Model of a South African MRAP vehicle. Features pendular suspension, 4×4 drive, 2-speed gearbox and lights.  

Datasheet:

Completion date: 18/08/2011
Power: electric (Power Functions)
Dimensions: length 41 studs / width 24 studs / height 22 studs
Weight: 2.074 kg
Suspension: pendular
Propulsion: 1 x PF XL geared 4.2:1 (low gear) / 2.5:1 (high gear)
Motors: 1 x PF XL, 3 x PF Medium

RG-35 4×4 is a modern small MRAP (Mine Resistant Ambush Protected) vehicle developed by BAE Systems South Africa as a smaller variant of base RG-35 6×6. It belongs to the second generation of the MRAP vehicles, which means that it combines high level of crew protection with impressive off-road capabilities. It was introduced in the first half of 2011, which means that it’s just starting to enter service, with the Canadian Army considering a massive order.

The model was built primarily to test the wheels and gear blocks from the 8110 Unimog set. It consisted of a short, fully studless chassis enclosed in a studfull body. Both axles had pendular suspension with 4 short shock absorbers on the rear, and 4 long shock absorbers on the front axle. The front axle had a Medium motor for steering integrated into it. The 8110′s set ball joints were used to attach axles to the chassis, as I expected them to support at least part of model’s weight thus reducing the friction on the driveshaft. Both axles also included differentials, as I expected them to be necessary for a vehicle with that short wheelbase. However, the presence of the differentials had a bad impact on model’s off-road capabilities.

The chassis, despite being very short and housing tall suspension modules, housed a remotely controlled 2-speed linear gearbox, a straight six piston engine with a separate Medium motor to drive it, and it even housed a motorized front winch unit until I decided to remove it to lower the model’s centre of gravity – and all of this with the right side of the hull recessed to accommodate for a spare wheel. The model had to weight at least 2 kg to be allowed to an outdoor Truck Trial race, and I achieved this weight by adding approximately 0.25 kg using weighed bricks. They were located at the very bottom of the body, thus lowering model’s centre of gravity.

The model turned out to have very soft suspension and additionally I have somehow mistaken the set-up of the gears in the drivetrain, resulting in an unusually low gear reduction. The latter rendered the model practically unable to drive outdoors, and it was eventually destroyed in an accident while I was driving it downhill. The short chassis was a disadvantage when climbing or descending, and the model tumbled forward over its front wheel and crashed.

I believe the model had a great potential, excellent ground clearance and one of the most effective chassis I’ve ever built. This potential was wasted due to my simple error in drivetrain’s construction and due to disadvantages of its short wheelbase.

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Model of the Humvee designed for Truck Trial races. Features full independent suspension, portal axles, 2-speed remote controlled gearbox, lights, opened bonnet, doors and rear hatch.  

Datasheet:

Completion date: 14/04/2011
Power: electric (Power Functions)
Dimensions: length 53 studs / width 26 studs / height 24 studs (not including antennas)
Weight: 2.319 kg
Suspension: full independent with portal axles
Propulsion: 1 x PF XL geared 8.3:1 (1st gear) / 3:1 (2nd gear)
Top speed: unknown
Motors: 2 x PF Medium, 1 x PF XL, 1 x micromotor

A little less than a year ago, I’ve built a simple Hummer H1 model designed specifically for the Truck Trial races. It turned out to perform better than expected, until the chain present in its drivetrain broke. I was relatively pleased with this model, until several months later I have come across a civilian H1 parked on a street. Having used this opportunity to inspect it as much as possible from the outside, I have come to the only proper conclusion: that my model was unsatisfactory.

While planning to build a new model – this time called Humvee to emphasize that it would be based on the military H1′s – I’ve decided to use the often-criticized black colour, because Humvees simply look excellent in plain black. I have also decided that I can’t simplify the suspension system like I did in my earlier model (which was suspended on simple pendular modules), but rather try and recreate the suspension system of the real vehicle. This is a tricky feature, as the Humvees have full independent suspension with portal axles. It’s fairly easy to build independent suspension or portal axles with Lego pieces, but it’s quite a different story to build independent suspension and portal axles. It means that Lego pieces that are designed for independent suspensions are pretty much out of the question. Instead, I had to create this kind of suspension using common pieces only.

Sophisticated suspension systems like this  are usually wide – building the new model in the same scale as the old one was impossible. When I’ve tried the old Technic wheels that have best diameter/width ratio, it turned out that I can make the suspension 23 studs wide, including the wheels (my earlier model was 20 studs wide). Since the model scaled to the size of the wheels would be 24 studs wide, that suited perfectly – except that it meant abandoning the 1/13 scale required by the Truck Trial rules, which means that the model would not be classified in the race. I decided to accept that rather than to build another small model with simplified suspension system. Additionally, the minimum weight limit for the race has been changed from 1kg to 2kg, starting this year, which meant that my earlier model would be far too small to participate.

Another decision was to use a gearbox this time (my previous model had none), and my recently developed 2-speed heavy duty linear gearbox was an obvious choice. The gearbox design was so good that I wasn’t the only one using it in the race – Maniek’s truck used a gearbox like this copied with my permission.

