Inverse Kinematics Rigging
Inverse Kinematics vs Forwards Kinematics
What Is Inverse Kinematics?
There are two types of rigging that you can use to animate your 3D models in Maxon Cinema 4D. Those two types are Inverse Kinematics and Forward Kinematics. Both of them are relatively simple tools that can be used to great effect in different ways. What's the difference between Forward Kinematics and Inverse Kinematics? Great question. The differences are important to understand so here's an explanation.
Let us say that you have a model with an arm that you would like to animate in a waving hello fashion. That means that you will need to move the shoulder, the elbow and the wrist to create that motion. Here is how you can create that movement with kinematics.
Forward Kinematics. With Forward Kinematics you need to animate and key frame every joint individually. That means that you need to adjust the position of the shoulder, then the elbow and then the wrist of your model's arm to simulate the waving activity. Forward Kinematics can be a lot of work but it also gives you a great deal of control and that produces very fine results.
Inverse Kinematics. Inverse Kinematics is a simpler way to rig and animate your models in some ways because, unlike Forward Kinematics, you don't need to adjust each joint individually. Using the same waving example that we used above is a very clear way to show an example of the difference between these two types of rigging. To create the same waving action with Inverse Kinematics, you would just need to animate the wrist joint. That is because the elbow and the shoulder will follow the motion of the wrist. So in that way, it does most of the animation work for you.
Things To Remember When Animating With Inverse Kinematics
Inverse Kinematics is a wonderful time saving tool because it does a lot of the thinking for you. When you move the control joint, the wrist for example, it thinks about how to move the rest of the Children joints in that arm chain. So it is fantastic that it does all of that thinking for you, it is just that the downside of it is that it does not always think right. It is smart but it still needs a little bit of help from you.
Elbows and knees are perfect examples. I have lost count of the amount of times that I have rigged a model, only to find that the joints bend the wrong way when I try to animate it. Now I can sit there, frustrated and blame the technology behind Inverse Kinematics all day long but the truth is that it is human error. My error. And it will happen to you too. The only way to avoid it is to be a little more careful and attentive to detail before you actually Bind the mesh to the Rig.
Do you want to know why it happens? Of course you do, so I will tell you. Whether you realize it or not, you are actually telling the IK rig which way to bend the joints. You might not be doing it deliberately but you are still doing it. It happens because rigging a model can be very tricky. It is not always very easy to position the joints exactly in the right place where they need to be inside the structure of your 3D mesh. So what ends up happening is that your Rig, or skeleton, might be subtly bent in one direction. For example, your model's are might be bent slightly back at the elbow when, obviously, you probably want that joint to bend forward like a normal person's arm.
The good news is that this is a very easy problem to avoid. All you need to do is to make sure that the joints in your Inverse Kinematic rig are slightly bent in the direction that you want them to bend. If you take a few moments to take this simple step then your models will bend in all the right ways that you want.
Examples of Inverse Kinematics
The Cinema 4D video tutorial below gives a simple explanation of the difference between the two types of kinematics.
Inverse Kinematics Tutorial
Hierarchy Is Important
The way you structure your hierarchy of joints or bones or elements is very important and something that you will be used to if you have rigged any 3D models before in C4D. Fortunately there are no new tricks or rules to learn when it comes to structuring your models when you switch from Forward Kinematics to Inverse Kinematics. They both use exactly the same ladder layout.
Hierarchy Of Kinematics
Freeze Transformation As A Home Position
Do yourself a big favor and set a home position for your model. Having a home position is essentially having a pre-set pose for your model to return to. Personally, I often use a basic standing position for any human or animal figure models that I am animating. During complex animations it can be easy to get your model all turned around and bent up and it really helps just to be able to return to your starting pose and work from there.
How do you set a home position? It couldn't be simpler and, just like many of the other functions in Maxon's Cinema 4D, you can do it with just a few very simple mouse clicks. First, get your model into the desired home position where you want it to return to if you ever need to do such a thing. then go into the Coord tab as you can see in the screenshot below. Simply press the Freeze Transformation button and you are all set.
But now that you have set up a home pose for your model, how do you get it to return to that pose? That is even easier. All you have to do is click the PSR button. You can either dock the PSR button permanently on your display or you can hold down both the SHIFT and C keys at the same time. This will initiate a pop-up menu where you can type in PSR and it will bring the command up for you. You click the PSR and your model will return to whatever pose you chose for it to call home.
You can also manually zero out the Coordinates fields too, if you prefer, but the PSR button does it all for you with just one click.
Freeze Transformation & PSR
Start Using Cinema 4D Now
Using Maxon Cinema 4D will bring you hours, days, weeks, months and years of entertainment so don't deny yourself the fun and, quite possibly, a new career path for yourself. Start today, it's one of the things you will never regret doing.