Model of a Liebherr excavator with tunneling arm. Features a blend of electric and pneumatic functions, custom stickers and lights.  

Datasheet:

Completion date: 17/06/2011
Power: electric (Power Functions) / pneumatic (external manual pump)
Dimensions (with arm in driving position): length 40 studs / width 16 studs / height 35 studs
Weight: 1.497 kg
Suspension: none
Propulsion: 2 x PF Medium geared 1:1
Motors: 4 x PF Medium, 1 x 71427

Model of a regular Liebherr excavator with an uncommon tunneling arm. Model of the very same machine created in larger scale was released in 2010 by my fellow LUGPol member M_longer and is available here. M_longer introduced me to this excavator before he started to build it, and I liked it so much that I intended to build it first. Eventually my timing kind of failed, because my model was finished 10 months after his

My version of the excavator was intended to be much smaller than M_longer’s: his was scaled to the new tread system, and I decided to use the old one for mine. The resulting difference in scale means that my model is roughly 40% smaller. Seeing that the model would be quite small for its number of functions, I have been planning to use pneumatics wherever possible and to have an external pneumatic controller permanently attached to the model. This solution is sometimes called a ‘pneumatic leash’ and it was used in many of the models created by my idol builder, Jennifer Clark. I have never really used it before and I thought of this as of opportunity to feel like Jennifer

While I was in the process of cramming the mechanics inside the hull, it occurred to me that I will be able to integrate all four pneumatic valves into the hull at the cost of making its upper surface uglier. I decided it was worth it, and eventually the model’s only external element was a single manual pump, which allowed for more accurate control of the pneumatic system than a motorized compressor would.

As for the aesthetic side, I didn’t want the hull to look like a box, which was pointed out with my earlier Caterpillar excavator, so I decided to build the sides and the back of the hull using body panels and SNOT (studs not on top) technique. I think the model looked generally worse than M_longer’s version, which is disadvantage of the smaller scale, but it did include a number of details that were omitted by M_longer in his model – such as e.g. the side and rear view mirrors.

The model had 5 motorized and 4 pneumatic functions. The propulsion system was obviously motorized and consisted of two PF Medium motors geared 1:1 and located in the chassis. The chassis also housed a third PF Medium motor, which rotated the superstructure. The fourth PF Medium motor was located inside the superstructure and drove two large linear actuators that controlled the elevation of the arm’s first section. As the actuators were effectively handling the weight of the entire massive arm, I have assumed that pneumatic cylinders would be too weak or too inaccurate for this task. Finally, there was a  71427 motor located at the back of the hull, and it was chosen because it’s shorter than a PF Medium motor. Its function was driving the milling head, which was done by a single long driveshaft that went all the way from the back of the hull to the tip of the arm and which was articulated in five places.

The 71427 motor was not controlled remotely, like the other four motors, but was instead connected to a switch located in the front right part of the hull. The same switch controlled two lights on the arm, as there was simply not enough space inside the hull to connect them together with hull’s front and rear lights. As a result, the lights on the arm lit up as the milling head works.

The whole electric system was powered from a single 8878 rechargeable battery located in the rear left part of the hull. The battery was accessible through a hatch in the left side of the hull, and was lying on its side in order to stay aligned with the side body panel.

The pneumatic system consisted of a single large cylinder that controlled elevation of the dozer blade in front of the chassis, two small cylinders that tilted the arm’s second section left and right, two large cylinders that controlled elevation of the arm’s third section and a single large cylinder that controlled the angle of the arm’s head. The arm itself was a fully studless structure partially covered by a studfull shell. Its range of movement was reasonably close to that of the original machine, and it was robust enough to support the model on one side. The milling head could be easily removed and replaced by e.g. a bucket or… something else.

It should be noted that the model’s driving speed and superstructure’s rotation speed were both inflated. I have done this on purpose, because I wanted to use the full potential of the model’s motors, knowing that I can reduce the abundant speed at any moment using the speed dial remote.

I was fairly satisfied with this model. It was compact yet full of various functions, it blended motors, linear actuators and pneumatics using the advantages of  each, and it looked quite good and accurate. Despite having no gear reduction at all, it was perfectly able to push and tow the 8110 Unimog set which weights over 2 kg. I consider it a noticeable step forward from my previous excavators in terms of blending aesthetics and functionality, and – unlike my previous excavators – it appeared free from severe disadvantages to me.

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Media reference:

TechnicBRICKs

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Simple arm with 4 motors, controllable and programmable with the LEGO Education WeDo software.

Datasheet:

Completion date: 19/06/2010
Power: electric (Power Functions) / pneumatic (fed from internal compressor)
Dimensions: height 58 studs / full length of the arm: 113 studs
Weight: 1.53 kg
Motors: 4 x PF Medium

I had access to the LEGO Education WeDo kit for some time, but it was only after I bought second USB hub that I was able to come up with some ideas on how to make use of it. The kit is in a way similar to the LEGO Mindstorms, except it employs the PF system’s components and it needs a computer to be run on. Therefore it is not as mobile as the LEGO Mindstorms with its separate CPU brick, but it’s much more flexible as it needs a computer and PF components that most of the builders already have.

