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Member postings for Peter Christy

Here is a list of all the postings Peter Christy has made in our forums. Click on a thread name to jump to the thread.

Thread: Taranis X9E
23/09/2015 16:58:13

Gonzo: Yes, that looks pretty close - back of the envelope calculation and lets assume 13dB, not 14 as its easier to do without a calculator and 1dB won't make any significant difference! wink

10 dB loss = 1/10; 3dB loss = 1/2, therefore 13 dB loss = 1/20 (If you add/subtract logarithms, you multiply / divide the actual numbers)

Square root of 20, approx 4.5, so (1/4.5) x 1500 = 333.333

What I cannot understand is why a minor change to the protocol (and it is minor) would have such a dramatic effect. And why haven't I experienced any range issues with new X series receivers? Not even a hint of an RSSI warning - which I do get very occasionally on older D series receivers? And the D series give warning LOOOONG before they run out of range. In flight its usually a momentary aerial orientation thing - not uncommon at UHF frequencies - and has no effect on the model.

There has to be something else at work here.



23/09/2015 13:56:42

Hi Gonzo,

Actually, we're both wrong! That's the problem of doing complicated stuff in a rush (that's my excuse, anyway!) wink

That figure for the reduced range that I gave should have been 475 meters, not 1025! (1/10 of the power, roughly 1/3 the range - all other things being equal!).

But remember that dBs are a logarithmic scale: dB=10log(P1/P2) So a loss of 20dB represents 1/100th of the power, 30dB is 1/1000, etc, etc.

Thus your second calculation should read 20dB loss: sq.rt.100=10 ; 1/10=0.1 ; 1500 metersx0.1 = 150 meters.

Sorry about the silly mistake! (Wanders off kicking himself hard.....!)



23/09/2015 11:43:03

It depends not only on the power output and receiver sensitivity, but also on the environment. Someone I know flies - or used to fly - gliders to extreme range on 459 MHz, using only 10mW power. He never had a problem, and that was just using basic PPM! Similarly, when I was developing my 459 MHz system, I modified one of Roy Lever's Merlin PCM systems to 459 MHz and flew a small trainer to a considerable distance with NO Tx AERIAL attached! It was just flying on what was leaking from the BNC socket on the transmitter, and never gave a hint of going in to failsafe.

What 100mW does buy is added security. Just because we CAN fly at 10 mW doesn't mean it will always be secure. It depends on what else is around! 459 MHz is generally pretty quiet - or was, until the drone boys discovered it! wink

2.4GHz, on the other hand, is quite a widely used band. There is no easy way of saying what effect a given power reduction (or loss of receiver sensitivity) will have as there are simply too many variables. You can predict what would happen under ideal conditions, but this has little application in the real world. In ideal conditions, even a 10mW transmitter ought to be more than adequate - but 100mW will give you added security.

The point I was trying to make - and I know I was grossly over-simplifying a difficult concept - was that you cannot simply string numbers together the way Martyn did and get a meaningful answer. No disrespect to Martyn, by the way. What he did is logical, but our 2.4 GHz systems operate on a different level of logic! And I haven't even started to consider "coding gain"...........

To use an analogy: Say your car does 30 mpg under ideal conditions. You have a 10 gallon tank. You might expect a range of 300 miles. But that does not allow for hold-ups due to road works, accidents, hills, etc. So you always make sure you have more fuel than you actually need before setting off on a journey.

100mW is more than we actually need - MOST OF THE TIME! But it does give us added security in less than ideal conditions.

But to answer your question directly (although I'll use simpler figures to keep the arithmetic simple!): If the power level dropped by 10dB (a ten-fold power loss), then you might reasonably expect the range to drop by 1/sq.rt.10=0.316 So if the original range was 1500 meters, it would *probably* reduce to around 1025 meters.

Again, this is an over-simplification, but it does give an indication of how it all works! Hope this helps....



