MercedesBenz / NAW SK 3550 8×4/4 with Modular Platform Trailer

4 Jan 2015 | Author: | No comments yet »
Mercedes-Benz SK

Mercedes-Benz / NAW SK 3550 8×4/4 with Modular Platform Trailer



Rear axles driven by 9V motor

Front axles steerable by 9V micromotor

Cab tiltable to reveal engine

Openable doors and sun roof

Detachable ballast platform with fifth wheel underneath


Platform modules with steerable wheels

Drawbar module to access steering motion

Bumper module with flashlight to access steering motion

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Although Mercedes-Benz is a German company, the original of the truck pictured here has partially been manufactured in Switzerland. Based on standard components from Mercedes-Benz, the heavy haulage tractor units used to be customized for their special duties at NAW. Located in the eastern part of Switzerland the company NAW (Nutzfahrzeuge Arbon und Wetzikon AG) was a well known name for heavy duty trucks.

The model designation SK 3550 8×4/4 reads as follows: SK stands for ‘Schwere Klasse’ meaning ‘heavy class’ and is the successor product line of the NG ‘New Generation’ Mercedes-Benz top of the line trucks. 35 stands for 35 tons maximum gross vehicle weight while 50 stands for the turbocharged Diesel engine OM 442 LA with 503 horsepower. 8×4/4 finally means that of the eight wheels four are driven while another four are steered. The maximum weight to be pulled is 250 tons.

Mercedes-Benz SK

The model is in scale 1 / 18.75 which at first glance seems to be a strange number. But scale was dictated by another creation, the Liebherr LTR 1800 crawler crane. And there, two studs on the model equal 30 centimeters in reality which resulted in an even number of studs for the three meter wide upper structure. The reason for the same scale on both creations is the fact that I wanted to build a heavy haulage truck being able to transport components of the crane. Another reason was to give an impression of the dimensions of the LTR 1800 in reality.


The Mercedes-Benz SK trucks were available with three different sized cabs. My model features the largest one which offers enough space for a comfortable bed behind the drivers place. Furthermore one could also chose wheter there should be side windows on the rear half of the cab or not. I opted for the latter one. Nevertheless the places where the windows would have been are clearly visible as there has been manufactured only one pair of side panels with window openings which could be closed by additional blanks. Therefore rubber was used to seal these panels which resulted in black frames on the side walls of the cab which can be seen on my Mercedes as well.

The cab features openable doors and sun roof as well as a detailed interior. The latter one includes a bed with pillow and blanket and many smaller details like cup holders, sun visors and a reading lamp. Details on the outside of the cab include rear view mirrors, flashlights, horns, a Mercedes star consisting of a printed round tile and directional lights on the fenders. Furthermore there are self made stickers with the model designation number.

The cab can be tilted to reveal the engine, a turbocharged V-10. Although there would have been plenty of room under the big cab, the engine mockup itself is squeezed in a small space between the two frame rails. The reason for that is that there is an old style 9V motor linked with a three stage reduction gear with a total ratio of 1:27 to drive the tandem rear axle assembly. There are two worm gears on the propellor shaft that directly drive the 24 tooth gears on the differential cages. This is a space saving construction and the biggest torque is produced in the final stage of the gear train.

The two front axles feature rack and pinion steering. They are linked with a common shaft with two different sizes of pinions – 14 teeth on the front axle and eight on the second. A 9V micromotor placed between the first and second axle and between the two frame rails drives the steering shaft with a one stage belt drive. Steering motion is transfered to the steering wheel in the cab which revolves when the wheels turn. While the cab is tilted, connection between the steering column and the common shaft is interrupted.

The Mercedes can be used in two different configurations to pull heavy loads. At the rear end of the frame in a lowered position there is a towing attachment. Furthermore there is a fifth wheel on top of the frame which can be placed in different positions along the frame rails to configure the truck for different trailer settings. When pulling a trailer connected to the towing attachment ballast is needed to make use of the mechanical advantage of the two driven rear axles. Therefore a ballast platform can be connected to the frame. On my model it is equipped with a box containing some tin and representing a reinforced concrete block. The weight of 1.5 kg is supported by the frame at three points – two on the front end of the platform and one at the fifth wheel. The ballast platform features openable side walls and a towing bar used when pulling or pushing trailers without a drawbar or when coupling more than one truck to move a bigger payload than one truck can bear alone.

Heavy tow tractors usually are quite short in length compared to standard trucks and feature up to five axles. Therefore there is often no room on the frame for all the special equipment that can be found on heavy duty trucks. These components are then put together on a rack which is placed behind the cab. My model features such a rack as well. First of all there is a large fuel tank at the center place. A standard tank would not be sufficient for towing applications as the 500 horsepower V-10 is quite thirsty. On the left side there is an additional oil cooling unit. On the right side are the exhaust pipes covered in the same way as the cooler on the left. Finally there are several air tanks for the breaking circuit placed on top of the fuel tank. A small platform behind the rack gives access to the different components and the hoses that connect to the trailer. On the model these are represented by the two wires connecting to the drive and steering motor respectively.

Finally the truck is equipped with a heavy duty front bumper complete with brushguard, register coupling and additional headlights. To be able to tilt the cab the brushguard can be tilted away as well. Further details include an air filter unit on the right side of the frame between the first and second axle and a fire extinguisher at the corresponding place on the left side of the truck. Axles two to four feature single fenders. Stickers with a candy cane pattern for the front bumper, license plates and the Mercedes-Benz logo complete the model.

Mercedes-Benz SK
Mercedes-Benz SK
Mercedes-Benz SK
Mercedes-Benz SK

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