ETFD = ET's Flying Disc

Here's my creation, a flying EPP foam disc that uses three 64mm EDF units. It can float and move about; with flight characteristics similar to a fixed-pitch helicopter (like a Blade mSR). A lot of my inspiration came from the RCExplorer Tricopter, and the transmitter setup is very similar.

The disc is quite durable; I've had to crash it hard to do any damage to it. It's fun in that it can safely bump into other objects, and I try to do things like roll it horizontally along walls. It's surprising how well the disc flies, and it gets a lot of attention.

See here for a gallery of pics.

Here's a video of the ETFD in action:

Four gyros are used for stability -- one for each EDF unit, and one for the yaw (rotational) control. The thrust on the EDF units controls the angle of the disc in all directions, and the rear unit is rocked left and right to achieve yaw (rotational) control. While rotating, the disc stays at the same angle in the air because of the gyro compensation.

The disc is 24" in diameter, made from two layers of 9mm 1.9# EPP foam. On the bottom are three legs made of 4 pieces of the foam (7mm x 4mm x 4mm). The EPP "fins" on the back help to maintain orientation while flying. For glue, I used mostly UHU-Por during assembly. Weight without the battery is about 20oz.

The ETFD makes a great sound while flying, with the three EDF units whirring away. It sucks down a lot of power -- 30 to 75 amps -- and can fly with a 3S or a 4S lipo in the 2200 to 4000 mAh range. I've found that it flies best with a 4S 3000-3300mAh 30C-40C battery (more available thrust), but the speed controllers run hotter with 4S. Flight time is 3-4 minutes.

I put six carbon-fiber strips into the disc for reinforcement, glued in with CA (3 on top, 3 on bottom; see pics). The front two EDF units have foam "collars" that make their mount positions a little higher and more even with the rear unit.

The rear EDF unit is held at the two pivot points, and its opening is elongated to leave room for it move. The EDF housing has some pre-drilled holes at the right locations, but they are oval (not circular). I found that it worked better to drill new holes.

The bottom pivot is just a machine screw epoxied onto the foam. For the upper pivot, the EDF housing is attached directly to the servo arm via the mounting screw. A longer screw is needed; I think one of the HXT900 servo-mounting screws works. I also put in a washer. Putting a second screw through the housing and into the servo arm prevents it from rotating. One thing to watch out for is to have the EDF pivot-position centered when the servo is centered. The servo will be run by the gyro, so there's no way to adjust the center point after it's all assembled. You have to angle-in a screwdriver to tighten the screws (unless you remove the EDF motor), but it's not that hard to do.

Before mounting the EDF units, it's good to disassemble them and then reassemble with thread-lock on the screws. After taking out the screw on the front on the rotor it pulls off, and then the motor-mounting screws are accessible. It's also good to test each EDF unit with an ESC before installation. I applied dabs of hot glue to hold them in the disc.

The ESCs are Hobbywing Pentium 30A. At one point I tried using Hobbyking SS Series 40-50A ESCs, but their response time seemed to be too slow and the disc would wobble uncontrollably. The Pentium 30A ESCs would overheat, so I added extra heat sinking made from aluminum soda can material. I put some on the top and bottom, cutting away some of the existing heat shrink and putting in heat-sink compound. I re-wrapped them with a bit of 30mm heat shrink. The 5V power inputs coming from the ESCs are tied together, which works fine because their BECs are the linear type (not switching). The Hobbywing Pentium 40A ESC might be able to stay cool enough without modification.

The battery mounts with velcro on the bottom and plugs into a Deans connector. I also run the main power through a pair of 4mm bullet connectors on the top side of the disc. This way I can turn it right-side-up, power it up by plugging in a bullet connector, and leave it still until the gyros initialize. The power wiring should be 12 or 10-gauge, as it needs to carry a lot of current. I use a battery monitor to warn me when it's time to land; otherwise the ESCs may cut out at different times, resulting in a crash.