One of the limitations of the WeDo system’s architecture is having just two independent outlets on each USB hub. While it is consistent with how the PF IR receivers work, it also means that you can only control 2 motors/sensors with the basic kit, and up to 6 motors/sensors maximum as the software can control up to 3 USB hubs at once. This is still, however, better than 3 motors that can be plugged to a single NXT brick.

The first version of the arm was built in a couple of hours to be displayed on the same public event as my Caterpillar excavator was. It was controlled by 4 PF switches, to allow viewers to control it manually. It was, however, built with the WeDo software in mind from the very beginning (hence just 4 motors) and after the event I fixed some minor shortcomings and plugged it to my notebook.

It was easy and convenient to control all the motors using a simple keyboard layout as presented below. Basically, there were two keys for each motor, for running it in one direction or another, and there was a single universal stop key. A separate key was responsible for executing complex programs, and I have prepared one such program for the video (it was a time-consuming task due to the need to manually pre-adjust range of each movement).

Another shortcoming of the WeDo software is that it controls motors using a timeout function and not a rotation counter like the Mindstorms do. The advantage of this solution is the ability to use any motor – the PF extension wires make it possible to plug any 9V motor into the PF system and thus to make it WeDo-controllable. The disadvantage is that motors are friction-sensitive, which means that a motor that is run forward and backward for exactly the same time rarely returns to the exact starting position because of the differences in friction it encounters. With the executable programs, I solved this issue by pre-adjusting every movement manually.

The arm itself consists of a simple grabber with 4 independent fingers, each with a rubber tip for improved grip. The fingers are controlled by an autovalve and thus are capable of adjusting to the shape of the grabbed object. The grabber has a wrist that can be rotated through 360 degrees and uses a safety clutch. The arm is elevated with two linear actuators, with the arm’s level being maintained throughout the elevation process. Two battery boxes are mounted on the rear side of the arm to act as a counterweight for the grabber and its load. Finally, the entire arm can be rotated through 360 degrees by a turntable at the top of the tower it sits on. It felt like something innovative to build, and had certainly a huge potential for various programs and arm’s modifications.

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Media reference:

Fascinating LEGO Model Of The Day, Robótica recreativa y educativa (Spanish only)

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Large model of a Caterpillar front shovel excavator designed for a public display. Features a drivetrain with a subtractor, superstructure rotation mechanism, V12 piston engine, arm with 3 joints controlled remotely by motorized linear actuators, pneumatically opened bucket, remotely elevated operator’s cabin, lights and custom stickers.

Datasheet:

Completion date: 11/06/2010
Power: electric (Power Functions) / pneumatic (fed from internal compressor)
Dimensions (with the arm in ‘resting’ position): length 80 studs / width 28 studs / height 35 studs
Weight: 3.5 kg
Suspension: pendular bogies
Propulsion: PF XL motor geared down 9:1, through a subtractor
Motors: 2 x PF XL, 6 x PF Medium, 1 x 71427

I wanted to build a front shovel excavator controlled by linear actuators for some time already. It took me a while to find a machine with a distinctive silhouette (as many large front shovel excavators are shaped similarly) and my choice was the Caterpillar 90-tonne machine with an unusual cabin elevation system.

The model would be built at much later time if it wasn’t for the people from the Focus popular science magazine, who invited me over to a Picnic of Science held in Warsaw (the largest popular science event in whole Europe). It was a kind invitation, but it also meant a fixed term to build something spectacular and, so to say, public-proof. I had to hurry to make it on time, I even used my absence of leave to finish the model, but I felt it was still not tested sufficiently.

The look of the model is accurate to some degree. The size and all the dimensions are kept faithful, and the colour theme is an exact rendition of one of the two Caterpillar liveries I’ve seen this machine with. The details on the top of the model, however, were intended to look diverse rather than accurate, the V12 piston engine model is completely unrealistic (but it turned out to be a great crowd pleaser, as anticipated), and the arm lacks a single actuator. Additionally, the way the bucket opens up has been changed slightly to make the bucket look better and be more structurally sound.

As for the functional side, it was largely affected by the unexpectedly huge weight of the model. While the chassis was providently built around a really massive studless frame, the drivetrain had to be additionally geared down to handle it. Even with the 9:1 gear reduction, some gears in the subtractor are still being grinded to dust. Not a single gear in the drivetrain was broken, but there was a plastic dust coming out whenever I opened up the subtractor. But in fact, the painfully low speed of the model is accurate as the real machine moves at 4.4 kmph.

