Metal Construction
|
Metal Construction |
|
Home |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Who has not heard of the "killer truck" from Steven Spielberg's first feature film,
"Duel"? After we had seen the film in the winter 2010/2011 again, and this time also recorded, the decision was made quickly to build a remote-controlled model of this truck from the elements of a metal building kit. The advantage was that over the years had accumulated a lot of worn material which would have to be painted before re-use anyway - so why not in the "colors" of the Duel Truck. While searching for pictures and information about this vehicle was soon apparent that the determination of the proportions and the characteristic details should be a lengthy undertaking. For the movie several trucks were prepared and used, which differ in many details. The data are to some extent contradictory, but the following information from the Internet seems assured: The original truck was a Peterbilt 281 from the year 1956 with a rebuilt engine recognizable by the horizontally lying and yellow colored air filter on the right side of the engine compartment. The 2 in the model number 281 means that the truck tractor had only one driven axle, and the second rear axle was merely a trailing axle. Spielberg had deliberately chosen this type, because the split front window and the round headlights looked similar to a face. Together with the optically thick wear and the rusty-dirty color finally the truck got its threatening appearance. This vehicle was destroyed at the end of the film during the fall into the gorge. Since the original truck was not in good condition, a Peterbilt 281 from 1960 was kept as a replacement vehicle. However this was not used in the film and therefore it is not visible. The original 74-minute television film from 1971 proved so successful that it was extended as a cinema release in 1974, about 15 minutes - and for this another truck was prepared. With a Peterbilt 351 from the year 1964 the laundromat scene, the railway crossing scene and the school bus scene was reshot. The 3 in the type designation indicates that both rear axles are driven. At a superficial view, the differences of the vehicles hardly can be noticed, but if one look closer, one can see these very well. Also this vehicle does not exist anymore.
The inspiration for the model was primarily the original truck, but some in the film bad or not recognizable details were taken from photographs of the still existing truck. To determine the proportions and the determination of characteristic details and color almost 150 pictures and plans have been analyzed, including photos of models as well as numerous pics extracted from the film of the original.
Duel Truck Tractor (Peterbilt 281) We started again with the construction of a ladder frame with all the carriers for the add-on parts - and already at this turned out that the existing worn-out material should not be roughly adequate. The missing material therefore was obtained from Metallus and repainted accordingly. In the procurement of materials was also found that the company Metallus now practically only provides Delrin gears - with the exception of crown wheels. Since the combination of brass crown wheel and Delrin pinion appeared problematic, the 90-degree angle drive was constructed entirely of brass. All spur gear reductions are made of Delrin - however, if these gears are suitable in the long run remains to be seen. The spring-loaded front axle has been designed in this way, that the steering servo could be attached directly to it and thus follows the movements of the axle. This reduces mechanical complexity and creates space for the rods and gears of the steering wheel drive. The steering trapezoid was adjusted so that the elongate steering lever cut between the rear axles. Due to the relatively large wheelbase, the steering trapezoid is only slightly marked.
The drive axle is a part of a spring-loaded rocker arm that can move with compression and rebound around a defined centre of rotation. In this pivot point also the gear of the 90°-angle drive for the force coupling is located. This has the advantage that the power transmission to the drive axle does not require any universal joints or a length compensation. In addition to the differential the rocker arm contains a total gear ratio of 15:1. The maximum torque thus is produced only directly on the differential, and the 90°-angle drive is only loaded with a relatively small torque. In terms of a longer shelf-life both the 90-degree angle drive and the power transfer onto the differential was carried out twice.
After installing the batteries and the remote control components, the chassis was already ready to go. All the remaining components were then placed mainly in modular construction and grown in succession.
As found on the internet also pictures of the interior, the cab of the model also inside could be designed.
Characteristic is the radiator, whose matt-silver color scheme is intended to represent a worn chrome plating. Although in the original 17 more or less bent lamellae are seen in the model but only 16 lamellae are housed. They consist of narrow strips, which at the ends are folded and strung on hidden mounted threaded rods. Like the original, also the model is provided with the Peterbilt emblem.
Also the cab roof was made of commercial aluminum not having to buy and to rework too many metalkit plates. The use of conventional aluminum sheet indeed is a massive aberration from the metalkit system, but the savvy "spanner" certainly will find ways and means to implement similar shapes with flexible plates of the metalkit system. The other attachments following are to be described at the complete model.
The left entrance step was similarly the case for the starter battery. This finding is due to an film error in the sequence as the Truck steamrolls the cell phone. There is one scene that shows the battery box without a cover, and for a brief moment the starter batteries are clearly visible. In the next scene, the cover was replaced.
On the right side behind the cab beside the exhaust the air pressure reservoir for the braking system and a box are located - probably a toolbox or something similar.
Interesting features had the mirror on the radiator and auxiliary lighs at the cab. In the 1950s and 1960s the control of combustion engines by far was not so advanced as today. So the driver had careful to prevent an overload of the engine - and an indicator for overload was the black smoke. To observe the color while driving, a mirror was mounted on the radiator. In darkness, also a spotlight was shining directed to the exhaust smoke. The holders of the additional headlight, and all other implied mirrors are also made of wires that are soldered into lugs. The bell of the horn on the cab roof is made of a rust-colored painted grommet and a shaft attached thereto.
