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Futaba Gold Box 2.4 Conversion

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A project I've been getting around to doing has made it to the bench.

My first radio was a Futaba Gold unit, so of course have fond memories of.

Would love to have one again for old times sake. 

Sometime in the near future, i'm going to build a vintage style model, so this would be perfect for that.

Picked one up recently, and decided to set about a 2.4g conversion.

Not the first one i've done i have had a JR9XII which went from 36MHz to a 2.4g plugin module to Frsky hack module.

This one i want to do a little more "factory" as if it was always this way.

This will be a permanent one-way conversion, in other words, there is no intention of ever being able to undo this conversion, so if there is any severe mods required, this won't be a problem.

Unit as received:


Is missing the battery and aerial but these are not a problem due to the work planned.

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I did my Futaba Challenger some time back.

Modules are available for easy-ish conversion.

The possible choice is to decide which module to use as this will probably determine which receiver system has to be used.

In my case this was/is FrSky D8 so will only work with this receiver protocol.

On my conversion I fitted a plug to the module input wires which plugs into the original output socket. So I can just unplug the 2.4 module and re-plug the 35 meg' back in. The only "hard" bit was how to fit the aerial. 
Must admit though - I have actually never flown with it yet . 



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Good work John, may it serve well!

So the first step was battery. Not much point doing anything else if i don't have a power supply.

These units originally had a built in NiCd, and about 8.4V if memory serves correctly, so had to find something that will fit in the space available.




I found a 3s LiFe that would, so this was duly purchased.

Located adjacent is the redundant trainer port, which will go on to find a new life as the battery balance connector.

So made this up, and the matching charge adaptor. 




So with that done, i can now power it up.

So the next step will be to temporarily connect the 2.4 module and see if that comes to life. 

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Several F series Futaba 'Golds' have been converted to 2.4 over on mode-zero. Mine being one of them.





  They tend to use one of Phil Greens encoder boards based on an arduino nano and a 2.4GHz Tx module of your choice. 



It looks 'busy' in there but it really isn't.  Using the existing encoders as you have done is also an option providing it works and all the pots are serviceable and not noisy.















The basic electronics is quite compact really as the processor 'fits' on the bottom of the Tx module, here is the bare bones before adding the stick units in a joypad type controller




    Happy tinkering!

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Before playing with the 2.4g module, i did a couple of other small jobs.


Firstly i verified that there is a direct link from the factory charging port to the battery, which there is. I had it in my head there was a diode in the circuit, which would interfere with charging via this port, but as there is not, then that's fine. So to can charge off two seperate input sockets on completion, being the original charge socket with it's center negative barrel connector, or the newly modified 6pin ex trainer plug.


Second job was to get the original voltmeter on the front of the Tx working. Not complicated. The positive side of this is connected direct to battery +ve via the power switch through a potentiometer, presumably to allow for fine tuning of the voltmeter. The -ve side however returns via the RF module. I understand that when the RF module is in operation, a transistor within this allows the -ve circuit to complete. In other words: no RF output = no battery indication. Since i won't be using a Futaba rf module, i put a link in on the motherboard, joining the batt meter's -ve connection to batt -ve. The onboard potentiometer, even at full adjustment wasn't enough to bring the voltmeter needle down of the stop, so the link is actually a resistor. So now when the Tx is turned on, the meter comes up to about 99% of scale. I'm not looking at it as a accurate voltmeter, but rather just as an indicator that the thing is turned on. So success here.


So the next step i thought i'd start playing with the RF side of things.

I picked this up recently to be the heart of the operation:



I thought i'd carry out a "test drive" before putting in a lot of effort to find there was a bigger issue at play here.

The unit is a DIY "hack" module, similar to the FrSky one that was popular (and i fitted to my JR a decade ago).


So as the trainer port is no longer in use, the connections for same gave me a convenient place to connect this up and "see if it worked".