There is a studless Technic turntable between the chassis and the superstructure. The stability is provided by four double rollers, consisting of two wedge belt wheels with rubber tires each, and integrated into the superstructure’s bearing frame (located, as usual, in its ‘floor’). The rollers are supported by large tiles on the top of the chassis. I have assumed that use of large rollers will be a convenient way of filling the gap between the superstructure and the chassis, and that the rubber tires will provide a degree of elasticity should the superstructure tilt while operating. Whether these assumptions were accurate or not is difficult to prove eventually. But I was right to only use four sets of rollers (front/rear/left/right one) as they provided sufficient stability for as long as they were part of a sound, rigid structure.

The major drawback of this model is the use of an 8-teeth gear wheel as the final part of the superstructure rotation mechanism. The weight of the superstructure coupled with the friction generated by the rollers’ rubber tires caused this gear to be severely damaged during final tests. Since it was very difficult to replace (read: it required to take half of the model apart) and there was no guarantee that the new gear wheel wouldn’t share its fate, I left if the way it was. Which means that the superstructure rotation works only when aided by hand. The video clearly shows that superstructure rotates as long as the rear part of the hull is being gently pushed (at some point I even use a single finger for that to demonstrate that there is indeed a mechanism working there and that I’m not simply rotating the superstructure by a hand). The use of the 8-teeth gear wheel, which worked fine in lighter models, was a mistake here to begin with. I should have used a worm gear instead, preferably one that would be mounted to the chassis and driven from the chassis.

The rear part of the hull houses the 8878 rechargeable battery which powers the whole model and which can be accessed by a small sliding lid. On its left, there is a big V12 piston engine driven by a separate PF Medium motor coupled with the drive motor (which means that there is no mechanical connection between this engine and the drivetrain whatsoever). The whole V12 is fully enclosed inside the hull, and can be displayed by opening up a two-piece lid. I always wanted to include a piston engine into an excavator model, and with a model that large I finally did. On the right side of the battery, there are four IR receivers and beneath them, there is a pneumatic autovalve which controls the opening/closing of the bucket.

The front part of the hull houses a massive frame around the arm’s main joint. The arm is 6 studs wide at this point, and there is a driveshaft, two pneumatic hoses and three electric wires going through the joint. On the right side of the arm there is a PF XL motor which drives two linear actuators that lift arm’s first section. There is also a PF switch which controls the lights on the arm, and which can be accessed by the means of a small door in the right side of the hull. On the left side, there is a cabin sitting on a scissor lift mechanism, which is moved by a single linear actuator driven by a 71427 motor located under the piston engine. The elevation range of the cabin is impressive, especially when you realize that the whole scissor lift mechanism is just 3 studs tall. The mechanism has its drawback too – it puts a very high load on the motor, so it has to be additionally geared down (hence the low speed of cabin elevating) and the weight of the cabin has to be kept low (hence the number of details is lower than intended).

The arm consists of two sections. The first one is controlled by the aforementioned PF XL motor which drives two linear actuators integrated into the front part of the superstructure’s frame. The second section is controlled by a PF Medium motor located in the hull, between the arm and the 8878 battery, which drives a single linear actuator integrated directly into the arm’s first section. There is another PF Medium motor inside the first section, which drives another two linear actuators that tilt the bucket. The second section of the arm is pretty much empty. The arm was built in the same way as it was with my previous excavator: it consists of a studless frame with directly attached actuators, and a studfull outer skin which provides extra stiffness but is not necessary for the arm to work. I am not quite pleased with the somewhat weird look of the pneumatic hoses on the arm – I could have enclosed these inside the arm, but I felt that an excavator’s arm ought to have some hoses on it. But due to the complex construction of the arm’s first section, there was no way to arrange the hoses in a more realistic manner.

The arm has some excellent movement range. In fact, it is somewhat better than that of the original machine – to the point at which it is not necessary to open the bucket to unload it, as it can be simply tilted.

As for the bucket opening mechanism, it is very simple and consists of just two small pneumatic cylinders. Some minor part of the load is usually left inside the bucket when it opens, but this is caused by the bucket’s inner shape which results from its internal studless frame rather than by the mechanism itself.

This has doubtlessly seen more practical use than any of my other excavators, as it was operated for a couple of hours straight during a public event. It has also successfully faced the devastating curiosity of little children present at the event, but I won’t describe the details lest I sound like a contraception promoter In fact, the failing superstructure rotation mechanism is the only thing that prevents me from calling it my best working excavator model ever. The model has been also highly acclaimed by LUGPol members – so highly, in fact, that I was genuinely surprised.

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Media reference:

Hobby Media (Italian only)

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Model of a human arm. Features 4 electric and 4 pneumatic functions.

Datasheet:

Completion date: 28/02/2010
Power: electric (Power Functions) / pneumatic (fed from external pneumatic compressor with an airtank)
Dimensions:  unknown
Weight: unknown
Suspension: none
Motors: 3 x PF Medium, 1 x PF XL, 1 x RC

Just another weekend build – this is basically a late realization of an idea I had back when I was a kid. The goal was to build a model of an entire human arm, with palm included, that would have as much realistic functions as possible while being of more or less accurate size. The look of the arm was considered insignificant.

