Experiences of a year with Spektrum 2.4 GHz radio
So who am I, and what are my radio credentials.
I started flying radio in the mid 1960's with home-built single channel super-regen radio, the kind of stuff that only sometimes worked, and when it did, would allow only one radio to operate at a time. I progressed from this through home-built reed equipment, home-built proportional radio, and a variety of commercial radio sets. Whilst flying thermal soarers in national competitions over a 12 year period I used only Multiplex radios. For the last 20 years or so my transmitters have been Futaba with a variety of receivers both very inexpensive, and quite costly like the Schultz receivers. I do not have radio problems. I never have. My 35 MHz gear worked perfectly; I have never been shot down and apart from the very early years I have not had radio failures. In short, I have no reason at all to change from my present 35 MHz radio. My Futaba transmitter has 16 memories and 14 are used up. That means that I have 14 fully equipped radio models. Changing to 2.4 would be an expensive operation requiring a shed load of new receivers. No way Hosé. So why did I change to 2.4? And why to Spektrum and not Futaba? I guess I was just a bit curious to find out about it. So read on.
How does Spektrum work in practice on the flying field.
I make it clear that my operating experience is of Spektrum and no other.
Once your Spektrum radio is set up [more later] you just switch the radio on and fly. No crystals to change or check, no peg boards and no frequencies to set. You can switch on the receiver first or the transmitter first as it makes no difference at all. Old habits die hard, but you can switch the receiver on first and leave the transmitter off, and nothing happens. It just sits there. No servos jamming at one end. No twittering, and no electric motor self-starting and going into orbit. The RX does nothing until the TX is switched on. You just switch the TX and RX on in any order, and fly. No checking for others on your frequency, because the gear does not operate in the way we are used to. Out of courtesy, you put your 2.4 peg on the board. But you just get on with flying. What if others are flying Spektrum too? No problem, as the Spektrum system allows 40 outfits to operate all at one time, with no interference.
So what if you were flying a different model yesterday, and today with this model the radio does not work? What do you do? Simple, you have selected the wrong model memory in the transmitter. Spektrum has a system called "Model Match". All you do is select the correct memory for the model you have with you today, and the gear then works. The receiver will not respond to any memory or transmitter other than to one to which it has been "bound" when you first programmed the RX for that model. [More on what this "bound" means later]. We must all have forgotten to change the model memory on our 35mHz gear at some time in our flying careers, and as a result we have wrecked a model because of reversed or wrong controls; well this is not possible with Spektrum gear. [Don't tell porkies, you know you have done it!]
So what is this "bound" or "binding" business.
When you are setting up a new model memory, as with any radio gear, you set up the mode, as in Acro or Heli or Glider, or what ever your make of gear allows, and you set throws, servo reversing, mixing, rates, exponential, etc, all for that particular model. With 35 MHz gear, any old receiver with the correct crystal will respond to this model memory. You can fly the "wrong" model any time you like, with dire consequences. Spektrum is not like that. What you do after setting up the transmitter, is to "bind" the receiver to that model memory, and having done this, that receiver will then only respond to that model memory. Any other memory selected on the TX, and that receiver sits does nothing in total safety. Any other transmitter switched on will not operate that receiver under any circumstances, what ever memory it happens to be set to.To bind a Spektrum receiver to the transmitter is simple. You fit a special "bind plug" into a special socket on the receiver [or plug it into the special Spektrum charging lead], and you then connect the receiver battery and power-up the receiver. In this state a little flashing light comes on in the receiver. [You don't need anything else plugged into the rx, but the servos can be plugged in if you like, it makes no difference to binding]. You then make sure the throttle stick is set to low, and then press a bind button on the transmitter, and hold that button whilst you switch the transmitter on, and still hold the bind button down until binding is finished. The receiver light then does a number of tricks; it goes off, comes on flashing again, goes off, and then finally comes on solid with no flashing. This takes about 10 seconds at the most. You then release the bind button on the tx, remove the bind plug from the rx, and the job is done. You only bind the receiver to the transmitter when you first set up the model. You do not have to bind the receiver each time you fly. Even when you alter mixers, control reversals or what ever, you never need to bind that receiver again for use on that model memory.If like many of us you need to change the receiver from one model to another, and each model is set up on a different memory in the transmitter, then you do need to go through the bind procedure when you swap the receiver into another model. The receiver does not know what model it is in, the system is not that good, [yet!].
What is the "Model Match" thing that Spektrum go on about?