Mechanically, the model used a custom independent suspension system with portal axles, with a 3:1 gear reduction at the wheels, and was driven by a single XL motors using a 2-speed gearbox with ratios 8.3:1 at lower gear and 3:1 at higher gear. There were four motors total: one for drive, one for steering (housed under the bonnet), one for shifting the gearbox (housed under the gearbox) and one micromotor for rotating the steering wheel as if it was actually working (which can be considered a cheat, but is not forbidden in the Truck Trial rules). 4 IR channels were used to control the model, with the fourth one used to turn on/off the lights remotely.

Aesthetically, I have focused on improving the shortcomings of my previous model and on modelling the features which are exclusive for the military Humvees. These included intake and exhaust snorkels, which I’ve never seen used in civilian vehicles, as well as the design of the whole rear end of the model, which is quite different in civilian versions. Namely, the location of rear-lights is different, and there are recesses for two jerrycans on the sides. Inside the model, there were two well-detailed seats in front and a radio station between them. There were no rear seats, as the space was taken by the gearbox control system, and the rear seats are usually folded in military vehicles, and thus can’t be seen from the outside. The model obviously included plenty of parts that could be opened: the bonnet, all four doors and the rear hatch which was split in two pieces: one opening upwards, another opening downwards. Just like in the real Humvee, the intake snorkel stayed in place when the bonnet was opened – this was one of the features I’ve missed in my earlier model.

The model performed well at the beginning of the Truck Trial race. It drove through the first section flawlessly, with lower gear used to climb uphill and higher gear used to descend downhill. The problems started at the beginning of the second section, where it simply stopped moving. As there was no easy way to locate the damage at all, I had to give up the race. It eventually turned out that I did a big mistake by meshing three 8-tooth gears in a row (which I did to split the main driveshafts in two, as required by the suspension system). Even though the gears were protected by 3:1 gear reduction at the wheels, they have shifted on their axles (as 8-tooth gears are slightly narrower than a single stud) and started to grind each other, severely damaging their teeth. Thus a careless drivetrain design resulted in six damaged gears and in the model utterly unable to move. Additionally, the front wheels had a strong tendency to bend, for no apparent reason. I would suspect some flaw in the suspension design, but the rear axle used almost identical design and the rear wheels did not bend at all.

Despite its obvious flaws, I consider this model a step forward from the previous one. It has proven my gearbox design reliable in the racing conditions, and it used a complex suspension system, to a moderate success.  However, as I’m unable to identify the reason for the bending of the front wheels, it seems I should abandon this suspension design.

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My final 2010 Truck Trial vehicle, built in less than single week after the previous vehicle failed. Features full pendular suspension, 4×4 drive, lights and opening doors, bonnet and rear board.

Datasheet:

Completion date: 03/09/2010
Power: electric (Power Functions)
Dimensions: length 48 studs / width 26 studs / height 27 studs
Weight: 1.985 kg (1.726 kg in roofless version)
Suspension: pendular, stabilized with shock absorbers
Propulsion: 1 x PF XL motor geared down 5:1
Top speed: 0.8 kmph in roofless version
Motors: 1 x PF XL, 1 x PF Medium

When I decided to abandon my Fiat SPA35 model, it was just a week before the Truck Trial race and my first decision was to pass on driving this time and to only take care of filming. Shortly after, I changed my mind and decided to try some simple 4×4 vehicle, just to drive something in the race. The vehicle was intended to combine the advantages of my two previous Truck Trial vehicles – Hummer H1 and Jeep Wrangler Rubicon, while also learning from Fiat’s failure. I wanted to try to model another famous 4×4 vehicle, so the classic Land Rover series 2 (dating all the way back to 1958) was pretty much an obvious choice.

While the complete model appears much like a Hummer/Wrangled hybrid on the outside, it was internally much closer to the Fiat model. The chassis was built completely with studless parts and used large Technic turntables to hold suspension modules in place – both solutions tested in the Fiat for the first time. The Land Rover shared engine location, gear ratio and wheels with the Wrangler and a studfull body with the Hummer. In fact, the Rover used studfull body around a studless chassis, whereas Wrangler used studless body around a studfull chassis.

The suspension has undergone some major changes in comparison to the version used in Fiat. The front axle was reverted to the version used in the Wrangler, and then a single turntable was attached behind it and the steering system was additionally reinforced. Both drive and steering were transferred through the turntable – steering by a solid driveshaft and steering by am empty differential sitting on it. The rear axle was built from a scratch between two turntables. There was no gearbox, and – just like in the Wrangler – the drive motor was located above the front axle, right under the bonnet. The racing rules we use state that every model has to be equipped with a piston engine of accurate configuration and placement, unless the actual drive motor is located where the original engine is. Thus, locating the motor under the bonnet meant that no piston engine was needed in the model, which saved space, weight and drive motor’s power. The steering was controlled by a single PF Medium motor geared down 15:1 and located low in the chassis, in front of the rear axle. The entire underside of the chassis was covered with studless parts, in order to create a single smooth surface that was unlikely to get  stuck on an obstacle, and in order to lower the centre of gravity as well.

