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(spin off from 'tree travel')
If the Japanese can suspend a locomotive and send it hurtling some 360 mph, how much trouble would it take to electromagnetically suspend and propel a 500 lb (car and passenger) riding on a cable?
Couldn't the maglev effects be increased with an extra long tube tractor
of magnets and wiring (or however the damned thing works) that rides over the cable? It would seem to require less power to control and suspend than riding on a rail.
And all much much cheaper? Cheaper than a road. Like flying but requiring less energy and risk.
Pop Mech MAGLEV article
http://www.popularm...tation/4232548.html
[MisterQED, Jan 07 2008]
tree travel Cable
http://www.gbgindus.../StrandedCable.htm.
cable strengths and weight [M Carter, Jan 08 2008]
tree travel cable
http://www.gbgindus...m/StrandedCable.htm
corrected above link had a period at end... [pashute, Mar 17 2008]
[link]
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// (or however the damned thing
works)// I think this indicates an area
where you might want to do some
reading. |
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If I understand, you want to set up a
sort of cable-car system, with the cars
suspended from the cable by some sort
of frictionless maglev system which also
propels them? |
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Well, OK, but the "cable" is going to
have to be a massive rigid structure,
and the car itself is also going to be
pretty hefty. The sensible thing would
be to have the "cable" build directly on
the ground (to avoid massive support
pillars every hundred metres). And the
"car" would be more efficient if it were
much larger, and capable of carrying a
few hundred passengers. Perhaps it
could called something like
"Transportation Induction" or "Train" for
short. |
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I'm a positive guy and I can usually look at an interesting idea and think of some way to make it work, but come on. |
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MAGLEV can be a good way to limit friction is certain types of high speed motion, but has no place here. MAGLEV needs something to magnetically attract to or repulse from. Cables are strong in tension, but nearly useless magnetically. |
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A massive merci Maxwell et Mister.
I obviously have only read enough about maglev to use the name, some Times articles decades ago. But with all the tech miracles flying around it didn't seem too great a leap to miniaturize the maglev effect to deal with only a fraction of the load of the existing trains. |
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Maybe this idea will have to wait for the technology to arrive. But there may be value in naive dreamers proposing half baked ideas that might not otherwise fall through the cracks of a learned technician's ceiling. The new comes from somewhere, usually hidden under piles of discarded notions. |
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What spawned this one was a gut feeling about electromagnetic force, the amount of force felt when holding close two small neodyni...magnets at similar poles or how much it takes to pull them apart - and all this force created by a few grams of magnet. |
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It seems they could be repeated along a wire for 20' to do some lifting. With the same level of power found in electromagnets there must be a way to transform a low volt current in a wire into a low weight maglev device. I guess the cable would have to be a magnet itself with the same pole as the inside of the tractor tube that floats frictionless around the cable. |
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How about: brushes on the tractor take the low current in the cable and power its long radial electromagnet system (basically just a coil, no?) surrounding the cable. And also reintroduce some wierd current back into the cable that transforms it into an electromagnet but only for the length of cable being passed by the tractor, something going on between the front and back re-contact brushes. An alternating current creating alternating polarity in synch between the cable and the tractor? How to turn a length of cable into a temporary electromagnetic? |
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What about rail gun technology? Is that the same as the maglev train? It reaches top power gradually, maybe my dream cable maglev suspension could build up slowly , accumulating magnetic power gradually while passing over a charged cable. |
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Otherwise, it's back to the pulley wheels for suspending the low weight gondolas in 'tree travel.' |
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5 am up in the mountains. Time for coffee. |
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Aside from the problem of making
maglev work with a cable instead of a
rail, there's also the question of "why?". |
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Even if you completely eliminate wheel-
related friction (the only advantage of
this proposal over a "conventional"
cablecar), you are only going to save a
small amount of energy (probably less
than you lose in all the maglev
circuitry). In a small vehicle such as you
propose, the major losses will come
from wind resistance (and the need to
climb a gradient). Much more efficient
to go for one huge vehicle than many
tiny ones. |
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I guess I'm just not seeing this. Sorry. |
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As dreamed up in 'tree travel' the goal is a cheap, easily deployed cable system that doesn't require a large infrastructure, but can be hung on tree trunks. Only a low weight system could do that, and that is part of the charm, to float through natural scenes in solitude or two. |
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Ski lifts pull the car attached to the cable rolling on pulleys, requiring supporting pulleys at each anchor station, but if the gondola rode across a single cable with its own electric motors, powered by a safe low current in the cable, there would be less shmuck to hang in the forest branches, much easier to deploy.
