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Old Jul 03, 2013, 03:29 PM
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Hitec Optic 6 conversion to FrSky ACCST 2.4GHz

I really like this transmitter. It is compact, functional, reliable and upgradable. FrSky is also manufacturing some versatile modules that are a direct plug-in upgrade, along with incredibly lightweight receivers using their ACCST technology. Thismode of operation uses a receiver that communicates with the transmitter module back and forth, and is able to switch channels 80 times per second to dodge dynamic interference if it is encountered. This conversion kit is easy to use and I explain how I mounted it for my own use. Also in this blog, I provide the binding, range test and failsafe instructions for anyone who is contemplating using an ACCST module in their own radio. Read more by clicking on the Comments...

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Old Jul 03, 2013, 03:32 PM
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I have to admit, I was a bit nervous of making the move to any 2.4GHz radio system after reading so much about various brands unbinding in flight, this higher frequencies inability to penetrate solid objects or contour to land formations, and of course there are the overwhelming number of protocols out there. In fact, I previously has a Spektrum DSM2 radio system that actually did lockup in flight. The switch back to FM 72 MHz was instant!

The problem I encountered for the first time in 7-8 years, was terrible interference with a switch mode BEC in a small EDF jet. No other ESC/BEC would provide the current required while fitting the space provided in the diminutive airframe. After reading many good things about FrSky, I decided the give it a shot.

The price of the DFT module and receiver was only $37, and some receivers are as low as $8 each. Now, I am far from cheap, but I have already spend $60 per receiver in the past, several times. On top of the good pricing, the heaviest of the receivers is a mere 14 grams and the V8 series use 30mA, while the telemetry D series use 100mA.

The DF Combo kit includes all the components to get get a model up and flying in no time. The light-weight DFT module plugs into the rear of the Optic 6 transmitter without any modification to the radio, and operates on the supply voltage just as the stock Spectra 72MHz module does. The DFT can be powered by 6.0 to 13.0V DC and draws 50mA. Stock output power is stated at 60mW with the included standard SMA 2dB antenna. I purchased a 5dB antenna for my own peace of mind. You can purchase 9dB and 11dB antennas as well, and of course each one increases the load on the DFT's RF amplifier, respectively. A patch antenna is directional but increased the output to about 14dB with no other modification. If you are looking for building a long range system around the DFT, a shielded coax cable can run from the DFT to a 2.4GHz Wi-Fi amplifier. A 4-6dB SMA attenuator placed between the DFT and the amplifier input will prevent clipping the signal input or over-driving the Wi-Fi amplifier. These can range from 1 to 10 Watts of Power.

The FrSky DFT 2.4GHz module compared to the Hitec Spectra Synth 72MHz module. The 2dB antenna comes standard with the FrSky but I purchased a 5db antenna for about $2.60. A 14dB directional patch antenna is about $15.

The receiver is very compact and the antennas are interchangeable with longer shielded plug-in replacements up to 60cm in length. Offering full range (1500m), 9 grams weight and 8 channels, this is an attractive package for aircraft where connectivity is required but space and weight are a premium.

In stock form, the output SMA jack was pointed downward. After removing two screws from the back and carefully opening the case, I relocated the output to the preferred orientation.

The 5dB antenna installed on the DFT module.

Absolutely not.

Above, the output jack is relocated outwards. I removed the cover and drilled a hole in the plastic case. It is centered for the transmitter, no the DFT's own protrusion.

This output mounting position offers the most versatility for me. I hold a transmitter at about 20-30 degrees above the horizon like an Xbox video game controller, and it is because of this that my antenna orientation is quite different from other flyers. In use, my antenna points straight out from this jack, but when I hold the transmitter, in relation to the horizontal plane, the antenna will be pointing vertical. I see videos with people using their mouth to advance the throttle during a hand launch, with a neck strap supporting the transmitter. I can actually hold a transmitter with one hand, use my thumb to advance the throttle at the same moment I hand launch. Oh yes, and I use my thumbs like an Xbox controller, too.

Here, the FrUSB is connected to the DFT module for firmware updating. You do not have to do this, but updates and improvements comes up every now and then for free download.