Knowing that my Wrangler model had abundance of torque, I wanted the Rover to be much heavier.  Our racing rules take power-to-weight ratio of each individual model into account, therefore more weight at the same power means more points. Thus, I wanted the body to be massive, but at the same time it was my goal to keep the model’s centre of gravity low, despite its significant ground clearance (up to 7 studs under cabin’s floor). Therefore especially the lower portion of the body was built so densely that model came out almost undamaged from some crash tests I conducted later.

The body was equipped with a pair of opening doors, an opening bonnet with a spare wheel fixed on top of it (a common sight in early Land Rover versions), and opening rear board with the IR receiver attached to it. Most of the Land Rovers can be accessed from the back by a single door, and a board is a rarity. I chose the board over door because this way the IR receiver was more exposed, and could be pulled out from the cabin’s inside to some extend if needed. Moreover, the rear part of the cabin has been adapted to house a camera. Due to weak mounting points, this solution worked well only on flat, level surfaces, as proven during the race.

It should be noted that the model’s body was inaccurate: the front radiator grille should be put further back under the bonnet. I couldn’t model it because of the frame that braces the suspension module of the front axle. Moreover, inspired by the Inception movie featuring a tracked Hummer H1, I have created a simple set of four tracks for the Land Rover. The tracks and wheels could be easily swapped in the chassis, and while I did not intend to use the tracks outdoors (our racing rules don’t allow tracked vehicles of any kind), I have used these to drive around my apartment. The general performance was apparently inferior with tracks on, and in particular the traction was much worse than it was with wheels.

The completed model weighed a whopping 2.1 kg until I removed ballasted bricks that were mounted under the bonnet in order to shift the centre of gravity forward. It reduced model’s weight to just below 2 kg, and I decided to leave it like that because there was no time left for changes. The model performed well at this weight, it experienced no mechanical failures and displayed superb traction, but it was obvious that it will be struggling against its own weight.

Land Rover was warmly welcomed by other contestants because of its look and its very short building time. It performed well in the race, no mechanical failures occurred, but its weight turned out to be a real problem. The model ran out of power to climb on several occasions, and toppled over once. It ended up at the last place in the race, much to my disappointment. Yet still, other drivers and viewers were greatly impressed by its look, which led me to believe that it would be a waste to take it apart, and that the model should enter our last 2010 race on October, with open body design that should significantly reduce its weight.

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Media reference:

GadgetSin

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Model of an Italian WW2 military truck designed for Truck Trial races. Features 6×6 drive and full pendular suspension.

Datasheet:

Completion date: 06/08/2010
Power: electric (Power Functions)
Dimensions: length 53 studs / width 25 studs / height 33 studs
Weight: 2.166 kg
Suspension: pendular, stabilized with shock absorbers
Propulsion: 1 x PF XL motor geared down 8.337:1 (low gear) / 5:1 (high gear)
Top speed: uknown
Motors: 1 x PF XL, 2 x PF Medium

My first Truck Trial vehicle equipped with a gearbox. It caught my attention when I was looking for something more complicated after building several simple 4×4 vehicles. There were two main reasons that made me model this particular truck: its excellent approach and descent angles, and its pair of spare wheels. It was a rare solution, present in a number of WW2-era vehicles, to have a pair of spare wheels mounted on the sides of the chassis, relatively low, and with ability to rotate freely. It was helpful while climbing over obstacles, as these wheels had a good chance of preventing the chassis from getting stuck on the obstacle. For some reason, this solution apparently did not survive to this day.

Technically, the Fiat was supposed to continue and develop the solutions from my two previous Truck Trial vehicles – Hummer H1 and Jeep Wrangler Rubicon. It was built around a brand new studless chassis, unlike the two mentioned vehicles which had studfull chassis. It was also equipped with a simple linear 2-speed gearbox that was controlled remotely with an extra PF Medium motor, and it had unusual rear axle with 4 wheels. While the original vehicle has three regular axles, I decided to combine the two rear axles into a single pendular module that would have 4 wheels suspended on it. It has two advantages: firstly, while the module itself has a transverse pendular suspension, the wheels had a longitudinal one, so their flotation was better that it would be in case of two separate pendular axles. Secondly, a combined module needed much less space inside the chassis, thanks to which I was able to put the model’s battery behind it and the gearbox in front of it. Finally, the Fiat’s chassis used pendular axles mounted on the large Technic turntables, with both drive and steering transferred through the middle of these (drive transferred through a solid driveshaft and steering transferred by an empty differential sitting on it), which eliminated the problem of shock absorbers pressing on the driveshaft and thus creating a significant friction on it. Using the turntables resulted in slightly worse ground clearance, but has greatly improved the structural robustness.

The gearbox was made of a module attached to the PF XL motor, that was supposed to slide inside the chassis back and forth by a single stud, thus shifting the gear. By attaching the drive motor to it, I was able to eliminate a complex transmission system between the fixed motor and the sliding gearbox (this idea was first presented by  Emilus). The gearbox has a very sturdy structure and performed well during the initial test. Only double bevel gear wheels were used inside it, to minimize the problems with engaging/disengaging.

