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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My third Monorail ceation, features a single loop with two Monorails, a cargo truck and a gauntry.  

Datasheet:

Completion date: 21/05/2011
Power: electric (Power Functions) / 9V (Monorail)

I have a soft spot for unusual machinery, and gauntries, with their distinctive construction and obviously huge fun factor, are exactly such a thing to me. I have already built one simple gauntry back in 2008, and this time I wanted to try to re-approach the subject using the Monorail system.

I started by looking at old Lego harbour cranes sets which used to fascinate me when I was a kid, and it prompted me to buy special Lego supports for cranes. With these at hand, I have built a single, long gauntry with a bogie housing two 71427 motors: one driving the bogie, another one driving a winch (both with safety clutches). Attached to the winch was a simple custom hook that was supposed to lift and carry three identical containers weighing 73 grams each. I have created two Monorails with rear cars serving as container platforms and with front cars occupied by the drivers and battery boxes. To let two Monorails use a single track, a fork was created using two track points. The Monorails were controlled with monoswitches, so they always stopped exactly in the same place. This, and the fact that the gauntry was stretched a lot and already facing problems with structural rigidity, made me decide to make the gauntry fixed, unlike the real gauntries which can move forth and back using special, usually short tracks.

The two Monorails have been completed by a cargo truck. As the Monorails were 4 studs wide, I was determined to keep the truck 4 studs wide too, while making it remotely driven and steered. It was achieved by using two motors: a 71427 motor for drive and a micromotor for steering. The 71427 motor was driving a single wheel hidden under the trailer, and the micromotor was geared down 3:1 and was rotating the whole tractor unit against the trailer. As a result, the truck could drive and steer successfully over a perfectly flat surface, despite the fact that it had no steered wheels and that none of its visible wheels was driven. Additionally, the tractor unit housed working headlights.

While the truck was remote controlled, and the Monorails were controlled by monoswitches, the gauntry itself was controlled by two switches located on its side. I have used the old 9V switches and the old 9V wires, because they were thinner and not as stiff as the Power Functions wires. The gauntry also had over 10 pairs of Lego LEDs installed on it, which resulted in a massive amount of wires.

The whole construction worked reasonably well, except that it was difficult to catch a container with the hook, and that the hook had a tendency to rotate left or right sometimes. This part of the gauntry was clearly underdeveloped. It was only after this construction was finished that I learned about the Lego crane grabber piece, which would solve these problems easily. This piece is so interesting that I’m planning to build another gauntry just to put it to use.

Note that this whole construction used no PF motors whatsoever. Each Monorail was driven by a Monorail motor, the gauntry used two 71427 motors, and the truck used one 71427 motor and a micromotor. The Power Functions system was used only to power the gauntry and its lights, as well as to power and control the truck.

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A typical truss tower crane. Features three types of truss, movable trolley and counterweight, and unusual rotation system.

Datasheet:

Completion date: 15/03/2009
Power: electric (Power Functions)
Dimensions:  length 184 studs / width 19 studs (not including the baseplate) / height 159 studs
Weight: 2.89 kg
Load capacity: accidentally collapsed at 438 grams
Suspension: none
Motors: 1 x PF Medium, 1 x PF XL, 2 x  71427

I’ve been fascinated by truss constructions for a long time, and it felt natural to eventually build a simple truss crane. Or, to be more specific – I thought a tower crane was simple until I actually started to build one.

I have used two important points of reference: a tower crane by Philo,  and a bigger one by Thomas Avery. The crane was meant to be realistic, and thus was built pretty closely after a typical scheme:

The most important part are obviously truss modules. Typically, a truss can be a subject to up to four factors: bending, twisting, compression and stretching. It is possible to build a truss resistant to all these factors, but such a truss is heavy and rarely has to actually bear all four factors. It is therefore a good solution to use the lightest truss possible, designed to bear only specific factors. This is the case of this crane – out of three truss types used none is capable of bearing all the mentioned four factors.

First, there is the tower mast. I have designed something I could call a perfect truss module for it, but it turned out to be too parts-consuming. Such a module can be built with bricks and beams, in a rectangular shape. It consists of vertical 9-studs long beams connected to a horizontal 10-studs long bricks, and reinforced slantways with 13-studs long beams. All these dimensions fit perfectly, and it’s very easy to stack such modules one upon another. I did not, however, possess enough parts to build a mast of desired height (I wanted the crane to be able to transport loads from the floor to my table) with such modules, so I used a simplier, less stiff version.

The tower mast is modular, with lower part reinforced by counterforts from four sides and by vertical beams on the edges. It would be perfect to reinforce the entire mast with the beams, but I did not have the sufficient number  of beams in a single colour, and I was unwilling to make the crane multi-coloured, nor to buy extra parts for it. The mast is resistant to compression, twisting and bending, but not to stretching because of its modular construction.

Secondly, the counterjib. It was meant to have empty space inside, so I used a rectangular truss with only two sides reinforced. It is resistant to everything except twisting.

Finally the jib. It was quite a challenge to make it triangular, just like in real cranes, but the triangular truss is much lighter than a rectangular one of this size would be, while being resistant to bending and compression. It is prone to twisting and to some extend to stretching, but is secured from the latter by a stay. It was very convenient to use as a crane runway.

