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ETFD2 = ET's Flying Disc, Version 2

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.

See here for a gallery of pics.
See below for a parts list and videos.

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.)

The three "legs" on the bottom are 2.375" tall, 1.5" square, and made from four layers of the 9mm 1.9# EPP foam.  The rear fins are  made from the same EPP foam and painted blue for better orientation in flight, with the bottom fin also serving as the rear "leg".

The motor-mount plates are plastic parts that a friend kindly created for me on his 3D printer.  Each one is made of two halves, held together by 4-40 (1/2") screws and locknuts attached to the motor X-mount, and with a bit of heat shrink and CA on the "arms" -- see
here for pictures and CAD files, and more info on 3D printing.  The mounting "struts" are made from two layers of 7.0mm x 1.2mm carbon strip, pressed into the motor-mount plates and glued (with CA) onto the foam.  The motor-mount to motor-mount struts are 8-5/16" (8.3125") long and the motor-mount to disc edge struts are 4-11/16" (4.6875") long.  Six pieces of 7.0mm x 1.2mm x 1000mm carbon strip are needed.  It's important to make sure the prop adapters are always tight.

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).

Parts List:

9mm 1.9# White EPP Foam, 1 Sheet, Size 24"x36" [RCF001600] $11.50 (2)

Carbon Strip 7.0mm x 1.2mm x 1000mm 20-112 $3.90 (6)

Carbon Strip 5.0mm x 0.6mm x 1000mm 20-109 $2.30

Hobbyking KK2.0 Multi-rotor LCD Flight Control Board 9171000073 $29.99

OrangeRx Spektrum DSM2 Compatible 6Ch 2.4Ghz Receiver ORNG6 $5.99

10CM Male to Male Servo Lead (JR) 26AWG (10pcs/set) 258000011 $4.00

hacker Style Brushless Outrunner 20-28M 1050kv KDA20-28M $11.75 (4)

Hobby King 20A ESC 3A UBEC F-20A $6.97 (4)

GemFan 8x4.5 Orange, Green, Black GF8x4.5  $0.99

Turnigy 2200mAh 3S 40C Lipo Pack (USA Warehouse) T2200.3S.40 $17.77

Hobby King Battery Monitor 3S HKing-3S $3.99

Peel-n-stick foam tape. 10x5inch 4mm thick ST-FOAM-DB $1.29

5.6mm x 21mm M3 Nylon Threaded Spacer (10pc) 9171000016 $1.78

HobbyPartz Red LED-60 Lights 79P-10190 $6.00

HobbyPartz Blue LED-60 lights 79P-10193 $6.00

Alternate Parts:

Turnigy 2209 28turn 1050kv 15A Outrunner TR2209/28 $11.19

2210N 1000Kv Brushless Motor (USA Warehouse) AX-2210N $7.67 (reverse shaft)

ELE RC A2826 1100kV Brushless Outrunner Motor  $16.95

eRC "Rapid Drive" 25A Brushless ESC ERCE025RD $19.99

GemFan 8x4.5 Normal Rotation - Green GF-8045-GRN $1.50

GemFan 8x4.5 Normal Rotation - Orange GF-8045-ORG $1.50

GemFan 8x4.5 Reverse Rotation - Green GF-8045R-GRN $1.50

GemFan 8x4.5 Reverse Rotation - Orange GF-8045R-ORG $1.50

Here's a video of flying my ETFD2 in the sports dome in Auburn, MA, 11/30/2012. Main video via cell phone and inset video from onboard FlyCamOne2.

ETFD2 PIP Video in the Auburn Dome:

(Converted cell phone .mp4 to .avi using AnyVideoConverter (mjpeg codec) and then used overlay function in Ulead VideoStudio 10 generation picture-in-picture video.)

ETFD2 in the Norton Gym:

ETFD2 at the Norton Parking Lot:

ETFD2 FlyCam Video Outside Above Auburn Dome:

Flying the ETFD2 via FPV in the Auburn Dome:

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