The model was equipped with a single body, which was completed just hours before the race. Despite appearing tall, the body has relatively low centre of gravity thanks to an openwork structure above the cabin and the cargo box. I didn’t have time to care about details such as doors, but at least I made the windshield able to be folded down, just like in the real truck. The cabin had a very basic interior and a simple inline piston engine driven from the driveshaft.

The truck’s performance in the race was arguable. On one hand it has shown good agility, surprising stability and I was able to drive it with great precision. On the other, it was pestered by constant problems with the gearbox, because the gears inside it started to slide along the axle under stress. I was able to temporarily fix it with tweezers until at some point the axle popped out of the drive motor and there was no way to put it back in without taking major portion of the body apart. It has forced me to give up and withdraw from the race.

At first I felt like fixing the gearbox would solve the model’s only problem, resulting in an excellent Truck Trial vehicle. Thus I was obviously planning to use it in the next race. Unfortunately, as I started to rework the gearbox, more problems occurred. The redesigned gearbox needed serious modifications of the chassis. Once the chassis was completed, the rear axle and the drivetrain started to fail. I have made several attempts at solving these problems, until I noticed that the knob wheels in the rear axle’s drivetrain are being worn down very quickly, most likely because of the resistance generated by four wheels. At this point I decided to give up on the truck, on assumption that combining two rear axles with large tires into a single module with drive transferred to by just a pair of knob wheels was a bad idea. The combined resistance of four wheels was simply too much for the knob wheels to handle.

The model became quite popular with the other Truck Trial contestants because of its unusual look and wheels set-up. It became known as “the revenge of Mussolini”, and my decision to give up on raised many protests.

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My third 2010 Truck Trial vehicle. Uses modified Jeep Wrangler’s chassis, features 4×4 drive, full suspension, opened doors, bonnet and trunk, headlights and rear lights with LEDs.

Datasheet:

Completion date: 21/05/2010
Power: electric (Power Functions)
Dimensions: length 41 studs / width 20 studs / height 19 studs (not including aerial)
Weight: 1.518 kg
Suspension: pendular, stabilized with 2 shock absorbers per axle
Motors: 1 x PF Medium, 1 x PF XL

My third 2010 Truck Trial vehicle was based largely on the previous Jeep Wrangler Rubicon. It took me over a year to come up with this model since the first plans for it appeared in early 2009 and were postponed since then. It turned out to be good for the model, as I was able to build it entirely in dark gray and using race-proven chassis components. The basic chassis concept remains the same as it was for the Jeep: two pendular studless axles held together by a studfull frame embedded into the cabin’s floor. All the components taken from the Jeep have been modified though: the front axle has a modified steering system that makes the wheels protrude forwards, the rear axle is narrower, and the frame is wider and fully covered with plates from below.

My goal from the beginning was to make this model accurate, even at the cost of its off-road performance. Unlike the Jeep, this model is scaled down accordingly to our Truck Trial regulations, which makes it much smaller than usual TrTr vehicle. Therefore it was clear that it share some disadvantages with the real Hummer, such as relatively small wheels and large wheelbase with low ground clearance. The latter resulted in numerous ‘getting stuck on belly’ accidents during tests.

The Hummer is much heavier that the Jeep was, which was exactly my intent. Based on the performance of the Jeep, which had enough torque to be practically unstoppable, I have estimated that its drivetrain and chassis components should handle weight of some 1.5 kg without problems. Since our rules take power-to-weight ratio into account, heavier vehicles get more points. Therefore I was trying to achieve greater weight while maintaining Jeep’s speed and performance. The speed is almost identical, despite smaller wheels (8 studs in diameter compared to Jeep’s 10 studs), as the gearing in the drivetrain was changed from 5:1 to 4.5:1. In order to obtain this exact gear ratio I have used a double chain between the drive motor and the driveshaft. A single chain would be broken instantly, while a double chain survived all tests I’ve ran. The use of a chain had one extra advantage: it required much less reinforcements in the surrounding structure that the gears alone would, since the gears were, well, chained together. Eventually, there were some minor inaccuracies in the model as compared to the real H1. The bonnet had a cut-out section in the middle of it, which was necessary to accommodate for the upper ends of the front shock absorbers. The air intake, which in reality is fixed to the chassis and goes through an opening in the bonnet, was attached to it in the model. I have also reduced the size of the front bumper and gave up some extra elements such as the famous “cow catcher” in order to achieve a better approach angle. Finally, there were openings in the sides of the cabin that allowed the doors to open up easily, as there was not enough internal space to use opposing hinges and I didn’t want the doors to require force to open.

