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 a Spanish armoured personnel carrier. Features full independent suspension, 6×6 drive, 2-speed gearbox, remotely opener rear ramp, deployable tracked drone and lights.  

Datasheet:

Completion date: 14/08/2011
Power: electric (Power Functions)
Dimensions: length 56 studs / width 29 studs / height 24 studs
Weight: 2.306 kg
Suspension: full independent
Propulsion: 1 x PF XL geared 6.5:1 (low gear) / 2.3:1 (high gear)
Motors: 1 x PF XL, 3 x PF Medium, 2 x micromotor

BMR-2 is a modern Spanish armoured personnel carrier. It’s a fairly typical vehicle for its class and I have chosen it mainly for its short chassis with first and last axles steered. I was hoping it would work well in an outdoor Truck Trial race. Unfortunately, it turned out that this kind of a steering system won’t work for a vehicle of that size, weight and with these tires without differentials. I haven’t been able to build it on time and therefore I abandoned plans to try it in a race.

The model had a full independent suspension that used 8297′s set components. Axles #1 and #3 were steered through a common steering shaft, by a Medium motor geared down 9:1, with a safety clutch. All wheels were driven by a single PF XL motor through a remotely controlled 2-speed linear gearbox.

The chassis was entirely studless, with majority of internal components located above the middle axle. The body consisted mainly of plates supported by a frame of Technic bricks. This solution resulted  in an unusually low weight – something I was expecting and which prompted me to try using only one shock absorber per wheel. The suspension created this was was very soft, and even though it worked, the model displayed apparent tendency to ‘sit down’ on the third axle.

Close to the end of the building process I have realized that I can save up some internal space at the back of the model. It led me to realize an idea that followed me for a while (or was it planted?) – a small tracked drone deployed from inside. In a way, this was a MOC within a MOC, and thus: a MOCception The drone was extremely simple, built around two micromotors with chains instead tracks. The micromotors were powered and controlled by two long wires connected to a separate IR receiver inside the transporter.  The drone could be deployed once the rear ramp was opened and it could operate outside its carrier. It worked well, but due to its extremely low weight it was somewhat struggling against the wires. I have also integrated something like a simple passenger compartment into the upper hull’s surface, and it turned out to be perfectly fit for a single dwarf hamster.

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Model of an ancient Roman treadwheel crane. Features a winch with a gearbox and two safety ratchets.  

Datasheet:

Completion date: 06/06/2011
Power: organic (hamsters) / electric (Power Functions)
Dimensions: length 23 studs / width 31 studs / height 49 studs
Weight: 0.342 kg (not including motor and hamsters)
Motors: 1 x PF Medium

I was recently asked to write a post about cranes for the official LEGO Technic blog, and the subject eventually came down to the history of cranes. This is how I came across a very interesting construction: the treadwheel crane invented by ancient Romans. It may appear primitive, but it introduced the treadwheel, which offers greater mechanical advantage than a crank, and it used multiple pulleys. The Romans were surprisingly well versed in the use of multiple pulleys, using blocks that combined up to five of them for a single crane. Together with the treadwheel, it made the most advanced Roman cranes able to lift up to 3,000 kg of load while operated by a single person. It’s quite an achievement for a simple construction of wood, string and few pieces of iron. Moreover, we know that Romans operated loads beyond the capacity of any single crane of the time, which means that they were using several cranes together to lift a single load, which required a great deal of co-operation between the workers.

The model was intended to be driven by hamsters, which made it more complex that I initially planned. Since hamsters are unlikely to stop and turn around when ordered to, a mechanism that would let operate the winch in both directions (lifting/lowering) independently of the treadwheel’s direction of rotation was required. I used a simple gearbox,  very similar to the one used in my RC motor output selector, which allowed to change the direction of the winch with a single switch of the transmission ring. To prevent the crane from dropping the load if a hamster stops or quits the treadwheel, I have also added two simple ratchets in the gearbox. They work in a typical way: when engaged with a gear, they let it rotate in one direction but block it when it rotates in another. A single ratchet is usually sufficient, but here it took two because the ratchets engage gear in the gearbox, which can rotate in one direction or another while lifting, depending on the driving ring’s position. The crane’s position is maintained by four guy-wires attached to a baseplate. The baseplate alone is enough to make the crane stand, but in order to lift any serious load, a counterweight is needed – hence the two yellow battery boxes.