Thread: BMFA on the BBC, Martin Dilly.
23/09/2015 08:50:12

Some of the glider classes (both free-flight and RC) require considerable physical exertion to get the models up to the required height. I recall being told that in one of the RC glider classes, it is not uncommon to employ a sprinter alongside the pilot in a team (think Usain Bolt!) just to tow the thing up to height!

And again, a lot of sport is about hand/eye co-ordination as much as physical strain. If darts can be classed as a sport because of that, then model flying should be a shoo-in....!!!



Thread: Taranis X9E
22/09/2015 22:43:48

BEB is right - it is an inverse square law, so you cannot use a simple linear progression. Also, you need to know what the total path budget is to enable any meaningful response to be made. For most 2.4 GHz equipment, the path budget is in excess of 100dB, so even following the linear model, a 14 or 15 dB drop in signal would only have a 15% effect. Factor in the inverse square law, and its even less. Simple logic does not always apply to RF - its more like black magic - especially when spread spectrum is involved!

I updated my early Taranis to the ETSI 1.8.1 spec when it came out, but did not subsequently update it any further. As a result, mine works with the new X series receivers just fine, but also is still compatible with the older D series too. Just as well, as I have a few of them, and the reason I stopped updating! There is nothing illegal in this, as my system pre-dates the rule change ("Grandfather rights"!). I have not experienced any range issues with new spec X series receivers. I have checked the output on my spectrum analyzer and it is identical to the output of my DSX-9, which has given many years of faithful service.

I have heard a claim that the little plastic aerials fitted to the new receivers can be problematic, and that this can be fixed by replacing them with the simple wire aerials as previously fitted. I haven't experienced this, though.

If people are having issues, then the cause must lie elsewhere, and until someone does an in depth case analysis on a suspect system, we are in the realms of speculation. To date, my Taranis - and my DHT "hack" module - have proven just as reliable and effective as any other brand, and it has my full confidence.

I have to say that the EU has seriously blundered over this issue. The original stated intention was simply to clarify the existing regulations, which were open to misinterpretation (the reason the Dutch and others initially banned model control on 2.4 GHz!). Instead, they've changed the basic rules, caused confusion in the market, and made an agreed international standard no longer standard - and for no good reason!

Time to give the Eurocrats a good kicking, methinks!




Edited By Peter Christy on 22/09/2015 22:46:29

Thread: Learning to fly alone
21/09/2015 19:08:42

I too learned mostly on my own, about 50 years ago! I too would say "go for it", but with a couple of provisos! 1) Make sure your insurance is up to date! 2) Only attempt this in an isolated location - well away from people or property - but make sure you have a "safety person" with you in case you gash your fingers in the prop! Its all too easy to put your fingers through the prop removing the glow lead or fiddling with the needle-valve! This is the voice of experience!

Finally - a word of advice - if the model is getting away from you, DITCH IT! Just throttle it right back and get it down as quickly as possible. Models are replaceable - people aren't!

You will find the simulator very different from the real thing. In the real world, the models don't vanish as quickly, and they are more easily disturbed by atmospheric conditions. There is no "reset" button! Take-offs are optional, landings are compulsory! Don't attempt it unless conditions are as near perfect as you can get.

When you do your first solo, it will give you a buzz you won't forget in a lifetime. Best of luck!



Thread: Raptor 30 Flybarless Conversion?
21/09/2015 16:18:37

You can convert ANYTHING to flybarless if you really want! You don't even need any extra electronics....

Thread: Classic Aerobatic Model Photo Thread
09/09/2015 13:48:48

Thanks Martyn! I think I'll have to pass this time, though! I've spent far too much travelling to modelling events this year already! We went to Austria for the heli world champs, and that gave the old bank balance a bit of a battering.....!



09/09/2015 12:11:58

Skegness is quite a long way from here - I'm in south Devon! Where are the details for Skegness?

I built this model to take to the single-channel and retro meet up in Pontefract, but then had to drop out due to other commitments. Hopefully I'll make it next year!



