Futaba Challenger 35MHz to 2.4GHz DSM conversion

[NoelParticipant @noel26080]

I had been after an extra DSM TX for a while.

Have read about DIY kits for converting older non module-ized transmitters to modern 2.4GHz systems.
I have an old Futaba Challenger 35Mhz 6 channel set that I inherited, so combination of that and an OrangeRX DSM DIY module at £25 seemed a good way of getting an extra transmitter out of something that is otherwise a bit obsolete.
Plus you end up with a nice 1980s Japan made Futaba tranny, which has a good weight and quality feel to it, for £25!

So I ordered the OrangeRX DSM DIY module and it turned up inside 1 week from Hobby King in Hong Kong:

Its nice and small, and simply has three inputs: Power (up to 12v), Ground and the PPM signal – and then an antenna which is easy to mount in place of the original extendible FM one.
There is a status LED and a bind switch, both pre-wired, so you only need to mount them in a convenient place.
The only bit to freak out the DIYer is working out where the PPM signal is in the transmitter, but I found this easily enough on the internet.

Opening up the Challenger, you can see it is conveniently organised with the FM transmitter on a seperate board joined with a 5 pin PCB connector:

Removing the FM board is simple, and I have noted what is on what pin on the PCB edge socket, because you can then attach the DIY module direct to this:

Now when researching this on the net, I found a lot of people got a hit hacky and chopped the plug off the FM board, then soldered the DIY modules input wires onto it.
But there is no need to do this at all, in fact there is no need to even get the soldering iron out, or do any butchery on the Challenger at all.
The leads from the DIY module just need a reasonably thick bit of wire or similar attached to the end: I used the legs from a 10W resistor, and then you can push these 'pins' into the PCB socket.
They fit snugly and look nice and tidy:

Yellow is signal, and red/brown are power.

A test at this stage proved it all worked as a normal DSM transmitter, and it bound to my OrangeRX DSM2 receivers OK.

Then a couple of holes were drilled carefully in the top of the case to mount the bind switch and the status LED. I used a little bezel mount for the LED, and it almost looks like Futaba put it there. Bind switch is a bit out of place but still tidy.
The module itself sits in the corner quite well with a bit of double sided tape to hold it in place. A couple of cable ties keep the switch and LED wires from flapping around.
The new aerial mount fits into the existing antenna bezel thing, with a small amount of lengthening of the hole internal to the bezel.

That's it:

A note about channel assignments.
This Challeneger is a "Mode 1" flight controller, so left stick is Evelator/Rudder and right stick is Throttle/Aileron.
The difference between Futaba and Spektrum DSM channels means you have to note what maps to each channel on a DSM receiver:

Futaba Challenger tranny :    Spektrum DSM receiver
Throttle (right up/down)           Elevator
Elevator (left up/down)            Aileron
Aileron (right left/right)             Throttle
Rudder, Gear (channel 5) and Aux (channel 6) all match up.

For boating use I will use it like a 2 channel box and use Evelator (left stick) as throttle and Aileron (right stick) as rudder.
There is a USB kit to re-program the DIY module and re-align the three channels that don't match, but for the sake of moving two servo plugs I really don't see the need right now.

Hope this is of use to people. Old Futaba transmitters are readily available and with a DIY module make a quality set up.

Noel.

Edited By Noel on 29/09/2017 14:49:11

Edited By Noel on 29/09/2017 14:54:33

[NoelParticipant @noel26080]

Making use of an older transmitter for DSM

[Dodgy Geezer 1Participant @dodgygeezer1]

Fine for a 35Mhz set – but spare a thought for the submariners if you have a 40Mhz set. These are getting rare, and it would be a shame to lose one of the only radios they can use…

[NoelParticipant @noel26080]

Fear not the beauty of this conversion is that it is 100% reversible with the re-installation of the original FM board and aerial!

[Charles OatesParticipant @charlesoates31738]

Noel, thanks for posting this, ive found it interesting and helpfull I would like to convert a couple of my old but loved transmitters. Can you give me an idea of the web sites you consulted.

Chas

[NoelParticipant @noel26080]

Chas,

The HobbyKing customer feedback /review entries for the module itself also has some useful info about channel re-assigning.

The site I pinched the connector pin reference from was **LINK**

They seem to have mounted the antenna internally, and imply that they soldered the connections in – although its not obvious how.

I politely suggest that my method is better as you want the antenna as clutter-free as possible, and of course I haven't messed with any of the original components – converting back to FM is probably a 10 minute job.
If there was a bit more space internally to leave the original FM transmitter board in place, you could make up fly leads, have a suitable double pole/throw switch, and have the whole thing switchable between FM and DSM.

Now that would be cool

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