The white plug at the bottom right of the motherboard is this. The 4 wires on it used to go to the trainer socket. They are batt +ve & -ve, (red & black) ppm out (brown) and ppm in (yellow). So the red, black and brown give me all i need to connect the Corona 2.4 module.

With that lashed up, a typical bind sequence carried out between Tx & Rx, success was had. I could operate the servo at the Rx.


I don't intend on using this for the permanent connections though, as i have noted there is no direct link between the PPM output terminal here at the trainer port, and the one at the (Futaba) RF module terminal. Reasons for, or if i would miss out on anything by connecting here, i don't know. Coming off the Tx at the point where the PPM signal was turned into RF makes more sense to me, then i'm transmitting as much as possible, so making the most of the factory features of the radio.


Next step I'll be doing a little more testing and then look to permanently mount and connect the Corona RF module. 





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Posted (edited)

So i had a proper play with the Corona module in my temp location.

All 7 channels respond in full, and all the "options" this radio has (D/R, Expo (called VTR on here), the built in mixes etc) all work when asked to. Happily drove 6 assorted servos and an retract unit on Ch 5, so there is really no need to look elsewhere. And this was an easier place to connect wires to, so I've decided to use this location, despite what i posted earlier.

So without further ado, i mounted the module and soldered in place. Note the white connector at the bottom right has disappeared from the previous photo, i removed it and soldered the power and ppm signal wires to the other side of the board here.



Also took out the pins at the center of the board where the Futaba RD module connected, as these were now unneeded and would be in the way of the next part.


I gutted the Futaba RF module enclosure, and cut away one side. This serves two purposes:

I'm going to mount the daughterboard on the side of the RF enclosure. This has the bind button and indicator LED. Since these functions won't be needed often, i'm happy to hide them away, and only need to pop the RF enclosure out to get at anyway. The cutout provides clearance where the button & LED will protrude into the cavity.

The other reason for the cutout is it gives me a convenient place to store the special balance charge lead so it doesn't get misplaced!




The next step was to mount the aerial.

I want to use the factory aerial mount, but there is a physical incompatibility here, so i have a small widget on order to resolve this.

So until this arrives, there isn't a lot left i can do. So stand by for the next update in a few days.




Edited by Dale Bradly
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On 20/05/2024 at 10:39, Dale Bradly said:

Tell me, what's the advantage/reasoning for "Phil Greens encoder boards based on an arduino nano"?

Well, it removes the old and crusty analogue components of the 20 year old existing encoder board which is usually full of potentiometers  and old analogue timing components. It provides you with a couple of mixers that the old encoder may not have, it has a throttle lock which the old board wont have, it has expo and rates, it has a beep alarm for the throttle lock and minute timer, it is seven channel with a speed selectable output on the gear channel, it is smaller, accepts a wide voltage range and it was created by one of our own! 