To Enter Bind Mode:
If you are binding to a D-series receiver and are using Telemetry, ensure that both little switches on the transmitter module are set to off.
With your transmitter already set to PPM mode, hold the F/S button on the DFT module while turning the transmitter power on. Continue to hold the button for several seconds, then release.
The RED light on the DFT module will continuously flicker at a fast pace, indicating that the module is ready for binding to the receiver.
Connect the battery to the receiver/your model aircraft while holding the F/S button on the receiver. It is a very small button and may require that you use the top of a pen or other object.
A light on the receiver will flash, indicating that binding is complete.
Unplug power to the receiver and turn off your transmitter.
Turn your transmitter on and connect power to your receiver like you normally would in your model aircraft.
The RED light on the DFT transmitter module will be steady on to indicate the RF amplifier is on and a dim GREEN light will continuously flicker to indicate it is transmitting.
A steady dim GREEN light on the receiver will indicate that it is bound and receiving commands from the transmitter.

To Enter Range Test Mode:
Remove your propeller and place the model at least two feet above non-metal contaminated ground. A wooden bench or picnic table will work great.
Keep the receiver's antennas apart.
Place the transmitter's antenna in an upright position.
Turn on your transmitter and then you receiver like you normally would.
Press and hold the F/S button on the transmitter DFT module for 4 seconds.
The RED light on the DFT will now be off, indicating that its range is now reduced to 1/30th the normal range.
Range test to 30 meters distance and continuously test the controls.
Press the F/S button for about 1 to 4 seconds and it will exit range check mode.

To Enter Failsafe Mode:

The receiver does not need to have failsafe activated to operate, it is a just a precaution.
After the bind process has previously been completed, move a control surface stick such as some up elevator to a position where you want it to stay if the signal is lost.
Briefly press the F/S button on the receiver.
The GREEN light on the receiver will flash twice to indicate that failsafe has been updated successfully.
If you wish to remove failsafe, simple rebind the DFT and receiver.

The DFT module works with several transmitters, a list currently consisting of the following:

Hitec's Optic 6, Eclipse 7, Prism 7
Futaba's 3PM, 3PK, 7U, 8U, 8J, 9C, 9Z, 10C, FN series, T10C, FC-18, FC-28

This module works with the following V8 & D series receivers:
-Current V Series (Non Telemetry):
VD5M (300 meters short range pico receiver)
V8R4-II (1000 meters range)
V8R7-II (full range)
V8FR-II (full range)
V8R7-SP (extra function: CPPM, 1.5-2.5km full range)
-Current D Series (Telemetry):
D4R-II (Full range, one analog and one Digital Data Stream port, RSSI, CPPM, low voltage & reception alarm)
D6FR (one analog Telemetry port, RSSI, FS & HS modes, low voltage & reception alarm)
D8R-II Plus (two analog and one Digital Data Stream port, FS & HS modes, low voltage & reception alarm, battery voltage sensor function)
D8R-XP (two analog and one Digital Data Stream port, RSSI (PWM) and CPPM output, FS & HS modes, low voltage & reception alarm, battery voltage sensor function)
-Discontinued Models:
V8R7-HV (discontinued)
V8FR-HV (discontinued)
V8R4 (discontinued)
D4FR (discontinued)
D8R (discontinued)
D8R-II (discontinued)
D8R-2 (discontinued)
D8R-SP (discontinued)
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Old Jul 04, 2013, 12:44 PM
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Hitec's Spectra 72MHz module was a great innovation, not unlike the variable frequency transmitters from Multiplex. This module did away with the need to change a crystal to fly different aircraft Unlike the multiplex system, however, there is no front-mounted user friendly dial. Instead, Hitec's Spectra Synth module featured two small dials and retuning required a 2mm flat head screw driver to turn the dials. This system have proved very reliable for me since 2005, but I began to get interference like symptoms two years back. There was never a case of loss of control, just ticking and twitching servos. As it turned out, I was not alone. The issue is caused by a high resistance connection between the transmitter and the Spectra where the 5 pins plug into the module. So if you have a problem with Hitec's Spectra or Futaba's Synth modules, check here first.

The 5-pin white connector, the source of your trouble is relatively simple. The connector is the female 5-pin Molex Connector, Digikey offers a replacement previously listed as Part# is WM3103-ND.

The RF amplifier stage is set on the outer-most end of the module and uses the surrounding aluminum shield as a heat sink. The Spectra becomes very warm after an hour or so, but this is normal.
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