Lifters
1 (ionic
wind powered device) These are a nifty thing
to do high voltage. In essence they are devices that levitate using ion wind
created from a DC high voltage external source.
(click
to enlarge)
In my Lifter Mk 1 (which is a typical beginners one) a 40 cm triangular ultralight
basla, aluminium foil and wire creation lifts up once around 40kV is
applied. A thin wire supported by balsa wood struts is the source of the
corona and the foil below is attached to the other polarity (positive or
negative). The supply wires are not clearly seen since they get very
agitated with the high voltages. The structure is tethered with cotton
taped to the base. There is occasional arcing across the 3cm between
the top wire and the foil at this voltage. My high voltage source is
the x-ray transformer described below run off a variac. The typical
output used is 30 kV AC which with the addition of a 290 kV diode and
capacitor gives a smoothed, half wave rectified output around 40kV DC. I have also used
the 100 k ohm resistor
in series to reduce destructive arcing as it burns out the wire.
Lifters 2
(click
to enlarge)
This is Lifter Mk 2 which is a much better flier. Smaller at 6 inches
(15 cm) per side, stronger and a more generous spacing between the foil and
the corona wire. It is powered by a dedicated 30 kV DC stabilized
power supply with one side referenced to earth which means no more sparks
from foil to ground. I use a 100 kohm resistor as above. The
height is limited by the wind outdoors.
(click to enlarge)
Some detail of one vertex of the triangular lifter showing the recession of
the foil and hot glue construction. Note that the upper wire needs to
have the enamel stripped off at least partly but preferably left on the
support wires to the HV source.
The ionic wind is enough to blow out a flame underneath the lifter and can
be felt. This form of propulsion is similar in principle to the ion
engine used to power
Deep Space 1
spacecraft which used on board Xenon. A normal lifter
will not work in a
vacuum. A comparison of the two.
Deep Space 1
Power:
1280 volts, 2500 W from solar cells
Propellant: stored Xenon gas
ionised to Xe +
Speed:
100,000 kph
Thrust:
9 grams (very low but efficient and can go for years)
Cost:
$200 million
Lifter
Power:
30,000 volts, 5 W
Propellant: air ionised to O+,
N+
Speed:
? 5 kph
Thrust:
3 grams (just enough to lift the very light structure)
Cost:
$1000 for full display (actually only $2 for the lifter itself)
Others have made lifters large enough to have a small payload such as a
mouse.
A
Japanese lifter is 15 ft (5 m) in diameter and is shown lifting to 45 ft
(15 m).
Lifters 3
Lifter Mk 3 was developed for a public display. It has custom argon tubes for the upright high
voltage wire supports. In addition it has small neon indicator globes
at the corners of the lifter itself. Very impressive at night. Not
really a high flier however due to the reduced voltage available after the
argons plus the added weight of the small neon tubes. One further
feature is the "Crash land" button. This uses a motorized switch to
short circuit the power supply. This causes a loud and bright spark
visible low down between the upright argons in the left picture, the tall
argons flash and the lifter loses power and falls. Kids (of all ages)
love this one.
(click to enlarge)
I have measurements of the plain vanilla lifter (i.e. no attached neon's)
which is a 30 cm triangle. This jumps up very smartly to its tether
limit at 2 feet.
Input
24 V 0.80 A = 19 W
Output (measured after argons).
no load (argons only but no wires to lifter) ?30 kV 100 uA
plus HV Meter (100 uA FSD movement) 28 kV 130 uA = 3.6
W
plus lifter (no dropping resistor) 22 kV
400 uA = 8.8 W
Threshold for lift is 14 kV.
Hence net current is around 270 uA and net power used by lifter is around 5
W.
The argon tubes drop about 500 V each with the load of the lifter i.e. about
1 kV is lost. (but gain about 50 kV of coolness)
My lifter, give or take, uses 5W to lift its 3g (= 0.6g/W).
This neat little
helicopter weighs about 2500kG, and lifts a further 2500kg using 1MW.
Proportionately 1MW would lift 600kg with my lifter specs. Only about 1/4
that needed to achieve lift of the helicopter. One wonders if
technology can't offer something more efficient than my triangular lifter
though. I have a few ideas .....
(click to enlarge)
This is the power supply setup using a 30 kVDC regulated supply from a 24 V
transformer and a small PWM (pulse width modulated) controller.
This will be used for the public display lifter soon to be completed.
It does not like repeated short circuits (and tends to blow the 2N3055
drivers) but this has been fixed by using a series resistance (12 kohm 5 W
plus 15 kohm 5 W in series). This weakens the "Crash landing" spark
which then had to be boosted with a 570 pF 40 kV doorknob capacitor.
(click to enlarge)
The left picture is a sunset shot and the right shows a view between the
argon tubes. I have highlighted the lifter separately. With this shot you
can see the range of vibration of the first order harmonic of the closest
wire which is about 1 inch in amplitude. If the tension is a little higher or humidity a
bit less, this changes to a second order harmonic with a node in the
middle. I guess this would be preferred as excursion is less, however the
lift will be more as the wire gets closer and if there is an inverse square
law then it may even be helpful.
My balsa supports started to track sparks and carbonise as the humidity
picked up this evening. This is a prelude to a crash and burn. In
desperation I used a light oil spray on the balsa supporting the upper wire
which seems to have worked fine.
(click to enlarge)
This shows the transparent control panel exposing the electronics of the PWM.
The two controls are a red "Crash landing" control and a rotary "Soft
landing" control. The right picture shows the lifter in the acrylic display during testing.
I am concerned by the radio frequency interference on both AM (~1Mhz) and FM
(~100Mhz).
There is no problem open circuit and the DC HV wire is shielded up to the
upright argon tubes which serve as supports for the HV wire. Shorting the
argon tubes does not seem to make a difference. I have tried a ferrite cored
coil in series with the active lead with and without a resistor (330K)
although the latter does decrease performance. The sealed 30kV HV unit
is driven by a switch mode supply. This supply is giving minimal RF
interference as a whine which I think I have fixed by putting a suppression
circuit in the 24VDC line. Some of the RF was corrected with a better
connection to the 2x2 ft ground plane. Unfortunately correcting the RF
at its presumed source, the corona from the upper wires, is not feasible due
to weight constraints.
I recently had to display the lifter within a few feet of a large plasma
display monitor fortunately without problems. Interestingly, in the
final version of the lifter, I did not remove the enamel from the support
wires which means that they are a lot less agitated and give a lot less RF
interference. I have also wound the support wires into a loosely
spaced coil of about 10 turns around the last 6 inches of the argons to try
to help block RF but I am uncertain if it helps.
The lifter has now (Nov 5th 2004) been installed at the
Gravity Discovery
Centre in a 1.5 m square acrylic enclosure. This is the public interface
to the gravity wave detector under development here in Western Australia.
(click to enlarge)
The left picture shows the display poster. The right picture shows the
full installation running. It has to
be public proof and withstand lots of 'crash landings' from about 18 inches.
The balsa frame is hot glued and also has some reinforcement at the point of
impact. The support cotton threads have been upgraded to string
from a small kite which is light and very strong. The display is lit
by small arrays of lights with 8 high intensity LEDs each with green, blue
and purple coming from different directions. The "Soft landing" switch
controls the power to the HV supply and is spring loaded to return to the up
position. It is a challenge to get a truly soft landing and is nicely
interactive in this way.
(click to enlarge)
A demonstration by the lovely Sylvia from the GDS who is practicing her
controlled flying.