09/09/2015 09:14:52

Hi Brian,

Its come in at about 6 1/2 lbs (no idea what that is in the new fangled units!). Most models of that era seemed to come in at about 8lbs back in the day, but then this one isn't lugging around 5 Bonner Transmites, a reed receiver and an 8.4 volt battery pack! That lot alone must account for nearly 2lbs! wink

It feels a lot more stable than I expected. Of course, it was designed to fly on reeds, but nonetheless, it was considered a "hot" model back in the day!

It rolls beautifully axially, and spins and recovers very easily - not like many modern 'planes that can be the very devil to get spinning! The thick blunt wing helps control the speed nicely, and the stall is very gentle. It is utterly vice-less!

I did beef up the ribs that are used to locate the undercarriage legs, facing them with thin ply. Some of the sites I fly from are a bit rough! The old Webra provides "ample" power, though I had expected it to be a bit more lively. Back in the day, it used to haul a "Tornado" (locally produced Taurus clone) around in grand style, and that DID weigh over 8lbs with its foam wings and a Bonner Digimite on board!!! I think the Webra might be slightly over-propped. Its fitted with a very broad bladed 12x6 - possibly intended for 4-strokes - and an HB "Quiet" muffler, which won't help either.

I'm not a huge fan of strip ailerons, and if I were building another would be tempted to fit conventional tip ailerons, but this one is as per plan.

Next up, I'm thinking of an Orion! I have an Irvine 46 looking for a good home, and the Orion was originally powered by either a K&B or Veco 45 IIRC! But that is a year or so off yet!

Yes, I'm delighted with the KingPin. Its a dream to fly and I hope to get a good few years enjoyment out of it!



Thread: First ever flight
09/09/2015 08:40:00

I think a lot of people forget how they got started in this hobby! Like the OP, I too had my first flight solo, and that was 50 years ago! There wasn't anyone around to teach or advise, we just got on with it! 10 years later, I was doing the same with helicopters - again, no-one around to help or advise, if you wanted to do it, you just got on with it.

Of course, there are provisos! My initial flights were well away from civilisation, where there was little chance of an accident causing any damage or injury. I could already fly control-line, so I had some modelling nous. And those early single channel models were little more than "radio affected" rather than "radio controlled". But so what? The sense of achievement was enormous, and probably one reason why I've stuck with the hobby for so long.

As long as the pilot is sensible about things, and chooses his equipment and site sensibly, then I see no problem. It would certainly be a lot easier today than it was in those far-off times.

Of course, if he had been some idiot trying to fly a scale Spitfire in a public park without any training, then it would be another matter. But from the post, it seems he did things sensibly and learned a lot from his experience.

Good for him, I say!



Thread: More EU changes on the way that may affect FrSky users...
08/09/2015 09:47:49
Posted by Frank Skilbeck on 07/09/2015 21:30:44:

We can then have our own unique UK standards........................................ Bear in mind these standards were written by industry not the bureaucrats.

I doubt very much if Futaba, JR, Spektrum or FrSky had any input at all. The "industry" you refer to seems to be limited to Cisco (a manufacturer of computer network equipment) and the major German car manufacturers, if what I've heard on the grapevine is to be believed.

Rumour has it that the German car industry wants to smother the roads with 2.4 GHz base stations, so that they can monitor their "smart" cars continuously - a bit like Formula One cars are currently monitored from the pits. However, to do this reliably in rural areas means having almost exclusive use of the band, hence efforts to make life as difficult as possible for other users.

Of course, they could apply to the world regulatory body for an exclusive international frequency - but that would take years, and more importantly, cost shed loads of money..........



Thread: Classic Aerobatic Model Photo Thread
07/09/2015 19:20:23

Just realised that I never posted an update on my "KingPin" project! Well, it had its maiden flight on the 6th of June, in the face of a howling gale! It handled it beautifully, and the 1967 Webra provided "ample" power:

More details in the video.
Just realised that I might have already posted this in the "What's your oldest engine" thread. Apologies if this upsets the mods....! blush
Thread: More EU changes on the way that may affect FrSky users...
07/09/2015 19:07:22

As far as I am aware, all the manufacturers bar Spektrum limit themselves to 100 mW wherever they are sold - and an increase to 200 mW only represents an increase of 3dB in a path budget of something like 120dB. In other words, its insignificant!

