Hi everyone, my name is Damien and this video is about how I turned Lego's Bucket Wheel Excavator
into this: a fully capable drilling, crawling, and dirt extracting Tunnel Boring Machine
Now i'm going to talk about all the features of the Tunnel Boring Machine throughout this video,
but first I want to start with a little inspiration. So the year was 2017 and I
had finished building the bucket wheel excavator the year prior, and the Bucket Wheel Excavator
is one of these huge sets from Lego - lots of pieces, about 3,900. Huge instruction booklet
and I said to myself it'd be great to rebuild it into something new.
Now Lego does provide a second model you can build with the Bucket Wheel Excavator, and that model
was not as not as exciting as I had hoped it to be and more importantly it didn't use
the cool new piece that Lego introduced for the Bucket Wheel Excavator. And that's these guys:
these ring racks or like big ring gears. The way these work is you assemble four of them
together and they form a circle, and you can put a small gear on the inside to drive it around,
and this is how the bucket wheel of the Bucket Wheel Excavator works. The buckets are just
attached to the outside and this guy is just driven round and round extracting dirt. So
I wanted to use this as a central part of my new model and after a few days of thinking,
the Tunnel Boring Machine idea was formed: The Third Model of the Bucket Wheel Excavator.
Tunnel Boring Machines, or TBMs for short, are impressive machines that we've been using for
over a century to dig tunnels underground where it would otherwise be impossible we've been using
them to dig tunnels for things like subways and trains, and even sewers. Modern TBMs have
a bunch of different subsystems. But they can be broken down into three main ones: the first
one is the cutter head. It's at the front of the machine that's what's cutting through the earth
creating that tunnel. Right behind the cutter head is the second one: the thrust system. The
thrust system is used to push the cutter head against the earth against the rock and steer it
in the correct direction. Finally you have all the support systems that trail behind.
I'm going to show you all these different subsystems and how I
implemented them in my Lego TBM.
First, to the business end of machine: the cutter head. The cutter head is where I started this
model and it's where I spent the most time. It needed to be perfect it needed to look the
part and it needed to be functional. So I put four buckets from the Bucket Wheel Excavator within the
ring itself and those buckets, like in the bucket wheel excavator, the Lego dirt is collected and
it's fed into the machine and extracted out the end. And for this design the way it works is as
the buckets go across, or move past the 12 o'clock position at the top, the dirt within the buckets
is dumped onto a small ramp which leads down to the conveyor belt within the machine itself.
And the conveyor belt then brings it all the way to the end,
and into the dump truck.
Next is the thrust system. For this I used the two linear actuators that
came with the Bucket Wheel Excavator and I placed one on each side of the cutter head.
As the linear actuators extend, the cutter head is pushed forward into the dirt. Once they're
fully extended, then I reverse the direction on the linear actuators and they start retracting.
But at the same time I'm also engaging the wheels of the main body and the body
inches forward at the same rate the linear actuators retract. When this is happening
the cutter head is stationary and the whole machine is moving forward like an inchworm.
The final piece of my Lego TBM is the support systems. The support systems consist: of a main
motor which drives everything, just like in the Bucket Wheel Excavator, a gearbox which allows you
to control the cutter head, the conveyor belt, and the linear actuators which inch the machine along,
and the conveyor belt. The conveyor belt is actually attached to the cutter head itself.
So when inching forward, the conveyor belt and cutter head move as one,
and then the body moves around it. The main purpose of the conveyor belt
is to extract the dirt from the cutter head all the way into the dump truck. The conveyor belt
also powers a small, additional conveyor belt on the dump truck itself.
Speaking of which, the dump truck is something I wasn't really excited about building. when I
had finished building the TBM. So I did the Tunnel Boring Machine first, and at the end of it I said:
you know what, it really needs a dump truck just like the Bucket Wheel Excavator had,
but I didn't really want to build it. However, now that it's built I actually, I'm a huge fan of it.
I think it looks really cool: it has a low profile design,
it's got this little racing look to it with a cab low to the ground, which is
kind of appropriate for something that's meant to be small going into tunnels.
It has this conveyor belt at the back which connects with the TBM and the TBM drives it.
That little conveyor belt is used to draw the dirt up into the main bucket
of the dump truck. And this is another cool feature I think that made this build
satisfying: is how it dumps. It doesn't dump like a normal dump truck, it dumps sideways.
And it has this very satisfying lever to make it happen.
I'm going to end this video by showing you three cool techniques that I used to build this Lego TBM
using only the pieces that I had available to me from the Bucket Wheel Excavator.
First up is the drive for the drive wheels. Now in order to get the drive to work properly I needed
the body of the TBM to move forward at the same rate that the linear actuators were retracting,
so that the cutter head doesn't move anywhere while we inch forward. In order to do that,
I need the wheels to rotate really slowly. Now despite the Bucket Wheel Excavator having loads of
pieces, it actually doesn't have many small gears and large gears, you needed both of those to build
a large step down gearbox. So I had to be a bit creative and I ended up using two of the
turntables as big gears. With those two big gears out of the turntables, I was able to calculate a
ratio necessary so that the body moves at the same rate as the linear actuators, and I was able to do
this within two percent: which is pretty good. So that means whenever the linear actuators move
their full movement of 41 millimeters the body actually moves 41.8 millimeters: so pretty close.
The second design feature I want to highlight is how the cutter head is actually driven.
Now in Lego's original Bucket Wheel Excavator, there was a known problem, or comment, about how
smoothly the bucket wheel actually rotated. Being its main feature,
people were really, stuck on it. And it turns out it didn't rotate that smoothly. And that's because
of a small imperfection in these large ring gears, these large ring racks. When two pieces
connect there's a small imperfection and when the driving gear that's rolling around the inside,
rolled over the the interconnection, the Bucket Wheel Excavator would lurch a bit.
And this is something I wanted to fix with my TBM, because it really bothered me at the time.
So I started by putting two gears, because two must be better than one.
But I put the second gear exactly on the opposite side. And that didn't fix the problem because
as the ring rotated around, both gears would cross that imperfection at the same time. So
I kept throwing gears at the problem. So I added a third driving gear. This third driving gear was
30 degrees offset from the first two, and with this third gear the lurching problem was solved
and the cutter head of this TBM rotates very smoothly.
The final design feature of this TBM that I'd like to talk about is how I designed the
gearbox to transfer power between two things that are moving apart and back together again
linearly. As far as I know there's no other model that
does this. A lot of Lego models transfer power through an angular joint,
or through a turntable.
But I don't think I've come across any that transfer power linearly.
And the way I did that was by using a worm gear as part of the gearbox. As anyone knows who has used
a worm gear before, they slide really easily on axles. And ever since I was a kid using these worm
gears, I wanted to use this property somehow to my advantage. And this TBM does just that. The way it
works is that the main power from the motor is transferred through the gear, this main gearbox,
and into the worm gear. And this worm gear engages a small eight tooth gear on the cutter head. As
the linear actuators extend, this axle is pulled through the worm gear and transfers power to the
cutter head. This gear box is transferring power to drive the cutter head and driving the conveyor
belt underneath, because the conveyor belt in this model is attached to the cutter head itself.
Well that's it! I really hope you enjoyed this tour of my Lego Tunnel Boring Machine.
And remember, if you have the Bucket Wheel Excavator, you have all the pieces you
need to make this model. I used over 80% of the pieces from the Bucket Wheel Excavator
in this Lego TBM, so about 3,200. However, I haven't written a manual yet, and I wouldn't
hold your breath on that. It's taken me over four years to put together a video just talking about
the Lego TBM, it might take me a few years more to make a manual. Thanks for watching!