It is as just described. Each receiver will only respond to the particular memory to which it has been bound. I have around 12 models each with their own receiver. Each receiver only responds to its own memory in the transmitter, the one it has been "bound" to. When I switch on the TX, the model memory that it comes up with is the last model memory that was used. To change memories there is a simple procedure when switching on the transmitter.Let us say I go to the field with my "Swift" electric Glider, but I was last flying my indoor electric helicopter called the "Chopper". When I switch my TX on, it is set to the Chopper memory, because I am dumb-head and I forgot to change it to the Swift. So I then switch on the Swift receiver. Nothing. The Swift just sits on the grass and sulks. Dead as a haddock. I know, I did just this at the recent Cramlington Great North Fly-in. The Swift just sits there doing zilch. It doesn't matter if anyone else has a Spektrum TX switched on, it is just not interested. I just switch off the TX, and switch on again in memory select mode, select the Swift, and within 3 seconds the Swift comes to its senses and we are ready to go, fully working. [And as it happens, we win the comp, bringing home a couple of trophies and a free year's magazine subscription]. If that had been on 35 MHz, and in the heat of the moment and stress of the competition, if I had not checked that the model responded with control throws and mixers all correct, I would not only have been taking the Swift home in a small bag, there could have been a serious accident since this was at a public event.
What is different "in the hand" about Spektrum radio?
Spektrum transmitters are much like any other transmitter but for the aerial. Transmitters on 35 MHz have a telescopic aerial that must be extended for flying, and can be retracted for rough range checking. Spektrum transmitters [all 2.4 gear in fact] have a very short aerial about 6 inches long which is not telescopic. It folds to one side for ease of transport, for ease of packing away in a case, and for making sure you get the best range. Since it cannot be telescoped down for a range check, Spektrum transmitters have a range check button that reduces the power, allowing a range check of about 30 paces to be carried out. In other respects, Spektrum transmitters are much like any other. The DX7 balances badly on a neck strap because it seems to be based upon the layout of a 35 MHz tx with an extended aerial. Without that aerial the balance is all wrong, and if you use a neck strap you will need a balancer thingy that Spektrum will sell you. [G-Force make a much nicer one though that does not obstruct the on/off switch, and lets the transmitter fit more easily into its case].
The main difference between Spektrum receivers and a 35mHz receiver, is in the aerials. The 35 MHz receiver has a flexible aerial about a metre long which you fit inside the fuselage or let it dangle outside. Most Spektrum receivers have 2 short aerials each a little over an inch long, and these must be kept sticking out from the receiver, in line with each other. Although they are of plastic covered wire they should not be treated as flexible, and the receiver needs to be installed in the model in a particular way to ensure the aerials are not bent or blanketed by nearby bulky objects like batteries or motors. More of that later. Some Spektrum receivers are actually made up of several receivers all plugged into each other. More about that later. What Spektrum radio gear is available?
Spektrum is distributed by Horizon Hobbies, the headquarters of which are in the USA. They have a very helpful UKbranch. It appears that JR and Spektrum are maybe the same company, but what ever the situation is, they use the same system of 2.4 GHz.I only have experience of Spektrum, not JR. In simple terms, Spektrum seems to be for club flyers, ranging from a very cheap and simple 5 channel 1 memory outfit , to a well equipped 7 channel outfit with 20 model memories.. JR seems to cater more for the "expert" modeller as their transmitters tend to be more complex with more model memories and more mixers and other tricks.
The current Spektrum outfits all use a system called DSM2. Any DSM2 receiver will work with any of the current DSM2 transmitters. This is easy since DSM2 is the only system they now use. You cannot mix and match current DSM2 receivers with the older DSM transmitters, and similarly the other way around.
There are currently 4 different Spektrum transmitters available, normally sold either as transmitter/receiver combos, or as complete outfits with servos. It is possible with some effort, to buy a transmitter on its own, and not as part of a combo.
Spektrum receivers are another matter. There are currently a range of about 8 different models. Some of these are just a single receiver weighing a couple of grams, but others are a receiver with another little satellite receiver plugged into it on the end of a flexible 3-wire lead. In this form each if these two receivers is in use all the time. The most complex receiver [ as used by Ali Mashinchy ] comes as standard with 3 satellite receivers plugged into the main receiver, with provision for adding even a 4th one! The popular receivers are types AR6100 and AR6100E, which are single so-called "Park fly" receivers, and the AR6200 which is a full range 2-receiver model. The 7 channel outfit comes with an AR7000 receiver which is a 2-receiver job, but is not particularly popular because of its size and physical shape. Rapidly becoming the most popular receiver for sports flyers is the recently introduced full range single-box 5 channel receiver, the AR500
Spektrum outfits in detail.
