Feet
Chapter Example Files:
chpt10_Marv_bird_RIG_v4.mb; chpt10_Marv_bird_RIG_v5.mb
If you think about the foot of your character, or even your own foot, there a couple of things that we want out of the rig. I’ll pull out my floppy, flexible shoe to demonstrate. Please, pull off your tennis shoe and hold it in your hand to help visualize the feet issues. If we were to put an IK handle on the leg we could lift the foot up, move it around, and could do a simple type of walk. (Lift and move your shoe around in the air.) We want to add the ability for the character to lift their heels up and stand on the balls fof their feet. (Place your shoe on a table or the ground and bend up the heel.) This is important when doing a push-off pose for a walk cycle. We want to add a toe tap so that we can bend the toe up and slap it down to get a nice contact point when animating a walk cycle. (You can set the shoe on a flat surface again and lift up the toe. On some shoes you can flex the toe down. In a cartoony rig, this movement, though not anatomically correct, needs to be exaggerated.) Even though we don’t physically walk this way, not noticeably, it helps to get weight into the animation to have this toe tap.
The other functionality that we want is for the character to be able to stand on tippy toe or wiggle their foot while placing the contact point at the toe. So, to break the functionality down:
1. Peel heel. 2. Toe tap. 3. Tippy toe.
4. Move the whole foot. 5. Rotate the whole foot.
These are the minimum functions we are going to put into this rig. There are some other things that you could do, like adding in the ability for the foot to roll to the inside or outside of the foot.
I’ve collected many ways to do this over the years, and the two basic types are creating this effect with a joint system driving it or using group nodes. Either one will work. I tend to use the group method since we have already covered grouping and pivot points way back in our first chapter together. Remember the pivot point animation? It is the same principle applied here. How about that?
The joint method involves creating a snowshoe type of joint system that is fitted onto the existing skinned joints. The shoe joints are orient constrained to joints to drive the feet. There are no extra IKs involved. The snow shoe looks like a reverse foot—it is where the name was derived. The joint reverse foot seemed visually cluttered so I gravitated towards the group system, even though it could be argued that the two IK handles that are created with the grouping method are extra steps. When toes start to get involved, I like the IK handles better for organization.
Figure 10.1 Joint based reverse foot system does not use extra IK handles.
Our bird character will only have an IK leg. It will not have an FK/IK switching leg. The reason a character would have an FK leg is if the feet were coming off the ground, the weight would be going somewhere else. That somewhere else would probably be IK. But the legs at that point would not have a contact and would be moved by the upper legs with no resistance, so FK would be the proper setup for that. That’s more advanced; we’ll ease our way up to an FK/IK switching appendage. We’ll do that with the arms/wings since many simple animations require an FK/IK switch in arms. What is this FK/IK switch? Hold on, we’ll talk about that in another chapter.
Incidentally, a leg is a leg is a leg. The bird and the human have hips, knees, ankles, and toes of sorts. The difference is the knee bends the opposite way. The pattern of rigging is exactly the same, only making sure the knee points the other way. Open file chpt10_Marv_bird_ RIG_v4.mb. Before we start, left mouse click on each hip and select “ Set Preferred Angle ” just so that we know that Maya knows this is the way the leg should rotate. It sets up good math for our IK handle.
1. Create a Rotational Plane (RP) IK chain from the Hip to the Ankle. Name it L_Ankle_IK. 2. Create a Single Chain (SC) from the Ankle joint to the Ball. Name it L_Ball_IK1. (Since
this bird has three toes, there will be three ball IK handles.)
3. Create a Single Chain(SC) from the Ball to the Toe. Name it L_Toe_ IK. (Since this bird
has three toes, there will be three toe IK handles.)
The very last joint of the toes is the claw. We’ll put one single chain IK handle from the ankle to the first joint of the dew claw. If you miss this step, the peel heel and toe tap will not rotate very well (I know; I learned the hard way). The leg should not have twisted or moved during any of this. If it did, remove the IKs and make sure you set preferred angle before doing it again.
Figure 10.2 IK handles for the ankle, balls, and toes. Only the ankle is rotational plane; all else are single chain.
Figure 10.3 Turning sticky on for the IK handles.
Before we continue, we need to temporarily turn on a feature for the IK handles. Select the
L_Ankle_IK and in the Attribute Editor>IK Solver turn the sticky attribute on. Repeat for all of the L_Ball_IKs and the L_Toe_IKs. This will make the IK handles hold still as if they had a controller
or keyframe on them. This way when we test we’ll know if our grouping/rigging in the next step worked or not. The IK handles visually change to have a red circle in the center when sticky is turned on.
Note: You don’t want sticky on normally. If you have it on when doing the arms, for example, the
arms will not behave correctly when you are testing. You’ll freak out and email your professor. Don’t do that.
A little note : When you add IK handles it tweaks the math in the joints and adds rotational
information. Usually, you’ll see negative zeros show up.
Now we will add group nodes to get the foot functionality. If this were just a shoed character with one joint system down the center of the foot—obviously, it would be much easier. The toed character gets a little more complicated, but the pattern is still the same, just less joints.