Here is an excerpt from the sketch describing the functions - 


// A simple seven channel PPM encoder. Six propo, one switched with servo-slow, single-channel escapement emulation mix, Vtail, Elevons, minute-minder etc
// Please do not use Arduino bootloader for programming, its startup delay messes things up and can strip servo gears with some modules (eg Corona)
// Connections:
// Pots are wired between ground and regulated 5v from Arduino. Wipers connected as follows:
// A0=aileron, A1=elevator, A2=rudder, A3=throttle, A4=aux1, A5=aux2,  A6=expo, A7=rates. Always use this wiring order regardless of PPM channel order.
// Ground A6 and A7 with links or Spektrum bind-plugs if rates & expo are not required. Dont leave them floating.
// If fewer analogue channels are used, tie unused ones to a used one, do not leave floating. Eg on a 4ch set, tie A4 to aileron wiper, A5 to elevator wiper
// Unwanted digital functions can be omitted except for button on D10 or D11 which is needed for calibrating the sticks. Omitting ch7 toggle (D12) means no range test.
// Note that the DIY More ProMini Strong has annotations for D0 and D1 reversed - the pins actually number 10234567.
// D0=PPM, D1=S/C escapement speed, D2=throttle reverse, D3=ch7 speed, D4&5=channel order, D6=75:25 mixer, D7=50:50 mixer, (D6 AND D7)=60:40 mixer
// D8=increment minute timer, D9=throttle lock, D10=sequential s/c, D11=compound s/c, D12=ch7 toggle switch, D13=buzzer NPN base, collector to battery pos,
// ... emmitter to buzzer+, buzzer- to neg (emitter follower). Parallel haptic with buzzer. Used for minute minder, inactivity timer & throttle-lock warning.
// Features:
// Calibration - center trims, hold either s/c button in, switch on, still holding button move all controls to extremes including auxilliary pots
// Center all controls including throttle and aux pots. Release button.  At this point the throttle-lock warning should chirp because the throttle is centred.
// Do not switch off during calibration, the calibration values cant be saved if the set has been switched off!
// Throttle response can optionally be made non-linear during calibration by 'centering' the throttle stick to say 2/3 rather than to neutral stick.
// Variable expo & rates on Futaba ch1, 2 & 4, ditto JR ch2, 3 & 4. Elevon mixer on Futaba ch1 & ch2, JR ch2 & 3, 75% aileron, 25% elevator or 50:50 for V-tails
// Mixer option can only be changed on power-up (avoids accidentally switching during flight).  Single-channel emulation mix, compound or sequential.
// Flick toggle 3x for range test.  Servo reversing by holding sticks over on power up (saved to eeprom). Servo-slow on channel 7 toggle.
// Auto and manual throttle-lock with warning.
// Follow the story on the single-channel forum http://mode-zero.uk/viewtopic.php?f=27&t=844
// Diagram and documentation on http://www.singlechannel.co.uk see Archive page
// If you use this software in whole or in part please acknowledge its source - Phil_G on most forums, [email protected] http://www.singlechannel.co.uk
// Special thanks to the late Dave Burton and Mike Kitchen for their improved expo maths, and Hasi for the interrupt-driven ppm.
// Thanks also to testers Ron, Shaun, Pat, Frank and Al


All info is here


However, you are well down the road using the existing encoder board and a soldered in Tx module so none of this is relevant. Well done on the conversion.

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So the antenna is the next step.

Wanting to keep it somewhat factory looking from the outside, i wanted to use the original antenna mount.

However, when putting the 2.4 antenna inside the Futaba mount meant that the antenna would not be able to hinge, as the hinge point would be inside the mount.

So i needed to "lengthen" the 2.4 mounting arrangement, so the antenna protruded a little further.

Hence the small sma extention at bottom of pic.




I considered screwing the 2.4 antenna base to the bottom of this mount as the original longwire antenna did, but this meant trying to do up all the securing fastenings from inside the mount, so this idea was quickly dumped.


I then cut a piece of scrap aluminium to fasten down with the mounting fasteners, that would then take the antenna mount, the extension, and the antenna itself easily.

with the bottom of the mount (where it protrudes inside the Tx out of sight) cut off, this then slips right over the whole new antenna and with 4 machine screws, the whole lot looks like it's meant to be.


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Antenna complete and installed. Looking like it should be.




And the factory stick ends were not up to the task, so a new set were duly purchased and fitted.


That actually completes the "modifications", the last real task i want to carry out is give the front site a decent clean, removing the remains of labels and grime that appear over the years. I can see me pulling the whole thing apart again to remove the everything from the anodized metal front cover to give it a good going over.

Job for this weekend perhaps.

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Posted (edited)

My only concern would be the condition of the stick pots. Being 'mechanical' the do wear over time although I accept that Futaba bits tend to be pretty "bullet prof"


The pots on my 6 channel Futaba Skysport 6A, still being used on 35 meg, have outlasted those on my old but considerably younger Spektrum DX6i.

Edited by Simon Chaddock
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