Hi there, welcome to the third part of this series, “How to Animate with Constraints in Maya”. Today, I’ll share with you how to constrain prop to hand in Maya.

But before I dive into it, here’s a little recap for those who have missed the first two parts.

In Part 1, I explained the 11 different types of constraints in Maya and what can they do. In Part 2, I used my analogy to explain the difference between parent and parent constraints. Below are the links:

  1. Part 1 – What Can the 11 Different Types of Constraints Do?
  2. Part 2 – Differences Between Parent and Parent Constraints

Why Use Parent Constraint Instead of Parent?


Difference in hierarchy between parent and parent constraint

First of all to me, parent is a rigging function, not an animation function. As mentioned in Part 2, when you use parent, there is a change in hierarchy. This change in hierarchy is permanent. You either have it or not have it. Your object is either a child of the parent or on its own.

So parent isn’t very useful in animation.

Because in animation, things are always dynamic. Characters are always moving. It’s not practical to have something like a prop sticks to a characters’ hand or body the whole duration in the shot, unless it’s meant to remain stuck. For example, a character wears a cap or a watch that he never removes.

Rule of thumb: Use parent constraint unless the prop is part of the character.

Whenever you have a character interacting with a prop, it’s best to use parent constraint because you are able to turn the constraint on and off. This means you can turn the interaction between the character and the prop on and off. Very useful if you have a character picking up and letting go an object in a scene.

The Most Common Mistake Made When Constraining Prop to Hand

The most common mistake that new animators made when using parent constraint is to constrain the prop or its controller directly to the IK hand controller.

I’m guilty of this too! When I was an animation student, I did this all the time.

Actually there’s nothing wrong with this method. If you are doing a simple shot and you are able to achieve the outcome you desire with this method, why not?

But most of the times, it doesn’t produce the outcome you want. Here are the disadvantages of using this method:

You Lost Your Ability to Animate the Prop


Prop will always snap back to follow the constraint. Its movement is restricted and you can’t create nice arcs with it.

When you constrain the prop’s controller directly to the hand controller, you practically lost your ability to animate the prop on the frames when the parent constraint is switched on.

It’s fine if your object is like a ball and doesn’t move much in the character’s hand. But what if you have a long object like a sword that needs overlapping action and nice arc when it’s moving? You no longer have control over the sword anymore if you use this method.

Your Constraint Doesn’t Work on FK Hand Controller


The prop still follows the IK controller, even though you switch to FK.

Furthermore, if you constrain your prop to the IK hand controller, what will happen when you switch to FK hand controller later in your shot?

The prop would still follow the IK hand controller. It won’t follow the FK hand controller. And there’s where the headache is.

So what should you do instead?

Ideal Setup for a Prop to Hand Constraint

The following setup is based on video tutorials recorded by Nick Arbeiter and David Latour. Basically, their setup has the best of all worlds. Their setup allows animators to:

  1. Switch on and off the hand’s influence on the prop.
  2. Animate the prop while the constraint is switched on.
  3. Have the prop follows the hand regardless if the hand is in IK or FK mode.

To sum it up, the ideal setup for prop to hand constraint is: Skin Joint + Prop Group + Parent Constraint. You can also do a variation of this, but essentially it works like this.

Please see this video tutorial below as Nick Arbeiter explains the ideal constraint system:


Why Constrain Prop Group to Skin Joint?

Why Use Prop Group?

To have the ability to animate the prop even during constraint, you must let your prop controller be free. Instead of constraining the prop controller, you need to constrain something else that is:

  • of a higher hierarchy than your prop controller, and
  • controls the prop controller, but
  • without locking its attributes to it.

Use prop group for constraint, instead of the prop controller.

The easiest way to do this is to create a group for your prop and prop controller. In Nick’s video, he called this a “Zero Group”. All you need to do is to select both the prop and prop controller, and go to the menu Edit >> Group.

You can also create a locator and parent the prop and prop controller to it. Then, use this locator instead of the prop group. It’s a bit more troublesome, but the fundamental is the same.

In production, most riggers would have created a group to house the prop and prop controller. All you need to do is to select the prop controller and hit the “Arrow Up” button on your keyboard to locate the prop group in the outliner.

Why Use Skin Joint?


Skin joint is often used as the parent instead of the hand controller since it’s not affected by IK and FK switching.

To locate the skin joint, you need to hit “4” on your keyboard to display the wireframe. Also make sure that you show joints in your viewport menu i.e. go Show >> Check the box “Joints”.

Personally, I like to parent constrain a locator to the skin joint. Then, use the locator as the parent for the prop to hand constraint. I do this because it’s easier for me to locate and select the parent even when I switched back to the textured display. More on this in future posts.

Next Post…

Hope these posts have been useful to you so far. For the next post, I’ll be sharing other common usage for parent constraint.

Read The Nine Old Men: Lessons, Techniques, and Inspiration from Disney’s Great Animators.

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