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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.