Model of a Scania R500 truck modified as a racing version. Features full suspension, powerful propulsion system with two independently powered RC motors, lights, custom stickers, cabin with full interior and opened doors.

Datasheet:

Completion date: 05/07/2010
Power: electric (Power Functions)
Dimensions: length 48 studs / width 18 studs (not including the side mirrors) / height 27 studs
Weight: 1.86 kg
Suspension: front – independent / rear – dragged axle
Propulsion: 2 x RC buggy motors powered from separate batteries through separate IR receivers, geared down 1.66:1
Top speed: 7.92 kmph
Motors: 2 x RC, 1 x PF Medium

I’m really fond of modern Scania trucks. I have built a model of a Scania dumper truck in 2009, which – while being technically simple – has gathered a significant acclaim because of the quality of its aesthetics and because of the number of details incorporated. I was not fully happy with it, however, because I found the cabin’s look inaccurate and simplified. This was the primary reason why I started to toy with an idea of building a much more accurate Scania model in a racing truck version. Right from the very beginning I wanted it to be red with some chrome and metallic silver elements, which is why I was not convinced of realizing this model, as it had to be expensive to build. Over the time, however, I have gathered a number of chrome and metallic silver elements, and I have determined that it would take less red parts that I initially thought, as Scanias usually have their lower part of the cabin plain black.

Building this model became eventually achievable when I designed the complete exterior of its cabin using the MLCad software and when I bought four metallic silver wheels (to go along with the two I already had). With MLCad model serving as a very accurate shipping list, it became only a matter of time before the red racing Scania would be built.

I have built a number of racing trucks before, which provided a significant building experience. Based on it, I didn’t want to focus just on the aesthetic side of the model – I wanted it to perform well too. The key to surpass the performance of any of my earlier racing truck was the use of RC buggy motors for propulsion, as they offer somewhat more mechanical power than PF XL motors do, and they are also more suitable for fast vehicles, with less gearing or no gearing whatsoever needed. To use two RC motors at the same time while keeping the model’s weight reasonable I had to use the 8878 battery as a power supply. Since it was downright impossible to power two RC motors to a single battery because of their extremely high power consumption, I had to no other choice but to get a second 8878 battery. Thus, the model needed some serious investments before I even started to build it.

The model’s chassis was initially built with both RC motors using no gearing whatsoever – both motors were simply connected directly to the rear axle. Thanks to their convenient shape, it was possible to use them as the main bearing structure for the whole rear suspension which dramatically increased the internal space available inside the chassis. Thanks to it, chassis housed not only two 8878 batteries and two IR receivers, but also PF Medium motor for the steering, with all these elements located between the front and rear axle.  The use of two IR receivers was necessary – since the drive motors were independently powered, they couldn’t be connected electrically and the only connection between them was rigid rear axle. With the initial rear axle set-up it was possible to use a differential between the motors but I dropped this idea for two reasons: firstly, a rigid axle was more efficient (no elements prone to slipping) and much less prone to a mechanical failure, and secondly the rear wheels had only limited traction while turning, since majority of the model’s weight was located above the front axle.

The independent front suspension was based strictly on my previous experiences with the models of racing trucks and used a blend of suspension components from the Lego sets 8448 and 8297. To handle the weight of the cabin, the front suspension was made very stiff, with two hardest shock absorbers set almost vertically above each front wheel. I have also used thin wedge belt wheels between the actual wheels and the chassis to prevent the expensive metallic silver wheels from rubbing away against the chassis – as it already occurred earlier, with slower and lighter racing truck models. The steering system had to be adjusted to the speed and the weight of the model, which is why it used a relatively insignificant gear reduction and no safety clutch whatsoever.

As for the aesthetic side, I came to think that the main disadvantage of my Scania dumper model was the fact that its distinctive front grill was completely flat, with air intakes simply marked with bricks of a different colour. Therefore I have put a lot of effort into inventing a system of recessed air intakes, which was eventually achieved with the use of 2×2 tiles. With plenty of internal space available in the cabin, this system could be used with a relative ease, providing an excellent aesthetic effect, as anticipated. Other than that, the cabin houses not only its own interior, but also a PF switch which controls all the lights (the lights are coupled with the drive motors and go brighter as the truck speeds up, so the switch is used primarily to turn this feature off when not needed, and thus to save energy which is so highly demanded by the RC motors). With 10 PF LEDs installed in the cabin, the switch takes a lot of space to contain 10 PF plugs with their respective wires. I was able to fit it in efficiently by mounting it on its side, so that the plugs are kept horizontally below where passenger’s seat would be located normally.

