Hey everone, Jason Here.
It has been on my list for a long time to build a LEGO Orrery, and a couple of months
ago I finally sat down and started
putting one together, and this is the result.
Now, if you don't know what an Orrery is, it's just a fancy word for a mechanical model
of the solar system, or part
of the solar system,
and in this case I just decided to focus on the Sun, the Earth and the Moon,
and trying to get the relative roations and orbital periods fairly accurate without making
it overly complicated
and it may look complicated, but trust me, it could have been a lot more complex than
it actually is.
Before I walk you through the drive system and explain how it all works let's just take
a look at how this model
stacks up to real life.
Every turn of the crank represents one day, and as you can see with every full roatation
the Earth also makes one full
rotation.
The Moon in this model rotates around the Earth once every 28 days, which is fairly
close to the 27.33 days it takes
in real life.
In the real world the Sun is actually not a solid object, so its observable rate of
rotation varies depending on what
latitude you are looking at, but at the equator it rotates once every 24.47 days and in this
model I have it set to
rotate once every 25 days.
And as far as the Earth and the Moon rotating around the Sun goes, in this model it takes
375 days, which is still over
97% accurate to the real 365.256 days that are in each one of our years.
Now, the best way to show you how the drive system works, is to do it digitally.
Here is a model I put together in LDCAD, and the nice thing about this is that I can remove
most of the surrounding
frame, so we can really see what's going on.
And we will start by just taking a look at the the gears that drive the rotation of the Earth.
I even set up a little animation here so that you can see them in action.
One thing to note is that these gears in the middle are what LEGO calls Gear Wheels, and
what's special about them is
that they have a smooth hole in their center, as opposed to an axle hole, and this allows
them to rotate around an
axle at a different rate than the axle itself, which will allow the Sun to spin more slowly
than they do once we add
it to the system.
Now, lets add the gears driving the moon. There are only a handful of them, and as you
can see they have been added to
the end of the main gear system. The moon is connected to the top of a small turntable,
which also has a hole running
through it, and which again allows the axle rotating the earth to spin at a different
rate than the turntable itself.
Next up we have the Sun, and as you can see, there are only a few additional gears used
to rotate it, that come off
pretty early on in the main gear train.
And finally, we need to rotate the entire upper frame that the Earth and the Moon are
connected to. And to do that we
are going to use this large turntable, which also has a hole in its center, allowing the
gears and axle rotating the
Earth, Mmoon and the Sun to rotate independantly of it.
And that turntable is driven using these gears that come off the axle rotating the sun, and
they actually rotate
pretty slowly, so it might be kind of hard to see in this animation.
I have created building instructions for this model, which you can find over at jkbrickworks.com,
as usual.
And as always thanks for watching, keep on building, and I will see you next time.