adrian Guy
08 August 2015, 02:58 PM
Hello everyone! I think I'm posting this in the right section, since it relates as much to the software as it does to general animation.

I think IK is a glorious thing, but I always end up using FK because it seems easier to get natural and fluid motions by rotating joints -rather than trying to get an IK goal to rotate and move appropriately. But I think the problem has more to do with my stupidity than anything.

So I just thought I'd ask you guys, just to get a feel for what the best practices are. What does it depend on? Do you prefer one for legs and the other for arms? I'm just trying emulate those who know better than I do. :)

My gut also says I should be nesting my IK goals inside of nulls more often, and using the nulls for most of the movement -instead of trying to do everything directly through the goal...

Anyway, I tried to do a search before asking this, but it didn't find anything, which surprised me, maybe the search engine acts up sometimes? Or I really am asking in the wrong forum. :)

Thanks!

ecore
08 August 2015, 03:50 PM
For the foot and leg: IK - foot needs to contact the ground without sliding
For the arm: FK or IK - depends on which kind of movements you need

I'm not a professional character animator, just out of curiosity how to use FK to make a walk cycle without sliding?

That Adrian Guy
08 August 2015, 03:58 PM
LoL, I generally use a whole bunch of keyframe tweaking and praying. :) I gotta get back to basics and learn walk cycles from scratch... I just found Brian's walk cycle tutorial, so that is a gift from heaven lol... https://www.youtube.com/watch?v=J8lkNz_gBJk

I'm starting to think that my question was dumb and using FK for legs is just bad practice. :)

51M0N
08 August 2015, 04:46 PM
When you want to lock something in place, usually you use IK. For arms swinging in space, FK is probably easier to achieve fluid animation, but it also comes down to personal preference. Some people just like to use IK for the most part.

Horganovski
08 August 2015, 04:48 PM
In part 2 of that video I discuss using IK vs FK for the arms. The first few minutes of this should help clarify the difference.

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For the legs I would always use IK as it's a much easier way to make ground contact look convincing. I have seen people doing a switch to FK while the legs are in the air but for me switching back and forth like that in the middle of an action is usually more trouble than it's worth. I'd just add more keys to the IK controller to get the same arcs/spacing.

So your poll here needs to clarify what body parts you mean!


Cheers,
Brian

That Adrian Guy
08 August 2015, 05:09 PM
Thanks Simon! That reinforces my hunch. :)

Well Brian, once again I'm smarter and more empowered because of you! Perhaps if my current project is powerful enough, I might convince you to team up with me sometime. LoL :)

Right now I'm doing a 60 second project of Yoda defending himself from an Imperial Star Destroyer, and then taking it down. The first 15 seconds are mostly keyed already, I just need to add in an elderly walk cycle to the legs to make Yoda look all the more vulnerable :)

Horganovski
08 August 2015, 05:15 PM
Cool, glad the videos help. I see a lot of people defaulting to using IK for arms and the results can be pretty weightless if you're not very judicious. FK is more mechanically correct really as it better relates to how our bodies work so it tends to give more natural results for arms.
For legs IK is a necessary evil I think because trying to make something look planted in FK is really tough, you'd end up having to counter animate all the time and it would probably still look jittery.

Wow 60 seconds, that's ambitious! I find the longer I'm animating the shorter the shots get and the longer they take to get done :) I'm working on a couple of assignments for iAnimate feature workshop 7 and both are around 150 frames each, been working on them for a month now (alongside my day job animating on a commercial) and they are still very much works-in-progress.

That's the tough thing about animation, the more you do it the better your eye gets and the more you realize what you once thought was acceptable now looks like crap to you, LOL.

It's a fun challenge though.. keep it at it!

Cheers,
Brian

That Adrian Guy
08 August 2015, 07:16 PM
You said it perfectly! My favorite part about 3D projects is that you start with a rough draft, and through a process of a million tweaks, you start having a project that looks way cooler and more professional than you thought you were capable of pulling off!

The downside is the ridiculously long time it takes to make a million tweaks.

Lately, every time I had the impulse to play video games (which is all the time!) I tell myself that I played video games last night, so play Cinema 4D instead. And then it's like minecraft, building your own world. I love it!

Ryonosuke11
08 August 2015, 05:17 PM
I use ik whenever possible for characters- I only switch to fk if I'm using a special rig I can't get to work correctly with ik or for arm animation where I need clean arcs like swordplay- then I use fk for that every time-

fluffouille
08 August 2015, 05:44 PM
Same here, IK for feet or hands that need to stick somewhere (to avoid slippage), and the rest with FK to get nice rotation arcs.
The only thing to watch out for with FK is Gimbal lock, but with R17 it is now easier to keep that under control!

mp-grafix
08 August 2015, 05:54 PM
IK for the feet, FK for everything up the pelvis ;)

http://www.augusta.de/~skynet/up/cheetah.gif

Venkman
08 August 2015, 07:07 PM
Solid work, Marius!

Horganovski
08 August 2015, 07:07 PM
A great thing with FK too is that you can 'break' the arm joints, ie have them bend backwards for a frame or two to show extra flex, it's not realistic at all but you see it a lot in classic cartoony walks. You can kind of approximate it with IK arms if you key the pole vectors just right but it can cause some weird looking deformations with the wrists depending on how the rig is set up.

IK legs come with their own challenges too - with a walk the poses that give you trouble are the contact (front leg) and push-off (rear leg). To get a good sense of weight the legs should be as straight as possible on those poses but with IK when you transition from a bent leg to a straight leg you often get a knee pop. Some people have come up with systems (often called 'soft IK' or 'snap damping' (not to be confused with soft IK in C4D which is something different!)) that try to lessen that pop but personally I find those just as bad as they take control and often prevent you from getting exactly the pose you want on the frame you want.
So what I do is use my ghosting tool or a screen marker (current favorite is Epic Pen, free for windows) to mark the position of the knee on the straight pose and then use scaling on the leg to fix the spacing. Fix the spacing and you fix the pop :) ~I think I cover that in my walkcycle tute video.

Hope that makes sense and is some use!
One other thing to keep in mind - many people think a run/walk is a good 'beginner' exercise for an animator, but it's really not! It's actually really hard to pull off a convincing one. Bouncing balls are the place to start really if you want to build solid foundations, everything you learn doing those will apply to a walk and all kinds of other actions.

I do walks and runs all the time and have never created one I'm 100% happy with.. I keep trying though, here are a couple I did a while back.

Generic run. FK arms.
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'Attitude' walk, based on the example in the Eric Goldberg book. I used IK for the arms in this as I was more concerned with the poses than convincing weight, you can see there are a couple of frames where the elbows lead the wrists though to try to get that sense of 'breaking' the joints in there.
With this walk there's no attempt to make it reaslistic, it's more about trying to show strong poses as long as possible and whipping through the breakdowns as fast as possible. Each key pose is 'favored' very heavily.

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Oh and one more I guess :)
I got a note to let his arms swing forward more which I didn't address yet, but other than that I'm about 50% happy with this one (which is good for me!). I'm using FK arms in this one and I'm breaking the elbows too for a frame as they swing forward.
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Cheers,
Brian

mp-grafix
08 August 2015, 12:56 PM
Solid work, Marius!
Thanks! :D


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