Maya Tips 03-FK or IK, What's the difference

Still reeling in from the death of my MSI monitor but fortunately with the prevalence of the internet and Online Shopping, I can get a replacement 27" 165hz Monitor sometime in February since I don't want to pay those high prices at places like Best Buy, Walmart, or London Drugs.

As of now, I've bought an ASUS TUF GAMING VG27AQ monitor....

but that's not important.

Let's get back into topic: FK AND IK.

As you haven't known about me, When I started experimenting with CG Animation, my knowledge was limited due to cheap hardware and a cheap open-source software.

But once I got my nearly $50,000 art school education, I broadened my mind to how it's really done in the industry using powerful software tailored to studio quality 3D Stuff.

During my Second year, I was introduced to a term I never heard in my life but is rather important in the realm of 3D Animation.

Those were FK and IK.

But what the hell are they?

Well let's truncate them into an individual description for each tool

First is FK which is short for FORWARD KINEMATICS.

This is the term to describe joints having an individual control for each limb. The furthest the control is to the torso or abdomen, the more dominant the limb control is since the dominant bones in a 3D Rig is always closest to the COG(Center of Gravity) control.

It may seem robotic to newcomers but once you get the hand of acting with FK, then it's a cinch. 

So what is FK primarily used for?

Mostly for Hand and arm gestures. Kind of like the hand gestures you see on a lot of Disney Films from old.

Brer Rabbit here will demonstrate Forward Kinematic hand gestures:

"Stop hypnotizing me with those FK Arms you stupid rabbit!"

"It ain't my fault! The guy with the Razer Mechanical Keyboard wants me to demonstrate acting in 3D Animation tools."

It's also the same gesture system used by David Murray from THE 8-BIT GUY on YouTube.

So in a sense, It's sort of overlapping action when you look at it.

Another great example of FK being used is for when you need to animate a hand action like Ren slapping Stimpy silly as shown below.

Or for when you need to animate a character kicking a Football or Soccer Ball.

IK just won't work your rounds that way so FK is good for animating an overlapping action of a kick.

Speaking of feet, FK is seldom used for the feet since like in real life, they need to stay on the ground or make things easier for the animator to animate a walk cycle or even in this case, place the foot on stationary objects like a box.

So IK is used for the feet but IK is not limited only to the feet.

What is IK?

Well that's INVERSE KINEMATICS.

This is a term to describe a dominant action that's dictated by hand, foot, or limb the follows the control of that rig.

It’s also used to hold a hand placement on something like a desk.

Just ask this pissed off Lion below.

Had the Lion's hand been animated on FK, his fist would clip through the Table but IK keeps his fist steady with barely any movement.

Of course, you still might need to animate slight rotations on the wrist or finger animations since the fist or a palm on the table is not always still, even when on IK.

But how does the elbow react? 

Well if you see your rig with IK arms or legs with IK set, you’ll see these controls called pole vectors. These determine the direction of the elbows. Sometimes they need to be manually animated or they are automatically animated via being set to follow the hand but even then, it still might need to be animated due to issues with movements and sticking to realistic acting. 

Alternatively IK can be used allow the hand to remain at a certain angle or pose that can't be done with FK alone such as this gesture of THE IRON GIANT holding Hogarth or any scene of the giant picking up or putting down Hogarth.

IK is somewhat popular with studios like Sony Pictures or Illumination since it allows the animator to have a character hold a sullen pose with their hands below the character's head but I don't have a screenshot from Hotel Transylvania or Despicable Me so I'm going to be cryptic about this.

IK is also used for animating a character lifting a very heavy weight such as this poor shmuck shown below struggling to lift a heavy iron ball.

Or when you animate someone eavesdropping:

Or when you need to hang on to something:

And yes, this includes holding things with bottom weight.....

or as in the case with Brer Fox, holding a rabbit by the ears:

"I told you to stop cahooting with the Razer Guy!!! I'm feeding you to the wolves!!!"

Which is better for you? FK or IK?

There's no definitive answer. Both FK and IK are used together to create your animations.

What really matters is having to take advantage of how to switch from FK to IK and vice versa.

Sometimes you can just alternate and spline the switch tangents on your Graph Editor when switching FK/IK controls but other times, you can't rely on splined tangents alone so you have to rely on locators to help pinpoint where you hand and elbow gestures connect to make a seamless change.

Believe it or not, The Locator Method is my least favorite but I have no choice since there are rigs like Jasper that don't follow the splined tangent rule for FK/IK switches.

This method involves creating several locators and then matching the translate and rotation values to these locators. It's tedious but it's surprisingly helpful.

My most preferred method is to go to my GRAPH EDITOR on MAYA, find the FK/IK keyframe if I Keyed it, set the switched key tangents to splined, set the keyframes further apart to let the switch feel seamless, and there you go.

Below is a piece of animation I did back in college that dives into the FK/IK switch realm in pantomime animation.

Pay attention to Malcom's hand. Tell me what is his FK hand or IK hand.

Maya Tips is far from over. I have more tidbits that warrant the title of MAYA TIPS but until I get my bearings and knowledge from my College years, consider this post closed.

But yeah, FK and IK switches is a must for 3D Animation.