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There is a functional separation between the lower and the upper carriages of stripping shovels. Nevertheless, the elevator connects them. Of course I started with the lower carriage as base for the turntable that will support the rest of the machine. I will apply this separation to this text as well. I will discuss the construction of the lower carriage in Part 2, while the upper section will follow in Part 3.
After I knew the size of the turntable, I could set the main frame dimensions of the lower carriage - a square of 50 by 50 studs. Each edge features a cylindrical shape that would be a hydraulic ram in reality. These four rams each attach to a pair of crawlers.
By regulating the pressure in the hydraulic rams, it is possible to keep a stripping shovel level. This is usually done automatically. Of course, it is not possible to model this feature with LEGO, not even with pneumatic cylinders due to the heavy weight of the finished model. A pneumatic cylinder can only lift about one and a half kilogram. Instead I used the rims of 20 x 30 wheels to simulate the piston.
I encountered the first problem when I started with the crawlers. It was not the number of track links available, I fortunately had enough to build eight tracks with 78 links each. A 1 x 6 plate attaches to every second link so that the track is wider, and the model looks like there are only 39 links on each set of crawlers. This is about equal to the number of links on the real Mountaineer.
The problem was that I needed a lot of sloped bricks to realize the special shape of the track frames. These shapes have more positive slopes than negative ones. Because I have more negative sloped bricks, I decided to solve the problem by building the track frames in a special SNOT (studs not on top) technique - upside down!
So, I managed to build all eight frames, each with a length of 26 studs and a height of 7 1/3 bricks. The width is five studs so that the track is half a stud wider on both sides.
There are five track rollers on each track frame. They are built using two rims (from the 17 x 24 wheels) side by side that grab into the groove of the track links. The track further runs over two large pulleys and two 40-tooth gears, one of which is driven.
A steering arm (that attaches to the hydraulic ram) supports two crawlers in such a manner that they can rotate independently from each other. They can rotate about an axis that lies in a left to right direction (sideways) with respect to the lower carriage.
Together, these two crawlers can also rotate about an axis that lies in front to back direction (in-line with the lower carriage). This is needed to negotiate uneven terrain. The front and rear pairs can be steered by means of gear racks that are driven by one old 9V motor for each pair. The racks attach to the steering arms.
Each crawler pair is driven by an old style 9V motor that attaches to the lower carriage. This means that the motive power first has to be brought onto the track frames and must work when the crawlers steer. The motors each drive a worm gear that drives a 40-tooth gear connected to an extendable axle. This is achieved by Technic axles that are fixed in the holes of a wedge belt wheel on the driving side and that can glide in a second wedge belt wheel on the driven side.
These extendable axles enter the inner track frames of each crawler pair and continue through the axis of rotation to the outer crawlers. Within the track frames the momentum is transferred to the tracks by gears and chain links.
To reduce the forces on the driving axle that passes through the crawlers’ axis of rotation, old turntables with a diameter of four studs are used. The driving axles can pass through the smooth center hole of the turntables. Two turntables connect to each other and are suspended by the steering arm so that rotation about an axis in front to back direction is possible. This assembly can be seen on the first picture on the crawlers page.
The next thing was to implement the center ring of the turntable into the lower carriage. Before doing this, I installed the electrical cables because some of them would pass through the turntable (to power functions in the upper carriage).
There are eight LEGO cables each with a length of three meters (available
through LEGO Dacta suppliers) entering the main frame. Three of them will supply the power for the drive motors and the two independent steering
motors. The other five will power the swing, hoist and crowd drives in the upper carriage as well as the elevator and the bucket door mechanism.
I use two center rings for the turntable, each made of four quarter circle pieces. They are mounted above each other at a distance of six studs. On top of the upper one, and below the lower one, there are two rings made of plates. They are connected by four Technic axles that carry rollers to guide the upper carriage on its rotational movement.
Additionally, the two plate rings are connected by four rails for the elevator cabin. Now that is a perfect bearing!
Beside the elevator rails are the five cables that pass the turntable
assembly. The elevator rails continue downwards and leave the frame of the lower carriage so that the cabin can be boarded from the ground man's platform that hangs below the box-shaped frame and between the front and rear crawler assemblies.
In the other direction, the elevator rails continue to the machinery deck in the upper carriage, and from there, up to the gantry. The whole elevator assembly is fixed to the upper structure and therefore revolves with it. This means that when boarding the elevator on the ground man's platform, you have to watch out because the rails, and accordingly the cabin, can start to revolve.
Before I could finish the main frame I had to implement beams that eventually would support the walkways going around the perimeter of the lower carriage. They can be accessed by stairways from the ground man's platform, and feature stairways themselves that lead to the walkways on the upper carriage.
This way the crew can board and leave the machinery deck in the case the
elevator is not working. Also, on part of the lower carriage are two cable drums on the front and back sides. On the real Mountaineer, they carry the electrical cables that feed the machine with power. On my model, the cables for the eight electric functions run once around one of the cable drums before they enter the lower structure.
Before I could build a ring of tiles (that would eventually carry the roller ring) I had to attach the gear ring for the turntable. This roller ring will later support the weight of the upper structure.
Unfortunately, the pre-made gear ring that you can see on the Heavy Duty Turntables #2 page didn't fit. It was made of 72 chain links so that the nine tooth driving gears would engage from the outer side. But the inner diameter of the gear ring was too small because the center assembly became larger as I planned for reinforcements.
I had to find a solution for a gear ring that would fit between the center assembly and the roller ring, and that had enough space for the driving gears. The solution was to build a slightly bigger gear ring, now with 80 chain links, that the driving gears could engage from the inner side.
So, I just inverted the principle. This showed an additional advantage. With 80 crawler links you have a better gear ratio between the driving gears and the gear ring, thus reducing the momentum on the driving gears.
I used four points to attach the gear ring to the lower carriage, thinking this was strong enough. When the main frame of the upper structure was already finished, I tested the swing drives and broke the gear ring!
So, I had to disassemble most of the upper frame again to fix the broken ring. This took me several hours, but when done, the gear ring was attached at eight points. I had no more problems with the swing drive in the future.
Except for some smaller details, the lower carriage was now finished. These details included flood lights and sort of a protective grill. The grill is attached to the lower structure between the front and rear crawlers on the side of the spoil pile. This protective grille was made of wooden poles that protected the ground man's platform from rocks rolling down the spoil pile.
As anticipated, the weight of the lower carriage was quite large and the finished model would be three to four times heavier. So I decided to support the crawler assemblies because they had already bent a little.
I achieved this by building four supports, each featuring a roller. I placed them between the two track frames of a crawler pair in a way that they were in line with the hydraulic rams. Steering was still possible because the additional roller was right on the axis of revolution.
Of course, rotation in both directions was strongly limited by this new construction. But I was never thinking of using the model on uneven terrain, such as outside of my room where it was built. So when thinking about it, I must say that it would have been a better idea to go without rotation of the crawler pairs, but instead, build them stronger so that they could better handle the weight and therefore needed no additional support.
With part three I will move on to the construction of the upper carriage and its components.
Move on to the third part of the story
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