The most complex part of the arm is obviously the palm with 4 fingers and a thumb. The thumb can be bent and raised/lowered, whereas the remaining 4 fingers have two joints in each of them. The index finger was operated independently, and it was fairly possible to operate every finger individually, except that it would take two times more pneumatic hoses, which were already quite numerous (8 of these was going through the arm). The palm can be theoretically rotated through full 360 degrees, but I never actually tried it for the sake of the hoses in the wrist. The whole arm was heavy and a bending under its weight a bit, but it worked well. I think it was pretty satisfactory for something that was built in just two days.

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Video:

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Media reference:

Brick Tales, Bricks in my Pocket, crave,  CrunchGear, Engaget, Fascinating LEGO Model Of The Day, Hack N Mod, Le Journal du Geek, NowhereElse, Sema Geek, Switched, Tamasindo, The Awesomer, The Geek Church, Tinkerology, Tom-Style

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New compressor design, using reciprocating motion instead of a rotary one. Smaller, stronger and more adjustable than traditional compressors, it can run up to 18 pumps.

I have presented some ideas for compressors earlier – they used at least two sets of alternatingly working pumps to keep the airflow fluent and the vibrations minimal. The problem, however, was that they all used a rotary motion to run the pumps, which made them large and structurally weak (e.g. because no central axle could be used to run the pumps, there had to be an empty space for the pumps to move). Both these problems increase rapidly with the growing number of pumps.

Having recently bought an extra supply of pumps, I was looking for a solution that would result in a compact and strong compressor. I have found it by replacing the traditional rotary motion by a reciprocating one. The compressor I’ve developed can use any even number of pumps between 2 and 18 (this limits results from the 12-studs long axle being the longest one we can use to put the pumps on), while being much smaller and stronger that the traditional ones. It can work with any motor, and has integrated gearing that can be adjusted to your needs by picking one of 4 available combinations. The only tradeoff is the fact that it generates more vibrations that the rotary compressors, but it still makes it a useful alternative. Even with 18 pumps, this compressor is only 14 studs long (not including the motor). The exemplary variant I’ve built for the video uses 8 pumps and its dimensions are just 9x6x7 studs (again, not including the motor).

You can find a complete instruction below, and the video is pretty explanatory. While many people tend to choose large compressor based on RC motors for large models, I dislike this solution because RC motors are noisy and difficult to use with the Power Functions system (they run at a current so high that it makes the battery boxes and batteries go off). Therefore for me, this solution will be a much better alternative in the future.

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Pneumatic excavator with a full remote control. Features internal compressor, 3-position motorized pneumatic valves, integrated manometer, infinite freedom of superstructure rotation, lights, flashing warning lights, custom stickers and simple suspension.

Datasheet:

Completion date: 09/01/2010
Power: electric (Power Functions) / pneumatic (fed from internal electric compressor)
Dimensions (with arm in the transport position):  length 72 studs / width 27 studs / height 56 studs
Weight: 2.77 kg
Suspension:  pendular bogies
Motors: 7 x PF Medium, 1 x 71427
Pneumatics: three circuits with motorized 3-position valves fed from internal 4-pump compressor; integrated manometer

The idea behind this model was simple: to build a fully pneumatically operated excavator with a full remote control. Such a mixture is unique – there are many pneumatic models of excavators, but nearly all of them are connected to an external controller, which houses all pneumatic valves and usually also the compressor. I thought it would be quite a challenge to make a similar model fully remote-controlled, and I was sure that a pneumatically operated arm would look more realistic that one operated by linear actuators (as demonstrated by my earlier Liebherr R996 excavator model).

I was looking for a classic tracked excavator, and – somewhat tired of Caterpillars and Liebherrs – I turned my interest to the Volvo machines. The EC290C excavator scaled down accordingly to the width of the tracks seemed a most proper vehicle to model.

When you think of a pneumatically operated excavator, it quickly becomes obvious that it needs a possibility to return the valves to the neutral position, or – more simply – to close them. With such a possibility all sections of the arms could be controlled independently (well, almost – they would still affect each other by changing the air pressure in the pneumatic system); without it every section would have to reach its extreme position to let another one operate. Therefore I was looking for a small, simple way of controlling the valves, and what I found was an invention of my fellow LUGPol member, Dmac. It’s a very simple solution, but a tricky one – it depends on the elasticity of specific liftarms in relation to the internal gearing of a PF Medium motor.

I have assumed that with all valves controlled in that manner and fed from an internal compressor whose speed I can control remotely, I will have a full control over the excavator’s movement with a satisfactory degree of accuracy.

