New and improved version of my earlier design, a little more parts-costly, but free from its disadvantages.

One of the areas of building I enjoy the most are very accurate, faithful models of wheeled vehicles. I have a special thing for trucks, which are not only fun to play with, but usually also offer plenty of internal space for mechanics. One of the ways of using this space to improve model’s authenticity is to install a working trafficators system, which I have first achieved with my Kenworth Mammoet model using my early idea for an automated trafficators system. I could call the system automatic because it was controlled by the steering motor and it did not affect it its functioning, thus being seamlessly integrated with the steering system. It did, however, have two serious disadvantages: firstly, there was delay is switching between left and right trafficators, and secondly there was a risk of both left and right trafficators blinking at the same time as high as 50%. I didn’t come up with any efficient solution to this problem until now, by developing a new version of the mechanism whose internals were significantly rearranged.

The new system uses three PF switches in a hierarchic set-up: there is a single master switch and two child switches connected to it. The master switch is powered from the same power outlet as the steering motor, so turning off the motor cuts off the power from the trafficators system. The master switch is also being switched continuously by the motor all the time the motor runs. The same motor switches the two coupled child switches, which have a gearing between them, making sure than when one switch is on, the other is off. A clutch gear is used between the child switches and the motor to prevent them from stopping the motor when an extreme position is reached. Unlike the master switch, which is switched through all three positions (on/off/on), the child switches need to be switched only through two (on/off). This is achieved by partially blocking one of the child switches, which subsequently affects the other child switch too, as they are coupled at all times.

The resulting mechanism is capable of controlling any number of trafficators and switching between the left and right ones instantly. Thanks to the gearing between the child switched there is no risk of left and right trafficators blinking at the same time (still, a very short initial blink of the ‘wrong’ trafficators may occur if the respective child switch is not switched fast enough), and powering the master switch from the same power outlet as the steering motor prevents the whole system from staying on when the motor goes off. Below is an electrical/mechanical scheme of the whole mechanism, which may look messy on the photos but is in fact rather neat. Since its only practical disadvantage is taking up as much as three PF switches, I intend to use it in several truck models and perhaps in some supercars if a sufficient amount of internal space is available.

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Simple table soccer game for two players, computerized and controlled with the WeDo kit.

Datasheet:

Completion date: 28/06/2010
Power: electric (Power Functions)
Dimensions: length 54 studs / width 36 studs (not including axles) / height 45 studs
Weight: 1.88 kg
Motors: 2 x PF Medium

A spontaneous build which started as a joke with my co-workers. It’s a simple realization of the classic table soccer game adjusted for Lego minifigures and automated with WeDo components. Since I have completely no interest in soccer whatsoever, I didn’t pay real attention to keeping the number of players or size of the pitch accurate. My goal (sic!) was rather to demonstrate an innovative use of the WeDo components that to render a realistic model of a table soccer game.

Counting the game score and returning balls to a box are both fully automated. The actual game remains, obviously, fully manual, with eight players on two axles for each team, and a single goalkeeper on a separate axle. The goalkeeper’s sideways movement is limited so that the gate is not accidentally left empty. The players’ axles use different colors for improved distinction. The game is played on a pitch paved with large tiles and surrounded with solid walls build of classic bricks. Both gates have WeDo motion sensors inside, arranged in such a way that incoming ball must pass in front of the sensor. The ball then falls into a simple system of hanging rails, with one rail for each gate and a single central rail that receives all balls and directs them to a box.

The motion sensors trigger a simple algorithm: there is a sound played, an announcement displayed on computer’s screen, and then a second sound follows. Finally, there is a sliding beam above the respective gate which is moved by a given distance.  Both gates have such beams above them, each with a sticker representing numbers from 0 to 10. The beam is concealed behind a wall with a 2×1 stud window, and the desired number is shown through the window. Every time the algorithm is triggered, the beam is moved by a single number, on an obvious assumption that only one goal can be scored at a time. Both beams are controlled by PF Medium motors with a substantial gear reduction – it is possible to control the motor’s speed precisely with the WeDo software and thus eliminate the need for a gear reduction, but it was easier to keep the beam’s movements accurate with a high gear reduction. Additionally, there is a clutch gear at each motor – thanks to this, it is possible to reset the beams’ positions with a single key press, regardless of their current position. Upon pressing R, there is an announcement displayed, both beams are  returned to the ‘zero’ position, and once the procedure is completed another announcement follows.