A cheap alternative to driveways into isolated rural homes, less harm to nature. |
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Doesn't have to go fast to be fun and functional, the gradient would have to be mild or the pulley wheels would slip, enter the desire for a maglev traction that might climb steeper grades, ride the cable more securely, no moving parts. |
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Ah, OK. Well, to be honest I don't think
you're going to come up with a maglev
system that can be tree-supported or
cheap enough to operate at low
capacity. Why on earth use maglev,
especially for small cabs at low speeds?
If
you have to get power to things, then
just have a motor in the cab pulling it
along a regular (current-carrying) cable.
Your proposal is a bit like suggesting
establishing a railway line for sight-
seeing or private access. |
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Also, there is no way you can hang a
500lb car from a cable slung between
trees. Have you stopped to calculate
the lateral force on the trees? It will be
several tons, not 500lb. |
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Your skepticism is appreciated. OK, for now, we'll skip the maglev idea and go back to multiple rubber pulley wheels on cable as described in 'tree travel' . You're right that, since we're going slow, the wheels would suffice. Maybe maglev is still too much like Diet Smith's Magnet Ship, "well, if the earth's a magnet, why can't we ride on it's waves?" |
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It seems to me that a typical pine of 16" dia. trunk at 20' height would not suffer from 500 lbs hung 1 meter out from it. If so, the hanger itself could be suspended from two close trees. Also, the connection to the tree will be spread up and down the trunk several feet with a large enough bracket. I'd say three guys could sit on a thick limb, 1 meter out from the trunk, without laterally over-stressing the tree trunk. Imagine the stress on it from a gust of wind. |
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But the idea is not at all like establishing a railway line. |
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I Googled this site for an idea of cable weight,
They list 1/4" cable with breaking strength at 7000 lbs, weighing 110 lbs per 1000ft (much less than imagined,now I'm skeptical)- Spans would be 100' - 300', though 1000 ft would probably work fine too. Aluminum cable also available. |
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International Space Station just passed at 7:20, right on schedule. 'Rosy fingered Dawn' appearing in the east... |
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//would not suffer from 500 lbs hung 1
meter out from it// |
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That misses the point - I should have
explained more clearly. If you just
want to fix your 500lb load to the side
of the tree, then the tree only has to
take a 500lb load. That's fine if the tree
is sturdy. |
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But that's not what you're doing. |
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You're running a cable between two
trees, and then asking to support a
500lb load from the cable. The physics
of this means that the sideways pull on
the trees is way, way more than 500lb -
it's just geometry. |
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For example, suppose the trees are
20m apart. Suppose that your 500lb
car is mid-way between them. Suppose
also that we allow the cable to sag by
(say) 5m - fairly generous. In this case,
there will be a force of 877lb pulling the
trees sideways (towards the cable car). |
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If you want less sag in the cable, or if
the trees are further apart, the problem
gets much worse. |
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Pulling *sideways* on the upper part of
a tree with a force approaching 1000lb
(or more) is not good for the tree.
