Animating Piano Key with Rigid Body
by Daniel Harjanto a.k.a misterdi
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As we already have a lot of headache animating the piano player,
now there is another challenge, how we animate the piano keys following
the player?.
It is possible to do a key-frame for each single touch of the finger,
but it is a pain in the arse when they ask to change the piano player
animation.
So, we need to find out a system that each key knows when they
are pressed by the finger and relax back to the rest position when
the finger is lifted.
To make live easier, we could use a rigidbody rig to do the task.
Here is the setup and work flow.
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1. The setup
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To simplify things we just do one piano key setup. (figure.1
setup.jpg). Since dynamics is sensitive to measurement, take
a look the setup from top view. (figure 2. topView.jpg)
As you see there are couple things we need to have in the
setup.
Geometry:
a. One piano key.
b. A pinned rigidBody (red) position toward the front side
of the piano key
c. A spring holder (blue) which also a rigidBody, about 3
unit higher from the pinned rigidBody
d. A dummy (which is a sphere) that will be constraint to
a finger of the piano player.
Rigid Body:
Even you can't see it in the picture, there are 4 rigidBody
connected to each geometry, which was created using Dynamics>Soft/Rigid
Bodies/Create passive Rigid Body menu ( figure.3 RB_creation.jpg).
As a start all rigidBody was created as a passive rigidbody.
Rigid Body Constraint:
a hinge constraint for the piano key, place where it should
be placed as a pivot point of a piano key ( figure 4. RB_constraint_hinge.jpg,
figure 5. orig_hinge_position.jpg and figure 6. final_hinge_position.jpg).
c. a spring constraint, which connect the spring_holder
to the pinned_rigidBody, with some initial value I set up
as figure 9. RB_constraint_spring.jpg).
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2. Why do we setup like this?
The reason I put a pinned_rigidBody in the setup, not connecting
directly the spring_holder to the piano_key is, spring constraint
always connected to the center of mass of the rigidbodies
(You can set it up differently if you are using the user define
position, but that is not intuitive enough). And if the spring connected
to the center of mass, you might run into problem of trivial solution
of the rigid solver.
But since rigidbody constraint will always required rigidbodies
to be connected, we use pin constraint to do somesort of constraining
the pinned_rigidBody to the piano_key. But we move the location
of this pin constraint exactly to the center of mass of the
pinned_rigidBody so it doesn't have extra transformation when it
is animated in dynamics.
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3. What's next
When everything is setup nicely, then it is the time to switch
the piano_key and the pinned_rigidBody to active rigid body. Select
both object in the Outliner (figure 10.Outliner01.jpg) and change
the Active attribute in channel box to on (figure 11. channel_box01.jpg).
 
Select pinned_rigidBody and spring_holder and set the collision
attribute to off in the channel box (figure 12. channel_box02.jpg).
This will ensure that those object will not be calculated for any
collision event happening during simulation.
To test out the rig, select the dummy (sphere) and animate it so
it goes into the piano key (do not worry that the piano key is not
pressed right now), set several key frame the sphere going up and
down.
Rewind your time line and hit play, you will see now the sphere
is pressing the piano keys (piano_RB.mov).
The scene (Maya 5.0) are included in this tutorial (piano_RB.mb)
or in zip file (piano_RB.zip)
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4. Beyond the tutorial.
When you feel the piano key is a bit to flexible, and you want
stiffer animation, play with the spring stiffness and spring damping
attribute of the spring.
If you want the piano key down a little at rest position play with
the spring rest length attribute.
You can also have other spring to hold the key from beneath, which
will give you more vibrant key movement.
When you familiar with one setup, you can look at the history part
of your script editor and try to create 84 rig with a mel script.
Instead of using one dummy, create 10 dummy and point constraint
this dummy to each finger tips of the piano player and let it run.
You will have the piano keys all animated within minutes only.
The same concept could be applied to different instrumentation
like Cool - lean - Tounge or Gah - Mae - Lan.
But the idea is you concentrate on the animation of the player
and let the system do the dirty work for you.
Next tutorial will be more simple "The domino effect".
And hopefully I got time to write down the tutorial of "Burning
those paper" in time.
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