Subject:
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Re: Yet Another Technic Creation
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Newsgroups:
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lugnet.technic
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Date:
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Thu, 3 May 2001 17:24:52 GMT
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Viewed:
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2212 times
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Geoffrey Hyde wrote:
> What problems did you run into when trying to put pneumatics into it? If I
> read the website correctly, trying this approach was abandoned early on
> mainly because of weight - were there any other constraints like the
> physical size and difficulty of not being able to use cylinders that are the
> right length, because they don't yet exist as LEGO parts?
The main reason for not using pneumatics was simply that they are awkward to
control electrically, and I wanted this truck to be totally radio controlled. I
had seen pneumatic valves on various websites controlled by motors and
micromotors, but they were all rather bulky and/or slow. In addition to those,
there would have been the overhead of the air compressor as well. None of these
are severe difficulties in themselves, but there would just not have been
enough room on the truck to fit them in an elegant fashion.
I usually find that it is possible to work round the fixed size of the lego
cylinders if you think long enough about the problem. As for the skip being too
heavy, I solved that one by having two large cylinders in series, but arranged
so that one had a larger mechancial advantage (and less resultant movement)
than the other. Since the force required for lift the skip gets less as the
lifting arm nears the vertical, the cylinder with the large mechanical
advantage is used for the initial horizontal bits and the lower mechanically
advantaged cylinder comes in as the force needed gets less. Because the air
flows to the easiest part of a pneumatic system in series, this all happened
automatically.
> Also, the travel on the telescoping boom is quite short, I have seen some
> trucks around here where the boom can telescope inward to quite a length,
> leaving about 1/3 to 1/4 of the dumpster hanging off the end of it.
Yes, this is indeed true. The reason I couldn't do this was simply due to a
lack of space; if I extended the worm gears for the telescoping section any
further back into the boom they would foul on the lifting mechanism when the
boom is flat in the chassis. You can get an idea of this from this picture:
http://vulture/jen/lego/skip_lrg/chassis_right_lrg.htm
Even with the small amount of lateral movement in the model, the difference it
makes to the skip loading angle and load moment is significant.
> A lot of the larger trucks have large rollers that the main rails underneath
> the bin simply slide on/off during loading and unloading. Was there not
> enough space to model something similar?
There are rollers on the truck I based the model on, you can see them in this
picture:
http://vulture/jen/lego/skip_lrg/real_hooklift_lrg.htm
They have a flattened V shaped cross section, presumably to help guide the skip
onto the truck. The reason I chose not to model them has nothing to do with
space or the difficulty of implementing them, as I suspect it would be quite
simple; it is merely that the first thing I tried was the red "wing front"
pieces, and I thought they looked great at the back end of the chassis, and
they worked well, so I left them that way :-)
Jennifer
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Message has 1 Reply:
 | | Re: Yet Another Technic Creation
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| "Jennifer Clark" <jen@vulture.dmem.strath.ac.uk> wrote in message news:3AF19464.B7A396...h.ac.uk... (...) If I (...) the (...) to (...) controlled. I (...) those, (...) these (...) lego (...) being too (...) arranged (...) movement) (...) the (...) (...) (24 years ago, 4-May-01, to lugnet.technic)
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Message is in Reply To:
| | Re: Yet Another Technic Creation
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| First off, let me say WOW! That is one impressive model!! But I have a few questions: What problems did you run into when trying to put pneumatics into it? If I read the website correctly, trying this approach was abandoned early on mainly because (...) (24 years ago, 3-May-01, to lugnet.technic)
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