Inverse or Forward kinematics - Blender animation tutorial

hi everyone this is pierre from p2 design in this sample from the new upcoming chapter of my blender animation course live i will explain you when to use forward or inverse kinematics in your animation and how to seamlessly switch between those mechanisms let's get started [Music] during the blocking stage i've switched between inverse kinematic and forward kinematic quite a few times with experience it's pretty obvious when to switch these rules might not be carved into stone they should help you figuring out when and how to switch let's first compare both mechanism forward kinematics is the most obvious mechanism we can consider the forward kinematic as being a chain with a root and a tip the previous bone in the hierarchy will influence the next bone in the hierarchy till the tip of the chain it's the perfect mechanism to create a great arcs and it generally offers the animator the best control over his character's shape making it the perfect fit whenever you are rigging or animating a tail it's personally my go-to whenever i'm animating character arms the benefit of powered kinematic is also its weakness since the behavior of a controller depends on the behavior of all the previous controllers it can be super tricky to deal with the position of a specific controller in space for example here i have a hard time matching the pose where the character will have his hand on his hips in a relaxed pose basically as soon as you are contacting with the feet or the hands you may want to switch to inverse kinematics here i'm trying to pose my character doing push-ups but the arms are in forward kinematics therefore they are following their hierarchy the dorsal move so the shoulder moves so does the arms so does the forearms and it's almost impossible to keep track of the hands and keep them on the ground while if i now switch to inverse kinematic the hand of my character will stay in position and it really facilitates this kind of animation of this kind of posing the inverse kinematics mechanism is built to calculate the rotation and orientation of each joints in a chain based on the transform of the initial joint but most importantly on the transform of the final joint in this case the hand of the character that's why most of the time legs are using inverse kinematics controllers this way when animating a walk cycle you can do most of the heavy lifting focusing on the foot motion on a landing animation once you figured out the contacting point from the feet you just have to focus on the root of your character and the upper torso this also make inverse kinematic the best choice whenever you are interacting with objects especially if both ends are on the object some rigs have built-in functions that allow you to parent the character inverse kinematic hand controllers to his various pieces of equipment if it's not the case the go to constraint is the child of constraint you first select the object then the hand controller press ctrl shift to c and add a child of constraint i can repeat the process for both hands controllers and they are now both following the spear but i can still fine tweak the hand position without moving the spear this makes both animating and posing double-handed equipment way easier once you're done with your animation and you want to get rid of the constraint you can select both inverse kinematic controllers and simply search for bake bake the action and get rid of the constraint in the baking option blender will write a new key pair frame recording the motion of the previously constrained hands but the constraint will be removed if you haven't polished your animation yet you may want to keep the constraints the cool thing is that you can insert a keyframe on the influence of the constraint and when you want to switch it off just set the influence to zero a very important thing is to switch between the one value and zero value of the influence over one frame this to avoid any interpolation but we'll see that later on you can use exactly the same technique on any kind of props with my hand inverse kinematic control selected i will add a child of constraint and sources sphere i can then repeat the process for the second hand or i can select the second end then select the first constraint end and use the copy to select operation in the constraint panel both and are now following the motion of the sphere another situation where inverse kinematic shines is when you want a straight motion path for your hands or your feet by default blender will interpolate the inverse kinematic controller along this straight path finally when the hands of the feet lead the animation it's way easier to use inverse kinematic than forward kinematic because you are more focused on the position of the hand in space than the arc drawn by the elbows the wrist and the fingers and you can still consider those later on using the pole target controllers and the tweaker of the fingers or the arms in this regard a lot of animators prefer to use inverse kinematic for the hands though inverse kinematic also have downsides inverse kinematics mechanism are not ideal to create good arcs since they are based on the location of the target in this case the foot of the character between two poses blender will interpolate in a straight line and to get nice arcs as you can see in the graph editor i will need to polish each location channel and this will require a lot of keys motion captures animator often combine this kind of inverse kinematic motion with additional constraint to draw better up if i was to animate the second bone on this forward kinematic chain with the root bone performing a swing motion when pausing the bone it will add a new keyframe and the motion path will update most of the time with smooth arcs and it's super easy to get a nice swinging motion only using one rotation curve while if i'm using inverse kinematic i will have a hard time pausing my mechanism and keeping a consistent curvature plus beyond the fact that i will need more data to get a clean arc there are big chances that some of them looks very bad with odd angles and straight lines so don't hesitate to switch back and forth between inverse kinematics and forward kinematics to facilitate your animation process now let's see how to switch between both first of all you may not switch between inverse kinematic and forward kinematic using multiple frame if you do this the interpolation of the ik or the fk will interpolate and you will have to fight with your rig to fix the poses so if i want to switch to inverse kinematics on frame 3 i will go on frame 2 and key my arm in forward kinematics with full influence now we have a proper snap between frame 2 and frame 3. then your job as an animator is to polish the animation from frame 0 to frame 2 so that you get a seamless transition between frame 2 and frame 3. if you don't have any snapping mechanism that allows you to match the fk pose with the ik pose automatically then what you can do is to try to match the current pause whether it's in inverse kinematic or forward kinematics with the other mechanism for example here i'm using inverse kinematic and i'd like to switch when the character will pull off the sword let's say i want to do this on frame 10 for the time being i'm using in their kinematic so i will go on frame 9 and i will key my constraint then i will go on frame 10 and switch to forward kinematics the inverse kinematic controllers does not work anymore now what i want to do is make my forward kinematic pose here to match the inverse kinematic pose so i will go on to frame 9 where i am still in inverse kinematic and holding d in the top view i will draw the silhouette of the arm of my character then switch to front view and do the same from there i will play with my forward kinematic controllers on frame 10 and i will try to match the pose you don't need it to be perfect because later on this is going to be a transition pose where the character starts to move the arm if he's not moving the arm or if you want the hand to stay still keep it in inverse kinematics and as soon as you start moving the arm switch this will also give you better result whenever you are baking your animation or exporting it for your game engine this is all i did it for my character intro animation here i'm in fk and on the next frame i will be in inverse kinematic during the polishing stage i made sure that i had nice arc on the wrist and this way i get a seamless transition from this point i was in inverse kinematic until there where i'm switching to forward kinematic just here again focusing on the spacing of the wrist and i'm transitioning a final time at the very end of the animation and the character is lifting the spear just there and i've used the same method throughout the whole animation [Music] you

Channel: Pierrick Picaut

Views: 2,857

Keywords: blender3D, modeling, shading, rigging, B3D, p2design, sculpting, digital, animation, cartooning, rendering, CYCLES, tutorial, Pierrick, Picaut, Pieriko, 3D, Computer, Graphic, blender, eevee, VIDEO GAME, rig, animate, stylised, best, Blender, art, digital art

Id: 0OFpKXpvdDU

Length: 11min 4sec (664 seconds)

Published: Mon Dec 20 2021