The construction has seen little of actual gameplay, as it was completed during a holiday weekend and it was difficult to find another player. It was, however, successful in using the WeDo elements exactly how I intended to. Additionally, it was my first opportunity to shoot a video using my new camera with a high-speed filming mode. Therefore a large portion of the final video is composed of a footage shot at 210 FPS.

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Video:

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Media reference:

Ekstra Bladet (Danish only), Engaget.com, Fascinating LEGO Model of the Day, Gadgets Now, Gizmologia (Spanish only), Hobby Media (Italian only), Hogargeek (Spanish only), Makezine, Omgunmen (German only), Sema Geek (French only), Technabob, Technoblogia (Polish only)

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Explanation of the functionality of automated trafficators mechanism. Step-by-step instruction and a video tutorial provided.

Probably the most acclaimed feature of my Kenworth Mammoet model was the automated trafficators system, which made the model’s turn signals blink automatically whenever it made a turn. I’ve spent some time making the mechanism more compact and simplier than it originally was, which was eventually achieved with a sliding worm gear solution, the same that was used in my pneumatic autovalve.

The advantages of this mechanism  are: compact size, easy implementation and efficiency thanks to which it uses only a very limited amount of the motor’s torque to function. The mechanism can be used in a number of different setups – the example shown below was installed on the axle connecting motor to the steering mechanism, but it can be installed after the steering mechanism as well.

The disadvantages are: a small delay in blinking while changing direction, which can be helped by gearing up the axle that drives the mechanism, and a large chance that one of the switches stops in ‘on’ position. In this case one sets of lights will blink while the other one stays on instead off. It should be possible to use rubber bands to reset a switch to ‘off’ position once the direction is changed, but I found it difficult to select a rubber band of the exact desired strength. The rubber bands are not quite reliable in such applications, so I suppose it’s simply not worth the effort.

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Model of the Kenworth W900 in a version customized by the Mammoet company. Features full pendular suspension, functional steering wheel, R4 piston engine, openable bonnet, sleeper’s roof and doors, remotely controlled front and rear lights, automated reverse lights and trafficators, remotely locked catch and custom stickers. My first construction powered by the Lego 8878 rechargeable battery.

Datasheet:

Completion date: 29/06/2009
Power: electric (Power Functions)
Dimensions:  truck – length 75 studs / width 19 studs / height 26 studs, trailer - length 111 studs / width 18 studs / height 12 studs
Weight: truck – 2.66 kg, trailer – 0.709 kg
Suspension:  truck – full pendular, trailer – none
Motors: 2 x 71427, 1 x PF Medium, 2 x PF XL

Kenworth W900 is one of the most iconic US-type trucks, and the Mammoet is one of the most impressive companies ever, handling stuff like transportation of bridges or houses on a daily basis. Moreover, it is a Dutch company, just like the Lego, and it uses almost entirely black livery for its vehicles which is very appealing for me. Finally, the Mammoet fleet, which consists of some of the world’s biggest and most powerful vehicles in their class, contains a number of customized vehicles, which makes them even more interesting.

There is one obvious point of reference for this model, that is my Tow Truck, completed almost a year earlier. I have assumed that it would be difficult to exceed its level of technical complexity, and if I tried to, it would most likely result in a vehicle of even bigger size and similiar look. That is why Kenworth was meant to be simplier and built with more focus on its aesthetic side.

