This model features a remote - or manual - driven 6x4 truck with a trailer having a steered twin-wheel. The mobile rolloader crane is able to ride on the trailer platform to pick the right pallet - with DUPLO® bricks - for (un)loading. The crane can be equipped with an easy exchangeable clamp or grabber.
The very unusual orange/lime color livery refers to a Dutch 'special and heavy transport' company, named 'Van der Vlist Group'..
Actually, the lime color does not complete represents the right 'green color', but it was the closed match available.
The 'green squidman aliens' on the truck's sunscreen and trailer rear-side are no reference to 'evil plans' or 'criminal activity' intensions like the 'Squidman' character in the LEGO® Space Police theme.
Driving
Steering
LED head lights
Cooling fan
Double differentials
Trailer 1st wheel steered
Crane with 2 booms
Crane 2nd boom extract
Clamp open/close
Cabin tilt to access engine
Swing down panels trailer
Spare wheel
Length - 41 cm
Width - 14,5 cm
Height - 21 cm
Weight - ~2,0 kg
Lowloader
Length - 65 cm
Width - 14,5 cm
Height - 25 cm
Weight - ~2,4 kg
Cargo load - 12 pallets
Cargo weight - 1kg (max)
Trailer - 1.798
Crane - 482
Clamp, pallets, cargo - 318
Development process
A rolloader crane trailer was already a couple of years on my mind; however the main requirement for the trailer was one or more steered rear wheels which I never got to work properly. In real life rear steering of a trailer is accomplished by:
- a cable connection between the kingpin and the rear wheel,
- a bar connection between a modified kingpin and the rear wheel, or
- by hydraulics and an electronic unit that measures the steering degree of the truck.
All methods are not suited for applying in LEGO®, mainly due to the fact that LEGO® is not stiff enough. There is always some slack, resulting in - after passing curves - the problem of not aligning the steered rear wheel in 'straight forward' position.
With the launch of the Power Functions Servo motor in combination with the Rechargable batterybox having 'speed control'I could overcome above challenges.
The combination took about 12 months to design and is the largest model I ever have designed (4.475 parts).
Truck
The truck 8x4 (see Truck with Lowloader) chassis base was reused for the design process of this 6x4 truck. The only minor challenge was relocating medium motor to the chassis side due to the shorter wheel base. I considered to usage of the servo motor, but it turned out impossible to connect the servo motor directly to the front wheels gear rack. Applying couple of gears, needed to relocated the servor motor, did not work out; a slightly misaligned auto-center function resists. So, I trust one have the right 'finger-spitzen' feeling to control the medium motor for steering.
5th wheel: Simple construction made of technic triangles whereof the trailer's kingpin axle locks in. This is important to hold the technic turntable - connected at the trailer - in a locked position.
As such, the steering position of the truck - in relation to the trailer -can can be 'measured'.
The truck can be operated with a remote control unit or manually. Just shift some gears to decouple both motors.
Trailer
The trailer took much more time to design, especially the rear wheel steering mechanism. The trailer's chassis itself was a straight forward build and relative easy. A small challenge - but not difficult - how to connect the hinges of the swing panels (both sides 6) in such a matter the rolloader crane is still able to ride on the platform, when the panels are swinged down.
A worm gear design is used for the parking stand being able to lift a loaded trailer of the truck's 5th wheel.
So how does the rear steering works?
The technic turntable (with inner axle) is used as kingpin to couple on the truck's 5th wheel. As mentioned, the turntable is locked, being able to 'measure' the position of the truck in relation to the trailer. The turntable's gear position is passed by chains to a 2nd technic turntable, located in the middle section of the trailer. That turntable passes (with a fixed inner axle) the position to the speed-control input (axle) of the Power Functions Rechargable Battery Box. This motor speed control dial can turn 90 degrees in both directions - in 7 steps - and is therefore precisely being able to control a servo motor in the same way. And, this servor motor drives a traditional double 1x4 gear rack setup, passing it's output to a technic turntable being part of the rear twin wheels.
Note: I tried a 3rd steered rear twin wheel, but a single servo motor is not powerfull to operate a double steered twin-wheel setup.
Rolloader Crane
The crane is able to ride on the trailer forwards until the first 2 panels. Both crane chassis sides do have 2 wheels 'with arms', securing the crane to the trailer bed. It's function is to prevent the crane skipping off the trailer when pallets are loaded/unloaded. The crane itself consists of 2 boom's powered by linear actuators, operated with levers on the fixed boom of the chassis. The 2nd boom section is able to extract ~ 7 studs. Means, the crane has a 22cm reach to unload pallets.
Compromise: According to the model's scale, the rolloader crane is actually 3 studs 'too high'. Translation to original sizes, the crane top in folding position is ~ 4,35 meters, whereof in The Netherlands the governmental regulation is max 4,00 meters.
In the first design, I used the mini linear actuator to comply the scale, but the mini LA's could not handle the pallets loaded with DUPLO® bricks. So, I had to make a compromise, playability and functionality in favor of sticking to the scale.
Clamp or grabber
The clamp legs are operated manually by a mini linear actuator. The legs lock into the pallets on both sides. The clamp has a mini technic turntable being able to rotate the pallet.
The grabber is just a 1:1 copy of the Technic LEGO® #42006 excavator set and modified to operate manually.
