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I have recently finished a Technic Tower Crane with Power Functions.
As with most of my Technic I was aiming for functionality rather than
aesthetics, and I think after many hours tinkering I have achieved a successful
Model. It stands at just over 2 Meters (6’6”) maximum height, and weighs in at
3.4Kg (7.5lbs) it is capable of lifting upto a maximum of 850g (~2lbs) or one
7905 City
Tower Crane!
Power Functions IR Controls: Slewing Rotation, Boom Hoist Winch, Hook Winch, and
Counterbalance Extension, via Linear Actuator.
More Pictures and some lifting specs in my
BrickShelf Folder.
When I started building this crane I wasn’t overly sure whether I should go with
a standard ‘flat top’ or a ‘luffing boom’ design, the boom truss was the first
part I constructed and would is suitable for either design the side rails are
clean enough to run a trolley(there are even stoppers at the end!) it is very
lightweight and of decent strength! (all in 325 grams /11.5 Ounces)
The Tower was the second component I worked on, this was actually far more
challenging than I first expected, I was determined to use studless Technic
which presented the first problem, My initial designs where not truly 3D and
were not able to provide enough cross bracing, and while strong enough end to
end and side to side, were far too twist-able, lacked Torsional stiffness, the
resolution to this was a true 3D truss with cross bracing in all three
dimensions, this is not quiet as easy as it sounds as studless Technic beams
connects in only 1 dimension, the holes, meaning that building in 3D needs lots
of connector pieces which have multiple dimensions, the
Technic, Pin Joiner
Perpendicular 3L with 4 Pins proved most suitable, and combined with
Technic, Pin Joiner
Perpendicular 3 x 3 Bent with 4 Pins provide all the connectivity I needed.
However there is an excess as there are pieces repeated in multiple dimensions,
and also a few aesthetic parts also, giving a heavy Tower. 98cm 1.4Kg (heavy is
not a bad thing! as it adds to stability)
Next came the turntable, I decided that loads needed to be transmitted by more
than just the turntable so I used the top beams of the tower as a load bearing
and mounted the turntable just below inside the tower, it turns out that using a
worm screw on the outside of the turntable is not as easy as it sounds due to
the required clearances inside the tower, fortunately one of the first designs I
put together fitted perfectly inside, and no amount of tinkering seemed to
provide any other method that would fit... so I gave up trying to improve it,
and just built a gear train that would drive the screw while fitting around a
load bearing structure, and housing a motor. The result I think is pretty neat
and compact. There is no tie down on the turntable I intended the crane to
balance hence would not need to support negative turntable loading. (it turns
out that the turntable is strong enough to hold until after the tower topples,
but provides ideal saftey breakaway, yes it has crashed..)
Eventually I decided upon the luffing boom, as I was interested in the swinging
counterweight design that is used on the Terex CTL 340-24-HD23 type crane,
however I wanted to add to this by placing an actuator into the balance-boom
connector arm providing additional balance stability and lift capability, and
using the fourth PF IR channel.
The next stage was to add the superstructure, this was simply a task of aligning
the boom mount above the turntable, Positioning the boom hoist A-Frame and
positioning and and checking clearances for the counterbalance swing arm
mechanism, the linkage is supported near to the boom pivot, and must clear the
turntable when the boom is in any position and also at both extents of the
actuator.
This was where I made a nasty error, as the motor driving the actuator also
needs clearance for the full swing, in both the extended and non extended
positions, unfortunately the clearance was lacking at full extension and while
test lowering the boom (with a balancing load) I realised too late that the the
boom-ballast connecting arm was no longer pushing straight as the motor had
caught, and that the middle of the beam was giving, this happened to be the
weakest point which is the end of the actuator, where the plastic is moulded
onto the metal shaft! I caught it before it snapped but I now have a deformed
actuator, doh!
Once the geometry was correct I fixed the A-frame position and working within
the space defined by the frame constructed two geared winches, this space was a
little tighter than anticipated, and due to the rear being wider and so able to
hold more cable on the winch drum, led to the odd cable routing, whereby the
longer hook cable is driven from the rear winch, and passes over the winch
mechanism (via the A-frame) then below the front winch and up the boom, this
routing allows both cables to snake from side to side winding evenly, without
clashing. If I were to redesign I might consider widening the superstructure,
both for more internal space and also for stability, by attaching the boom more
securely. The narrow frame made it impossible to mount the IR receivers inside
the structure, and although the receivers can be placed back to back one stud
apart the plugs will not allow this due to them being 2x2.5+cable in size (seems
a daft size now! if only that protrudance were a cable width shorter....) this
left me with no alternative than to mount them above the frame. The middle
proved most convenient for cable lengths (1 length from the turntable motor) so
they were mounted onto the A-Frame.
The final task was mounting a cab onto the side of the turntable, and the crane
was complete!
Any comments or questions welcomed!
Mike.
PS yes that is me.
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Message has 2 Replies:
 | | Re: MOC: Tower Crane
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| A truly amazing MOC! I tried in the past to build studless truss - and I failed to get something stiff enough. Fortunately it seems that the new beam and L-shape beams with studs help a lot! Congratulations! Philo (16 years ago, 2-Nov-08, to lugnet.technic, FTX)
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