What I missed in my design was the organic factor: the hamsters. They all have treadwheels in their cages and use them enthusiastically, but they were not interested in a Lego treadwheel, not even slightly. Worse – while I expected them to be an obedient labour force, they turned out to be the destruction incarnate in small, furry 4-legged packages. I was eventually forced to give up and to resort to the use of electricity. I suppose the hamsters simply didn’t like the spokes in the treadwheel, or perhaps it was too hard for them to make it rotate. Efficiency of a treadwheel depends largely on the weight of its operator, and dwarf hamsters rarely exceed the weight of 60 grams.

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A mechanism that selects which of the RC motor’s two outputs is used, and can effectively work as a gearbox.

As you’re probably well aware, the RC motors are unique for having two outputs, with the inner output (the one closer to the middle) having roughly 35% more speed and less torque than the outer one. Usually when using an RC motor, one has to choose one output that seems better suited for the job. With this simple mechanism, it is possible to switch between one output and another, and since the outputs have different characteristics, it can effectively work as a gearbox.

Please note that I can’t claim the authorship of the very idea, which has been around for years. I know that such a mechanism was invented long ago, but I was unable to find the original author nor any documentation, not even a single picture. I have therefore created this mechanism the way I would build it, which is probably very close or even identical to the original concept, as this mechanism is so simple that it’s difficult to build it in an entirely different way.

Also note that even though I used two RC motors in the instruction, the mechanism can be used just as well with a single motor. It’s just that I and many other builders tend to use the RC motors in tandems. Additionally, two 6-studs long axles has been used as the output of the entire mechanism here, but you can obviously change it as you see fit.

Finally, you can notice that the instruction, despite its general simplicity, has been created with the wonderful Lpub software by Kevin Clague. Thanks to the use of it, the instruction is very similar to the instructions from the official Lego sets, with a parts list for each individual step and with lengths of the axles and beams clearly specified. This is the standard for all my instructions I intend to provide from now on.

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A monster truck with Power Puller wheels. Features 4×4 drive, three steering modes, full independent suspension, remotely controlled gearbox and lights.  

Datasheet:

Completion date: 29/05/2011
Power: electric (Power Functions)
Dimensions: length 44 studs / width 28 studs / height 31 studs
Weight: 2.113 kg
Suspension: full independent
Propulsion: 2 x PF XL geared 6.5:1 (1st gear) / 1.6:1 (2nd gear)
Motors: 3 x PF Medium, 2 x PF XL, 1 x 2838

A construction I’m definitely not happy with. It doesn’t work or look exactly how I wanted, and I couldn’t make the video the way I wanted neither. The chassis of this truck has been entirely reworked three times. The first version was using 4-link floating axles suspension from my Sandrail, but it turned out unstable and it pressed strongly on the driveshaft. I then turned to the independent suspension based on the 8297 set’s suspension components, and using knob wheels instead differentials for a better off-road performance. It proved slow and it was struggling very hard to make a turn. Eventually, the third version had differentials and increased gear reduction. It drives and turns well, but the Power Puller wheels which I wanted to own and put into use for a very long time, turned out to create an amazing amount of problems.

The chassis has 4×4 drive with the differentials enclosed in 5×7 studless frames, with universal joints and CV joints – a simple solution using specialized Lego pieces, and putting these pieces at a considerable risk of getting damaged. Each wheel is suspended on three shock absorbers: two long ones and one short one, with the short one located closed to the middle of the chassis to preserve the suspension’s long travel distance. I was prepared to see some broken CV joints, and I had spares at hand, but surprisingly not a single piece got damaged. In the centre of the chassis, there is my heavy duty 2-speed gearbox controlled by a Medium motor and a single mini linear actuator. There are two XL motors attached to the gearbox, they are coupled with knob wheels and connected to a switch inside the cabin. By turning this switch off, it is possible to shut down the main drive and play with the V8 piston engine which is coupled with the drive motors. The engine is driven by a 2838 motor reaching well over 1000 RPM, and includes a fan and a fiber optics unit. It creates interesting sound effects, especially when used with the speed control remote.

Both front and rear axles are identical. Each includes a Medium motor reduced 5:1 and controlling steering, so there is no mechanical connection between the steering of front and rear axle. Instead, the rear axle’s steering motor is connected to a switch that is motorized with another Medium motor using the spring-loaded Lego connector. Thanks to the connector, the switch returns to off position when the motor is turned off, thus allowing to switch the switch remotely through three positions. This results in three steering modes: normal steering for front axle, normal steering for two axles and crab steering for two axles.