The model uses an uncommon chassis. It is held together by a single transverse beam which houses two PF medium motors inside it, along with a reinforcing frame made of liftarms. Thus the beam appears small and almost completely smooth, with the motors completely enclosed. It puts quite an extreme load on the beam’s components, but it results in a realistic look, as the real machine also has a single transverse beam in the chassis, and its drive motors are not visible, housed in the superstructure.

Another important thing is that the original Volvo excavator has its drivetrain fully enclosed within the tracks , with no parts protruding out at all. To model it, I have used two long sections of LEGO Technic chain, each connecting one drive wheel to the motor and remaining within the tracks at all times. The colour of the chains matches the colour of the chassis bearing structure, which makes them almost impossible to spot. Together with the enclosed motors, it has lead some viewers to ask how exactly is the whole model driven.

The construction of the hull may seem simple, but it was challenging. First of all the hull is flat but large, and it sits asymmetrically on the turntable. To keep it structurally solid, a supporting frame was needed – it was built around the turntable and integrated into the hull’s floor, taking 1 stud of its height. To make things more complicated, I have decided to use the newer turntable variant because it matched my needs better, but its width was odd while the hull’s width according to the scale was even. To compensate for this difference, a half-stud wide liftarms were used in the frame to give it an even width. There is an additional structure integrated into the frame right above the turntable, which holds together the base of the arm and the base of the pneumatic cylinders that raise its first section, as well as the motor used to rotate the superstructure. Additionally, the compressor was attached to the frame – firstly to minimize its vibrations and secondly to compensate for its height.

The construction of the rest of the hull is pretty traditional – there is a rechargeable battery at the back, serving as a counterweight, and motorized valves on the sides. The right front part of the hull houses the flashing lights mechanism activated by a lever inside the operator’s cabin, which controls four warning lights: two at the rear end of the hull, one on cabin’s top and one on the arm’s side. The cabin has a full interior, despite the fact that it’s slightly smaller (mainly in length) that its real counterpart.

The arm is relatively narrow – only 4 studs wide. It was built by blending two structures: bearing frame made of liftarms which holds it together, and the outer ‘skin’ made of bricks which makes it stiff and gives it a realistic look. All the mounting points for the pneumatic cylinders are attached to the frame: the cylinders were integrated with the frame right at the beginning, in order to work out their optimal positions. There are three sets of pneumatic cylinders on the arm, two consisting of two cylinders, and one consisting of four. All of them are connected to the pneumatic system inside the hull: a mixture of elastic & rigid hoses is used to connect the pneumatic system to the arm. It should be noted that the sets of two cylinders tend to rotate around their longitudinal axle; to prevent this, they are connected to the arm by two axles that slide through certain points of the arm’s structure as the cylinders extend or retract.

The model worked well, given its strongly experimental construction. It has a number of significant flaws, however, the most important being the compressor which worked too slow. It was discovered only at the end of the building process, when the arm gained more weight that it had when the compressor was initially configured. The use of the manometer has paid off – the tests have shown that the pneumatic system was prone to breach at certain pressure. The turntable was a bit unstable, but it didn’t break – despite the fact that it had no supporting rollers or structure of any kind, and that at least 80% of the model’s weight was located in the superstructure.  There is a point on the video when you can hear the turntable squeaking as the superstructure rotates. The final drawback was the use of the standard bucket – I was planning to have a detachable custom bucket and some add-on devices to replace it with, and I even placed an extra outlet of the Power Functions system in the arm to let some motorized devices be connected and controlled. It turned out, however, that both the bucket and one add-on device I have prepared (a demolition jackhammer) were too heavy for the arm (the custom bucket was almost 5 times heavier that the standard one).

I was satisfied with this model despite its flaws. I had little experience with large pneumatic remote-controlled models before, and this proved to be a good lesson – especially when it comes to configuring the compressor. Usually, pneumatic models of this size use large compressors driven by the RC motors, which can fill the whole airtank in a couple of seconds. I had just four pumps and a compressor running at roughly 100 RPM, and it had to fill a system including over 3.5 meter of elastic hose (not including the rigid sections) and 19 pneumatic T-pieces.  Still, I was glad to have an unique self-contained pneumatic model with a fully wireless control. I liked its look to – the decision to use dark grey where I could theoretically use black as well has definitely paid off.

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Video:

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Media reference:

TechnicBRICKs

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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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Video:

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Media reference:

TechnicBRICKs

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Model of my favourite vehicle from the Unreal Tournament 3 game. Features 4×4 drive, full suspension, pneumatic rear differential lock, rotating front & rear turret, lights and custom stickers.

Datasheet:

Completion date: 24/03/2009
Power: electric (Power Functions) / pneumatic (fed from internal electric compressor)
Dimensions:  length 46 studs / width 29 studs / height 30 studs
Weight: 2.35 kg
Suspension:  front – independent / rear –  live axle
Motors: 3 x PF Medium, 1 x PF XL
Pneumatics: a single circuit with an autovalve fed from a dual-pump internal compressor

Being an ardent fan of the Unreal Tournament series, I have finally decided to join two passions and build a model of my favourite UT vehicle. Which is Hellbender, underestimated by many, but absolutely lethal if used properly. It was also an opportunity to test a suspension I have developed with Truck Trial races in mind, as well as the 3 studs wide differential lock mechanism I have recently published.