The model participated in a Truck Trial race on May 22nd, and it generally performed above my expectations. It had sufficient torque and displayed some excellent manoeuvrability. The stability was satisfactory, except for one incident when I managed to flip the model over somehow. There were some traction problems, but not larger than those experienced by other vehicles (we keep having problems when driving on a dry forest bed). After the first section of the race Hummer placed 4th out of 11 vehicles, which was partially thanks to the power-to-weight ratio more favorable than it was for the Jeep. During the second section it easily climbed over a large branch that seemed too big for its ground clearance. Then during the third section both chains in the drivetrain broke at once. Since it was impossible to fix it on the field (large portion of the cabin had to be taken apart to access the chains, and I needed tweezers), I was forced to give up the rest of the race and thus the model ended up on the last place. It seems that the model had a considerable potential and could effectively compete against larger vehicles, but the idea of using chains in the drivetrain was clearly wrong. The thing I’m happiest about is that I’ve finally managed to put the damped shock absorbers to some practical use, even if it didn’t look as good as simple plates on hinges would.

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Datasheet:

Completion date: 18/04/2010
Power: electric (Power Functions)
Dimensions: length 47 studs / width 24 studs / height 23 studs
Weight: 1.224 kg
Suspension: pendular, stabilized with 2 shock absorbers per axle
Motors: 1 x PF Medium, 1 x PF XL

After the disappointing failure of my Tatra T815 truck, I was left with less than two weeks time until the next race. Re-using Tatra was out of the question, so my only option was to build some simple and small 4×4 vehicle. Since our current rules allow this type of vehicle into competition, I decided to model the iconic Jeep Wrangler in the acclaimed Rubicon version. It was built in roughly 4 days.

The basic rule of this construction was to keep everything as simple as possible and to reduce the weight to minimum. This is why the body was built with the new Technic panels, which provide the best combination of stiffness and lightness. Both front and rear axle are built entirely with liftarms, but the frame that connects them is built with Technic bricks. The reason to use bricks was that I wanted to build a roofless version of the Jeep in order to obtain low center of gravity, and since the sides of the cabin are made of single panels, the whole model had to be kept together by the cabin’s floor. Therefore there are bricks in the floor, that provide excellent stiffness and robustness while keeping the floor thin.

The chassis, which weights just 0.75 kg, consists basically of the studfull frame connected with studless axles. Since there is very little space in front of the front axle, both drive and steering had to be transferred to the front axle from behind. This was achieved by placing a 16-teeth gear with a clutch on the driveshaft – this gear works as an idler gear between two other gears, thus transferring the steering independently to the drive. Front axle is compact but massive, strong enough to handle much heavier vehicle, and it’s bottom is entirely covered with liftarms to prevent it from getting stuck on an obstacle. It should be noted that both axles use knob wheels instead of differentials, and both are portal axles with an integrated 3:1 gear reduction. Each axle is stabilized by a pair of short shock absorbers located between the axle and the frame for maximum structural integrity. In order to minimize the effect of central driveshaft’s torque tilting the body, which occurs when only pendular axles are used, the axles are stabilized with the hardest shock absorbers available. The rear axle is built around the 7×5 liftarm frame and is not covered from below.

The model is driven by a single PF XL motor with a total 5:1 gear reduction, and the motor’s location is strictly related to our current rules. Our rules state that every model has to be equipped with a piston engine whose set-up and location are consistent with the original engine. This rule, however, can be omitted if the drive motor is located exactly where the original engine is. This is Jeep’s case – the PF XL motor occupies exactly the same place that is taken by the original engine in a real Jeep, hence there is no need for the piston engine and the model can be simpler and lighter. You can see the top ends of the front axle’s shock absorbers next to the motor. It should be noted that the PF XL motor actually touches the front axle, but because it’s located in the center of the chassis and because it has a round shape, the axle can still oscillate under it. Such a trick was necessary to fit the XL motor under the bonnet.

The steering is controlled by a PF Medium motor with a 9:1 gear reduction. The motor is located between the seats in the cabin, and the steering wheel is connected to it. The cabin has a safety cage built on top of it, which is strong enough to survive a turnover without any damage. Finally, there is the 8878 rechargeable battery box and the IR receiver located over the rear axle, as a counterweight against the PF XL over the front axle.

One special feature of the bodywork is a droppable modules design. The obstacles used in our races are often larger than the ones the real vehicles are designed for, so the usual practice to handle this difference is to increase the model’s ground clearance. I wanted to avoid it, however, to keep the Jeep’s center of gravity as low as possible. It meant that some parts of the body are very likely to touch the ground e.g.  when the approach angle proves to be insufficient. Therefore I designed a number of body elements as independent modules that would fall off when stressed, on assumption that it’s better to drop something than let it get the whole vehicle stuck. The list of droppable elements includes front and rear bumper, rear spare wheel and front mudguards. The sides of the cabin are somewhat elastic too. This design is also helpful when the front wheels’ steering lock makes them collide into some parts of the body.

The model turned out to be pretty stable, with a well performing suspension and an excellent amount of torque available. It was my goal to prefer the torque over speed, since I did not want the model to get stalled under any circumstances while its speed didn’t seem crucial. This is second model of a Jeep used in our races, and it’s much different from its predecessor, the Jeep Willys built by Atr. Among other things it is heavier, larger and slower. Observing the two models compete against each other and comparing their performance will be certainly a great experience.

