The tipping of the dump bed is achieved by using the pneumatic system, as this saves significant on space within the rear chassis, needed to apply the suspension. This rear suspension is based on a 3-point suspension for both rear bogies, interconnected with a 3-point bogie beam pivoting on the trailer chassis. Suspension of the tractor is based on a rotating hitch.
It took some time to design the tractor's front, to achieve it's characteristic 'looks', including LED front lights.
Driving
Steering
Driver's steering wheel turns
Working V6 engine with fan
6x6 drive-train
Triple differentials
Suspension: rotating hitch
Suspension: 3-point bogies
Pneumatic tipping dump bed
LED head lights
Engine hood open/close
Pneumatic tipping
Width - 17 cm
Height - 22 cm
Steering - 33 degrees
Rotating hitch - 360 degrees
Tipping angle - 43 degrees
Ground clearance - 4 studs
Weight - ~2,4 kg
Development process
The model dimensions are based on the original Volvo A40D Hauler.
The scale is determined on the balloon tire size is 94.8 x 44 R (part 54120), unfortunately this part was (in 2011) not available in yellow. The tractor mudguards needed to be circular, which was achieved by using the flexible tubes of Technic LEGO® Tow Truck set 8285. The interior of the tractor comes with a dashboard and again... a coffee machine.
Total development time was ~125 hours, another 25 hours added for creating Building Instructions.
Steering
Volvo uses are hydro-mechanical steering system. Within the model, this is realized by using a twin linear actuator mechanism, powered by a single medium motor. A double clutch gear is used to safeguard the medium motor when the steering mechanism is blocked. The twin linear actuators do operate contrary, meaning one actuator 'pushes' whereof the other actuator 'pulls' during steering.
The design of the steering mechanism was more or less straight-forward, although it took some redesigns to have a sturdy chassis structure for the tractor.
The steering wheel within the drivers cabin is connected to the steering mechanism and therefore operates as well. Regardless the nice detail of the operating steering wheel, it became very handy when the model is remote controlled; as such the 'operator' can notice if steering is 'going on' or 'stand-still'.
Drive train and V6 engine
A single power functions XL-motor is used to drive the hauler, geared down in three stages, each one with a reduction of 5:3 (12 tooth double bevel - 20 tooth double bevel). This results in a total reduction of approximately 4,63:1. Due to XL-motor force in relationship with the weight of the model, the drive train in the tractor consists of twin gears for each reduction step. The output of the 1st reduction step in the tractor is used as input for the trailer. Within the trailer, a single gear combination is used for the 2nd and 3rd reduction step per wheel unit. Each wheel unit has of course a differential unit.
Suspension
The trailer containcs a replica of the original Volvo hauler 3-point suspension based on:
- 3-point bogie beam (a 1x16 Technic brick) at both sides of the trailer chassis, which can move independent from each other. The center of this bogie beam is connected at the trailer chassis and is able to rotate. See red circle.
The bogie beams outer sides are connected to both rear bogies by a rubber 'Technic axle joiner double flexible'. See blue circles. - 3-point rear bogies. Each rear bogie is connected at the front side by a 'Technic Steering Arm 6.5 x 2 with Towball Socket Rounded' to the trailer chassis's 'Technic Steering knuckle arm with ball joint'. See green circle.
The combination of the bogie beam and the towball combination with the rubber axle joiner results in a large wheel movement while the body of the trailer stays leveled.
Due to the wheel movements of each rear bogie, the drive train axle to the wheel unit must be able to slide its effective length. This is achieved by using a 'sliding joint' in the original vehicles. The first attempt for the hauler model was based on the 'Steering CV joint axle' which was released in the same year, 2011, together with the 'Steering CV joint'.
Although this works fine from a technical point of view, it was not able to deal with the XL-motor's force. The joints just disconnect from each other under heavy conditions.
The work-around - and 2nd attempt - was based on the 3L universal joints. The sliding of the bogie drive train is achieved by using a tan gear 20 tooth double bevel on the trailer chassis; this gear permits axles sliding relatively easy. See purple arrow.
The tractor itself as no suspension for the wheel unit; the suspension is realized by the rotating hitch of the trailer. The Volvo haulers do have a 3-point suspension as well for the wheel unit of the tractor; however applying this to the model would lead to serious drive train issues, regardless the fact limited bullding space is available either.
3-point bogie beam pivoting on the trailer chassis
Final Note
Although I did succeeded in my opinion, the lack of center differentials come into account when the model makes sharp curves. Not a huge issue, but noticeable on flat surfaces.
Unfortunately, applying center differentials was not possible due to the lack of space. Besides that, I was not sure if a center differential would be able to deal with the XL-motor force (especially the 12 tooth bevel gears).
As well, I think the limits of the Technic LEGO® system are reached for models of this size; given the available parts in 2011.