The model is certainly not 100% accurate, as the original vehicle was quite challenging to reproduce. It is, however, entirely functional and fitted with 4 motors total. Power is delivered from two battery boxes, not because of some particularly high energy consumption, but because it turned out to be optimal to locate the battery box on the side, so I have used two battery boxes, one counterbalancing the other. The 4×4 drive is powered by a PF XL motor, and the steering is operated by PF Medium one. Another Medium motor rotates two turrets synchronously. The third Medium motor drives a dual-pump internal compressor via an autovalve, thus controlling the differential lock mechanism in the rear axle. As the rear axle is floating and quite complex already, I found it to be an optimal solution – thus, almost entire pneumatic system is located inside the hull, and there is only a sinle small pneumatic cylinder with two pneumatic hoses in the rear axle.

As for the off-road performance, the model certainly suffers from a short chassis and perhaps too complex rear axle. The short chassis was the reason why the drivetrain is complicated, with steering system located behind the front axle, and the drive being transferred to it from the front. A single, common driveshaft located in the center of the chassis would certainly perform better, as it is a popular solution in the Truck Trial vehicles. The rear axle, on the other hand, has its differential mounted not steadily enough because of the lock mechanism, which results in the gears’ tendency to snap. The model performs well on the floor, but has difficulties with even easy obstacles. It is, however, an interesting study of how the independent suspension based on the 8297 set’s components performs.

The model was presented by me at the official UT3 forums, where it has been acclaimed by some members of the Epic staff.

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BeyondUnreal

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A number of solutions to create a compact, fluently working compressor.

It’s pretty easy to create a motor-driven compressor. The challenge is to create one that works fluently while providing a satisfying air pressure. The easiest way to build a powerful compressor is to either use a large number of pumps or a fast motor. There are compressor designs built around e.g. RC motors, but I consider it too much for my needs. When an internal compressor powering some vehicle’s pneumatic systems is required, I find PF Medium or 71427 motors quite sufficient (both provide speeds below 300 RPM).

There are basically two cases where a compressor of a particular power is needed. First case can be called direct powering, which means that the air is pumped directly to the pneumatic cylinders of the circuit we chose to use. In this case, the power of compressor determines how fast the pneumatics work, which means that it’s not always “the more the better”. Sometimes precision is preferred rather than speed, and here a low-power compressor comes handy. Even a single-pump compressor operating at approximately 200 RPM (as I tend to use rechargeable batteries, which means that motors operate at 7.2V instead of 9V) can be used successfully. For medium-sized models of machines such as e.g. front loaders, where pneumatic circuits are usually composed of no more than two cylinders, a double-pump compressor is quite sufficient to operate pneumatics at realistic speed.

The latter case can be called indirect powering, and it happens when there is an airtank between the compressor and the final circuits. This is a less popular solution, where the compressor is activated manually or automatically (by e.g. a pressure switch) to maintain the pressure inside the airtank. In this case the speed at which the pneumatics operate depends on how the valves are switched, and only partially on the provided air pressure. It means that a high-power compressor is often a good solution, because of the relatively large airtank’s capacity as well as of the low precision of pressure switches. For instance in my Snowgroomer, where two pneumatic circuits could be operated at the same time, each consisting of at least four large cylinders, there were four pumps inside the compressor.

As the number of pumps increase, so does the challenge of making the compressor work fluently. Setting all the pumps in the same position and the same working cycle is a bad solution for two reasons: firstly the air flow becomes irregular (which can be compensated by increasing the compressor’s working speed), and secondly there are vibrations transferred from the compressor to the rest of the construction. Both effects are highly undesired, and – just like with piston engines – can be reduced by splitting the working cycles of the pumps. The Snowgroomer’s compressor will be a good example here:

There are four pumps here, clearly divided into two sets. When the first set is extended, the other set is retracted; when the first set draws air from outside, the other set pumps air into the pneumatic system. It means the two sets work against each other, and the compressor’s working cycle is split in half. Thus, the air flow is twice as fluent as it would be without such a division, and the vibrations that occur in the compressor are only half as strong as they would be without such a division. Similarly, if we split the working cycle in three, the air flow becomes three times more fluent, and the vibrations three times smaller – and so on. Personally, I have never needed to split the working cycle more than in half – such a compressor performs dramatically better than a single-cycle one, while being only a bit more complex. I did, however, build a number of compressors with the working cycle divided up to four times, and these can be seen below.