An important thing to know is that the real racing trucks are usually subjected to very radical visual modifications which make them look pretty much unlike any stock vehicle. Being a huge fan of the original Scania design, I wanted to avoid this. Therefore my approach was to use a stock Scania R500 as the model’s point of reference, with a few typically racing elements added so as to minimize their impact on the model’s look. Eventually, it ended up with five such elements: the four extra headlights (which are not really used for racing, but I viewed it as an opportunity to experiment with the PF LEDs a bit), the racing air intake on top of the roof, the engine moved back from under the cabin, the large spoiler instead of a fifth wheel, and a custom rear bumper. Additionally, the cabin’s interior has been arranged in a ‘racing’ fashion, with a mock-up of two blue N2O bottles replacing the passenger’s seat and with a distinctive safety net in the driver’s window. The net itself is not a Lego element – I made it as a sticker, by printing a black square with a dark grey grid on it, carefully cutting it to net-like shape with a modelling scalpel, and then painting its other side black with a felt-tip pen (I could also print the black square on both sides of the same sheet, but since large portion of it was meant to be cut out, it felt like a waste of ink). Eventually, the paper net was fixed to the door with a thin stripes of a Scotch tape on its edges.

The other, more traditional stickers, have also been intended to reflect the racing ‘nature’ of the model, with the most obvious example being a note in front of the driver’s window that says “Tävlingsfordon”, which is Swedish for “Racing vehicle” (all stickers use Swedish as a nod to Scania’s country of origin). The sticker above the windshield says “Sagodjur”, which can be translated as “Griffon” (the animal used as Scania’s brand mark) and which was intended to look like driver’s nickname, while both front and rear registration plates feature a miniature Scania’s griffon head and a number 5AR13L, which is an obvious reference to my own nickname.

As the model was getting close to its final weight, the propulsion system started to show signs of weakness. To solve this, I have moved the rear axle back a little while keeping the motors intact, and  added a 1.66:1 gear reduction between the motors and the axle, with gear wheels doubled to handle the significant torque. It has greatly improved the overall performance of the model by making it faster and decreasing its accelerating and braking times, but it also made the chassis seem a bit longish and it made the rear suspension very soft. The manoeuvrability of the model, on the other hand, was not noticeably affected by this change. I have ran a number of tests with Lego speedometer mounted on the truck and the top speed it recorded was 7.92 kmph. This is more than any of my earlier racing trucks could achieve, but I feel like it could be surpassed by this very model. The model clearly has plenty of power in the drivetrain and appears to best build up its speed in long runs. It led me to believe that it could break 8 kmph given a long section of a perfectly smooth floor (unlike the floor I had to run tests on). Anyway, 7.92 kmph is a fairly good result, as it requires model’s wheels to rotate at over 600 RPM (that is 10 rotations per second) and – given the model’s 1:17 scale – corresponds with the speed of 135 mph in the real life.

The truck was highly acclaimed for its aesthetics and performance, both emphasized by the video which took me 4 hours straight to produce. It was my second construction to use a slow motion footage (shot with Casio Exilim FS-10), and my first construction to be accompanied by 1200×800 px photos rather than usual 800×600 px, as I really liked the look of the model and the results of its photo-session.

The model will be kept intact at least until a public event that takes place on July 10th, giving my fellow LUGPol members the chance to see, and perhaps even to drive it.

Photos:

Work in progress photos:

Video:

Click here to view the embedded video.

Media reference:

Legocn.net (Chinese only), Mancave (Dutch only), Town Truck Brick! (Spanish only)

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Model of a dump truck based on Scania CB8x4. Features full suspension, two axles steered with a different steering lock, elevated cargo case, full interior, lights and custom stickers.

Datasheet:

Completion date: 23/11/2009
Power: electric (Power Functions)
Dimensions:  length 68 studs / width 20 studs / height 29 studs
Weight: 3.35 kg
Suspension:  independent on axles 1&2, double pendular on axles 3&4
Motors: 1×71427, 1x PF Medium, 2x PF XL

My first model after a short break. It was supposed to be relatively simple technically, but elaborated aesthetically. Basically, I wanted to built an improved version of my 8-wheeled dump truck created 2 years earlier, and my very good source of inspiration was Scania tractor unit by Pedro Agnelo. It was Pedro’s great work that made me want to built an entirely black truck with some dark gray elements. The trick that makes cabin’s door open easily (double opposing hinges) is also takes from Pedro’s model.