You're going to need some quite
substantial trees. |
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And it's worse. The whole thing has to
be cantilevered out from the tree to let
the car pass. So, you'll actually be
applying a force of 1000lb to a lever of
at least a couple of metres which is
trying to twist the trunk. |
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Thanks for your attention Maxwell. Would not these lateral forces be largely taken up by the next spans on either side? And the total vertical weight on the support stations would be that of the cable, gondola and passenger, 500lbs. |
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We're only 1 meter out from the trunk. |
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We're not connecting high in the tree, but low in the tree - 20' high, I suppose that depends on the tree, but if that is a concern, the cable can run at 10' high. |
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Thanks for your glimpse at Suspension Statics, I've always wondered about the numbers and weights concerning suspended objects. Wondering if an object held out on a clothesline creates more force than if it was simply hanging. And I had a feeling that the lever principal would be involved, but then I get on the web, and there goes the day. |
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You came up with a generous 800s lbs, but that will divide into the two supporting stations. Though the neighboring cable spans will take most, of the lateral force. |
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//Would not these lateral forces be
largely taken up by the next spans on
either side?// Sadly, no. Not unless you
happen to have another car in the
middle of each adjacent span (see also
below). |
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//And the total vertical weight on the
support stations would be that of the
cable, gondola and passenger,
500lbs.// Sure, but the
vertical weight is not the problem. The
problem is the **lateral** force, which
is much more than 500lb, as I
calculated. |
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//You came up with a generous 800s
lbs, but that will divide into the two
supporting stations.// No, it won't. If
your cable car is mid-way between two
trees (A and B) then tree A will
experience a net lateral force of 800lb
toward tree B. Tree B will also
experience a net lateral force of 800lb
toward tree A. |
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//Though the neighboring cable spans
will take most, of the lateral force.//
No, they won't. They will only take a
part of the lateral force if the cable is
stretched tight between them to begin
with (so that deflection of one tree is
resisted by the cable alone). But if you
do this, the lateral forces generated by
the passage of the cable car will be
even higher and, overall, you lose out. |
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Listen, try this. First, find the heaviest
weight you can lift. Next, take a length
of rope (say 15 or 20 feet) and tie one
end to something
solid a few feet off the ground. Hold
the other end of the rope tight and pull
as hard as you can. Now get someone
to put the weight on the middle of the
rope. You will then understand what I
mean. |
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It does indeed all come down to
leverage, and all that leverage is
working against you. If you prefer, it's
easier to use the concept of virtual work
to do the calculations. But the simple
experiment with the rope and the
weight is really all you need. |
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Think of it this way. Suppose you've
done the experiment described above,
and you have a 100lb weight sitting on
the floor. The weight is attached to the
middle of the rope. One end of the
rope is tied to a wall. You're pulling on
the other end. Now, to raise the 100lb
weight by two feet, you have to pull the
end of the rope a distance of much
*less* than two feet (to pull it taut and
lift the weight). Yet force x distance has
to be the same for both you and the
weight. So, if you have to pull the end
of the rope a only a short distance to lift
the weight by 2ft, it follows that you
need a much bigger force (ie, much
bigger than the 100lb force of the
weight) to do so. |
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So, go and read a bit more about
leverage, virtual work and so on, or do
the experiment. |
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I'm beginning to see your point and will be looking for the laws of suspended weights-tricky business. I'll try some experiments. But I've seen several obstacle courses set up with a harness hanging trolly that rolls from tree to tree, maybe 100' long. |
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Off to Thun for the weekend. In fact, there's one at the cheap resort I'm staying. |
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regarding the physics, it's pretty easy. Just
use phythagoras to figure out how much
the cable-car would go up for every foot of
sideways pull on the supporting cable.
The lateral force is related to the weight of
the cable car by the inverse of that ratio. |
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I appreciate the illuminations on tension in cables. My once crack Statics and Strengths has atrophied from 30 yrs of zero application, can hardly solve an equation. No, seems I traded in those skills for those of a penniless artist. But you're explanations are very illucidating. |
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Though we see these cable runs in trees very often. I just rode on one. What if the spans were limited to 30 m and the load 400lbs. At 15' high on a two ft dia tree, I can't see more stress than a gust of wind. Though you're right about my cantileverd support. Maybe it could work with a thicker iron bar set at the correct angle to balance the force vectors between two spans. |
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Or a support station could consist of a heavy cable between two close trees, (drilled straight through, with careful antiseptic slopped on and inside the wounds, with the main cable attaching midway between, that should share some load between two trees. How to glide the gondola over this connection is a question. |
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But I will do some experiments, back burner, wait for some miracle arrival of general cash in my life ...first need a home near the forest.... |
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//What if the spans were limited...//
Well, yes, if the load is light enough
then there'll be a point at which it won't
break the tree. The length of the spans
is not important, except for (a) the
weight of the cable per span and (b) the
'droop'. Basically, if you keep the ratio
of 'droop' to span constant, and ignore
the cable weight, the load on the trees
will be constant. |
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Drilling trees is no problem (I've put two
2-foot x 1-inch stainless steel bolts
into a beech for a treehouse, and it's
quite happy). The tree only 'sees' the
hole made through the bark (and the
layers immediately after it). The only
important point is not to have two holes
less than 18 inches apart, or the tree
will just kill off the wood between the
two holes to try to seal the wound. |
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//enter the desire for a maglev traction that might climb steeper grades, ride the cable more securely,/
Cant wait for the power outage. |
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(Maglev: Idea gets boned) as (Putracine: Flies arrive). This idea takes MAG(ic) LEV(itation) to new heights. |
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