In this tutorial we're going to learn more about the Bone Tool and constraints that you
can place on the joint rotation.
You can have more flexibility and control over the joint constraints if you use something
called a null circle or an extra object in the joint chain.
First let's use the Bone Tool to rig up an arm in the normal way with just 3 layers.
Remember each of these layers are already a graphic symbol.
Click on the Bone Tool and then start where you want the arm to rotate.
In this case it's going to be up by the shoulder, so I'll click and drag down to the elbow.
Then it selects the next symbol.
Then I'll click and drag down to the hand.
If I get the selection tool by pressing V, I can now drag the arm around.
This is great but I can't control the restriction of the hand movement.
Remember that if you click on a bone, you can restrict its joint in the properties panel.
So for example, if I click on this first arm joint, I can constrain the right and left
offset.
If I only want the shoulder to rotate a certain amount, I can constrain that.
Generally for a shoulder you wouldn't want to constrain it but just for an example.
Now the arm can't rotate past this point.
This is great, especially for elbow joints.
This is where you really want to constrain a joint.
For example here I want the arm to be able to bend in one direction but not in the other
direction.
Now I have this nice joint rotation but if I push the hand up like this, that is a little
bit too far for rotation.
It would be great if I could constrain that.
Well we can if we use another object at the end of the bone chain.
Here I have an arm, a forearm and a hand but I also have this red circle.
This red circle is also a graphic symbol and I've labeled it null.
You can label it anything you want and it can be a square or a triangle.
Select the Bone Tool again and I'll start at the shoulder.
I'll click and drag down to the elbow.
Click and drag down to the hand and then click and drag down to our red circle.
Now Adobe Animate has created a new bone layer here.
Everything seems to act as before but now I can have more constraints.
For example, I'll click on the forearm and I'll constrain in its joint rotation.
Then I'll click on the hand and I want to constrain its rotation as well.
The hand should be able to bend back and it should be able to close but not all the way.
Let't take a look to see how that worked.
See, now the hand can only bend so far.
We can also change the speed and stiffness of the different bones.
For example the shoulder probably moves less fast than the hand.
Click on the shoulder bone and then on this stopwatch icon over on the right, I can lower
that speed down to maybe 10 percent.
Then I can select the forearm bone and lower that speed to say 50 percent.
Then I can click the final bone going to the circle and leave that at 100.
Now if I drag the bone around the arm moves much slower.
It almost is as if I'm dragging the skeleton's hand around.
We can put in some frames by pressing F5 on the timeline.
Then we can animate our bone layers.
This makes it very easy add animation to a bone structure.
Remember if we don't want to see the circle all we have to do is go to our library.
Open up the symbol, click on the properties panel and adjust its fill to none.
We can always bring it back to make fine tuned adjustments.
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