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Mods, Tips, and Tricks can be found here. You will also find some engineering jargon and the deep thoughts from Dr. Dankeinspank with more cheese than soggy nachos.

Fisheye Lens for Hubsan X4 H107D

The Hubsan  H107D first person view model can show you some amazing views up high and the stock lens is great for this.  The stock lens can makes things appear closer than they really are.  For flying indoors the stock lens is not quite optimal due to it’s narrow viewing angle (~45 degrees).  So here is what we found after testing 3 different lenses.

Here are the 3 lenses sampled with their weights in grams with the “out of the box” setup on the left.  The lenses are all purpose built for cell phone camera’s and close to $10.  This is the view 6 ft from the first doorway. Continue Reading →

Trick Out Your Chopper

We sauced up this little chopper so it will really stand out during our races. We painted it with day glow florescent yellow. It still wasn’t enough cheese for Dr. Dankeinspank so we spanked some stank on it by adding a layer of glow in the dark paint, a Cali Bros decal, and finished it off with green proper’s all around.  Customize your chopper yet? Contact us and show us what you got. 

H107L paintedH107L custom

IMG_1160h107glow

IMG_1190

We started out with a bare replacement frame.  This required disassembling the entire quadcopter including de-soldering and re-soldering the motors. Alternatively we could have masked off the motors and LED’s with tape.
body_H107L
We scuffed up the frame with a Scotch Brite pad to roughen up the shiny surface and promote paint adhesion. It is not recommended to use alcohol or solvent to clean the frame (it will make the plastic brittle).
First a white base coat of Tamiya spray paint was applied. The paint is made for flexible polycarbonate RC car bodies. Next a coat of florescent yellow was applied and finally a light coat of Rust-Oleum glow in the dark spray paint. To be honest the glow in the dark paint is not as cool as it sounds. It doesn’t glow as bright as expected and you pretty much have to hold it under a bright light before it will glow, no worries in the daytime it still looks cool.

Dr. Dankeinspank’s Spray Painting Tips:

  • Wear a mask and paint in a ventilated area (don’t breath this stuff)
  • Heat up the cans in the sun or in warm water, warm cans will spray a finer mist and have more pressure (don’t exceed temperature warnings on can)
  • Shake often
  • Spray lightly, perform each coat in 2-3 steps. For the first step spray very lightly, just mist it.  You want the base color to still show through (fogging).  Wait about 5-10 minutes and lay down another light coat.  Wait 5-10 more minutes and then a slightly heavier one. Use just enough for the paint to fuse together and leave a shiny gloss.  Most people will just lay down one heavy coat. This is really hard to do without getting runs and drips while still using enough paint to get a gloss finish.  If you use the method described you won’t get drips and you will still get that gloss finish.  Allow the paint to fully dry between coats.

IMG_1200

IMG_1199

Quadcopter Antenna Design and Optimization: Part 1


Antenna_Part1

ANTENNAS:
Part 1

Overview:
In this post we will look at the a) type of antenna and b) location of
an FPV antenna for a typical quadcopter. We will use an open-source
software (NEC2) to determine the performance of many configurations for
comparison. We will also do some crude tests to validate our
conclusions. The Python programming language is used to rapidly iterate
through configurations. Everything is provided here so that you can
follow along.

Introduction:
First lets learn a little vocabulary that is common in antenna design/analysis:

GAIN
— This is what antennas are all about. Gain is a number that describes
how the antenna radiates energy, electromagnetic energy. The gain can
vary significantly (orders of magnitude), that is why we typically use
units of decibels aka dB. Here is an interesting fact about dB, 3dB is
half, therefore an antenna that has 6dB radiates twice the energy as
that of a 3dB antenna (but only in one direction). A plot of an
antenna’s gain is called its radiation pattern. There are a few common
plots, gain vs. azimuth, gain vs. elevation, and gain vs. azimuth &
elevation. We will take a look at each of these to determine the best
antenna configuration for our quadcopter.basic_patterns

FREQUENCY
If you were at the beach and two waves crashed within one second, the
waves would have a frequency of 2. Frequency has the units of Hertz aka
Hz. An FPV transmitter might have a frequency of 900MHz, or 900
mega-Hertz, or 900,000,000 Hz, or 900,000,000 cycles per second, which
would all mean the same thing. For this post we will use Gigga-Hertz
aka GHz. So 900MHz = 0.9GHz. Lets take a look at at what different
frequencies look like plotted. I have included the python script so you
can follow along.
import numpy as np # numpy is numerical python
import matplotlib.pylab as plt #matplotlib is a plotting package
deg = np.linspace(-360.0,5*360.0,1000)
wave_1 = np.sin(np.radians(deg)/2) + 2
wave_2 = np.sin(np.radians(deg))
wave_3 = np.sin(np.radians(deg)*2) -2
plt.plot(deg, wave_1)
plt.plot(deg, wave_2)
plt.plot(deg, wave_3)
plt.axis('off')
plt.show()