The entire crane is obviously modular: it consists of the tower mast, the upper arm (jib and counterjib together) plus a turntable crown. The turntable is not a usual one. There is a regular Lego turntable used to connect the upper arm to the mast, reinforced by six rollers (in two sets, 3 in front, 3 in back) located above it. The rollers rest on a crown that encloses the turntable. Up to this point it is quite a usual solution, but it’s the first heavily reinforced turntable I’ve ever built, and it performed flawlessly (largely thanks to the rollers being located several studs above the turntable, I guess). Now, the unusual thing is how the crane rotates – it does not use the actual turntable. Instead, as I’ve learnt from Thomas Avery’s work that any rotation-transferring mechanism may be prone to twisting at this size, I have used a vertical 16-studs long axle from the Jumping Giant set, which is made of a more flexible material that the usual axles, and the entire crane rotates around that axle. It goes through the entire turntable, its lower end is fixed to the turntable’s lower part, and the upper end is set inside the upper arm structure so that it may rotate inside. Thus, the axle is deliberately twisted by rotation, and softens the jib’s movement when the rotation motor starts or stops. A motor speed control would come very handy here, but it was only possible with the WeDo system at the time. In fact, I have successfully tested the rotation mechanism with the WeDo set, controlling the rotation speed, but it was very inconvenient because the crane had to be placed near a computer, and connected to it by a wire.

The counterjib contains two counterweights – a fixed one at the end, and a movable one inside. Note that a movable counterweight is as far as I know a purely fictional idea, not used in the real cranes. I have used it on assumption that it would help to balance the jib’s load and thus improve the crane’s load capacity – which it did. Initially, I planned even to make the counterbalancing automated – by means of the stay connected to jib and counterjib, and to an axle in the middle of the crane. As jib would lower itself under load, it would pull the stay and move the mentioned axle, which would then turn a PF switch on, thus activating the counterbalance’s drive system.  I believe it was a theoretically correct idea, but in reality it turned out impossible to calibrate the PF switch’s sensivity and the movement range of a loaded jib relatively to the middle of the crane.

Inside the jib, there are two sets of ropes. Both are connected to individual hoists; one of them lowers/rises the hook, while the other one moves the trolley along the jib. Because the space in the counterjib was taken, I could not use a very convenient and realistic solution present in the Philo’s crane – that is hoists  located in the rear part of the crane. Instead, hoists are located on the top of its middle part, and there is a complex system of pulleys that connects the hoists’ drums to the ropes inside the jib.

First set of ropes controls the height of the hook. It consists of a single rope, which through a system of pulleys makes it possible for the hook to maintain constant height while the trolley moves. It is obviously possible to operate the hook and the trolley at the same time, and the entire arrangment is shown below.

I have decided to use two drums in the hoisting block in order to have the hook suspended on 4 sections of rope, thus limiting the hook’s side sway while the crane rotates.

The other set of ropes, controlling the trolley’s position, doesn’t work so well. Philo has used a brilliant solution in his crane, where a single rope is kept tight by a shock absorber, and it goes through a single hoist drum that moves it. I tried to reproduce this mechanism, but in my case the rope tended to slip on the drum. Expecting heavy loads to be moved, I have dropped this idea and used two separate sections of rope on two separate drums (driven by a single motor). It is much more complex and much worse solution, because the drums work unevenly and the ropes get loose or strained all the time, depending on the trolley’s position. It was not possible to make their tensions even with a shock absorber, because the difference is simply far too great. So, the system I have created works, but not as smoothly as Philo’s one, and it needs manual corrections of ropes from time to time.

The crane was impressive due to its size and the regular truss modules. It was the first time that I was able to  sit under my construction, or that I was forced to get out of the way as it rotated. It went through a lot of testing, but collapsed before I managed to have some actual fun with it. It was really tiresome to build, but I consider it a precious experience that will be useful for my future constructions.

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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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Media reference:

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

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Simple crane. Features two sections controlled by linear actuators, extendable final section and linear clutch.

Datasheet:

Completion date: 31/08/2008
Power: electric (Power Functions)
Dimensions:  unknown
Weight: 0.74 kg
Suspension: none
Motors: 4 x PF Medium

A simple construction designed to test new Power Functions elements, such as linear actuators and switches. I wanted to gain some experience with actuators in particular, and to test various solutions of transferring the drive between a motor and an actuator along the crane’s arm.

The crane is able to rotate through 360 degrees, and lift approx. 0.25 kg. The steering is quite precise, thanks to the actuators. The motors at the back of the turntable are set at angle, in order to keep the universal joints that transfer drive from these motors from bending to much. As you know, universal joints don’t work properly when bent by more than 45 degrees. There is a single linear clutch of my design used to transfer the drive of the crane’s extendable section. As for the other motor, I relied on the internal clutch of the linear actuators.

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Rare case of my construction other that a vehicle. Features remotely elevated and slided hook, and ability to drive the gauntry remotely along rails.

Datasheet:

Completion date: 17/02/2008
Power: electric (Power Functions)
Dimensions: unknown
Weight:  unknown
Suspension: none
Motors: 3 x PF Medium

From time to time I become interested in something other than typical vehicles. Here I was absorbed by the concept of a fully functional remote-controlled gauntry, with focus on functionality rather than aesthetics. The result is a relatively simple construction able to elevate and slide the hook crosswise, as well as to drive along the rails. Since the battery box is mounted on the gauntry, the construction is top-heavy, which prompted me to use smooth rails and tireless wheels – a solution that works like a natural clutch when the end of a rail is reached. Hence there is no risk of the gauntry loosing stability if it’s driven too far on rails.

The load capacity has not been tested. The drive range and size of the gauntry could be easily increased, and with more attention to the aesthetic side, it could probably be an interesting part of some larger Lego town.

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