Rosco’s LugNet Page
These pages are no longer updated. You can view my LEGO related pages here.
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Tower Crane with Luffing boom
The workers
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| | “Hey, Jock*, can you climb up and check the cables? I’ll make sure everythings OK down here.“
(*) Subtle reference to Jock Ewing (alias Jim Davis), my all-time favourite soap-opera patriarch.
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| | “OK, Bob, we need to move this beam. Bring the crane over this way.”
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| | “Right, start lifting.”
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| | “This is where we need it please, Bob.”
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| | “OK. I’ll drop it here.“
You can see the sinker on the hook cable, which serves two purposes - it activates the limit sensor well before the hook reaches the top, and it adds more weight to the hook, which is needed when it has no load! (Notice also my dog “Nala” in the background - looking a bit disgusted at having to be tied up)
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| | Here’s Bob moving a bunch of old tires. (That’s three 24 x 43s). I’ve actually lifted an 8855 plane while I was building but that was with a shorter boom. I may try again with the full-length boom, if I do, I’ll be sure to put the pictures here!
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A-frame
| | The above shots show some detail of the a-frame. This shot shows a bit more, along with the inspection platform near the top. You wouldn’t catch me up there!
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Boom
Here’s some detail of the boom. Well the tip really. The main boom structure is just technic beams, joined using 1x8 plates, with diagonal bracing using #12 axles with connectors. This changed from my original design (see preview page), which used beams for bracing. This change reduced the weight of the boom considerably, at the expense of bending strength. It now bends (& breaks) fairly easily if any significant non-longitudonal force is applied. Note how it’s angled inwards in both planes.
Tower
The tower is modularised. All modules are the same except the top (which carries the turntable & associated mechanism) and the bottom (which is modified to provide a greater footprint for stability). The modules are inspired by Fredrik Glöckner’s tower design, but are wider. The only downside to this design is that each side is separated from it’s neighbour by half a stud. This means:
- It’s hard to attach the base to a base-plate, and
- Getting the turntable in the centre of the top module is not trivial.
Anyway, here’s a couple of pictures. It’s hard to see, but the black beams holding the turntable are offset from the sides of the tower by half a stud, using 1x2 plates with centre stud.
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Controllers
| | Here’s a shot of the RCX controllers from above. You can just see the top of the cab on the left, and if you look really closely between the RCXs, you can just see the tops of the two un-geared motors used for rotating the platform. And yes, that’s the hook cable going across the top.
Note that RCX 1 (right) is attached to the moving part of the platform, RCX 2 (left) is attached to the static part. I originally tried to use these as counterweights, but attaching all the wires was a problem (see preview page). Then I used them as static ballast near the back of the platform, but soon figured out that this limited the height to which the boom could be raised. So finally I moved them both to the front of the platform, where they’ve stayed ever since...
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Power
I alluded to the rotation motors above. Unfortunately, most of the power train for this is enclosed, but I’ll try & get some shots at a later date. Meanwhile, here’s some shots of the other power trains.
 
Well here they are. I took shots from either side because it was hard to get a single shot that showed it all clearly. Two un-geared motors, of which I’ve shown one in each picture, drive the shaft which goes down through the centre of the turntable. It has a worm gear on it which drives the 24 tooth gear on the horizontal shaft. This shaft also has a worm gear which drives a 24 tooth gear on the second vertical shaft, which has an 8 tooth gear driving the (56 tooth) turntable.
Note also that the shaft running through the turntable is not a single shaft, but two joined by a universal joint. I did this in case of disaster - instead of potentially snapping a shaft, it would just bend.
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| | The power for the boom comes from 2 geared motors (bottom left & right). They both have a 14t bevel attached, both of which mesh with another 14t bevel (centre), which drives a 24t gear via a worm gear. Both spools are driven by a shaft from this 24t gear. The boom cable is a single long strand, one end connected to each spool. The pulley system at the top of the a-frame allows for uneven winding of the two spools.
| | The power for the hook is on the left of this shot, and the spool in the centre is obviously for the hook cable. It is driven via the worm gear to a 24t gear, which then drives a 8t gear on the spool shaft. I introduced this speed increase because without it the hook movement was really slow. It’s still able to lift reasonably heavy loads (see above).
The motor on the right powers the counterweight. Again, most of the counterweight drive train is hidden, but you can see the rotation sensor, and the worm gear, which meshes to a 24t gear. There’s a further 3:1 reduction, before it ends up with a 16t gear driving the chain, which runs the length of the platform, and is connected to the counterweight cradle.
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Lifting radius
OK. These figures are a bit misleading - it can’t lift a huge amount at maximum radius, and it can’t acheive minimum radius at all with no weight attached to the hook. Also, I can get a smaller radius with a heavier load, but I haven’t got any shots of that. But here’s the numbers anyway, using the 182 cm boom:
Min radius
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| | 65 cm
| | 175 cm
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Balance sensor
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| | Here you can just see (one stud of) the light sensor used to detect balance. The beam with the white & grey plates is attached to the fixed part of the platform, and contains a structure similar to the shot on the right. You can read more about how this works on the programming page.
You can also see the connection panel - three 9V connectors go from here to the front (where the RCXs are), and the sensors connect to them here. That’s the light sensor, the counterweight limit sensors & the boom limit sensor.
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Differences from preview version
It’s not too different from the preview version, but there’s a few notable ones:
- I moved the mounting point for the boom forward about 5 cm. This helped with balance, especially when the boom is up high. It’s now mounted about 2cm behind the centre of the turntable.
- I increased the base of the a-frame by approximately the same amount. This was just to keep the proportions right, although it probably makes it a bitmore stable too. Also added the inspection platform.
- It no longer uses a differential in the hook control - it’s all done by the RCXs. See the programming page for more detail.
- You can’t really see it in the preview, but it used 2 light sensors for balance - one on each side. Each only had to sense the difference between black and white (does that make it a racist censor?). After some experimenting, I found the light sensors can easily discern the light grey shade as well, so I removed 1 sensor, and used it’s input for the hook limit sensor.
- It has extra limit sensors for the boom & hook.
Back to the main tower crane page
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Site last modified November 4, 2004 Home
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