The center gyro is an HK401B, which operates the pivot servo for yaw (rotational) control. I have its travel limit adjustment at its minimum setting (so that the pivot servo doesn't bind).

The three "motor" gyros are piezo-type Telebee/Zoom units that I salvaged from old helis. The HK401B gyros could be used for the motors, but there may be an issue with ESC arming (as described in the RCExplorer Tricopter article under "Tricopter V1.5"). The Turnigy GR302 gyro might be another good candidate. The gain inputs from the three "motor" gyros are connected together and plugged into a single receiver channel.

For the transmitter setup, the starting point is to configure for a CCPM heli like a T-Rex 450. The RCExplorer Tricopter article "Setting up your own Tricopter" was very helpful. On the disc, the three ESCs take the place of the three cyclic servos on a CCPM heli. The standard throttle-output channel has no use on the disc, so it is decoupled from the throttle stick by setting the throttle curve to a flat line. The receiver channel can then be used for gyro gain. On my transmitter setup, I set the throttle curve to a flat 50% line and use a programmable mix (offset) to set the gyro gain.

It was a big help during the initial setup to connect servos to the "motor" gyro outputs (as described in the RCExplorer setup article). I ran into a strange issue where the piezo-type Telebee/Zoom gyros would not setup correctly when their gain inputs were plugged into the modified throttle channel. When plugged into the "gear" channel (Futaba channel 5), they worked correctly. The HK401B worked fine with either channel, so I plugged it into the modified throttle channel.

The three "motor" gyros need to configured for "rate" mode, not heading hold (aka AVCS) mode. This is done in the transmitter gyro setup. The pivot-servo gyro should work in either mode, but heading hold is generally preferred (like on a heli tail setup).

I use a Futaba 9C transmitter (with a Spektrum DM8 module); here are some of the settings:

AIL(ch1), ELE(ch2), PIT(ch6) reversed
SWASH AIL -40%, ELE +40%, PIT +75%
PIT-CURVE 0%, 40%, 50%, 65%, 100%
THR-CURVE 50%, 50%, 50%, 50%, 50%

If I were building the ETFD again, I might put the pivoting EDF unit at the "front" and have two EDFs units in the "rear". That way, during forward flight, a single EDF unit (and ESC) wouldn't have to run harder than the other two.

Here is a parts list:

9mm EPP Foam (1.9#) 24"x36" 11-405 $11.50 (qty 2)

EDF64 with ADH300 Motor Assembled 252W(4300kv) EDF64-ADH300 $19.99 (qty 3)

Hobbywing Pentium 30A Brushless ESC 25g $16.50 (qty 3)

Hobby King 401B AVCS Digital Head Lock Gyro HK401B $11.99

OrangeRx Spektrum DSM2 Compatible 6Ch 2.4Ghz Receiver ORNG6 $7.95

HXT900 9g / 1.6kg / .12sec Micro Servo $2.69

Turnigy 3300mAh 4S 30C Lipo Pack T3300.4S.30 $28.29

Turnigy 3000mAh 4S 40C Lipo Pack T3000.4S.40 $35.53

Turnigy nano-tech 2650mah 3S 25~50C Lipo Pack N2650.3S.25 $19.49

HRPoly-X Lipo Low Voltage Warning Device 335444 $27.99 (auto cell count)

Hobby King Battery Monitor 4S HKing-4S $3.49 (cheaper)

EDF64 Impeller for 64mm (6 Blade) system EDF64-FRTR $2.94 (spares)

Turnigy Pure-Silicone Wire 10AWG (1mtr) BLACK B10A1780-06 $2.99

Turnigy Pure-Silicone Wire 10AWG (1mtr) RED R10A1780-06 $2.99

Here's a video taken with a FlyCamOne2 mounted on the ETFD; in the Auburn, MA sports dome on 2/25/2011

ETFD FlyCamOne2 in Auburn Sports Dome:

Click here to contact me

Return to previous page

ET Heli