The main disadvantage of this model is its size. The standard scale used for vehicles in our races is 1/13. I was in hurry while building the Jeep, so I picked up the wheels I found most suitable and scaled the whole model accordingly to their size. Eventually it turned out to be in 9/1 scale which is much different from the required one, and will probably result in letting this model race outside the official ranking (in a so-called ‘open class’). Still, building and testing this model was a valuable experience, and driving it in a race will be so too. It was also acclaimed by other builders and race contestants for its look, its authenticity and its performance. If it turns out to be successful in the race (meaning that it suffers no fatal malfunction and doesn’t end up last), I will prepare and publish a complete step-by-step instruction for it, as well as schemes of front and rear axle along with their individual instructions.

Update: since the Jeep performed well at the race, the instructions are under the photos.

Photos:

Full instruction with parts list:

Photo-instruction for the whole model:

Videos:

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Click here to view the embedded video.

Media reference:

AutoMotto, GadgetSin

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My first Truck Trial vehicle for 2010. Features 6×6 drive and full independent suspension.

Datasheet:

Completion date: 10/04/2010
Power: electric (Power Functions)
Dimensions: length 66 studs / width 25 studs / height 31 studs
Weight: 2.624 kg
Suspension: full independent with swinging half-axles
Motors: 1 x PF Medium, 2 x PF XL

My first 2010 Truck Trial vehicle had a rather difficult creating process. Even though I started to build it more than a month before the race, the final version was created under two weeks time. It was mainly because of the chassis, which wasn’t stiff enough to handle the torque of two PF XL motors, and got completely rebuilt three times.

The goal of the Tatra was to have a realistic suspension with swinging half-axles which are typical for all Tatra trucks. It was achieved by removing differentials and transferring the drive with the knob wheels. The modern Tatras have their half-axles offset a bit – this was not modelled in order to keep the steering system simple and sturdy.

The steering system was located entirely between axles 1 and 2 and consisted of two complex sliding beams with links. The beams were sliding in different directions for axle 1 and 2 and were controlled by a driveshaft whose direction of rotation was inverted in between these axles. Because of insufficient internal space both beams were given the same gear ratio, resulting in an identical steering lock of both axles.

The drivetrain was kept as simple as possible, and the main portion of it, including the drive motors, was located between axles 2 and 3. Both drive motors were located between two stringers of the vehicle’s frame, one behind the other, and were not connected directly but by a common driveshaft located beneath them. Since the space between axles 1 and 2 was occupied by the steering system, an extra driveshaft was needed to transfer the drive to axle 1. It was located above the axles, under the cabin, and it transferred the drive to a V12 piston engine located inside the cabin as well. Thus the transmission of the axle 1 was located in front of it and in order to prevent such a vital mechanism from damage, a cover made of liftarms was installed before the axle.

The body of the truck was rather simple, with the cabin built almost exclusively with the new Technic panels to reduce its weight. The cargo case was simple and shallow, and there was a transportation handle built into vehicle’s frame behind the cabin – a solution I’ve used in some of my earlier Truck Trial vehicles, and which proved very useful as every Truck Trial race involves a lot of carrying the vehicles around. The cabin had a safety cage built on it, which was meant to give it extra stiffness and a more Tatra-like look, as the real Tatras participating Truck Trial races are always equipped with distinctive external safety cages.

The Tatra suffered from the same thing that most of my earlier Truck Trial vehicles did – insufficient amount of testing. The problem with this kind of vehicles is that they can be only fully tested once finished, because test are most revealing at full vehicle’s weight. As you can guess this implies that a finished vehicle has to be taken back apart if it fails tests, and to avoid this arduous procedure it is a common practice to test just the chassis alone with extra load on it simulating the anticipated body’s weight. It doesn’t always work as it’s difficult to precisely anticipate the final weight of the body if it wasn’t built yet, and it’s almost impossible to simulate its exact weight distribution. I have to admit that being short on time, I have only given a minimal amount of testing to the final version of the Tatra – this was also because I was afraid of damaging it right before the race.

During the race, the model experienced two problems – the first was a failing transmission to the front axle, which snapped. There were also minor problems with axle 3, which meant that only the middle axle worked at full efficiency, and it didn’t really help while climbing obstacles. The reason was a faulty construction of the chassis – the suspension itself worked fine, all the snapping occurred in the transmission system inside the chassis. The second problem was sideways stability. While building this model, I have given a lot of attention to make sure its weight distribution prevents it from falling forwards or backwards – and I succeeded. The sideways stability, on the other hand, proved much below what could be expected. It seems that the problem was not related with this particular vehicle but with this type of suspension in general, as exemplified by another Tatra model, the T813 built by Lomero and used in the same race. His Tatra had the same suspension type while keeping a considerably lower silhouette which suggested a better stability. Surprisingly, it kept tumbling over a couple of times per each section of the race. It convinced me that it’s practically impossible to model the Tatras’ suspension system in such a way that the resulting model is stable.