The key to make the compressor efficient and compact at the same time, is to use the full range of pumps’ movement  (2 studs forwards, 2 studs backwards), and to drive the pumps by a common, simple driveshaft. I have tested several variants where pumps were located closer to each other at the cost of a more complex driveshaft, but they turned out to be much larger – which obviously doesn’t mean that it’s not a proper approach in some cases. Similarly, it may be sometimes a better solution to use a simple compressor with a limited pumps’ movement and a single working cycle, to sacrifice its performance for the sake of size. It should be noted that the designs I have shown here have been created with focus on the performance, which is not always the key factor.

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Inspired by PistenBully snowgroomers. Features full independent suspension, dual longitudinal subtractor drive, pneumatic system with motorized valves and automated internal electric compressor, 3-section crane with infinite freedom of rotation, and lights.

Datasheet:

Completion date: 01/02/2009
Power: electric (Power Functions) / pneumatic (fed from internal electric compressor)
Dimensions:  length 84 studs / width 30 studs / height 39 studs (with crane in transport position)
Weight: 3.9 kg
Suspension: full independent with shock absorbers
Motors: 9 x PF Medium, 2 x PF XL
Pneumatics: two circuits with motorized valves, fed from internal electric compressor with a pressure switch and an airank

Somewhat spontanical construction, inspired by some PistenBully snowgroomers I’ve seen over winter. I wanted to model the entire functionality of such a snowgroomer, and this eventually turned out to require 11 motors. Here’s a full list of motors and the functions they control:

1. PF XL – drive (left tread)
2. PF XL – drive (right tread)
3. PF Medium – steering
4. PF Medium – pneumatic valve #1
5. PF Medium – pneumatic valve #2
6. PF Medium – crane rotation
7. PF Medium – lower crane section
8. PF Medium – upper crane section
9. PF Medium – compressor
10. PF Medium – flashing lights
11. PF Medium – front blade tilt

As can be easily seen, we have 3 motors more than the number of channels available with the PF system. To deal with it, we need to control these 3 motors by some other means. Namely:

1. both drive motors are controlled by a single channel
2. the flashing lights motor is permanently on, so it needs no channel
3. the compressor motor is controlled automatically by a pressure switch

The vehicle is suspended on 8 road wheels, each with an indepent suspension module with a shock absorber. There are shock absorbers of two different hardnesses used (first and last modules use harder shock absorbers than the middle ones). The front retracting wheels, and rear drive wheels are not suspended. The drivetrain consists of a dual longitudinal subtractor, where two PF XL motors drive the vehicle (one motor per one track), and the PF Medium motor controls steering by slowing down one PF XL and speeding up the other. It is, of course, possible to turn in place too.

A very unusual feature of the model is its pneumatic system. It consists of just two circuits, one with 3, the other one with 4 large pneumatic cylinders. Both circuits use regular pneumatic valves, which are motorized by PF Medium motors via safety clutches. The entire system is powered by a large electric compressor, that uses 4 small pumps divided into two units; when one unit is retracted, the other one is extended. It enables the compressor to operate more smoothly, reduces the vibrations it transfers to the hull, and makes the flow of air more fluent. The compressor is connected to an airtank, due to the high pressure needed straight off to operate the circuits quickly. The motor driving the compressor is controlled by a pressure switch, and thus the entire compressor module works in an entirely automated mode.  The construction of a pressure switch is strictly based on a concept created much earlier for the old pole reversers. Here I have just used the new PF switch instead. It is switched by two small pneumatic cylinders wrapped by a rubber band. Only the lower inlet of both cylinders is connected to the pneumatic system, therefore given a high enough pressure they overcome the rubber band and extend, turing the switch off. When the pressure drops, the rubber band forces the cylinders back, thus turning the switch on. I have used two cylinders due to a higher resistance of the PF switch compared to the one of the old pole reverser. The functioning of the pressure switch is shown in detail in both videos.

The front blade has one additional feature – it can be tilted left or right. The tilt is controlled by a PF Medium motor, via a safety clutch and a shaft that uses a number of universal joints to reach the blade’s head, where through a worm screw it rotates a vertical axle. Both front blade and rear smoothing plate are mounted on parallel levers, so they maintain their angle regardless of the elevation. I’ve tried to make the rear plate work more realistically by suspending it on two shock absorbers that press it against the ground. Thus the plate remains raised towards its front regardless of the ground’s shape. It does not, however, have the option to tilt left/right which is present in some snowgroomers.

Another important feature is the crane. It has the typical construction of small cranes (called HDS cranes in Polish technical terminology) used e.g. on cargo trucks and trailers: namely three sections, first vertical, two movable, with a hook at the tip. Two linear actuators are used here, both driven by PF Medium motors located inside the first, vertical section, without safety clutches. It provides precision and strength that pneumatics could not ensure. The crane’s first section is particularly complex and compact, due to space limitations imposed by the closely located battery box. One minor drawback of the crane’s design is the universal joint used to transfer drive from first to second section. It can’t operate when bent too much, so the third crane section becomes immobile whenever the second section is low. It is very inconvenient while connecting / disconnecting the load from the hook, but it provides load capacity far better than in a version with bevel gears instead of the universal joint (approx. 180 g compared to 50 g). On the video, the crane is carrying a 50-grams heavy truss module without even slightly bending under load. With loads heavier that 180 grams problems with the turntable’s stability begin to occur.

