Original subtitles

- [Zach] In this video let's explore the constraints a bit

to better understand them before we go

into adding constraints to our character rig.

So, in a nutshell, constraints are there

to better control our objects for animation.

They basically should save us a lot of manual work

and with constraints we can either limit our objects

or we can set up certain dependencies

or relationships between objects.

So, here we have this very simple canon object

which consist out of three main parts,

this gun here, this top part here,

and this bottom part here.

Let's disable the ground for selection

so we can't accidentally select the ground

and the first and very basic constraint

kind of thing you know is the parenting.

So, just imagine this canon should follow a plane

and maybe shoots on the plane

and then we need to, in this case here,

select these two objects, make this somehow rotate

in the animation process and you can imagine that doing this

with many separate objects, it's a pain in the butt.

So, the first thing we can do,

let's select this one here, and then this one,

hit Control + P and set the parent to object

and I will also wanna connect these two objects,

so let's select this one, then this one here,

Control + P and click on set parent to object.

You can also right click and go into the parent options here

and click on object.

Now, if I move this one here,

you can see all the other objects are moving along.

If I move this one here, the gun is also moving along.

So, this one here is a child of this object here

and this one is a child of this object.

So, that means if I now rotate this,

I can simply animate the rotation of this object here

and I could animate the rotation of this object here.

So, this would make our life already easier,

but let's see what else we can do

with the use of constraints.

So, here in object mode we have the object constraints

later on for the bones we have a different tab

for the bone constraints.

So, and in this case, I wanna set up a target object

and the cannon should follow

the target object automatically.

So, let's select the gun here,

press Shift + S and then click on cursor to select it.

So, the 3D cursor is over here and let's hit Shift A

and add a simple empty object.

Let's move this to the front and let's call it target.

Let's up here, enable the local transform orientation

and let's also enable the move tools

so we can see the local axis of the selected object,

which is quite important when working with constraints.

So, the first thing I want to do is that the main part here

will always point to this target object.

For that let's select this, go to the constraints,

and here we have different categories like transform,

tracking, and relationship.

Motion tracking is something we can fully ignore here

because this is done for VFX post-production

in the camera tracking and motion tracking field,

so we don't need that.

And in the transform category,

we can either copy transforms from other objects,

like rotation and location, or we can limit this

so we can say that we only can rotate to a certain degree

in a certain direction for example.

Then we have the tracking constraints

which allows us to like look to a certain object

or a stretch to a certain object, for example,

and then we have other relationship constraints,

like follow a path, make an object always hit a floor,

for example, or the child of constraint

which is basically the same thing as parenting objects,

with the only difference that we can turn constraints

on and off.

So, in this case, we want to use the track to constraint,

which means always look to a certain target object

and the target object we can define in this field here,

either click here, select the correct one

or use the eyedropper and select the target object.

Now, the canon is rotated weirdly.

However, it's already always looking at the target,

but we have to change the axis.

We can see the local axis of the object here

on the transform gizmo in the direction where the arrows

are pointing is always the positive direction

and the opposite is the negative direction.

Now, it's pointing down here, which we want to use as axis,

which is the opposite of green,

which means it's the negative Y-axis

and we need to define which axis should point to the top,

which is the blue Z-axis in our case.

And now, if I move the target the cannon

is always looking in this direction.

This looks good already, however,

I don't want the cannon to rotate up and down,

it just should rotate around the Z-axis here.

So, let's add a limit rotation constraint

which we can find over here.

Then I want to block the Y and the X-axis here,

so let's select X and Y

and I leave minimum and maximum at zero.

That means if I now rotate this,

it can only rotate around the Z-axis.

However, maybe we'll wanna limit the Z-axis as well

so it can only rotate to a certain degree.

So, let's enable this and maybe let's set the max to 90

and the minimum to negative 90.

That means if I look from the top here, and if I move this,

when it hits the 90 degree mark

or the negative 90 degree mark,

it will just stop rotating.

And now, the last thing I want to do

is that this object here is also pointing to the target

but it only should move up and down.

For that, first of all, let's also add a track to constraint

and pick the target object.

Now, it's flipped, as you can see, in this case,

we need the blue positive Z-axis to point to the object.

So, let's use positive Z and the Y-axis

should point upwards which is already selected here.

Now, it should do the right thing.

However, I want to also limit the rotation here

for Z and Y so it's only a rotating around the X-axis here.

So in this case, again, limit rotation,

I want to block the Y and the Z-axis

and I also want to limit the X-axis.

However, for this, let's open up the sidebar,

here you can see, since I rotated the object

to point in this direction here,

it has already the 90 degree rotation.

That means if I now enable X it will go back to zero

because here we now limit this to zero.

That means we have to set the maximum to 90

at least to point in this direction here.

Now, it can go from 90 up to zero.

However, maybe we don't want this to go fully up

so maybe let's pick 45 degrees

so it can only go up to a certain degree

and maybe the cannon can also move down a bit

so we can increase the maximum value a bit maybe to 100

then you can see it can move between 90 and 100 degrees.

So, this looks all good,

right, well, not right.

You can see that the gun in the front

is still doing something weird and this has to do

with the space.

Well, not the outer space,

here we have the world space and the local space,

custom space we can fully ignore,

but world and local space is important

when working with constraint.

We can see we have these options in many constraints

and there we can define if the whole interaction

of the constraints should happen in the world space

or in the local space of the object.

So, the world space is basically the global axis,

the global coordinate system here.

So, that means zero is here in the center,

it's using always the global axis here

so it's very static in the whole world.

However, this object here is parented and it is rotated

so it has its local space inside the parent

of this object here.

So in this case, we have to set

the limit rotation constraint to the local space

which gives us already what we want.

However, just in case up here in the track to constraint

we can also set that the owner,

which is the object here in this case,

should also be in local space.

However, the target here can stay in world space

because it's freely moving around in the world.

And now, you can see what we did with the constraints

instead of animating and rotating this and this object

manually to always point to a certain thing in the world

we can now only animate one object here.

So, for example, if I add a key frame here for location,

so we only need to animate the location,

then go a bit further here, then move this here

and maybe a bit upwards, insert a new key frame,

and now play back the animation.

You can see we animated the full object here

by only moving the controller object

and this is the whole point of using constraints.

We want to make our animating life easier.

So, I hope now you have a very basic understanding

on how we can work with constraints

and in the next video, let's add the constraints

to our character rig.

If you like, you can save.