The cheapest Spektrum outfit is the DX5e, a 5 channel transmitter with a full-range single receiver, the outfit selling for about £65 without servos. The very useful AR500 receiver included with this combo can be bought separately for about £35. It is listed as a full range receiver. It is useful because although it has 2 aerials, one is the normal short aerial, but the other although still a short aerial, is on the end of a flexible wire about 12" long. This wire can be arranged to exit the fuselage so that the actual aerial part at the end is totally outside the fus. This is invaluable for such as models with a carbon fuselage, which would totally shield a normal Spektrum receiver from all incoming signals making it unworkable. The DX5e transmitter is as limited as the receiver is brilliant, because this transmitter has just one memory, the currently used settings. Just like the old non-computer sets of the last century, it is just a transmitter. You set the throw directions and rates and that is about it. All your receivers respond to that one memory. What a bummer!Next and perhaps the best for many, is the DX6i transmitter combo. It is normally sold with the full range AR6200 receiver [actually it is 2 receivers plugged together with a short 3 wire link]. The DX6i transmitter has 6 channels and 10 model memories. It operates on only 4 AA batteries; even the supplied dry batteries will run for about 20 hours, and it is very light and well balanced in the hand. The TX/Rx combo sells for about £95, with the Tx available separately for about £45 and the Rx for about £48. This is a super outfit and I only changed to the next model in the range because I ran out of memories.The top of the range Spektrum is the DX7SE [Special Edition] outfit. This is a 7 channel transmitter with 20 model memories, enough mixers for any sane person, all kinds of tricks, and operates at twice the speed of normal outfits, which is apparently a feature needed by helicopter fliers. It sells with the AR7000 receiver, which again is a 2-receiver model, somewhat up-market for no reason I can see, from the AR6200 receiver. I bought my DX7 transmitter for £145 on its own, as I had no use for the receiver normally sold with it. The outfit with a receiver is around £220 and with servos I have no idea. I don’t buy outfits, I like to choose my separate servos and receivers.
Any of the DSM2 receivers will work with any DSM2 transmitter, so you can mix and match any RX with what ever your TX is. You will only get the number of channels that your Rx has of course.In detail the receiver range covers an ultra light indoor receiver with unusual tiny and very light servo connectors compatible only with Spektrum micro servos, right up to a power-house of a receiver that has a heavy duty connector setup for loads of digital servos drawing very high currents.For normal use the AR500 is a good choice as it is a full range receiver and currently the cheapest available. The AR500 is only a 5 channel receiver, so if this is not enough the AR6100 or the AR6100E [with end connectors] are suitable, with great actual range as long as you are careful where you install them in the model. The AR6100 receivers are listed as park-fly receivers, not as full range items. I have flown these receivers in electric models to in excess of 1200ft altitude, which is as far as I can reliably see to fly a model, and I personally regard them as full range. If you are not prepared to trust these receivers at long range [I do and have not had a problem] then the next most suitable is the AR6200 receiver which is comprised of the main receiver into which the servos plug, complete with its 2 aerials, and a second satellite receiver connected to the main one, which also has its 2 aerials. This is a full range receiver. Its only disadvantage is for small models, because it has old-fashioned top connections for the servos rather than the more accommodating end connections. If you want end connected servos with a double receiver, you go for the AR7000 receiver, which does have end connections but is a slightly more bulky shape.
NOBODY makes receivers that will work with Spektrum [and JR] transmitters other than Spektrum [or JR]. Eventually this might happen, but not at the time of writing.
What are the choices I made when I went for Spektrum.
1. Buy a 2.4 Futaba module from Futaba to plug in the back of my Futaba transmitter and buy a load of Futaba 2.4 receivers. I didn't like this because it makes the transmitter lumpy at the back and difficult to fit into a case. The receivers are too big for the small models that I fly, and they are expensive [compared to Spektrum they cost more and are bigger]. The actual transmitter module costs more than the price of a complete Spektrum transmitter. On the plus side however, I would be using a transmitter that I am familiar with, all the models are programmed-in, and I have several Campac memory modules giving me literally hundreds of model memories if I need them. A serious reason not to buy Futaba is their gross incompetence at sending out 2.4 GHz radios with programming faults meaning every transmitter had to be recalled and replaced. I lost my faith in Futaba as did many others.
