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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Fri, 4 May 2001 02:05:57 GMT
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Viewed:
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2176 times
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"Jennifer Clark" <jen@vulture.dmem.strath.ac.uk> wrote in message
news:3AF19464.B7A3960C@vulture.dmem.strath.ac.uk...
> 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.
Yes, I can almost picture how it would happen, although I presume there
would have to be some thought given to lateral movement and travel limits in
order to pull it off correctly, let alone make it look good.
> > 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
Hmm - that appears broken there, are you sure that's the correct link? The
one further down would also appear broken!!
> 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 :-)
I see, however I should warn you that there will be quite a bit of scraping,
as LEGO parts tend to scratch other LEGO parts a lot when they are in close
contact, and the heaver it gets, the more frequent the scratches will be.
:-)
Also, about the dumpsters having wheels, not all of them have wheels - some
just lie there stationary, and the truck is put in neutral or is slowly
driven back/forward when the dumpster is in touch with the ground.
I can say personally it is not unheard of for the larger varieties of
dumpster to get so heavy during loading that they will cause the front of
the truck to lift up a bit. I witnessed this once when a truck was carrying
away demolition material, the load on it seemed quite heavy, but the lifting
on of the dumpster still seemed to progress smoothly.
--
Cheers ...
Geoffrey Hyde
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Message has 1 Reply:
 | | Re: Yet Another Technic Creation
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| (...) Ooops, that was a local alias I cut and pasted by mistake. The correct address is: (URL) There are rollers on the truck I based the model on, you can see them in (...) (URL)I see, however I should warn you that there will be quite a bit of (...) (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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| (...) 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, (...) (24 years ago, 3-May-01, to lugnet.technic)
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