Ready to start with a 7-cell accumulator the truck tractor has a mass of approx. 8,5 kg, resulting to a weight of approx. 42N onto each axle. Because the rear axles additional are loaded with the trailer the required springs could be calculated not before completion of the trailer. Duel Truck Tank Trailer From the trailer of the original Duel Truck virtually nothing is known. However, since it has some distinct differences from the trailer of the surviving truck, the model has been constructed solely on the basis of extracted images from the movie. It is striking, for example, that the original trailer in contrast to the still existing vehicle had no stand wheels. Since the tractor and the trailer usually formed a unit that had to be separated only rarely, one could often dispense with support wheels - and also the model was made easier. On closer inspection shows that the left sidepart below the tank protrudes more forwards than the right sidepart. Behind these sideparts are storage compartments for fittings and hoses, and - so far it can be seen - are sealed with 2 doors in a different arrangement. This asymmetry has also been applied to the model.
For reasons of weight and complexity from the outset only the visible part of the tank should to be modeled, in principle only the upper half. But because the viewer from below does not see only in a large cavity, the tank bottom by means of obliquely mounted plates were indicated.
Accordingly to the storage boxes also the sideparts are unbalanced. They contain the necessary access openings which on each side are closed with 2 doors, these doors can be opened. The rear of the side parts is chamfered whereat on the basis of the available images an inclination of about 16° to the vertical was determined. Because of the curves and slopes the facing of the side parts with the relatively thick Metallus flexible plates is impractical. Thus at some places - as in truck tractor - small pieces of 0.5 mm aluminum sheet from the hardware store are used.
The side parts are secured with 4 screws on the frame and similarly is bolted to the storage boxes. The tank of the original trailer has an elliptical cross-section which should be replicated at least for the upper half passably accurate. For this, first the axles of the ellipse were determined and with a width of 19 holes (horizontal semiaxis = 9.5 holes = 120.65 mm) and a height of 13 holes (vertical semiaxis = 6.5 holes = 82.55 mm) a good first approximation was provided. The calculation of the scale revealed with the aid of a numerical integration of 644mm, that is, for the upper half to 322mm corresponding to 25.35 holes. Since cladding panels with a length of 25 hole = 317.5 mm should be used , the vertical semiaxis was gradually reduced and the amount calculated in each case again. A half outline of 317.5 mm thus results from a vertical semiaxis of 79.34 mm = 6.25 hole. The calculation with fractions of grid intervals may seem unusual and disturbing, but by hindsight it was quite beneficial, a justification will follow later in the description of the tank rear panel. With the determined axles by means of ellipse construction according to de la Hire a bending templete for the boilerplates was drawn to paper . The tank consists essentially of aligned Metallus cladding panels that have previously been bent to the stencil. In the front and rear region, the tank is rounded and the tank rear wall also is inclined. Maintained so as not to cut Metallus flexible plates, the transitions to the tank front and rear tank wall were also made of 0.5mm aluminum sheet. The tank top has a total of three access openings, and these were indicated in the model as well as the boundary of the access openings (upper tank completion).
With 10 fish plates the tank was bolted to the side parts:
More difficult was the construction of the tank back panel because it has an elliptical shape, is inclined to the vertical, and also is convex. Since this form is difficult to achieve with steel plates, the tank rear wall was also made of cardboard and painted accordingly. For the preparation of the curvature, the cardboard was moistened and in this state the camber was molded. After drying, the form was conserved, but for reasons of stability at the border Metallus curved strips and fish plates were attached which partly also were to cut to the required lengths. Prior to installation, both parts the tank rear wall and the trailer rear side were to be assembled as a unit.
At this point it should also be established why the vertical semiaxis of the tank with an optimum length of 6.25 hole mathematically quite makes sense: On the basis of the images was - as already mentioned above - for the tank rear wall an inclination of about 16° from the vertical was determined, and in this position teh tank and the tank rear wall must match. The projection of the tank rear wall has also concluded a vertical semiaxis of 6.25 hole, but the actual length of the vertical half axle L considering the inclination is calculated to A semiaxis length of 6.5 holes corresponds to an axis of hole 13 hole - and this fits into the grid. As final structural components, the doors, the ladder and the slant to be applied covers of the side parts were mounted.
Calculation of the spring suspension Front axle of the truck tractor
Axles of the trailer
Rear axles of the truck tractor The springs of the two rear axles carry the weight of the rear part of the tractor of approx. 42N less an assumed value of 10% for the weight of the axles, and a part of the weight of the trailer of about 34N - thus a total of about 72N. Because the fifth wheel is not situated halfway between the rear axles, but closer to the drive axle the weight force of 72N is distributed in proportion to the 64:36 on the drive and the trailing axle (at the original Duel Truck it was 60:40), so in the ratio 46N:26N. Since both the drive and the trailing wheels are mounted on a rocker arm and the springs are not situated directly above the axles, there is a further distribution of the weight forces in the ratio of the effective levers; because of the present design approx. 29% of the forces is assigned to the anchor and about 71% to the point of the spring suspension. These forces are to halfe again as each axis has 2 springs. Finally it to note that the travel at the springs to the lever ratio is greater than the travel of the wheels. In the present case at a spring travel at the wheel of 10mm the springs are compressed by 14mm.
All springs could be made of 2 different existing blanks (bulk stock). After installation and testing of the suspension again is turned out that the assumed spring travels can be approximated very well despite of this simple calculation. Although the color scheme of the model was based on the original truck resp. on the existing truck, the model does not look worn and dirty, but more like a new car. On the one hand surely this is due to the shiny screws, but also to the missing artificial aging.
To what extent in the future at this model an artificial aging is carried out is still unclear. Possibly first certain technique has to learn such as airbrushing, etc., to achieve a satisfactory result.
|