Th EU are really making a pigs ear of this. Half the countries in the EU misunderstood the original specification, and banned 2.4 GHz model control gear on the basis of this misunderstanding. Then when that was sorted out, they decided that they would re-write the rules in a clearer fashion to avoid future misunderstandings. The original stated aim was not to change the spec at all - just to make it clearer - but it is now suffering from typical bureaucratic "mission creep".

If they keep changing the rules at this rate, stuff will be obsolete before its even leaves the factory! The sooner we can get rid of the Brussels Bureaucrats, the better!




Thread: Any broadband wizards around?
02/09/2015 18:43:44

Good call! thumbs up



02/09/2015 09:58:02

Be careful! "Upto 4 MBs" means that's the best you can ever hope to achieve - probably downhill with the wind behind you! The actual speed will probably be a lot less!

I'm with Plusnet on fibre, and have found them good to deal with - much better than BT, despite being owned by BT! Fibre here is rated at "upto 75MBs", but we never see more than 35 MBs due to our distance from the cabinet. If they are telling you "upto 4 MBs", assume that in practice it will be roughly half that! And also bear in mind that at peak times, when everyone else is on-line, it will slow down even more. Better to have bandwidth in hand so that you still have plenty, even at peak times.

I wouldn't even think about giving up fibre for adsl, but you can probably get a better deal than you are on at present. And I've found Plusnet good to deal with.



Thread: What's Your Oldest Engine And Do You Use It?
02/09/2015 09:42:07

Got a few Cox .049s dating from the early 60s, still in running order. Also an AM .049 (Wen-mac copy?) that came out of a Jetex Mobo hovercraft (remember them?)! But the one currently in active use is a pre-blackhead Webra .61 - bought in 1967 to replace a knackered Merco .49, and still hauling a vintage aerobatic job around the skies today......


Edited By Peter Christy on 02/09/2015 09:42:34

Thread: Model Suggestions for OS 30FS
01/09/2015 14:04:32

+1 for the Flair Attila! Cracking little model. Quite lively with a .20 2-stroke, and mine was "adequately" powered by and OS20FS. Sounded great, too!

A 30FSshould make it a spritely performer! Worth adding the optional ailerons and reducing the dihedral.

A word of advice: I mounted my 20FS inverted, and needed to re-position the tank to the floor of the fuselage to get the fuel height right. Never had a problem starting it inverted, though always careful to check for hydraulic locking. But before I lowered the tank, I did have problems getting the mixture setting right.



Thread: FRSky Receivers
21/08/2015 10:00:33

Keep it simple, folks! As Gonzo points out, FrSky now do 4 channel receivers in the X-series range that are directly compatible with Darran's Tx without the need for any external modules.

There are two options - the basic X4R, just a simple 4-channel receiver (probably what the OP wants) and the X4R-SB, which adds an SBUS option for up to 16 channels. This latter is intended for use in quad-copters and the like, I suspect, where there is an external decoder / stabiliser circuit. I believe it only has three outputs in conventional mode, so its probably not what he wants.

Darran: Go with the X4R, as illustrated here:


which should do what you want.



Thread: First Light
02/08/2015 17:54:09

I actually met Geoffrey Wellum back in the late 60s! Between leaving school and getting a "proper" job, I worked as a salesman and van driver for a local electrical retailers that was owned and run by his sons. I remember him coming in to the shop on a number of occasions, a very quite and unassuming gentleman. It was the store manager who, aware of my interest in aviation (I was already flying RC back then, and had also done some full size flying), told me that he was a Battle Of Britain pilot.

My respect for him - already pretty high - went up several notches at that point!

I seemed to have a knack of being in the right place at the right time back then, because a couple of years earlier, I was completing the flight logs of a Piper Colt that I was learning to fly when Douglas Bader came into the club room! He'd just landed and was seeking the whereabouts of his would-be passenger. I couldn't believe who I was talking to and must have seemed like a stammering idiot to the great man!



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