After building my ETFD and an SK450KK2
quadcopter, I created the
ETFD2. It has four 8" props mounted in a 24" EPP foam disc.
The ETFD2 uses the same props and 3S 2200mAh battery I used with the
SK450KK2. It flies great, whether gently floating around or
moving fast and doing flips.
The ETFD2 is a great FPV
platform, especially for FPV beginners. The foam disc surrounding
the blades makes it possible to bump into things and not have it be
catastrophic. See below for an FPV video.
The disc is made from two layers of 9mm 1.9# EPP foam, cut from two 24" x
36 sheets.
The openings are 9 inches in diameter, and the motors are about 350mm
apart. For the design I drew circle shapes in Photoshop and
tweaked their size and position until it all fit evenly -- see here for PDF files.
The multiple-pages version can be printed onto standard 8.5"x11"
letter-sized sheets, and the sheets trimmed and taped together.
(When printing, set "Page Scaling" to "None".) I
attached the sheets to the foam with double-sided tape and simply cut
along the lines to create the frame, making two of them and gluing
them together with UHU
Por. (The outermost circles on the openings are the ones to
cut along.)
Two 23" lengths of 7.0mm
x 1.2mm carbon strip are glued into the foam, one along each axis,
for rigidity. Lengths of 5.0mm
x 0.6mm carbon strips
are glued into the foam along the outside part of each opening. I
glued the strips into the foam with CA. (I've found that the
7.0mm strips can get cracked after hard crashes. Applying CA can
usually fix them up, but an improvement would be to install two layers
of strip on each axis during the initial build. An extra 1000mm
length of the 7.0mm strip would be needed to do this.)
See here for a picture
of mout-mount plates and struts attached. An alternative to using
the fabricated motor mounts would be to glue the carbon-strip struts
directly to the X-mounts of the motors using CA and thread. The
struts would need to be a bit longer than the lengths noted above.
The outrunner motors need to be mounted with the can downward and
the shaft upward (to get the height of the props at level of the
foam). I used KDA20-28M motors. The Turnigy TR2209/28 motors should also work
well. The AX-2210N
motors could also be used if their shafts are reversed. (To
reverse a motor shaft, remove the 'C' clip from the shaft, pull off the
motor can, and shift the shaft so the other end of it is coming through
the can. A socket-end piece and a vise can be used to do the
shifting.) With the AX-2210N motors, 3mm prop adapters would also be needed.
(Another possibility is the ELE A2826 motor.)
The speed controllers are HobbyKing
F-20A ESCs, which I flash-updated
with SimonK firmware. It's also possible to get pre-flashed ESCs, but they cost more. I'm
using GemFan 8045 props (2 normal and 2 reverse rotation); see the parts list below for links. This picture
shows where the ESCs are mounted and how they're wired. I run the
battery power through 4mm bullet connectors on the top of the disc so
that the power can be switched on with the disc upright and flat (see pic).
I recommend putting a bit of tape around the bullet connectors to make
sure that can't pull apart (this happened to me once during a flight).
I'm using the KK2.0
controller board connected to an OrangeRX R610 receiver via five male-to-male
servo leads. I added a satellite receiver to increase range.
Here are my KK2.0 settings: KK2.0_ETFD2_settings.txt.
The foam disc seems to provide a lot of mechanical dampening, so the PI
Gain values can be significantly higher than those on a standard
quadcopter. The higher values are needed to keep the disc from
"pitching back" strongly when braking out of fast-forward flight.
The KK2.0 controller board manual is here.
The rcgroups
thread on the KK2.0 contains lots of information on tuning and has
links to firmware updates. The KK2.0 may be flash-updated using
the USBasp
adapter and the KKmulticopter
Flash Tool. (See here
for connector orientation.) I
have the stick-scaling values on the KK2.0 turned up to 100 (for fast
flips), and 75% expo setup on my transmitter.
I mounted the controller board using double-stick
foam, with a large square piece on the disc and smaller pieces
contacting the controller board at the corners and center. I
mounted nylon
spacers and the bottom from a plastic dish around the controller
board to protect it. I also put on some packing tape to seal
things in.
For battery low-voltage alarming I have a 3S
battery monitor and I use the voltage-alarm input on the
KK2.0. To access the alarm input I had to solder a pin onto the
KK2.0 board -- the pin is circled in this
picture. With the "Alarm 1/10 Volts" setting at 105 the KK2.0
will beep first as an early low-battery warning, and then the 3S
battery monitor will beep and flash red when it's really time to land.
With an FPV setup, there is usually audio transmitted along with the video. The MC495A-120-24 camera
I use has a microphone on the camera, so I extended the wires on the
KK2.0 low-battery warning buzzer and mounted it near the
microphone. This allows me to hear the battery alarm through the
FPV system. I put a tilt system on the camera using the Pan-Tilt Camera Mount Q005
setup with a single servo operated via a slider knob on my transmitter
(a 3-postion switch could also be used). Being able to tilt the
camera downward while flying up high is a big plus. I also highly recommend the DIY Headtracker.
I installed red
and blue
LED light strips into the foam on the bottom of the disc about 1/2"
from the edge. I cut a channel into the foam and pushed the LED
strips into the channel, with the LEDs facing inward (which provides
more glow and less glare), and used UHU Por glue at various places
along the channel to seal it in. I also put a discrete LED on the
top fin which, along with the illuminated battery monitor on the bottom
fin, helps
with
orientation. I run the LEDs via an old brushed speed controller
plugged into an extra channel on the receiver, allowing their
brightness to be controlled using a knob on the transmitter.
Weight without battery is 775g (1.71 lb). Weight with battery is 980g (2.16 lb).
(Converted cell phone .mp4 to .avi using AnyVideoConverter (mjpeg
codec) and then used overlay function in Ulead VideoStudio 10
generation picture-in-picture video.)
