This is my latest Lego creation — a fully
motorized, remote controlled Star Wars imperial walker. It can walk, turn, move its head,
and shoot rubber bands. It’s the coolest thing I’ve built out of Lego so far.
I’ve actually built and re-built this robot multiple times, making it a bit better each
time. I think it’s pretty much as good as it’s going to get right now.
I started from one of Lego’s own designs — this AT-AT from the dark side developer kit. I
never actually owned this Lego set, but when I found the instructions online, I just had
to build it. However, the design itself was somewhat unsatisfactory.
Its single motor could only move the robot forwards and backwards in a preset pattern.
I wanted it to be able to walk and shoot, but I only had one motor, and it was only
powerful enough for one thing at a time. What to do?
Turns out, there’s a simple solution called a ratchet. A ratchet will change its position
depending on which way the gears are spinning So in this case, when the motor was spinning
clockwise, the ratchet would send power to the legs, and when the motor was spinning
counter-clockwise, the ratchet would send power to the gun.
Mechanical power like this is transmitted through a gear train, which is pretty much
what it sounds like. It’s a series of gears with the teeth linked together.
Now, I used to build gear trains that looked like this one. This turned out to be a terrible
idea. It’s actually best to use as few gears as possible. This minimizes both friction
and backlash, which is what happens when the tiny spaces in between gear teeth add up over
the length of a gear train. Too much backlash is a bad thing.
Anyway, with all the gears in place, my robot was successfully able to walk forward AND
shoot intermittently. However, the gun I had built was weak and
impossible to aim. I wanted something more powerful.
That’s when I picked up this book. The authors call it “forbidden Lego” because The Lego
Group would never publish instructions this dangerous. I actually did almost shoot my
eye out with this powerful and fully automatic Lego gun.
My version of this gun was somewhat smaller, and didn’t require that I physically cut of
any of the gears to make it work. I wanted to mount the gun onto my walker,
but this gun requires a LOT of force to shoot, and my single motor simply wasn’t powerful
enough. Now usually, when a motor isn’t powerful enough
to do something, you can just gear down. I’m sure you’re already familiar with the idea
of gearing up and down if you’ve driven a car or a bicycle.
These two vehicles are exactly the same, except for the gearing on the side.
The vehicle that’s geared up is a lot faster, and the vehicle that’s geared down has a lot
more torque. To fire my awesome gun, I had to gear down
SO much, that the gun was just way too slow. [Silly music]
I wanted a gun that could fire rapidly, so clearly I needed a better design.
With a bit of googling, I found a design for a simple rubber band gun like this one that
perfectly suited my needs. This gun doesn’t need a lot of power, it can hold a lot of
ammo, fire rapidly, and it has decent accuracy. My version of this gun needed to have a worm
gear. Worm gears impart a lot of torque, and they cannot be moved by the gear they are
meshed with. Without a worm gear, the rubber bands would fire themselves as soon as the
motor stops running. This new gun worked very well, and I was satisfied
with my model, which could now walk forwards and shoot rubber bands, intermittently, using
only one motor. Then one day I found this set on craigslist
at half price and I couldn’t pass it up. I hadn’t bought any new Lego since I was a kid,
so I figured, why not? As far as I’m concerned, this is one of the
greatest Technic sets ever produced. The model is brilliantly designed, and it’s got four
motors, with everything you need to remote control them, along with treads, linear actuators,
and lots of other useful parts. Once I’d had my fun with the excavator, I
disassembled it and used its parts to completely rebuild my imperial walker. At this point,
the only thing remaining from Lego’s original instructions was the design of the legs. Long
robot legs are really hard to design, so I left them alone.
Now that I had four motors to work with, I could get rid of the ratchet. Now my motors
could have dedicated functions. One for walking, one for shooting, and a third motor I wanted
to use for steering. Of course, steering a vehicle with wheels
is much easier than steering a vehicle with legs.
I had no idea of how to do it, I watched Star wars again just to see how those robots moved
around. [Effects DOP — Dennis Muren, 1993]
Turns out, these are not robots. They were animated with stop-motion. Here’s one of the
animators talking about how they did it. So anyway, the movie didn’t have anything
useful to show me about how to make my robot turn.
Then I remembered a type of steering I had read about in a book — called articulated
steering. With articulated steering, the entire vehicle is split in half, and it rotates around
that point. This allows for wheels to remain fixed onto the chassis, which is important
for certain kinds of vehicles. But would it work with legs instead of wheels? I had to
build it to find out. As it would happen — yes it does!
I used a turntable to split my robot in half. Unfortunately, this would also split the main
driveshaft in half. The driveshaft has to extend across the entire robot, because, in
this case, all four legs have to be perfectly synchronized for the robot to walk properly.
The solution was a carefully placed universal joint, which allows power to be transferred
at any angle I used another worm gear for the articulated
steering. Again, because a worm gear cannot be forced to move, the robot remains rigid,
and only moves when I want it to. This steering system works really well! The
legs do slip a little bit while the robot is turning, but it’s not a big deal as long
as it stays on a solid, flat surface. This thing was not built for rugged terrain.
[Robot breaking] So now my robot had walking, steering, and
shooting. That’s three different functions using three motors, but I had four motors
available. What else could I add? A friend suggested that the robot’s head should be
able to pivot up and down. I realized that this would greatly improve the accuracy of
the rubber band gun. Perfect. I used a linear actuator to make it work.
The basic idea here is that you’ve got two worm gears meshed together. Because the pieces
can move freely past each other, rotational motion is converted into linear motion. This
model illustrates the same concept, using a rack gear instead. And with that, my robot was finally complete.
That’s the whole thing. If you’d like to build or take a closer look
at this robot, you can download the Lego digital designer file, which I’ve linked to below.
You don’t have to be an engineer to make something like this. I just took a lot of ideas from
lots of different sources and put them together. When I started building with Technic, I didn’t
know anything useful about mechanical engineering. I learned everything I know by messing around
with Lego, reading books, googling things, and watching YouTube videos.
And if you’ve been paying attention to my YouTube video, you’ve now learned a little
bit about ratchets, gear trains, backlash, torque, worm gears, articulated steering,
universal joints, and linear actuators. All of these concepts are much bigger than
Lego. We’re surrounded by mechanical things all the time. It’s undoubtedly useful to know
even a little bit about the functionality of your bicycle, or car, or whatever you happen
to drive. A lot of concepts are easier to grasp when
you’re able to PLAY with them. And Lego is a great way to learn about this stuff, because,
if you can get your hands around it, you can get your mind around it. If you’re interested in learning more about
engineering with Lego, I highly recommend this book, which I’ve linked to below. Or
any book, really. Go to the library! I hope you enjoyed this premiere episode of
Self Taught — there are plenty more videos in the works, so if you’d like to see more,
hit the Subscribe button. Thanks for watching, and stay curious.