Model of a Caterpillar tracked dozer. Features remotely controlled drive, steering, blade and ripper.

Datasheet:

Completion date: 09/05/2009
Power: electric (Power Functions)
Dimensions:  length 50 studs / width 26 studs / height 25 studs
Weight: 1.56 kg
Suspension:  none
Motors: 5 x PF Medium

I was interested in the unusual Caterpillar tracked dozers for some time, but I couldn’t build such a dozer earlier because the triangular shape of tracks required 6 sprocket wheels and I only had 4. Having finally acquired the missing 2 wheels, I proceeded with the construction right away.

Nowadays, when one builds a yellow tracked dozer it will be obviously compared to the famous Lego 8275 set.  Since it was clear from the beginning that my model would be significantly smaller, it was my goal to include in it more functions than the 8275 had, and thus surpass it in terms of functionality.

The basic difficulty is that the Caterpillar tracked dozers are unusually narrow – the width of the hull is only slightly greater that the width of a single track. When I calculated dimensions of model with the new tracks system which are 5 studs wide, it turned out that the hull will be just 6 studs wide.  It happened to be just the minimal possible size to house a battery box and several motors inside. Since with the coming of the new 8879 speed control enabled handset the subtractors have become obsolete, the model was supposed to be driven by two identical motors located side-to-side. With the hull just 6 studs wide the only possible choice were the PF Medium motors, and they turned out to be a fortunate one. However, to make them fit in the hull it was necessary to make openings in its sides, so that the motors actually traverse through it.

Another difficulty is the layout of the tracks: they have contact with the ground at a relatively long area, yet they are just 6 studs apart from each other. It makes the model’s weight distribution crucial for its handling. Hence the entire model is built in a perfectly symmetrical way, both externally and internally, with the only exception of bevel gears at the linear actuators and the on/off switch. Placement of the battery box low between the front part of the tracks was a second factor that contributed to the proper weight distribution.

With the drive motors successfully located in the hull it was relatively easy to make the rest of the motors fit in.  Several tricks were needed to handle the problem of model’s limited size; for instance the axle that controls elevation of the ripper is driven not by gears but by a system of very short levers. The gears would simply take too much space, and since the axle’s rotation is very limited, the levers can do the job. Moreover, the fifth motor that changes the ripper’s tilt is controlled by a switch inside the cabin, because a switch is much smaller than another IR receiver.

The ripper’s geometry makes it maintain its tilt as the elevation changes. The ripper is strong enough to lift the back of the dozer off the ground, but not strong enough to endure when the dozer drives in such position. The blade, on the other hand, is robust enough to lift the front of the dozer and endure any kind of manoeuvres. I tried to make the dozer lift itself entirely on the blade and the ripper, but in this case the ripper couldn’t take the load.

Other than that, the model’s performance was satisfactory and it was quite a pleasure to drive it, especially with the new handset (the difference in driving with the old and the new handset is presented in the video below). I was happy with its aesthetic side too, although I was aware of several compromises between model’s look and functionality. For instance the driver’s cabin was made longer by 1 stud to house the IR receivers, and it resulted in the changed shape of the dozer’s rear side. Additionally, the bonnet protrudes forward a little more than it should, because of the battery box located right behind it. On the other hand the model has no suspension whatsoever, since it was the only way to fit it with the proper number of properly sized bogies. And I have used metallic silver cheese slopes as the tips of ripper’s blades because it looked more realistic than any usual colour. A minimal amount of custom stickers was used to make the model appear more realistic. I chose not to use the lights, partially because of the limited internal space available and partially to avoid the wires hanging from the headlights, as was the case of my 854G wheeled dozer model.

The model was well welcomed as a good example of my building abilities. It was not better than was expected of me, but it did not disappoint anybody either. Personally, I have considered it to be a relaxing project noteworthy only for its compactness and the first example of the use of the 8879 handset.