Finally, the model’s drivetrain was pretty much obsolete in terms of the rules used in Polish Truck Trial. The rules take power-to-weight ratio of each individual vehicle into account in order to prevent builders from winning by simply adding more drive motors. Each vehicle is given its own points conversion rate based on its power-to-weight ratio, which basically means that you can win with a vehicle that can race despite having a very low power-to-weight ratio (resulting in high points conversion rate) or with a vehicle that has a high power-to-weight ratio but is very fast and can complete the race in short time. Tatra was neither of these cases – it had a relatively high power-to-weight ratio because of two PF XL motors, while not being really fast. The current tendency among the top Truck Trial builders is to use complex gearboxes with 3 or even 4 gears available. Thus even a truck which is much heavier than Tatra can be driven by a single PF XL motor whose gear ratio is changed as needed by the means of the remotely controlled gearbox. This results in a models that are slow but still capable, while having an extremely high points conversion rate. Two good examples of such trucks are Emilus’ GINAFs and Atr’s Volvo – both being large, heavy, and driven by a single motor.

Upon observing the race, I’ve decided to abandon the Tatra project. While the transmission problems could be solved given a sufficient amount of testing, the suspension system would still not provide satisfying stability. With the next race being only two weeks away, I decided that I would focus on building a new, small, lightweight and efficient vehicle rather than fixing Tatra. This is also the reason not to document the Tatra’s technical solutions – I think it’s better to build something more successful and then document it once it’s solutions are proven in a race. Right not I have a complete front suspension of my next Truck Trial vehicle, which looks very promising, and if it succeeds in the race, I intend to publish a complete instruction for it.

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My fourth Trial Truck vehicle. Features 6×6 drive, two axles with different steering lock, full independent suspension and front winch with a quick release lever. The first vehicle powered by the Lego 8878 battery in Polish Truck Trial.

Datasheet:

Completion date: 05/09/2009
Power: electric (Power Functions)
Dimensions:  length 53 studs / width 27 studs / height 24 studs
Weight: 1.875 kg
Suspension:  full independent
Motors: 1x PF Medium, 1x PF XL

My another attempt to create a successful Truck Trial vehicle. Having my previous experiences with Unimog U900 and Star 266 in mind, I focused on a vehicle that would be small, light, low and simple. I have chosen to model the Alvis Stalwart truck because it was one of the shortest off-road vehicles with three axles. I liked the idea of having six wheels so close to each other, because if offered good traction and good weight distribution.

The chassis was complex but compact, built almost exclusively with liftarms. It consisted of two steered axles both of which were copies of the module I have used in the front axle of my earlier Hellbender model. The third axle was not steered. The intervals between all three axles were identical, which meant that the second axle was supposed to have 50% of the first axle’s steering lock.

The problem was that two aforementioned modules  were located in ‘mirrored’ positions in order to simplify the drivetrain. Therefore the steering driveshaft had to have its direction of rotation reverted between the modules. It was achieved with a simple setup of small bevel gears, but it also created a significant backlash. Initially there was 16-teeth gear in the first axle’s rack & pinion mechanism, and an 8-teeth gear in the second axle’s one. In theory it provided the desired difference in steering locks of two axles, but in practice that difference was heavily degraded by the backlash. I have solved it eventually replacing the 16-teeth gear in the front axle with a 12-teeth one. Coupled with the backlash, it created just about the perfect steering lock difference.

The drivetrain was somewhat complex, with two separate driveshafts for the third axle and for the two first ones. The model was driven by a single PF XL motor located just above the third axle, and the 8878 battery was located at the very rear end of the chassis – together with the PF XL motor it counterbalanced the weight of the cabin.  I expected the front winch to be a very important part of the vehicle – it was driven by the drive motor through a driving ring with a quick release lever. When the lever was engaged, the winch was driven accordingly to the direction of vehicle’s movement. When the lever was disengaged, the winch was disconnected from the motor and the string could be quickly extended by hand. There was a number of pulleys used inside the chassis to reduce the friction of the string, and the entire winch was enclosed within model’s frame. The winch proved so powerful and robust that when forced to stop, the string split before there was any mechanical damage.

The model was a bit heavier than expected, but it had a very good weight distribution and the suspension worked flawlessly with its weight. It was also quite manoeuvrable and very, very stable. I expected the low ground clearance to be a problem, but it was helped by the bottom of vehicle which was covered by a protective layer of smooth liftarms, so that the model could slide over obstacles to some extent. The main problem of the vehicle was failing drivetrain plus non-lockable differentials. A lot of slip situations occured, and the drivetrain would snap when a really high torque was needed. It could have been helped by the use of the winch, but it worked way below the vehicle’s travelling speed, which proved fatal – the winch was simply to slow to take the load off the wheels. It would work much better if the release mechanism disengaged wheels from the drivetrain as the winch was engaged.

The model has lost its first and only race, but in some aspects it performed much better than any of my previous trucks – it remained stable at all times, it did not suffer any damage despite the use of many delicate parts such as CV joints or universal joints, and it did not formally malfunction – it simply suffered from the drivetrain being unable to handle high torque. It was also acclaimed by other Truck Trial builders for capturing the original vehicle’s look, which kind of surprised me. Moreover, the experimental use of the 8878 battery turned out to be a success – the model’s performance was not degraded, while its weight with a traditional battery box would exceed 2 kilograms.

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Media reference:

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My third, unsuccessful Trial Truck. Features 4×4 drive, full indepent suspension and R6 piston engine.