2. Buy a Spektrum module to fit into my existing Futaba transmitter, then use Spektrum receivers. Unfortunately this would not give the model match function; and model memory would operate any model, and this is loosing a serious advantage of the full Spektrum system.
3. Buy Assam, Coronaor some 3rd party transmitter module and receivers for my Futaba transmitter. Unfortunately tests show that none of these independent systems exhibit anything like the required level of interference rejection and are best left alone.
Known issues with Spektrum radio gear.
Fail Safe
All Spektrum radios have built in failsafe whether you like it or not. You have no choice.The instruction manual appears to contradict itself, and it suggests that what the controls do when the receiver goes into failsafe, is programmable. With the exception of the throttle position, this is not true. Fail-safe is set when a receiver is bound to a model memory. When the signal is lost, all controls hold their last positions except throttle, which goes to the position the stick was at when binding took place. Normally this would be low throttle, but if by mistake throttle was at a mid position when binding, this is the position the throttle will go to when the receiver goes into fail-safe. Spektrum does not give the option for all controls [except throttle] to go to neutral; it is not an option.Two things will cause a Spektrum receiver to go into fail-safe. One is simply a loss of signal. The other is low voltage to the receiver. The Spektrum receiver needs a minimum of 3.5 volts. Less than this and it goes into fail-safe. Although this seems a low voltage compared to the nominal 4.8 that a 4 cell rx pack provides, modern servos particularly of the digital variety, can draw high currents and reduce the supply voltage to the below the critical 3.5 volts for the receiver. As a result a number of fliers particularly those using large numbers of servos in their models, use a 5 cell receiver battery to unsure a voltage above 3.5 is guaranteed. Spektrum acknowledge this to be a problem and they can supply a small plug-in capacitor that will in theory prevent short term voltage dips. The safe course if worried, is to use a 5 cell rx battery. This is not a problem that I have personally had to address as I do not use digital servos nor do I use large numbers of servos.When the cause of the fail-safe is removed, meaning that either the signal comes back, or the voltage returns to above 3.5 volts, full control returns within about 2 to 5 seconds.
Signal blockage.
Radio waves from transmitters on 27MHz, 35MHz and 40MHz, which are our normal model frequencies, will in general pass through just about anything. The only thing you need to bother about is carbon fuselages. These radio waves do not easily pass through carbon, so we usually dangle the long aerial outside of a carbon fus.Radio waves on 2.4GHz however do not readily pass through anything solid at all. Almost anything solid will have some effect on them, and carbon will totally wipe them out. If we place our 2.4 receiver in a model sandwiched between a big fat battery and some other solid lump, the radio waves will likely not get through and we will have a problem. A 2.4GHz receiver needs to be placed a little away from carbon or solid metal objects like batteries, engines or fuel tanks if problems are to be avoided. Other construction materials like wood, plastic or foam will not block 2.4GHz radio waves at all. Do not install a 2.4 GHz receiver in a carbon fuselage. It will not have any significant range at all.On the positive side, 2.4 gear does not suffer from interference caused by what we generally call metal to metal noise as generated by metal clevis and metal control horns, so that is a point in favour of 2.4If Spektrum receivers of a type that have 2 receiver boxes each with their own pair of aerials are used, the aerials on each box should be arranged to point in different directions, to give maximum possibility that at least one of the aerials will have a good chance of picking up a strong signal. This is called "aerial diversity".Although 2.4GHz receivers need more thought than 35MHz receivers when being installed in a model, this does not pose a problem in all but the slimmest fuselages.
DX6i Transmitter.
I have used a Spektrum DX6i for about 4 months, with receiver types AR6100, AR6100E, AR6200 and AR7000. I sold the AR7000 because it was too bulky for my models with slim fuselages.I have never had any failure of any kind with this gear, but one issue has come to light with my flying pal's DX6i transmitter. The DX6i has 10 model memories and as described and "model match" technology means that a receiver bound to any one of these memories, will respond only to that memory and to no other. However, on some DX6i transmitters this does not work with memories 9 and 10. We discovered on a particular DX6i that any receiver bound to memory 9 will also respond to memory 10, and any rx bound to 10 would also respond to memory 9. This is a know fault and it can only be corrected by Horizon Hobby who have a firmware fix. The offending transmitter was fixed and returned in a couple of days. Horizon say only "some" transmitters are affected, but we can only guess if this is true. It may be by now [it should be] that this fault has been corrected and that it does not appear in recent DX6i transmitters.Binding a DX6i transmitter can be a little confusing since the manual is written for Mode 2 transmitters. The bind switch on a DX6i transmitter doubles as the buddy box switch, which is shown in the manual at top left on the transmitter. In fact on a Mode 1 transmitter, it is top right. Unless you realise this, you will not be able to successfully bind a Mode1 DX6i transmitter!