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Video:

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Model of a Caterpillar articulated wheeled dozer. Features 4×4 drive, suspension, remote steering, remotely raised and tilted blade, lights and custom stickers.

Datasheet:

Completion date: 17/12/2008
Power: electric (Power Functions)
Dimensions:  length 57 studs / width 30 studs / height 22 studs
Weight:  1.73 kg
Suspension:  front – none / rear – pendular with shock absorbers
Motors: 4 x PF Medium

Another articulated Caterpillar vehicle. Partially similar to my earlier 990H front loader, but slightly larger and with different functionality. I wanted to use linear actuators instead of pneumatics, and that required more internal space that available inside a front loader. Therefore I decided to build a wheeled dozer, which offers more space inside the front hull’s part.

The drivetrain was simplier and more compact thanks to the use of new, 3-studs wide differentials. Only two motors were needed in the rear part of the hull, which could be therefore less massive and more realistic in size. The battery box was located in the same place, that is low behind the rear axle. It caused some problems with the weight distribution in case of the front loader, which did not have any heavy parts inside its front part. Here, another two motors were located above the front axle, so the weight distribution was much better.

The steering system was changed too. Earlier it was based on the horizontal 36-teeth gear braced in liftarms traversing the vehicle’s frame. This time, I wanted to try to save some space, and used a 12-teeth gear instead, with much weaker, yet more compact bracing. I was not satisified with the final result – the steering system worked, and supported model’s weight even when carried in hands, but the precision of steering was poor, and the central joint lacked stiffness.

As for the blade, I have attentively studied the construction and functionality of its real counterpart and decided to make it simplier and less functional. In the real 854G, the blade has the ability to turn to sides to a limited angle. Only a single hydraulic cylinder is needed to control this mechanism, but it meant that blade’s every point of attachment had to have two degrees of freedom. Thus the entire structure supporting the blade would become much more complex, and probably less rigid. Eventually, the blade was controlled by four actuators and turned out to be strong enough to lift the dozer’s front axle off the ground. The dozer performed reasonably well, except for the forementioned poor precision of steering. It could use a PF XL motor for drive to be able to push heavier loads, yet still the Medium motor provided a satisfactory torque.

The model was received much better than I expected. For me, it was merely a development of my earlier Caterpillar models, built partially for relaxation after the arduous work on the Colonial Marines APC model. Still, a considerable number of viewers expressed their accolade for the dozer.

Photos:

Video:

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Media reference:

Focus.pl, TechnicBRICKs

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My first tracked vehicle, features a subtractor in the drivetrain, illuminated engine block and a pendular suspension.

Datasheet:

Completion date: 06/07/2007
Power: electric (wire-controlled) / pneumatic (fed from internal electric compressor)
Dimensions: length 34 studs (plus blade) / width 22 studs / height 16 studs
Weight:  0.89 kg
Suspension: pendular bogies
Motors: 2 x 71427, 1 x 47154
Pneumatics: 1 circuit with electric compressor

My first tracked vehicle ever, not too big, but packed with features. The most important one is a drivetrain that consists of a subtractor. Subtractor basically connects two treads to two motors so that one motor drives them in the same direction, and the other one drives them in opposite directions. As result, it is possible to drive with one motos and steer with the other, just like in a car. That solution has several advantages, including ability to turn in an arch (while both motors are running), and easier steering, and it makes the vehicle able to drive ahead in a perfectly straight line, which is often impossible when treads are drive by two separate motors. There is a more exhaustive explanation of the subtractor mechanism in the Ideas category, and here is just a basic diagram:

The use of the subtractor makes it possible to use a V8 piston engine driven by the drive engine (kinda difficult if you have two motors, each driving one tread). The engine block, entirely in the trans-clear color, is illuminated from below by a LED brick from Exo-Force sets.

Other features include a detachable battery box, and an internal electric compressor with a manual valve, raising and lowering the blade. The dozer has a very simple suspension, that worked well against any obstacle that relatively weak 71427 motor was able to put the dozer through.

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