Datasheet:

Completion date: 31/03/2009
Power: electric (Power Functions)
Dimensions:  length 46 studs / width 25 studs / height 31 studs
Weight: 1.95 kg
Suspension:  full independent
Motors: 1 x PF Medium, 1 x PF XL

An unfortunate result of my attempt to enter 2009 Truck Trial season with a brand new vehicle. It was intended to be small, lightweight and as simple as possible. Therefore I’ve decided to model the shortest version of the legendary Unimog truck being produced at the time.

The truck was built in a traditional way, with layers of bricks and plates reinforced by vertical liftarms. There were no differentials at all and the suspension utilized the 8880 set’s suspension components, replacing the universal joints with knob wheels as the universal joints get damaged in the Truck Trial quite often. The number of motors and electric components was limited to a single battery box and a single IR receiver controlling drive & steering. For the sake of stability both battery box and the drive motor were located low under the chassis, with the battery box moved close to the rear axle in order to compensate for the cabin’s weight. I have initially intended to build the cabin with liftarms and panels, but I didn’t really like the look of it and eventually chose to build a ‘fullbrick’ cab. I have, however, failed to maintain the proportions and the resulting cabin was too tall and placed a bit too high.

The decision about the cabin has dramatically increased truck’s weight – from approx. 1 kg with bare chassis and 1.4 kg with cargo platform to the final 1.95 kg. It had a great impact on the stability and performance of the model. Eventually it turned out that the truck was having serious problems with everything but driving straight ahead. A meticulous analysis revealed that it was because of the bracings keeping the knobs inside the suspension’s rocking levers. While they performed quite well before, now they tended to bend under the truck’s full weight. As a consequence the knob wheels became slightly displaced, and came into contact with other parts of the suspension. It has crippled the truck so severely that I decided to abandon this chassis design entirely, seeing no space for improvements. My first idea was to rebuild the truck from a scratch, but after a careful consideration I have canceled the Unimog project and started to build a 4×4 truck with longer chassis and two differentials. So after all,  this model has never been driven outdoors.

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My second trial truck. Features a truss frame, 6×6 drive, full pendular suspension, front winch and R6 piston engine.

Datasheet:

Completion date: first half of 2008
Power: electric (Power Functions)
Dimensions: length 64 studs / width 24 studs / height 34 studs
Weight: 2.44 kg
Suspension: full pendular, front module with shock absorbers
Motors: 1 x PF XL, 2 x PF Medium

My second complete Truck Trial vehicle, model of a Polish military off-road truck. It has been built over a span of several months, with some test-driving inbetween, but eventually the tests turned out to be insufficient, as the truck’s drivetrain severely malfunctioned at its first and only Truck Trial race. The model was high and not stable enough, which resulted in two accidents of falling off a steep slope. The second accident left the truck completely destroyed, as it tumbled down a long slope.

Despite the failing drivetrain, the model had a number of interesting features. It looked much better than my previous one, thanks to a full-brick cabin and more attention to the details. The whole structure was kept together by an experimental frame made of two liftarmic truss stringers. I considered it stronger and lighter than a traditional solution involving several layers of bricks. It seems to be true, as the frame survived even the fatal crash that destroyed the truck, and protected all electric elements enclosed in it from any damage.

Another noteable feature was the front winch, driven by a PF Medium motor. While typical winches in TrTr models need disconnecting the drive motor from the drivetrain (often the same motor drives the vehicle or the winch via a distribution gearbox), Star’s winch was designed to work together with it. In order to achieve that, the winch’s gear ratio has been carefully calculated so that it would pull the vehicle at the exact speed of its normal drive. It turned out to work as planned, and pulled the truck up a sandy slope, when its tires’ grip was insufficient to climb on its own. This solution, however, could be problematic should the drivetrain be unable to work, because the winch was too weak to pull the stopped vehicle.

I intended to re-build the model after its fatal crash, but I became absorbed in other project, and eventually gave that one up.

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My first trial truck built specifically for Polish Truck Trial races. Features 4×4 drive and steering, full independent suspension and V8 piston engine.

Datasheet:

Completion date: first half of 2007
Power: electric (wire-controlled)
Dimensions: length 66 studs / width 24 studs / height 30 studs
Weight: 1.68 kg
Suspension: full independent with shock absorbers
Motors: 1 x RC, 2 x 71427

My first complete Truck Trial vehicle, preceded by numerous and various prototypes. After trying out a great number of solutions, the final truck was fitted with full independent suspension using the 8880 set parts. The differentials have been removed from both axles to save space. The truck complied with the rules of the Polish races, which are quite restrictive; for instance, any vehicle must be an accurate model of an existing truck, with all wheels suspended and driven, and it must not exceed the width of 25 studs.

The model has been ugly and had somewhat flattened silhouette. Its performance was satisfactory, mainly thanks to the greatly simplified drivetrain. It did not suffer any significant malfunctions, except for one case when an universal joint in the front axle has been broken. It seemed able to compete with other trucks built at that time, but on several occasions while its performance was sufficient, my driving skills were not.

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