Mechanical Beaver

Canada Day is coming up and this year is a pretty special one, as it marks the 150th anniversary of our country’s confederation. The entire country is celebrating, with many ‘Canada 150’ events going on throughout the year. In fact, LEGO builders from around the country have already joined the celebration by building many Canadian themed models, which can be found at the Canada Builds 150 website, with more being posted throughout the year.

I thought it would be an interesting challenge to build a mechanical LEGO sculpture of our national animal, the cute and industrious beaver. You can watch the video to see it in action, along with an explanation of how it works. Building instructions and more details are below.

It’s a pretty simple mechanism, consisting of a single drive shaft with a cam that slaps the tail and a crank connected to a piston that opens and closes the teeth.


Building Guide

PDF File

Digital Model Files

LDraw File

Additional Resources

Parts List


You can operate it with a hand crank inserted into the side of the body, or by using a Power Functions M-Motor. The slapping of the tail is pretty loud, especially on a hard surface. I would recommend putting something soft under the tail to dampen it unless you are intentionally trying to annoy everyone nearby. If you connect a motor to it, I would also recommend either gearing down the motor, or using the Speed Remote/IR receiver to control the speed of the motor (or the rechargeable battery box). Directly driving it with the motor at full speed can result in some pretty spectacular tail slapping!

I had a lot of fun building this model, and Kristal and I are working on a couple of other Canadian themed models to continue the Canada 150 celebration.

The Bat

Update 3/19/2017: Instructions for building the core flapping mechanism are now available here.

As I mentioned in my post about our trip to Australia, Brickvention is held in one of the coolest venues for any LEGO event I’ve been to. What I didn’t mention was that the Royal Exhibition Building is surrounded by some really wonderful green space, and that every evening as left we would see some cool Fruit Bats flying around. This was the inspiration for Kristal’s latest LEGO model, The Bat.

It took quite a few design iterations to finally get the mechanics of this model compact enough to fit in and under the body, but still evoke the unique movement of a bat’s wings. This includes the flapping motion, their expansion and contraction, and sweeping them forward with every beat.  The stand also moves the entire bat up and down. In the video I explain how the mechanics work together to achieve these movements.

The wings are built mostly with LEGO flex tube, to keep them as light as possible. Even so, you can see that they do bounce a bit when they reach the bottom of the downward beat. This is mostly due to the backlash that is present in any LEGO gear system, which is taken up as the wings turn over at the top of their cycle. The wings then recoil a bit as the gears ‘catch up’ to them at the bottom.

As these bats are mostly active at night, Kristal designed a brick built sunset on one side of the stand, which transitions to night as you turn the model around.


Bat Left