I have spent a considerable amount of time testing the chassis and getting it to perform better, and I’m disappointed with the result. Despite the fact that the truck is relatively light and driven by two XL motors, it is slow and can get stalled on large obstacles. All because of the Power Puller wheels, which are heavy, extremely wide and with very soft tires. The amount of torque required to drive these wheels at all is shocking, and they tend to tilt a little every now and then, even though the chassis is extremely rigid and the suspension is very stable. I have tested the truck with different wheels, and changing to any other wheels resulted in an instant improvement of the overall performance, at cost of the look. It seems that the reason the Power Puller wheels are rarely seen in practical use is not only because how rare and expensive they are.

Even despite my disappointment, the truck was a valuable experience on how the 8297-based suspension behaves in extreme conditions and on how durable are the pieces it requires. While the truck itself was never intended for the Truck Trial competition, I hope to make use of this experience when building my next Truck Trial vehicle. I have also used this opportunity to work on the photos a little more, e.g. by artificially re-creating the so called ‘Michael Bay flares’

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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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Compact, simple gearbox designed for use in Truck Trial races and high-torque applications. Step-by-step instruction and a two drive motors variant included.

Last year, the continuous development of the Truck Trial vehicles in our country resulted in the common use of gearboxes. Since the power-to-weight ratio of each vehicle decides how much points it gets, it is favourable to reduce this power to minimum. This is where gearboxes come in handy – they allow to use less motors, or less powerful motors, increasing gear reduction when needed, and decreasing it when less torque is needed. Without the gearboxes, all vehicles would have to use a gear reduction high enough to climb obstacles, which results in reduced speed and in a waste of time when e.g. driving downhill.

The loads exerted on vehicles’ drivetrains in our races are so high that it’s very difficult to use a gearbox with driving rings. In most cases, it results either in the driving rings disengaging under load, or in mechanical damage to them. Therefore it’s a common practice to use simple linear gearboxes, with as few gears as possible, as most vehicles can do very well with just a 2-speed gearbox. The need for reducing amount of gears to minimum resulted in integrating the drive motors into the moving parts of the gearboxes, so that the motors slide as the gears are changed. The idea, introduced by Emilus in his Truck Trial models, eliminates the need for complex transmission mechanisms between sliding driveshaft and stationary motor, and has practically no disadvantages, except for slight shifts of the vehicles’ centre of gravity caused by motors’ weight.

The following gearbox has been developed from a version used in my Fiat SPA35 Dovunque model. The Fiat’s gearbox has failed during the race, but it has given me the opportunity to observe exactly what are the causes of its malfunction. Based on this experience, the new gearbox has been reinforced in all the crucial spots and is practically immune to mechanical damage, while still being relatively compact and simple.

I have provided schemes, views from various angles and a full instruction for the gearbox, as well as a scheme and views of a version using two drive motors instead one.  Note that the sliding mechanism has not been included, because my experiences with Fiat have shown that it’s best to make it part of the chassis close to the gearbox, that part of the gearbox itself. Still, building such a mechanism should be fairly simple, as all it has to do is to slide the central bracing a single stud back and forth, and keep it in place. The mini linear actuators are one of the many options that can be considered here.

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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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Compact gearbox design, with two linear shifters, fixed input and output shafts, and large span of gear ratios provided.

This particular idea started with the Truck Trial vehicles in mind. As the trucks used in the Polish Truck Trial are being constantly developed, more and more of them became equipped with simple gearboxes. Such vehicles have the obvious advantage of being able to adapt their drivetrain’s gear ratio to the requirements of the track, sacrificing speed when more torque is needed and gaining extra speed when less torque is needed. Developing a gearbox that would last through a Truck Trial race is quite a challenge, which is why gearboxes only became popular recently.

Aside from highly experimental or lightweight vehicles, all gearboxes currently used in our races are linear gearboxes. There are two reasons for this: firstly, a linear gearbox usually has more compact and thus more robust structure, and secondly the transmission driving rings used in more sophisticated Lego gearboxes are much less torque-resistant than the gear wheels are. Since linear gearboxes only use gear wheels, no transmission driving rings at all, this problem is eliminated. Additionally, with very simple, usually 2-speed linear gearboxes the shifting mechanism is typically very simple too, making the general complexity level of such a gearbox fairly low.

