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Tow Truck

January 6th, 2009 Leave a comment Go to comments

Big tow truck. Features full suspension, V8 piston engine, 4-speed manual gearbox, functional lights, openable bonnet and doors, pneumatic outriggers and towing hook, pneumatically raised 2-section boom, pneumatically lifted second axle, motorized dual winch, internal electric compressor and custom stickers.


Completion date: 15/07/2008
Power: electric (Power Functions) / pneumatic (fed from internal electric compressor)
Dimensions:  length 84 studs (+ boom, hook and outriggers) / width 20 studs / height 33 studs
Weight: 3.8 kg
Suspension: axle 1 – pendular with shock absorbers / axles 2, 3 & 4 – independent with shock absorbers
Motors: 5 x PF Medium, 1 x PF XL
Pneumatics: four circuits with manual valves

My first model of an American truck. Not a model of an actual machine, but to a large degree based on the iconic Kenworth W900. It used some new PF elements, like lights and switches, and it was my first model with custom stickers.

The chassis was suspended on 4 axles. Axle 1 was fitted with a simple pendular suspension, because I anticipated that it would be too heavily loaded for an independent one. The pendular suspension offered a fairly good steering lock, and was stabilized by a pair of shock absorbers. All three rear axles were suspended independently on the longitudinal rocking levers – a solution that sacrificed some robustness to keep the suspension narrow and gain space for a towing hook’s bay at the back of the truck. It took at least two axles with this kind of suspension to support the weight of the truck. Axle 2 was suspended on the pneumatic cylinders instead of shock absorbers, and could be pneumatically lifted up. All three rear axles were driven, with a substantial gear reduction between axle 2 and the gearbox, used in order to protect the drivetrain from high torque. The gearbox was of the type I’ve used before, a compact 4-speed manual version inspired by Erik Leppen’s design. It eventually proved to be slightly too weak to handle full weight of the truck, so the model was driven only at two lowest gears, as the reinforcement of the gearbox would need a major redesign of the cabin. The cabin itself, together with the bonnet and front mudguards, was covered entirely with smooth, non-Technic bricks. I didn’t at that time have the number of these bricks sufficient to build the entire truck in that manner. The cab’s doors and the bonnet were openable, and there was a V8 piston engine under the bonnet, driven via the gearbox in a realistic way (i.e. it was running at the same speed regardless of the gear selected, including the idle gear).

Below the cab and the gearbox, there was an electric compressor, controlled by a PF switch located on the side of the truck. It powered four pneumatic circuits, all with manual valves. One circuit lifted the second axle of the truck, while the other three controlled the towing equipment: two rear outriggers, the towing hook, and the elevation of the boom. The boom itself was the exact copy of the boom of my Telehandler Mk.2, with its self-contained extension mechanism driven by a worm gear on the racks. Here, the space on the boom was utilized even more efficiently, by the addition of a rope with a dual winch (with twin drums). The rope was located on the top of the boom, partially traversing the crown of its first section.The winch was located in the superstructure behind the truck’s cab, and was controlled by a second PF switch located on the side of the truck, just like the first one. One serious disadvantage of the winch was that it was fully enclosed in the superstructure, so there was no access whatsoever if the rope tangled up. Typically trucks with this type of the boom have two hooks, but I only had one Lego metallic hook at that time. Hence, I did not use another one, and suspended the only hook in such a way that it would be stabilized by its own weight, even if the drums of the winch worked unevenly (and they almost always did, because the amount of the rope on each drum was different).

The rear outriggers were pretty simple, while the towing hook was more complex. I wanted to limit the complexity of the pneumatic system, and control the entire hook with a single pneumatic cylinder. At the same time, I intended to make the whole towing hook move forward and backward, so that it could be retracted into a bay at the back of the truck, and remain enclosed within its body while retracted. These two goals have been finally achieved by the use of an advanced lever that lowered the hook as it was extended backwards. It worked pretty smoothly, as you can see on the video, but in fact it was completely unrealistic. What I didn’t know at that time, was that the towing hook needs the ability to move up and down in horizontal position, because it must touch the ground for the towed car to be connected to it, and then lift the car up a little bit. I have mistakenly assumed that the towing hook may remain above the ground, and that the car can be lifted by the boom and winch, and then connected to it.

The model was equipped with a large number of lights, all turned on or off by a central PF switch inside the cab. There was a pair of lights on the sides of the roof that were not turned on constantly, but kept flashing instead. It was possible by powering them through another PF switch, that was constantly switched on/off by a PF Medium motor with an eccentric mechanism. There was also a number of stickers that I designed and produced in a very simple way: they were pieces of printed paper attached to the bricks by an adhesive transparent tape. While pretty amateurish, this method was easy, and produced stickers that were relatively good-looking and easy to remove. I’ve been creating stickers for my later creations in exactly the same way.

The truck was one of my ambitious projects that suffered from some minor malfunctions and mistakes in design, such as too tall cabin. Still, I was satisfied by the way it blended technical complexity with aesthetics, and I consider it not bad as for a first approach to the subject of these specific vehicles.


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Categories: Trucks Tags: , , ,
  1. Sariel
    December 21st, 2010 at 06:29 | #1
  2. Sam
    December 21st, 2010 at 05:58 | #2

    what is pendular suspension?

  3. SEAN
    June 7th, 2010 at 23:42 | #3

    the tow truck is awsome, but it sould be a rotator.

  4. Eric
    December 9th, 2009 at 21:49 | #4

    Ok you are awsome with lego’s better than me. but i have one question that always stumps me HOW DO YOU ALWAYS STEER THE MACHINES because i always have problems with the steering not being able to hook with the rest of my inventoins. can you make a tutorial on different steering techniques and include how to steer multiple tires in sync. and 1 more thing could you tell me how to creat suspension i have the pices but i dont know how to put them to gether.
    P.S i love your work and you are my idol

  5. Sariel
    July 17th, 2009 at 17:08 | #5

    @big fan owen
    Just where I get everything else – look in the FAQ.

  6. big fan owen
    July 17th, 2009 at 16:47 | #6

    where do u get your pneumatics because i cant find them anywhere online?
    great work

  7. admin
    January 7th, 2009 at 21:06 | #7

    Dzięki, czuj się zaproszony do podpatrywania, a syn to świetny pretekst przed żoną żeby kupić klocki 😉

  8. Darek
    January 7th, 2009 at 20:48 | #8

    Stary! Jestem w ciężkim szoku :)! Pozytywnym rzecz jasna :)! Twoje prace są niesamowite! Masz talent! Gratulacje! Jak miałem kilka lat (a dawno temu to było, w legośredniowieczu), to z moim Bratem ciotecznym budowaliśmy różne cuda z LEGO wykorzystując sterowane silniki z zabawek (silniki obudowywaliśmy w celu łatwiejszego montażu w pojazdach). Nie było jeszcze wtedy tylu wspaniałych zestawów, które dzisiaj są normalką … chyba miłość do najinteligentniejszej zabawki na świecie powróciła ze zwielokrotnioną mocą :)! Ciekawe co na to powie moja Żona ;)! Dobrze, że syn rośnie jak na drożdżach :)))! Trzymaj się … będę podpatrywał Cię co jakiś czas jeśli pozwolisz.

    Z pozdrowieniami i wyrazami zachwytu,

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