The first and second axle have been fitted with an independent suspension based on the 8297 set’s components. Both axles have been suspended on shock absorbers, with the axle #1 using doubled shock absorbers to support cabin’s weight. This solution – a very hard suspension of the front axle – made the entire model very stable; almost unbelievably stable for a model driven by pendular axles. The steering system was controlled by a 71427 motor located in front of the axle #1 (a place where a PF Medium motor was too long to fit in), with the usual 9:1 gear reduction and a safety clutch. Both front axles are steered by a single common steering shaft, which was a very good solution for two reasons. Firstly, it kept the steering systems of both axles synchronized at all times, and secondly if any of the steered wheels became stuck or reached the maximum steering lock, the whole steering system of both axles stopped without losing its synchronicity. The ratio of the steering lock of the two axles was 2:1, and it was achieved by using gear wheels of different size for steering. Two IR receivers have been hidden between the mudguards of the two front axles.

Axles #3 and #4 have been suspended on a special pendular module with a transverse and longitudinal swivel points.  Both axles have been pendular with a longitudinal swivel point, so that one wheel could rise above the other. Both axles have been attached to a central structure with a transverse swivel point, so that one axle could rise above the other. It was a compact and strong suspension system with a very good off-road performance, but it was unsprung which resulted in its poor stability as well as in the tendency for the wheels to slip under the torque (the suspension would rise one wheel off the ground if a sufficiently high torque was applied). Moreover, the truck suffered from a disadvantageous weight distribution: axles #1 and #2, which were not driven, handled most of its weight. Therefore the truck performed better while driving backwards than forwards, and some extra load above the rear axles was needed to improve its traction.

The drivetrain was unusual and realistic at the same time. There was a driveshaft connecting axle #3 with the motors in the chassis, but since the height of the axle  wasn’t constant due to the suspension type, it needed an extendable section. It was located between two universal joints and consisted of a number of wedge belt wheels connected by short axles. This is an old solution, found e.g. in the linear gearboxes, but it worked perfectly well here, even though it was handling a serious amount of torque.

It should be mentioned that the gear reduction in the drivetrain was really minimal, and the truck’s speed dependend heavily on the raw power of two PF XL motors. This approach has paid off – the truck was faster that my previous Kenworth Mammoet driven by two PF XLs too, despite being much heavier. However, when some demanding obstacles have been met, the motors would become so strained that they made the Lego battery go off for a moment.

The truck’s cabin housed the drive motor, full sets of lights including rooflights, and the battery along with a full interior that included a detailed cockpit, a steering wheel, seats, pedals, and even flags on the rear wall. The doors could be easily opened thanks to the double opposing hinges system invented by Pedro Agnelo. I have initially thought about using the cabin to house an automated trafficators system, but since I didn’t have a sufficient amount of lights, so I’ve decided to use it for an interior instead. The cabin couldn’t be lifted and its bonnet was fixed, not openable. The ‘Paul’ badge visible in front part of the cabin’s interior is a nod to the recent Lego 8258 set, which is a 4-axle truck too, and which has stickers with driver’s name intended to go in the very same place (the interesting thing is that set contains a number of badges with various names to pick from, including Paul as well as Wabra – the set designer’s surname). One thing I wasn’t happy about was the use of stickers to imitate the air intakes on the sides of the front Scania logo. I’ve decided to use stickers because I couldn’t find any brick of appropriate shape, but the result was way below my expectations.

The cargo case was elevated by two linear actuators driven by a single PF Medium motor located above the second axle. A 3:1 gear reduction was used, but no clutch, since the amount of torque required to lift the case up would make any clutch slip. Please note the very robust way in which the actuators have been attached to the chassis – it was intended to limit the torque losses caused by the actuators bending under the load. Moreover, they needed little space inside the chassis – basically just some openings in the mudguards of axle #3.

The cargo case was large, robust and heavy. I wanted its sides to be perfectly studless and to look interesting, which was achieved with a modular system of tiles. The system itself was just two layers of tiles thick, but to obtain proper stiffness the sides of the case have been made up to five layers thick. It could be built practically up to any length or height too. I believe the look of the case sides was worth the final, surprisingly high weight of the model.

I was pleased with the model despite its technical simplicity. While it was not large enough to house e.g. a gearbox, it was still quite functional, it looked very well, and its mechanical elements have been nearly invisible. Despite some rear suspension problems the truck was relatively fast and handled very well. I believe the key feature of this model was the realistic look, which is more than I need to justify the mediocre number of its technical features.

Photos:

Video:

Click here to view the embedded video.

Media reference:

Bricks’n'Gears, Fascinating LEGO Model Of The Day, kockak.hu

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