As Truck Trial races involve a significant torque to be handled, the gearboxes are made as simple and robust as possible, rarely using more than 2 speeds. We stick to the rule than any mechanism can be complex or robust, but not both – and it works very well for the Truck Trial constructions. Even a gearbox with just two gears is quite an advantage; a vehicle that can gain extra torque to drive uphill and extra speed to drive downhill will always beat the one that has no gearbox and drives at constant torque and speed. Since the amount of torque required to overcome any given obstacle is more or less the same for every truck, the gearbox-equipped trucks win by simply jumping to high gear and driving faster whenever possible.

There are two basic problems involved when building a torque-resistant linear gearbox: the choice of the gear wheels that will engage and disengage, and the length of the axles that will transfer the drive. As for the first problem, the double bevel gears are a very common choice because the shape of their teeth makes them engage and disengage easily, and also because they are strong (the smallest double bevel gear wheel, the 12-teeth one, is many times stronger that the smallest regular gear wheel, the 8-teeth one). As for the latter problem, the solution is simple: the axles have to be as short as possible and reinforced in as many places as possible to prevent them from bending under torque. Additional protection from the torque for the gearboxes is achieved by using gear reduction between the gearbox and the wheels. Thus a gearbox is placed directly on the drive motor’s output shaft, and it only handles motor’s nominal torque, not the torque multiplied by the gear reduction.

With this said, I started to work on a gearbox for my next Truck Trial vehicle. I wanted it to have fixed input and output shaft, with the only moving elements located somewhere between, to eliminate possible weak points. It meant that I had to use separate shifter axles. Moreover, to keep the axles short I had to keep the moving by a single stud only, so a single shifter axle could only provide two gears. That’s why I used two shifter axles, looking for a gearbox that would provide at least three gears.

The resulting gearbox was supposed to be mounted vertically, but is shown laid on a side in the pictures and video in order to show its internals better.  First video shows bare gearbox and its construction, while the second one shows a version with remote-control already integrated into it, and reinforced adequately. The gearbox provides a wide span of gear ratios, from nearly 8:1 reduction to nearly 1:3 overdrive. It is reasonably small and can shift from any gear to any other gear. Unfortunately it needs two separate motors for remote control and has a rather unusual switching pattern. As shown in the videos, the shifting time is reduced to as short as possible in order to make the gears engage and disengage seamlessly every time.

Eventually, I kept this gearbox for practical testing in some more ordinary vehicle and choose a much simpler 2-speed one for my Trial Truck. I do, however, find it very useful and convenient to control remotely, and I will certainly look for more than just one opportunity to use it in my future models, most likely some at least medium-sized trucks. If it proves successful, it may very well be installed on a Truck Trial vehicle, as intended from the beginning.

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New gearbox concept – a 3-speed sequential synchronized pneumatic gearbox that can be operated entirely remotely.

The gearboxes are very useful even today, with the speed control feature available with the Power Functions system. They are even more useful when they are remote-controlled, because this way the vehicle doesn’t need to stop to shift gears – instead, the gears can be shifted while driving. This type of gearboxes can work just like the real ones: it can have some gears that are unable to start the vehicle, but can speed it up once it has some momentum already.

The easiest type of a remote-control gearbox is a 2-speed one, because it can be easily motorized like an end-to-end device; it can shift between 2 gears with a single motor easily. I always wanted to build a remote-controlled gearbox that would have more than 2 speeds and still require only a single motor to be operated. It was eventually achieved with the AeroShift gearbox (I made up that name because the ’3-speed remote-controlled sequential synchronized pneumatic gearbox’ didn’t sound too catchy ).

This gearbox is, as mentioned above, sequential, which means that it can’t shift from any gear to any gear. Instead, it has to shift through gears in a sequence, e.g. from 1st to 2nd and then from 2nd to 3rd. This type of gearbox is quite popular in motorbikes. The gearbox is also synchronized, thanks to the use of the driving rings, on assumption that it would be troublesome to watch for grinding gears in a gearbox that’s supposed to be operated remotely.

