The Great Mouse Launch – Part 2: Adding Physics and Scale

blueprint-part2Continuing on from The Great Mouse Launch  Part 1: Building The Dominoes, it’s time to start adding dynamics to our dominoes and making sure they “feel” like dominoes as they fall.  The first time I set up a domino simulation, I was so enamored with the idea that the little blocks were hitting each other and bouncing around I didn’t even notice that they were moving too slow!


One thing I’ve learned while working on multiple projects is that it’s very important to create your assets at a consistent scale.  If you do this, you can share assets across projects and allow yourself to get up to speed on new projects extremely fast!  One way to do this is to make sure you are modeling in real-world units.  628px-Soft_ruler

What does “real-world” units mean?

Essentially this means that you’re going to build something that matches its real-world counterpart.  For example, if you’re modeling a chair, it might be a good idea to model it at a similar size to a real chair.  For example, a standard chair might be 44 cm from floor to seat height.  If you are consistent with your modeling scale, that chair will work with any character in any scene you create.  If not, you’ll have to make adjustments to the chair each time you try and use it.

Chair vs Man.. one of these is scaled right!

Chair vs Man.. one of these is scaled right!

This may not seem like such a big deal, right?  Just scale the chair!  But imagine you’ve got hundreds or thousands of assets in your library.  If they are all at different scales you’ll spend time adjusting every… single… object.  Blarf!

Who wants to do that?  What a waste of time!

By default, Blender uses its own units.  They aren’t really based off of real world units, but they’re consistent.  If you’re not doing dynamics, or integrating with other software or people.. then using Blender’s default units consistently is absolutely fine.

However, it’s highly unlikely that you will never work with another person.. and also even though Blender has the ability to do a lot of things, most of us will be translating data between various tools.  For example, most modern-day highend pipelines utilize Alembic for geometry i/o.  Currently Blender doesn’t have Alembic i/o, but there is a branch where it’s being worked on.

In order to save yourself headaches down the road, it is in your best interest to work in either metric or imperial units.. whichever you are used to.  I prefer metric, because it makes the math easier.  And I like easy math.

To switch this in Blender, you would head on over to your Properties panel and switch to the Scene mode.  Slide your gaze south a little bit and you’ll find the Units area.  You have three options… NoneMetric, and Imperial.  None doesn’t literally mean “None”.. as in “no units!”.  It simply means Blender Units.  Where a value of 1 = 1.. Blendy?  You can easily swap over to Metric or Imperial, depending on your inclination and the current state of your country’s educational system.

I’ve only found two issues when working with “real world units”.

  1. When working on something that’s very small, Blender’s rigid body dynamics become quite unstable.  We’ll discuss methods for working around this in the tutorial.
  2. When working on scenes that are HUGE (i.e. a character flying through an entire city, like in Megamind) it can be difficult to maneuver such a gigantic space.  At times, it might make sense to work at a particular scale.. like 1/10th real world units.

The key is to attempt to be in real world as much as possible.. and when you’re not, try and stay consistent with your deviations.  That way it’s easy to know what to scale to, and it removes some of the guess-work.

Anyway, in this video tutorial we’ll be taking the domino from the previous tutorial, add physics to it, make it bounce off the floor, and then add a whole line of dominoes.  Once we do that, we’ll tackle the scale issue.


Jason Schleifer
Jason Schleifer
Jason and his mad scientist eyebrows have been pushing the boundaries of CG animation and sharing his knowledge for nearly 20 years. Widely recognized as an industry leader and mentor to hundreds of animators, Schleifer, formerly of Weta Digital and Head of Character Animation at DreamWorks, now works as Head of Content and is a co-founder of Nimble Collective.

1 Comment

  1. Very nice discussion of timing and scale. You can also adjust scale by changing the gravity. For example making the gravity x100 larger makes a 4 meter tall domino look like it’s a 4 centimeter tall domino. But it’s better to adjust scale as you show in the tutorial.

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