DX7 Transmitter.
I sold my DX6i and bought a DX7 because the DX6i has only 10 memories and the DX7 has 20. Since then I have bought a second DX7 because I need even more than 20 memories.
I have had but one oddity with the DX7, which has also been reported on forums on the internet. Once and once only, when I turned on the transmitter, the whole display on the LCD display at the bottom of the transmitter, was upside down. I had not been drinking, and the transmitter was the correct way up, but the display was upside down. It returned to normal when I switched off and immediately back on again, and it has never happened since. There are reports on the Internet of someone else seeing a similar problem. I contacted Horizon hobby who advised me that this is probably due to an intermittent connection between the ribbon-wire connection of the display screen to the rest of the electronics, and that in no way is the operation of the tx affected. They offered to take the DX7 back for inspection but advised me that this was actually unnecessary. They suggested unplugging and reconnecting the suspect connector, so this I did. Realising just how difficult it is to remedy an intermittent fault, I accepted their advice and did not send the tx to them. I have not seen this peculiarity since, and the DX7 has worked faultlessly since then. I am so satisfied that I now have 2 DX7 transmitters.
Some coments about range.Many would believe that as you go up the Spektrum receiver price range, you get a "better" set of receiver electronics, leading to better range. Certainly the claims of better range are justified, but I believe that the reasons are not obvious. I suspect that the "single box" receivers, of which there are about 4 or 5 types, all have the same electronics, and their real difference in the aerials. Ignoring the ultra light indoor receivers, the single box receivers are the AR6100 [and E] and the AR500. Except for fewer channels, I would suspect that the difference between these two is only in the aerials, the electronics being the same in each. The 6100 has two tiny aerials which would normally be in line with each other, and inside the model. It is listed as a limited range park flyer receiver. The AR500 has one short aerial and one 12" long screened wire with a short aerial at its end. This aerial can be outside of the model and it can be at 90º to the other aerial giving better aerial diversity. I believe this is the sole reason for the AR 500 to be listed as a full range receiver.Then there are the "two box" receivers, where the main receiver with the servo sockets has a second satellite receiver plugged into it, with its own pair of aerials. In effect this is 2 receivers with four aerials and hence more chance of picking up a weak signal, because there is more chance of an aerial pointing in a favourable direction, and hence they can claim better range. And in addition the satellite receiver is in a slightly different location in the model, lessening any effect of signal blanketing by solid objects within the model. These 2 box receivers can justifiably claim better range because they have doubled-up the number of receivers and aerials, which are also better positioned to pick up the transmitted signal.
Then there are receivers with 3 or even 4 satellite receivers plugged into the main receiver. In fact these satellite receivers can be bought for £20 each as separate items usable on any of the receivers into which they can be plugged. These satellite receivers are all the same, no matter whether you have bought the cheapest £50 AR6200 receiver, or the most expensive £125 AR9000. The satellite receiver is the same in each case, in fact the AR9000 Spektrum receiver used by the likes of Ali Mashinchy, can use 4 such £20 satellite receivers all plugged into the main unit, and the main unit is not a receiver at all, it is just a junction box for connection of the servos. The only receiving parts of this most expensive Spektrum receiver, are the 4 satellite units plugged into the power box, the very same £20 items used by the cheapest of the two-box receivers.
It appears that all the basic receiver electronics are the same; you get better range by having more of them, in differing locations in the model, with more aerials, pointing in a greater variety of directions!
Summary
My experience is that Spektrum radio does what it "says on the box", it just works.
It really is a relief not to have to think about frequencies and interference. The idiot who thinks he is on one frequency but is actually on another, is of no concern to me any more. Nor is it a worry that I might unwittingly have a senior moment and myself be the cause of a frequency clash. I can switch on and fly. Anywhere.
I can no longer drop a goolie and attempt to fly a model with the wrong memory selected. If you say you have never done that, I shall look out of the window for the approach of the 3 wise men. [They appeared at the time of the last known miracle.]
Receivers are small and high quality at a very reasonable price, [compared to other high quality 35Mhx receivers]. They appear to be very robust.
Horizon hobby, who distribute Spektrum in the UK, provide an excellent service. They are approachable on the phone, they reply to emails, and their turn-round service is quick.
Ken Croft
Teesside MFC
BMFA 15260