 different_frequencies

In
the plot above you see three sin waves representing three different
frequencies. The lowest frequency is in blue and the highest frequency
is in red. Look at the distances between the tops of the waves, this is
the waves wavelength which brings us to our next subject.
WAVELENGTH
— This is just the distance between two crests of waves. For
electromagnetic waves you just divide the speed of light by the
frequency: wavelength = (speed of light)/frequency. We will be using
inches for our unit of wavelength. A wave with frequency of 1 GHz has a
wavelength of 11.8 inches, almost a foot. So lets calculate the
wavelength of our 900MHz FPV antenna. wavelength = 11.8/0.9GHz = 13.1
inches. Just divide 11.8 by your frequency in GHz to find your
wavelength in inches.
import numpy as np
import matplotlib.pylab as plt
deg = np.linspace(0.0,2*360.0,1000)
wave = np.sin(np.radians(deg))
plt.plot(deg, wave)
# Add annotation
plt.annotate(
'', xy=(90, 1), xycoords = 'data',
xytext = (90+360,1), textcoords = 'data',
arrowprops = {'arrowstyle':'<->'})
plt.annotate(
'WAVELENGTH', xy=((360+90)/2, 1), xycoords = 'data',
xytext = (5, 0), textcoords = 'offset points')
plt.axis('off')
plt.show()<br>
 wavelength
POLARIZATION
— Electromagnetic waves (this is what is radiated from the antenna)
have an orientation. There are two common polarizations, horizontal and
vertical. Horizontal means that the electrical field is to your left
and right. Vertical polarization means that the electrical field is up
and down. On your transmitter your dipole antenna is usually pointed
up, this means that you are radiating vertically polarized
electromagnetic waves. It is very important that the antenna on your
ground station is at the same polarization as the antenna on your
quadcopter. Proper placement is also important, with poor placement of
your antenna you can have the waves bouncing off of motors, propellers,
and batteries which change polarization.

Wow, that was starting to get boring. Lets move on to
something more interesting. Lets familiarize ourselves with different
types of common antennas.

  • MONOPOLE
    — Mono = One, Pole. This is a simple antenna with one element
    extruding out of a ground plane. The element is isolated from the
    ground plane by an insolator. For a quadcopter we don’t really have a
    ground plane unless your chassis is conductive, which could be
    dangerous so close to the high voltage system. We will ignore monopole
    antennas for this study.
  • DIPOLE
    Di = Two, Poles. This is another simple antenna with two elements. A
    typical dipole is the 1/2 wave dipole, which means that each element is
    1/4 wavelength. Lets equate this to our 900MHz FPV antenna and
    determine the overall length of the antenna. We already determined that
    900MHz has a wavelength of 13.1 inches, so divide that by half and we
    get 13.1/2 = 6.56 inches. Take a look online at 900MHz dipole antennas,
    right around the same length, cool. A 1/2 wave dipole antenna is what
    you will typically find stock on your transmitter and receiver. Why?
    Well that is because of the radiation pattern. A dipole pattern looks
    like a doughnut, radiating everywhere but at the poles.
half-wave_dipole_1

The
image above shows the radiation pattern (gain vs azimuth &
elevation) for a half-wave dipole. Where the maximum gain is at 0.0
degrees elevation and nulls at plus/minus 90.0 degrees elevation. This
is typical of the pattern from your transmitter and receiver if using a
dipole. Now you have to sit back and think about all the times you have
been out flying and reflect on the orientation of your
airplane/quadcopter relative to you. A dipole should look like a good
choice of antenna for FPV. No matter what direction the quadcopter is
flying we have about 2dB gain! 2dB doesn’t sound like much, but it can
get much worse. Lets look at some directional antennas.

  • YAGI
    These look like a bunch of dipoles in a row, but only one of the
    dipoles is actually being fed a signal. The rest are there to react to
    the electromagnetic waves. These interactions of the elements are very
    complicated, which make them very difficult to design and optimize. I found one on the internet to copy which is designed for 16dB (pg. 15).
 yagi_15el
The
image above shows the radiation pattern of a 15 element Yagi antenna.
As you can see the antenna is very directional in both elevation (up
& down) and in azimuth (left & right). So if the antenna was
pointing directly at the ground station we are in luck, imagine the
range this baby will get you! But, wait, what if you need to turn
around and come home? Lets look at the radiation pattern another way,
gain vs. azimuth:
 yagi_15el_2
Now
we are only getting -6.85dB gain in the side sector, what a bummer.
Well, this is a good lesson on antennas. With antenna gain you cannot
get more gain without loosing it somewhere else. The Yagi antenna might
be better suited to a ground station where you have someone or
something tracking your quadcopter very closely. Lets look at one more
directional antenna.
  • BIQUAD — aka “bow-tie” antenna. This is becoming a very popular
    antenna for ground stations and for good reason. The radiation pattern
    has a nice wide lobe and they are simple to build. Check out IBCrazy’s
    post on how to build your own here. Lets take a look at the pattern for the 910MHz biquad described on IBCrazy’s post.
biquad_gain_1
  • You
    can see that there is a wide main lobe. So this is another high gain
    antenna which is more appropriate for our ground station rather than on
    our quadcopter. For this study we are working to optimize the FVP
    transmitter antenna on our quadcopter, so a biquad probably isn’t the
    right choice.

Part 1 Wrap Up:

  • You cannot have high gain at all azimuths and elevations
  • A high gain (directional) antenna is best suited for a ground station if you want long range in one direction
  • A dipole antenna is a good choice for a quadcopter FPV transmitter antenna because it radiates in all directions
  • Next post we will look at optimizing the size and location of the dipole antenna on our quadcopter

~Dr. Dankeinspank

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