First thing about the aesthetics are somewhat missed proportions – although according to Mammoet’s blueprints only the bonnet is 2 studs too long, and the rest of dimensions is more or less correct. Nevertheless, the truck looks long and narrow. I have recreated Mammoet’s livery on the body, but not on the bumpers, preferring to keep them free from paint job. Instead, they were fitted with small warning badges, and on the front bumper has a set of guards that Mammoet company uses in trucks intended to push some loads. There are no warning lights, either. I’ve put a lot of work into the bonnet, which can be opened up together with the front mudguards, which is a realistic solution unlike the one used in my earlier Tow Truck. The sleeper was made taller to fit the mechanics in, the catch was increased in size to achieve more accurate shape, and rear mudguards were added.

The model was designed for use with a standard Power Functions battery box, and only in the last stage of building it received the Lego 8878 rechargeable battery instead. The battery decreased sleeper’s height and truck’s weight (by considerable 160 grams) while not impacting the performance in any apparent way.

The suspension system consisted of three simple pendular modules, with axles #2 and #3 using my 3-studs wide differential bracings, each stabilized by four hardest 6.5L shock absorbers available to handle the truck’s weight and load. The front axle had no shock absorbers at all, because too much place was taken by the bonnet and front mudguards. Since the entire suspension is pendular, the truck is susceptible to a transverse tilt resulting from the driveshaft’s load, but it is greatly limited by the hard shock absorbers.

The model is driven by two PF XL motors facing each other and connected by four bevel gears. I have tested this setup before, and I liked how simple and effective it was. Additionally, the use of two motors facing each other substantially reduces the strain on the drivetrain. When I tested it with a single motor, it had a tendency to pull the driveshaft down or up if it was not reinforced properly. With two motors, the driveshaft remains in place because while one motor pulls it up, the other pulls it down. One of the four bevel gears is an idler gear, used only to keep the other three gears in place. It can be easily noticed that the motors would look better if they were located along the body – they would then look just like the fuel tanks. It’s a nice solution, but it makes the vehicle’s frame and transmission much more complex, and so I gave it up. I have to mention that the truck turns surprisingly smoothly, most likely thanks to the long span between the steered axle and the driven axles. And it feels very pleasant and realistic to drive it with the speed control-enabled 8879 handset.

It may come as a surprise, but there is no gearbox whatsoever. I’ve done a lot of tests with a linear 3-speed manual gearbox, which seemed most adequate due to it size and robustness, but it proved somewhat loose and the model performed much better with no gearbox. I intended to use the speed control feature anyway, so the gearbox was eventually removed.

The catch lock mechanism is very simple and compact. It uses a worm gear to hold the trailer in place, and a linear clutch to avoid damage. It was located just above the last axle, which is why I’ve used a custom casing (the standard Lego casing wouldn’t fit in), and it was driven by a motor located in the chassis, directly in front of the second axle.

Slightly in front of the second axle, there is also the steering system’s power output, intended to be connected to the trailer’s own steering system to couple it with the truck’s steering. I have tested a trailer with such a system, but I eventually faced the choice whether to make the trailer with steered axles or to make the trailer which is strong and looks realistic. I have chosen the latter.

Between the fuel tanks, there is a reverse lights activator in the chassis. It consists of a single PF switch whose movement is limited to a neutral and one extreme position , and which is connected to the driveshaft through a clutch. The reverse lights are powered from the same output as the drive engine, thanks to which they go out as the truck stops.

The doors of the cab can be fully opened after removal of their side bars. Inside the cab, there is a functional steering wheel and a simple cockpit. There are no seats, because the respective space is occupied by the trafficators mechanism. I will now explain how it works. Imagine a PF light powered through a PF switch – it blinks as the switch’s position changes. Such a motion can be easily motorized by means of an eccentric mechanism – that kind of solution was already used in the forementioned Tow Truck, and can be well seen in my Snowgroomer. Now, imagine a ratchet that is sensitive to the direction of rotation – it has been used in my direction sensitive gearbox. We can attach the motor to the ratchet, and then prepare two separate eccentric mechanisms with two separate PF switches and two separate set of lights (of any size – in fact, I would make the rear trafficators work too if I had 9 lights instead of just 7). It will result in a mechanism when only one eccentric mechanism is driven at a time, and it changes as the direction of rotation of the steering motor changes. Thus, it is perfectly possible to use the steering motor for it, as it can easily control one more mechanism, and I have used a separate motor here only to be able to locate the trafficators mechanism independently of the steering motor’s location. The trafficators’ lights are powered from the same output as the steering motor, so they go out when it stops working, regardless of the wheels’ position.

