class notes |
| Lecture 8: Forward K and Constraints
The parent controls the child but the child can animate separate from the parent
Creates a node that does not have geometry
Create the mechanical device
Create three cubes and arrange to have one on bottom, one going up vertically and one on the top of the other and horizontal.
Use the Modify - Align tool to get things lined up
The last object you select is what the other objects will align to
Use the Select by Hierarchy tool to make it easier to select the cubes if you made NURB cubes
Open the Outliner to select levels of the hierarchy
After positioning the objects:
Select the cube and Modify Menu - Freeze Transformations
Do this for each cube (notice it sets the channel box attributes back to 0)
Don't forget to Edit Menu - Delete by Type - Delete History
Move the Pivot points of the cubes so the objects will pivot correctly
Try rotating the pieces
Parent the top to the middle (select top then middle in Outliner then hit P) then parent middle to base (select Middle then Base then hit P)
Hide the channels not used
First figure out what you want each element to be able to do
General Editor - Channel Control - Move the ones you don't animate out
Select the channels you want to get rid of and Right click the channels and Hide selection
Set keys and animate
FK (Forward Kinematics) and Point Constraint
Build a simple claw structure out of cubes
Create a sphere or cylinder for the claw to pick up
Align the objects in the Orthographic windows
Set the pivot points where they should be
Freeze Transformation, Delete History and Name them
Use the Outliner to Parent each one to the other to make an FK system
Select the Sphere (the object you want to constrain to something else)
Then select the base of the claw (the object it will be constrained to)
Constrain - Point - Options
Maintain Offset: will keep the same distances between the center points of the two objects
Constraint axes: You can specify which axes will be constrained
Weight: How much of a pull it will have on the object 1=fully constrained and 0 = not
constrained at all.
Weight can be keyed!
In the Attribute Editor, select the object you want to pickup then click the Point
Then click Select at the bottom of the page to load the attribute to the timeline
Go back to Channel Box
Then move to a spot in the timeline and set the W0 key where you want it to be
Change the graph editor to Stepped
Set keys and try to get your claw to pick up the ball and drop it off
Set Driven Key
Links one attribute value to another. Creates a relationship between two objects.
There is a Driver attribute and a Driven one.
The Driver controls the driven.
An attribute value (like Scale X) of the driver is linked to the attribute value of the
Set Driven key creates animation without using the Time slider.
There will be no red marks in the time line to indicate keyframes.
In the Graph Editor, the vertical markings = the Driven; the horizontal markings = Driver
Graph Editor shows a relationship between the two attributes (linear by default)
Example: The X translation (move) of a car controls the Z rotation of the wheels,
Car -X move is the Driver and Wheel -Z rotation is the Driven
Make a cube and cylinder and arrange like a cart
Freeze Transformations, Delete History
Name the cart and the wheel
Parent the wheel (child) under the cart (parent)
Map some 2D texture on the wheel so we can see it turn
Animation Menu Set - Animate -> Set Driven Key -> Set ...
(can select the driven before opening)
Use your Outliner and select the Driver - the one who will control the other
In the Set Driven Key window, click Load Driver
Use your Outliner and select the Driven - the one who will be controlled
In the Set Driven Key window, click Load Driven
Select the attribute to be the Driver
Then select the attribute to be the Driven
Position the two objects in starting position
Change the attributes of the 2 objects and click Key.
You have now set 2 keys to define the relationship between these two objects.
You can keyframe the Driver and the Driven will animate in relationship to it.
In your Graph Editor, you will find the keys under the driven.
To have the relationship repeat forever, you need to select the last keyframe and select
Curves - Post Infinity - Cycle
Select the Driven object and under Animate -> Set Driven Key -> Go to Previous or
go to Next will show you the driven keyed positions.
Setting up your own Attribute
This allows you to set up sliders and channel attributes that give you easy control over
For instance, in this case we have a cart that we know how far it needs to travel
Make another cube and cylinder
Position them and Freeze Transformations and Delete History
Select the cube
Modify Menu - Add Attribute...
Add Attribute Name: MoveAlong
It will be of type Float
Enter minimum (-10) and maximum values (10)
Set Default to 0
(this only specifies the slider attributes)
Animate - Set Driven Key - Set...
Select the Cart and load as Driver
Click the MoveAlong Attribute
Select the Cart and load as Driven
Click the Translate x (or whatever attribute makes sense)
Key at the start point (MoveAlong 0 and Cart 0)
Go to your channel box and change the New Attribute to 10
Change the Translate X to a new number (or move the Cart) - the maximum distance the Cart should go
Set Driven Key - KEY
In the Channel box set the MoveAlong to -10 and then move the Cart to the minimum
Translate X value it should go
Go to the Channel Box and select the the MoveAlong attribute name
In the Persp window, middle mouse (MMB) move
Now set up your wheel to be controlled by the cart
You can Set Driven Key it to the MoveAlong or the Translate X
You don't need to parent it if you also have the translation keyed to the set
Hide all other attributes except for the MoveAlong Attribute
IK Joints (Inverse Kinematics)
They are used to animate jointed characters and objects
They do not render out
Prep: Turn on Snap to Grid and make 3 long cubes
Make 2 spheres
Align them to look like a robot leg
(Turn off Snap to Grid)
Move the pivot points to where they will need to pivot around
Name ALL pieces of Geometry
Testing out joints:
In an Orthographic View Window:
To set the joints click with your Right mouse button for each joint you want to set.
You can move the last joint you set by using the middle mouse button
Hit RETURN when done
Animation Menu - Skeleton - Joint Tool Options
Degrees of Freedon: By default the joint can move around all axes. You can limit it to
a single or two axes.
Orientation: Select NONE
If you specify NONE, it will use the World Axis. Otherwise it sets the rotation axes of
the joints to a new axis (might be useful later).
All other attributes we can change later
Name all joints:
Select the joints and name each one.
The top joint is typically called the Root
Start with the Hip Joint
Create a set of Bones for your Robot Leg in an Orthographic Window using the Joint Tool
Set to Orientation: None.
Don't forget to use the Middle Mouse to move joints to the right location
Select Joints and Freeze Transformations - notice that the transform will not change to 0
Change the Radius for each joint so you can select them easily:
In the Channel Box for the joint, you will see Radius. This enables you to scale up the
joint to see and select it better
Parent the Geometry to the Joints
Using your outliner, middle mouse button drag the Thigh into the RootJoint
MMB drag the Knee and the Shin into the KneeJoint
MMB drag the Foot and Ankle into the AnkleJoint
Don't worry about the Toe Joint
Setting the IK Handle
Skeleton Menu - IK Handle Tool Options
OFF Auto Priority
ON Solver Enabled, Snap Enable, Sticky
Click the Root (Hip) then End Joint (Toe)
Select the Toe and Translate it in various ways.
To Key IK:
Hide all attributes you will not be keying
Select the joint, rotate it then set key (s)