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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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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Big mobile crane, based on Liebherr LTM 1400. Features full suspension, 8 wheels drive, 10 wheels steering, 3-section telescopic boom with a 2-block situation indicator, star system outriggers and V8 piston engine. Built entirely in Technicfig scale.

Datasheet:

Completion date: 29/12/2007
Power: electric (Power Functions) / pneumatic (fed from internal electric compressor nad internal manual pump)
Dimensions: length 125 studs / width 22 studs / height 33 studs
Weight: approx. 5 kg
Suspension: full pendular without shock absorbers
Motors: 2 x PF XL, 2 x PF Medium, 1 x RC
Pneumatics: two circuits with internal electric compressor, and additional manual pump with an airtank

An ultimate result of a fascination by the mobile cranes. I have spent a lot of time since my previous crane was built, planning how to make the next one better. In the meantime I’ve finally bought the 8421 set, which has greatly influenced the project.

The boom was the first thing I’ve built. It consists of 3 sections, with the same extension mechanism by Jennifer Clark as in the last crane, using hybrid rack & pinion plus pulleys system. The boom weights approx. 1.2 kg and can be extended from 112 to 290 studs (approx. 2.3 meter). It is fully covered, with all the mechanics and ropes included inside. The third section of the boom includes the LED brick from Exo-Force sets, which turns on when the third and second section are squeezed together. This situation, when the boom is being retracted too far back, is called a 2-block situation, and the LED brick is intended to indicate when it’s about to happen. As the linear actuators were still unavailable at the time the crane was built, I have designed my own mechanic cylinder, which was huge and looked unrealistic, but proved able to lift and support the boom.

The carrier was the second thing to be built, and the most complex one. Most of the space inside is taken by the suspension, drivetrain and steering systems. There are basically three systems of axles: axles 1 & 2 are steered and driven, axles 3 & 4 are only driven, and axles 5, 6 & 7 are only steered. All axles have pendular suspension, most of them with transverse modules without shock absorbers. The crane is kept stable by axles 3 & 4 which use longitudinal modules. The steered axles obviously feature various steering ratio. The carrier is kept together by a complex frame, strong enough to let the crane be carried by a hand. The frame required a lot of planning, as it had to be as strong and compact as possible, as well as to be placed in the upper part of the carrier, as the space below was needed for suspension. Finally, the frame consists of a number of smaller modules joined using Technic Pins Long with Stop Bush, simply to make the assembly easier – it would be quite a bother to be forced to move the entire 1-meter long structure every time the access to its other side was needed. Front part of the carrier includes a PF battery box, a V8 piston engine, and a Technicfig-scale cab with a functional steering wheel. There is also simple amortized bed to support lowered boom – a solution present in the real Liebherr crane. In the middle of the carrier, there are 4 star-system outriggers that are deployed and lowered by two pneumatic circuits.

The superstructure is connected to the carrier by a regular Technic turntable of the newer type. It turned out to be a bad idea, as the turntable was unable to withstand the tensions generated by the elevated and extracted boom. The lack of space in the carrier forced me to locate an electric compressor in the superstructure. It was driven by an RC motor powered from the old-type battery box attached at the back of the superstructure, as a counterbalance. Since the compressor had low efficience, I have added a manual pump with an airtank attached to the pneumatic system, to be used in need of a high pressure. It was in fact unnecessary, as the pneumatics powered only the outriggers, which don’t require much pressure. There is also a PF XL motor that drives the winch inside the superstructure. My intent of using it to extend the boom failed due to the transmission between the motor and the boom being too weak. The boom was eventually extended manually by a crank. There is also a V4 piston engine in the superstructure, as the real Liebherr crane has a separate superstructure engine.

The crane has been a very aspiring project, perhaps too aspiring in face of the lack of linear actuators. Many solutions that worked well in smaller models were rendered useless here by the sheer size and weight of the vehicle. It has, however, been a precious experience, that taught me a lot about the limitations implied by the huge size of a model. One year later, it still remains the biggest thing I’ve ever built.

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First serious mobile crane, features a full pendular suspension, 3-speed gearbox gearbox and 3-section telescopic boom.

Datasheet:

Completion date: 02/06/2007
Power: electric (wire-controlled) / pneumatic (fed from internal manual pump)
Dimensions: length 61 studs / width 20 studs / height unknown
Weight: 2.34 kg
Suspension: full pendular
Motors: 1 x RC, 1 x 71427, 1 x 2838
Pneumatics: 2 circuits with an airtank

The result of my fascination on the 8421 set (which I didn’t have yet at that time), the Mobile AT Crane (AT stands for All-Terrain) was my first serious take on the subject of the mobile cranes. Despite somewhat limited resources, it has many functions, works well, and bears some degree of a resemblance to some real machine. It’s fitted with pendular suspension that needs no shock absorbers for stability, because it uses a transverse module in front and longitudinal rocking arms in rear. The drivetrain consists of an RC motor with huge gear reduction (including a worm screw) and a manual linear 3-speed gearbox.The V8 piston engine on the top of the crane is driven by the same motor.  Once again, the use of a chain (directly after the gearbox) proved a good idea. The drive is transfered by a single differential to the 4 rear wheels. A noticeable feature is the Ackermann steering geometry, which pretty much defined the size of the crane by limiting its wheelbase. The steering wheel in the cabin is functional.  One of the videos shows the crane towing a trailer with approx. 8 kilograms of load – an achievement beyond the range of many of my later constructions.

The 2838 motor is used for steering, and the 71427 powers the superstructure. Note that the latter motor is located not in the superstructure, but in the hull, under the turntable that has a vertical axle transfering the drive inside. Within the superstructure is a simple linear distributive gearbox, which makes it possible for the motor to drive either the winch or the boom extension mechanism. The latter function doesn’t work so well, however, due to insufficient motor’s torque, as well as its drivetrain not being stiff enough.

The boom consists of 3 sections built entirely from liftarms. Its sides are completely uncovered, which helped to reduce the weight but made the boom more likely to bend under load. The extension mechanism uses the idea developed by Jennifer Clark, where the middle section is extended by the rack and pinion mechanism, and the third section follows its movement thanks to a system of pulleys. This solution turned out to work quite well, despite its assembly being troublesome, and despite the string being exposed to really strong forces. It is easy to understand how it works from the diagram below, if you note that X marks places where the string is attached, and the red rings mark the pulleys. Thus, if you extend or retract section 2, section 3 will follow it immediately.

The crane has very limited load capacity, even though I used a burton to lift the hook. The most likely reason is the construction of the boom, which is too weak for its length. Limiting the boom to 2 sections would certainly improve its performance.

Pneumatics, finally, includes a manual pump located in the rear part of the hull, near the gearbox.  The pump is connected to an internal airtank, and the airtank is connected to two manual valves. One of the valves controls 4 cylinders that deploy 4 outriggers on the sides of the crane, and the second valve controls 2 cylinders that raise the boom. Note that these 2 cylinders are connected to the boom by a pair of shock absorbers. It’s basically intended to stop the cylinders from rotating (just like in the 8421 set), and I was hoping that it would help the boom to go down a little bit more gently.

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