One drawback of this solution is that the eccentric mechanism remains in whatever position it was when the ratched moved to the other one. It means that there is a high risk of having all trafficators come up at the same time, because the ones that should be off will have the PF switch stopped in ‘on’ position. It can be prevented with rubber bands that pull the eccentric mechanisms to a specific position once they no longer mesh with the ratchet, but I did not use such means of prevention because of the available space limitations. Please note that the truck already houses approximately 5 meters of electric wire.

Under the bonnet, there is a R4 piston engine with moving pistons and rotating front fan. It is small because of the limited space under the bonnet which results from its specific construction. As you can see on the photo below, there is an interesting area near the front axle where the model’s smooth external surface ends and a Technic structure can be seen beneath it.

Finally, the trailer. I wanted it to wear a different colour scheme. Trailers of this type usually have red and white warning stripes on the edges of main platform. I didn’t have the needed number of red and white parts, and I disliked the look of these colours combined so I replaced them with two shades of grey. The trailer has no steering system nor suspension of any kind, and it is attached to the truck in a fairly simply way. I have to admit that the truck took a terrible amount of work to build and I really didn’t like the idea of even more work with the trailer, especially since it was difficult to show or film together with the truck due to its length. Therefore the trailer is an addition to the truck rather than a proper model.

Overall, the model enjoyed a fairly good reception, despite many people pointing the proportions issue out. The trafficators feature was widely acclaimed, and there was even a number of people who were very critical about the proportions and accuracy of the truck, but still regarded it as an impressive model. Few people declared that the focus on the truck’s aesthetic aspect was much greater than expected of me, and that its functionality was degraded because of this.

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Video:

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Media reference:

Bricks ‘n’ Gears, kockak.hu, 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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Video:

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Media reference:

blog.kockak.hu, Bricks ‘n’ Gears

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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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Videos:

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Click here to view the embedded video.

Media reference:

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

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A simple add-on to a regular differential, that locks it automatically whenever a slip situation occurs.

Those of you who have tried building and driving off-road vehicles with differentials, are probably familiar with the so-called slip situation. It happens when one of the wheels driven via the differential slips, or loses contact with the ground. The regular differential transfers then the entire torque to that wheel, leaving the other wheel stopped. As result, the entire axle stops, which may easily stop the vehicle completely.

Lego differentials can be locked with the driving rings, manually or by a motor, but I wanted something smaller and fully automated. The solution is simple – all it takes is to add another pair of semi-axles to the ones that go through the differential, and place a pair of cams that are not connected to each other between them. As long as both wheels maintain equal speeds, the cams remain separate. When the speeds differ, the cams will eventually lock against each other, thus disabling the differential and forcing both wheels to run at equal speeds.

Please note that due to the simplicity of the design, no adjustment of cams position is possible. Therefore, they may lock occasionally while e.g. the vehicle is turning, but that should not cause much trouble, because the difference between wheels’ speeds is insignificant in such case. A perfect situation for the mechanism would be to have the vehicle turn right just as much as left – the cams would then return to their initial position. Since such situation is unlikely to happen, this mechanism may, in fact, slightly degrade the vehicle’s performance by disabling the differential while turning. At this cost, you get a 100% guarantee of being saved from the slip situation.

Moreover, please note that the efficiency of the mechanism may differ when it’s used for a differential on the axle, from when it’s used for a central differential. I have not tested the latter case, but I suppose this solution would be useless for the central differential, because of the difference of the travel done by steered and unsteered axles while turning. Such difference tends to be constant, and thus the cams would have no chance to return to the initial position. The same would happen if the mechanism is used in a normal axle, but the vehicle keeps turning only left, or only right.

Video:

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Media reference:

Autoblog, TechnicBRICKs

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