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Hello group,
nice stuff and very exciting, but against my background of arcs
and sparks I would recommend to consider the following before
making tests with quadrocopter carried antennas:
1. Every conductor being intentionally in a high voltage field
has to have a well-defined electric potential. If you use direct
DC feeding of the quadro this happens self-acting, if you use an
inverter at the skyside end you have to make a galvanic connection
between the feeder line and the quadro electronics.
2. Assuming the quadro to be a sphere in free space with a
diameter of 1 m it would have a capacity of about 56 pF against
ground. Feeding it with 10 kV at 136 kHz this would result in a
current of 480 mA emanating from the conducting parts of the
quadro. This impressed current wouldn´t care about any pn-junction
on its way - not at all a healthy situation for the quadro´s
electronics (the 1945 3-phase-AC motor heli would have laughed at
this challenge!).
3. To overcome this problem it would be useful to install some
field shaping items which reduce the voltage gradient around the
quadro. At its best this could be a wide meshed cage around the
quadro from light conducting material being connected to the
quadro´s electronic ground, e.g. aluminum wire (welding wire) or
balsa wood with a coat from aluminum foil, self adhesive like that
used for repairing roofs. Of course this cage shouldn´t disturb
the aerodynamic properties of the quadro. The second best solution
(a little bit theoretical?) could be to make two wide meshed
ellipsoids (as a limit case spoke wheels), diameter exceeding that
of the quadro if possible, one piece being mounted upside of the
quadro, the other piece one to three meters downside at the
feedline, both connected to the feedline resp. quadro´s electronic
ground. Mounting has to be so that wind and vibration won´t tilt
over these electodes to the quadro rotors ...
As a minimal solution as much as possible of the quadro´s surface
should be coated with self adhesive aluminum foil connected to
electronic ground to give root points for the lines of electric
flux outside the vulnerable parts.
4. Having done this, during start keep in mind the galvanic
connection to the feedline ;-)
5. There should be a DC path from the antenna system to ground to
bleed off electrostatic charges.
6. Let´s pray that the brushless motors of the quadro don´t work
on your favourite QRG - the effect would be disastrous both at
TXing and RXing ... For the latter you should take an conventional
loop and detune the TX ant anyway.
After this marginal modifications your quadro will hopefully be
still going strong;-)!
73,
Tom, DK1IS
Am 06.08.2013 14:37, schrieb Markus Vester:
Hi
Stefan, LF,
the quadrocopter which we tried was a DJI Phantom. It is
smaller than the F550 and currently goes for around 570 Euro
(ready to fly, including battery and a 2.4 GHz remote control).
A similarly equipped model, Blade 350QX, should become available
soon for about 450 Euro. Very light quadrocopters can be had for
as little as 60 Euro but they could presumably lift only short
and very thin wires.
With GPS, gyro and compass sensors, the Phantom was indeed
extremely easy to fly even by an unexperienced person like me.
With 11.8V 2.2Ah LiPo battery it will stay aloft for 10 to 15
minutes, so power consumption must be around 120 W. The motors
are said to be able to stand continuous duty. Lifting capability
should be around 0.3 kg, and my friend intends to install a
first-person-view video cam later. We have not tried to lift a
wire or string yet, so I don't know how much the behaviour would
be affected eg. by wind drag on the wire. With 6 m/s climb rate,
the heli could theoretically go up to 2000m and more on a
battery charge. The remote control is specified for 300m range,
which could probably be fixed by a higher gain 2.4 GHz transmit
antenna.
Yes power could be fed continuously by making the LF antenna
a twin wire. On the ground either an Austen transformer or a
bifilar wound loading coil could be used (maybe by splitting up
groups of strands in the RF litz). The heli then cannot be
separated by a distance from the antenna tip which may aggravate
potential EMC issues. Alternatively, I am still wondering
whether enough charging power could be extracted by capacitive
coupling to the LF transmission...
Currently in Germany there seem to be no general restrictions
about flying light helis (less than 2 kg) even over inhabited
terrain. I am not sure though about legal implications of a
tethering wire or going to higher altitudes. Basic liability
insurance seems definitely recommended and can be obtained eg by
joining a model flight club. While hovering over houses after
sunset with bright green and LED bars on, we were confronted by
one neighbour who strongly expressed her dislike of the
activity. People mostly seem to be concerned of "Papparazzi
drones" invading their precious privacy, the acoustic noise when
flying low, and surely the fear that these things might end up
falling onto their heads.
Best 73,
Markus (DF6NM)
-----Ursprüngliche Mitteilung-----
Von: Stefan Schäfer <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Di, 6 Aug 2013 1:43 am
Betreff: Re: LF: Quadrocopter antenna, sri, a bit OT
Hi
Warren, LF/VLF,
I just found this: http://www.youtube.com/watch?v=G3yR-GxD1is
Take a look at it. I can't find the words. I think i must have
one :-)
That must be SEVERAL 100m above ground. I think we
could even do VLF experiments with such a copter. Maybe a 500m
vertical? I remember the weight of the wire in my 300m kite
antenna test was about 1.5 kg, not more. So with 500m we could
come lower than 5.17 kHz, like i did in 2010/2011.
73, Stefan/DK7FC
Am 06.08.2013 01:02, schrieb Warren Ziegler:
Stefan,
But 100m is not better than your kite
experiments!
Yes you gain control but not height.
You will still need a battery to land the quadcopter
in the event of a failure of the power carrying wire.
73 W
On Mon, Aug 5, 2013 at 6:53
PM, Stefan Schäfer <[email protected]>
wrote:
Hi all,
I just gathered some informations from the web. Just
one example for a, probably, suitable hexacopter to
carry a LF transmit antenna.
For example a DJI F550, see a video at http://www.youtube.com/watch?v=veDrtdE6njo
or http://www.youtube.com/watch?v=2QC9so2so3Y).
Looks like they can easily lift 1 kg! You can fly
about 10 minutes with a 5.3 Ah battery. The battery
voltage is to 11.1V...14.8V. So the power consumption
may be 200...300 W ! With a compact SMPS on the copter
and a 2 wire line it could be possible to carry the
antenna. And 100m is no problem too!!
I consider to buy one! And look this, most
fascinating. http://www.youtube.com/watch?v=JecyY79K7kY
73, Stefan/DK7FC
Am 05.08.2013 15:25, schrieb Stefan Schäfer:
Am 04.08.2013 17:52, schrieb DK1IS:
[...]But with nowadays quadrocopters and a
"little" reduction of the demands it should be
possible to feed them from the ground with DC
(or AC plus converters for reduction of current)
via 2 wire line and having a good antenna too.
73,
Tom, DK1IS
That's it! So, Markus, could you ask your friend
abot some technical details? What is the supply
voltage of the system and power consumption (or
lifetime at a certain battery charge)? Is it
possible to lift 1 kg and how does it change the
power consumption? It should be no problem to feed
DC to the system or a compact power supply in the
sky and normal 230V mains at ground (todays PSUs
have an input voltage range of 85...240V AC, so a
certain voltage drop on the thin wire should be no
problem.
Maybe you can do some tests?
The advatages are clear. A quadrocopter keeps the
position and height, even in smaller wind blasts
while a balloon bounces left and right. The costs of
Helium will quickly overcome the costs for a
quadrocopter. Ah and such a project is simply more
interesting i guess :-)
73, Stefan/DK7FC
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