The infinite freedom of rotation is provided by a PF Medium motor located in the hull, and by the fact that there are only two wires going through the turntable. After a large number of revolutions these wires would eventually become entangled, but I assume that such situation is unlikely to happen during a regular utilization.

The last feature are the model’s lights, some of which are flashing. It is possible thanks to the solution used already earlier in my Tow Truck – a motor that drives the PF switch by an eccentric mechanism. The second video clearly shows details of this mechanism.

The model was well received, even though personally I did not consider it to be a project of a crucial importance. Perhaps the reason is that it was not my intention to try to use as much motors as possible, I simply wanted to model the functions of a particular vehicle. I liked, however, how well pneumatic system and linear actuators are compared in this single construction. The pros and cons of both these systems are clearly seen here – a pneumatically controlled crane would lack strength and precision, whereas LAs-controlled blade and plate would not adapt their elevation to the ground, not to mention how troublesome would it be to transfer the drive to LAs that would fold their wings. Thus, I have come to consider this model a good example of PF system’s potential not restricted by the 8 channels limit, as well as an excellent study of how pneumatics and linear actuators complete each other.

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Media reference:

Klocki, Particolarmente urgentissimo!, TechnicBRICKs, YFOLe (Polish only)

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

Datasheet:

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

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

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

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

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

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

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

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My second telehandler. Features 4×4 drive & steering, crab steering mode, full independent pneumatic suspension, pneumatically raised boom with a self-contained extension mechanism, pneumatically tilted fork, internal electric compressor and a high precision remote pneumatic valve.

Datasheet:

Completion date: 06/07/2008
Power: electric (Power Functions) / pneumatic (fed from internal electric compressor)
Dimensions:  length 54 studs + boom / width 31 studs / height 21 studs
Weight: 2.1 kg
Suspension: full independent pneumatic
Motors: 4 x PF Medium, 2 x PF XL
Pneumatics: three circuits with manual valves and one with a remote high precision valve

My last complex project based on old parts – it used pneumatics for the lack of linear actuators, and the suspension components from the 8880 set. Built in a somewhat obsolete way, but with a number of new solutions.

The goal of the project was very simple: to take the subject of telehandlers and develop it further than I did when I approached it first at 2007. It has been fitted with a full independent suspension with 4×4 drive and steering – all based on the 8880 set’s suspension components. The suspension used pneumatic cylinders instead of shock absorbers, which not only allowed to control the ground clearance, but also to tilt the vehicle forward and backward, as the front and rear suspension used two independently operated pneumatic circuits. This feature prompted me to give up the outriggers system, which is present in some heavy telehandlers, because I could simply make the model rest on the ground. Furthermore, the steering system could operate in two modes: normal and crab steering. The modes have been selected mechanically, by a ratchet mechanism operated by a separate motor. It didn’t work quite well, because of some problems with engaging and disengaging gears. The steering wheel in the cab was not functional.

The boom has been raised by two pneumatic cylinders, controlled by a remote high precision valve. The valve consisted of a regular pneumatic valve switched by a 40-teeth gear, that was driven by a PF XL motor with a huge gear reduction (240:1). I have chosen this kind of solution, because my experience with pneumatics convinced me that Lego pneumatics can handle almost any load with a good precision, provided the valve is operated carefully enough. It’s purpose here was to lower the heavy boom carefully, and it worked well. The boom itself has been built in an entirely new way. There has been two sections, one enclosed completely in the other, and extended by racks. The novelty was the fact that the racks were operated not by a regular gear, but by a worm gear directly, so it was not the conventional rack and pinion mechanism. It was a bit tricky to get the worm gear in the proper position, but once there, it worked smoothly and saved a great deal of space, resulting in my first completely self-enclosed boom. The boom was extended by a PF Medium motor located at its base, because the size of that motor made it fit in there perfectly. The only disadvantage of this solution was the lack of a clutch between the motor and the worm gear, but that could be easily solved by the use of a linear clutch that I have developed later.

At the end of the boom, there was a simple fork tilted by a single pneumatic cylinder. Just like in my first telehandler, I found no solution to the problem of placing pneumatic hoses on an extendable boom, so there is some surplus of the hoses hanging free – an ugly and unrealistic solution. The load capacity of the boom was limited, because of the heavily loaded pneumatic system.

It was an ambitious project, perhaps too ambitious for the availability of Lego parts at the time. Shortly after it was built, a range of new elements appeared, that could significantly improve the overall performance of the model. Additionally, the aesthetic side of the vehicle seemed half-baked at best. Still, it has been a very good test of some new ideas.

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