If you look closely enough, you’ll notice that the gearbox consists of two identical modules set as ‘mirrors’ of each other. It is perfectly possible to build more than two modules – the first one will provide two speeds, and each next module will provide one extra speed (hence 3 speeds with two modules). The gearbox would have 5 speeds with four modules, 7 speeds with six modules, and so on. I did not attept to use more modules, because for me 3 speeds with a gearbox of this size was a good solution, while 5 speeds with a gearbox twice as large was not. Additionally, it would require more than a single pneumatic cylinder to be operated, and thus greatly complicate the pneumatic system.

It should be mentioned that this gearbox can be operated without pneumatics. It would, however, require a number of gears, including gears with clutches, as well as a mechanism that would work like a stepper motor. Since a single pneumatic cylinder can replace all these mechanic parts, I have chosen this solution as a significantly simpler one.

The picture above shows a testing setup. The pressure gauge and speedometer are obviously not needed for the gearbox to work, and the pneumatic valve is supposed to be operated by a motor. The parts that are important for the proper functioning of the gearbox and may not appear so on the photo include the rubber band which makes sure that the driving rings are switched sequentially, not simultaneously, and the grey thin plates described as ‘limiters’ above, which make sure that the movement of the pneumatic cylinder is contained within a desired range. The cylinder can be mounted with its inlets pointing downwards to take less space, but it requires placing the pneumatic hoses in such way that they don’t interfere with the moving parts of the gearbox. I believe that this photo along with the ones that follow it are sufficient to build a copy of this gearbox, so I will just list the pros and cons of this gearbox according to my observations.

Pros: relatively small size,  ability to handle huge torque (the critical elements are the driving rings that tend to disengage when too much torque is applied), convenient location of the input and the output, identical functionality for the driveshaft rotating clockwise as well as counterclockwise, and a minimal chance of the mechanical failure in the gearbox (e.g. because all the gears that transfer the drive are encased in solid bricks).

Cons: uses pneumatics, doesn’t work well with high air pressure (it causes strain on the driving rings and thus slows the gearbox down, so use of an airtank with this gearbox is not recommended), is sequential (impossible to omit the middle gear, though it can be switched through it really quickly) hitting the medium gear precisely can be tricky (depends mainly on the proper calibration of the rubber band and the pneumatic pressure in the cylinder), the gears are shifted relatively slowly,  and there is a number of dead gears that generate additional friction.

The gearbox offers the following gear ratios: 1:1, 3:1 and 9:1. If these differences are too large for your use, it is perfectly possible to replace the 8t & 24t gears pairs with 12t & 20t gears pairs. It will result in the gear ratios changed to 1:1, 1.66:1 and 2.77:1, while the functioning of the gearbox will remain the same.

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Media reference:

TechnicBRICKs

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My first automatic gearbox, based on a design by Misha van Beek, but improved and simplified.

I always liked the idea of incorporating automatic gearboxes into large models, unfortunaltely such gearbox designs are unique and I only know two by Misha van Beek. While both are advanced and show great knowledge of the author, they are also large, complex and none changes gears smoothly. I thought that the new, small differential may give me a good opportunity to create a more useable design. I had three simple goals: to make a gearbox that is small, simple and above all capable of changing gears without jamming. The two first were easy, the third one took some time to work out, but eventually I got exactly what I wanted.

The basic idea of Misha’s design is to use a differential to transmit the drive in such a way, that if the resistance of the output grows, it will at certain point trigger the gearbox to switch to lower gear. Thus the motor will have a better chance to overcome the resistance, and once it’s done the gearbox will switch back to the higher gear. Whereas Misha has taken this idea further, and created gearboxes with more than just 2 speeds or with no fixed gear ratio at all, I considered two smoothly operating speeds a better option than three or more jamming ones. The lower gear has 2.77:1 gear ratio, and the higher one has 1:1 gear ratio. I have been experimenting with more different ratios, but as the difference increased so did the tendency to jam while changing gears. The 2.77:1 ratio difference should be sufficient in most cases, and it offers a reasonably smooth functioning of the gear change mechanism.

The construction of the gearbox is really simple. It fits into a 8×12 studs rectangle (plus the middle shaft protrudes out by 1 stud on higher gear), and axles of any length can be put into input and output without taking the gearbox apart. Moreover, the horizontal liftarm which servers as the gear change lever, provides a lot of space to adjust the tension of the rubber band accordingly to the weight the gearbox is supposed to handle (namely, the towballs it sits between can be put closer or further from each other).

