LEGO Techniques - Using DUPLO

DUPLO (if you haven't noticed) is a larger sized LEGO compatible brick made by the same company.  The target audience is usually pre-schoolers and under.  The idea is that the larger bricks are easier to handle and harder to swallow.  My 2 year old handles 1x1 round plates without a problem so this concept is lost on us.  Nonetheless we have a sizable collection in our house and I find it very hard to pass up the opportunity to add to it.  Reasons are multiple.

First off, you can build large and fast.  DUPLO bricks are twice the size of regular bricks in every respect.  If you remember your high school geometry, this means a 2x4 DUPLO brick occupies 8x (twice the size in three dimensions) the space of a 2x4 LEGO brick.  So you could replicate the size of a 2x4 DUPLO brick with 8 2x4 LEGO bricks.  This means towers to the 8' ceiling can happen in about 5 minutes or less.

Second, DUPLO comes in a myriad of colors.  The 2x2 DUPLO brick comes in 49 colors.  This is surpassed only by minifig arms and 1x2 bricks (according to the Bricklink catalog stats for parts in the most colors).  So you could build the most beautiful rainbow, flowers, or color gradient.  All in blocky 2x scale of course.

Finally, and most importantly to this post, DUPLO is completely and utterly compatible with LEGO.  The designers of DUPLO did us a great service by integrating two crucial elements into DUPLO bricks.  The first is the knob on top.  All DUPLO knobs are open.  The interior diameter of the knobs is the same as the outside diameter of the tube on the underside of a 2x brick.  This dimension (for the engineers) is 6.51mm O.D.  So a 2x4 brick will fit very snugly down onto and clutch with a 1x2 DUPLO brick.

Check out my amazing clutch powers

The underside of DUPLO bricks have ribs that make up for what should be thicker walls.  But economic geniuses that they are, The LEGO Group has decided to make the walls as thin as practically possible.  In order to clutch well, ribs are placed at every point where they meet knobs in order to take up the difference in thickness.  By making the walls thinner the DUPLO elements also accept the 1.6mm offset of LEGO element knobs and allow them to be placed on the underside as well.

The only major geometric difference between LEGO and DUPLO is that DUPLO plates are 1/2 the thickness of bricks rather than 1/3 as LEGO are.  This makes DUPLO plates the same thickness as LEGO bricks.  If DUPLO followed the 1/3 rule, the plates would be 2/3 of a brick and would require a touch more finessing for integration between both systems.

So, how to use DUPLO and LEGO together?  The most practical reason would be to take up big chunks of filler space in a large project that needs very stout support.  At the last Bricks Cascade conference I witnessed a very large bridge that was created with what must have been 100,000 brick bricks.  But as the pieces were being assembled I caught sight of the large DUPLO knobs inside.  "Aha!" I thought.  Here's someone who understand economy.  Besides that, the mass of DUPLO bricks are less and so several pounds were shaved from a gigantic creation.

Skate ramp, DUPLO style

You could also use DUPLO elements where a feature is desired that can't be replicated with LEGO.  There are many interesting shapes that have been created via DUPLO.  Some of them can be simulated with LEGO, others cannot.  So embedding a DUPLO brick into a LEGO creation can possibly lead to one of your MOCs getting branded with NPU, crossover dude!