Much as I love my Jeti DS16 radio, there’s no getting away from the fact that, particularly in the indoor and parkfly sectors, there are some nice ready to fly models available that necessitate the use of a Spektrum (or compatible) transmitter. For the indoor scenario I initially addressed this problem by buying a cheap Spektrum-compatible transmitter - the Orange T-Six.
At the same time I took the opportunity to upgrade my older indoor models (Mini IFO, SE5a and Walrus) from 35MHz to 2.4GHz operation by fitting them with Orange receivers. This Orange equipment uses the Spektrum transmission protocol of the time, DSM2, and has proved perfectly satisfactory.
A few years on, I found myself with no suitable indoor venue for flying the SE5a and Walrus and was also presented with a MicroAces Fokker DVII for Christmas. This is a beautiful little model, just a bit too nice to be subjected to the melee in the small school hall which we currently use. The SE5a and Walrus live in a modified garden shredder box so, when I established that the little Fokker could be squeezed in there too, the idea of taking all three of them up to the flying field from time to time was born.
Now, I am so used to flying everything off one transmitter (there are 38 active model memories in my DS16 at the moment!) that it's a racing certainty that I’d turn up at the field with a shredder box full of models and no compatible transmitter. Also, by this time, the DSM2 protocol was obsolete and DIY 2.4GHz transmitter modules (and DSM2 transmitters generally) were rapidly disappearing from the market so, if I was going to get around to building a Jeti/Spektrum conversion box, it was now or never.
Having sourced an Orange DIY DSM2/DSMX Transmitter module, there were in principle three choices:
The first two options are both substantially cheaper than the third but have the drawback of having to take a drill to the DS16’s lovely aluminium case. Rationally, there’s no real risk in doing this but I couldn’t quite bring myself to do it, so opted for option three.
All Jeti receivers have the capability to output the PPM signal required by the Orange Tx module so it was just a question of choosing a suitably compact receiver, in my case the R5. As well as the Tx module and receiver, the other main component is a battery. The module has a voltage range of 6-15v. The Jeti receiver is specified at 3.2-8.4v. Since this box is likely to be used fairly intermittently (and will live in the shredder box so it can’t be left behind!), a low self-discharge battery is essential so, since I had a couple of 2s 800mah LiPo batteries around which had lost their edge for flying my V912 helicopter, one of those was pressed into service. The only other component required was a switch.
Laying the components out on the bench, it seemed that they could all just about be fitted into an old servo box (remember the days when even the humble Futaba 128 servo was sufficiently expensive to merit being sold in a ‘jewel case’?!). The picture shows the general layout.
When I connected everything up there was absolutely no sign of life. I was beginning to think that I had a duff Tx module but a cup of tea and a bit of research revealed that the Tx module will not wake up until it sees a valid PPM input. A further bit of research established that, although I had correctly configured the receiver to output PPM, it was, contrary to my expectations, doing it on servo pin No.5. So, with the plug re-located, all of a sudden it all sprung into life.
The Jeti receiver had already been bound to the DS16 so, with a basic model programmed into the Jeti DS16 following the Spektrum channel numbering convention, the next step was to bind a model to the Orange Tx module. This follows normal Spektrum practice: bind plug in the receiver and power up the Tx module whilst holding down the button. Of course, having established that the module won’t power up without a PPM input, the Jeti link has to be activated first. As long as the correct sequence is followed, this all works well.
For each extra model, a new memory is created in the DS16 in the usual way and the model is bound to the Orange Tx module as above. There are no ‘Model Match’ issues on the Spektrum side but, because all the model memories use the same Jeti receiver, the DS16 cannot warn you if you have the wrong model memory selected.
The Orange Tx module can work in DSM2 or DSMX mode at either 11ms or 22ms frame rates. Unfortunately it doesn’t remember which to use for any given model - it has no model memories at all of course. So it is necessary as part of the switch-on procedure, to observe the flashing pattern of the LED and, if necessary, switch to the appropriate transmission protocol by a sequence of button presses. My old Orange receivers are DSM2 but the Horizon ‘brick’ in the Fokker is DSMX so I dutifully switch modes accordingly. However, it has just occurred to me that the ‘brick’ came out of a clubmate’s Horizon SpaceWalker and my own SpaceWalker flies fine on my DSM2 Orange transmitter so maybe I could leave the module set to DSM2 all the time?
One bonus of having the Jeti receiver in the box is that the receiver battery voltage appears on the transmitter display. So, once everything is working, the box can be closed up without the need for a battery-checking lead hanging out the side. As I mentioned, I use 800mah 2s LiPos for a couple of other small electric models so I try to remember to put a charged battery in my flight box when taking the shredder box to the field so that, if the one in the bridge box is low, I can simply swap it out at the field.
It has been pointed out that leaving an intriguing-looking box laying around while you are flying, with a switch clearly in the ‘on’ position, is perhaps inviting some well-meaning clubmate to helpfully turn it off for you. so far this hasn’t been a problem but if I were to take this setup on a visit to another field I might be tempted to slip the box into my pocket or at least position it where I could see it!
This is a workable and very convenient solution to the challenge of flying Spektrum-compatible models from a Jeti transmitter. I’ve only used it on small, lightweight models which don’t get flown at long ranges. Would I entrust something big heavy and valuable to it? Well, that’s a bit like the earlier quandary of drilling a hole in the case of the DS16 - I can’t come up with a rational argument why not, but really would prefer not to!