You can see the smooth functioning of the gearbox in the video. I have also provided a parts list (just 45), an LDR model of the gearbox at lower gear and higher gear, plus an exact instruction which can be found below.

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blog.kockak.hu, Bricks ‘n’ Gears

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An experimental halftrack vehicle. Features three types of suspension, a 4-speed manual gearbox and openable doors.

Datasheet:

Completion date: 13/04/2009
Power: electric (Power Functions)
Dimensions:  length 54 studs / width 17 studs / height 16 studs
Weight: 1.41 kg
Suspension:  front – independent / rear –  torsion bars + pendular bogie
Motors: 1 x PF Medium, 1 x PF XL

Having built a dozen or more tracked vehicles, I eventually felt compelled to try a halftrack. Halftracks are an interesting blend of tracked and wheeled vehicles, combining the advantages of both. Namely, they perform better off-road with tracks than typical wheeled vehicles, and they can steer much easier than typical tracked vehicles thanks to the wheels (which results in a simplier construction rather than in a better performance).

There is a number of problems involved in building a halftrack, and I was curious as to how they would affect a small, lightweight model. Basically, the real halftracks often have the front wheels driven for better traction and better steering. There is usually a differential between the tracks, which serves the same purpose, and some of the heavy German halftracks were fitted with automatic brakes that would slow down one track while turning.

There was a single technical solution that greatly affected the look of the vehicle: the torsion bars. I was earlier suggested to try this kind of suspension, popular even in heavy tanks of the WW2, but it did not occur to me at that time how to make such a bar bend without sustaining any damage. Only sometime later it hit me that the elastic 16-studs long axles from the Jumping Giant would be an ideal and natural choice. It’s just their limited length that was not ideal, and hence the width of the entire vehicle was limited by the transverse 16-studs long axles used as torsion bars.

With the vehicle’s body only 16 studs wide I’ve given up the intent to make the front wheels driven. Instead, they were just fitted with a simple independent suspension, and the suspension of the tracks was complemented by a central pendular bogies because I only had two axles that could serve as torsion bars. The drive was transferred through the usual 4-speed manual gearbox I’ve used many times before to the tracks’ front return rollers without the use of a differential. I have assumed that it would be catastrophic to drive a lightweight vehicle with a slippery tracks via a differential – the slip situation would be more than likely to happen.

Eventually, the vehicle had a surprisingly efficient steering system – which was due to the tracks’ poor traction rather that to its construction. The turning radius was even slightly better than it would be with two regular rear axles instead of tracks. I suppose that given a sufficient speed it could be a great drifting truck.

As for the look of the truck – I had no clear idea what should it look like, but I definitely didn’t want it to look like German military halftracks of the WW2, which are often considered iconic for this type of vehicle. That is why I pursued the look of a vintage truck, which eventually proved to have a lot in common with the US Army’s halftracks (M3 and its successors in particular). Still, I was unhappy about the bonnet which had to be tall and wide to cover the shock absorbers of the front suspension. Actually, the front of the truck was so massive that its center of gravity ended up below the cab – despite the fact that all motors and the battery box were located between the tracks. I felt that the back of the truck should be openable, but that was impossible because of the battery box being fixed there. The battery box and the motors were left uncovered deliberately: this way they could appear to be the truck’s load, and the cargo space seemed much larger than it would with these parts covered up.

The truck was technically very compact, which resulted in some limitations. There was no place for working lights nor for the reinforced drivetrain, the latter resulting in an inconsiderable vehicle’s top speed.  The suspension system, however, worked pretty well. The torsion bars functioned in a proper and realistic way, even though they were probably too weak to support the entire truck’s weight. Still, there was a margin of calibration available, as I created a 2 studs long ‘torsion space’ – that is a space between the actual suspension and the point where the torsion bars were fixed to the chassis. If this space was reduced to a single stud, the suspension could probably handle a significant weight. Tests with the gearbox proved the torsion bars to be a bit unreliable; they tended to produce vibrations at lower speeds and worked smoothly only at the higher ones. I suppose that this effect is proportional to the size of tracks’ links, which means that the newer tracks system would require even higher speed to run smoothly with this suspension system.

Although I have initially considered it a minor, highly experimental project, the Crusader performed almost flawlessly and was more fun to drive than many more advanced vehicles. Moreover, to my sincere surprise its aesthetic aspect was much acclaimed at the LUGPol and beyond.

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Media reference:

Klocki, The Brothers Brick

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