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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: Linear Servos
15/12/2008 18:53:00

Yes, you didn't need to bother with servo reversing either! On my old Bonner Digimite, the servos are completely symmetrical. If you want to reverse it, you simply take it out, rotate throught 180 degrees and put it back!

The "Microprop" servos used by Sprengbrook were pretty good too!

And they were perfect for mounting in wings to drive conventional ailerons......!

I've still got a few Dunhams servos that had both linear and rotary outputs!



Thread: 2.4 GHz gear
15/12/2008 18:48:00

Hi Myron,

No, we don't need to worry too much. The path "budget" for 2.4 GHz is so high that for our purposes, we don't need to worry. The British Waterplane Association have done extensive tests with flying boats and seaplanes, and not had any issues. Avoid totally enclosed carbon fibre fuselages though, as these can work as a "Faraday Cage" and effectively screen the signal.

However, I have suggested to the BMFA that tying a (potentially) wet pennant to the end of a highly tuned 2.4 GHz antenna is probably NOT a good idea. If they haven't dropped that recommendation already, they soon will!

Sorry about the use of the dreaded four-letter word! I've been doing a lot of long/late shifts lately and my mind must have been slightly fuddled this morning.........




15/12/2008 14:54:00
Ooops! Sorry! Replied in a hurry before I left for work this morning! I should have addressed that to Myron of course......!
15/12/2008 10:33:00

The protocol that dictates that systems should co-exist harmoniously only applies to *digital* technology!

 There's quite a lot of gear out there - especially video cameras - that are analogue! A PAL colour TV signal (analogue) needs about 5.5 MHz of bandwidth - and will fully occupy that bandwidth!

It will also transmit continuously - not in bursts like a digital signal. This will have the effect of "deafening" any nearby receiver, digital or not! It would be a little bit like trying to hold a conversation with someone on the other side of the street, whilst standing next to a pneumatic drill!

 Of course, analogue equipment is slowly being phased out as digital is generally cheaper to mass-produce. But there's still quite a bit out there, and because it is obsolescent, it is quite often sold at very tempting rock bottom prices!

So I repeat my original advice - be very wary of installing 2.4 GHz video equipment in a model controlled by a 2.4 GHz link!

 Timbo - the reason that 2.4 GHz is the "magic" frequency is that it is useless for serious communications work! Because 2.4 GHz is the resonant frequency of a water molecule, signals tend to get absorbed very quickly by our damp atmosphere. Also the noise generated by microwave ovens raises the background noise level substantially. That means that about the only thing it can be used for is short range communications. Ideal for us, and computer networks, but totally useless for anything requiring long range!



Thread: Vertigo VTOL model video
14/12/2008 17:40:00

Don't know about the stability - remember the pilot is having to learn how to fly it too! How steady were any of OUR first landings with conventional aircraft - or even helis?



Thread: Reftec 459 megs
26/11/2008 16:38:00

Well, I still make my own 459 MHz gear, but only for my own use now. Mick Wilshere manufactured them for a while, and they were very popular with the vintage crowd. I still get them back occasionally for service - usually just duff cells in the Nicads!

 Winter Hill! That brings back some memories! I spent a very nice summer working at the Holme Moss transmitter back in the early 70s, and we used to pass service messages on to Winter Hill most days!

Which brings me to another thought! Back then I was flying a Simprop Digi 5 - another dog of an outfit that gave me no end of grief! In fact the only place it ever worked reliably was on the soaring site at the end of the Holme Moss driveway! About 200 yards from a 100KW TV transmitter, three 10 KW VHF radio transmitters and two 1 KW local radio transmitters, and it worked like a charm! Anywhere else, and you never knew if it would get off the ground before it ran out of range!

Perhaps that's why you've never had any problems! The local TV transmitter must have constantly been kicking it back into life!!!!

 Its an ill wind..........!!!



25/11/2008 18:20:00

Hi Eric,

Sorry - don't mean to offend - but my experience with Reftec gear was far from unique! About two years ago I gave the receiver to an old boy who wanted one for a boat - probably about the only safe place to use it, I reckon!

The problem was that the reputation of 459 MHz suffered enormously as a result. The Cotswold was a superb system, as was the Multiplex (still have mine) and modesty forbids me from extolling the virtues of my own

I also had the dubious pleasure of doing some tests on a Reftec 934 MHz CB radio (remember them?). It was an another appalling design susceptible to any tiny fluctuations in supply voltage, and horrendously unstable.

But the Mk1 Reftecs took the biscuit! There appeared to be NO FILTERING at all of the pulse train, resulting in enormous sideband splatter, and there was certainly no filtering of the RF stages, with the Tranny aerial being directly connected to the output transistor!!!

 The receiver used a single crystal to provide both local oscillator frequencies, with the result that the IF varied depending what channel you were on! The only way this could possibly work was by using an extremely sloppy (wide-band) receiver - so that's what they did! I wonder if they ever attempted to fly two on adjacent channels? It would certainly have been fun to watch!

I remember a car racing friend buying one and wondering about the poor reliability. When we opened up the receiver, we could actually slide the transistors throught the globs of solder on the board with our fingers! A good shake, and out they fell! Cold Joints? We've heard of 'em!!!!

I had to resolder every joint in my receiver to make it airworthy. On its first flight it shed a coil in the oscillator circuit - luckily the model crashed into a bush without sustaining much damage, or I might never have discovered the cause!

So I'm afraid I have to disagree with you on this one. No doubt a few escaped that were serviceable, but it was a poor design, and for the most part, badly assembled as well!

Now, does anyone know where I can get hold of a Space Control, or a RCS Tetraplex???



25/11/2008 11:55:00

I bought one of the "MK2" Reftecs just after they went bust. Avicraft seemed to have bought up all the bankrupt stock, and I bought one cheap to see if they were as bad as reputed! The answer was a resounding "yes"!

 There were so many design flaws, that its difficult to know where to start!

At the time, everyone ws still using 27 MHz. The first IF of the Reftec double conversion receiver was - 27MHz!!! This would have probably been OK if they'd put the receiver in a metal case - but they didn;t! It was plastic! So everytime it got anywhere near a 27MHz set (like doing a low pass, or carrying the model out to the runway) the receiver went beserk!

 Then there was the crummy soldering, with parts actually falling out of the boards when shaken hard! (I had a coil fall out of the receiver board in flight!)

Still, at least the "MK2s" had some filtering on the Tx output! The original Mk1s had no filtering at all! When I looked at one on a spectrum analyzer whilst repairing it, it went right of the 'scope at both ends, completely filling not only the 459 MHz band, but a goodly chunk of spectrum either side as well! Just as well few clubs had more than one set! If ever a Tx deserved a "black pennant", it was a Mk1 Reftec!

 However, it proved a worthwhile purchase, as I knew what mistakes NOT to make when I designed my own 459 MHz system a few years later! My original prototype is still flying 20 years on in my old "Lark" helicopter.....

The best place for a Reftec? In a display cabinet, NEVER to be switched on!



Thread: From the archives.......
28/09/2008 17:53:00


sorry for the delay in replying!

I'm afraid the model is not up for sale. With retirement visible on thwe horizon, I'm gearing up for a nostalgia fest - which will include renovating my Bonner Digimite-8, and getting that flying again!



03/09/2008 16:48:00

Hi, Roger,

 Yes, mine is the bigger one - about 30" span, powered by a Cox Bay Bee .049 and controlled with an Elmic Compact escapement!

I must have made dozens of them back in the 60's! That and the Sharkface were my favourite designs! 

 I also made a slightly modified one - currently powered by a PAW 80 diesel - with 2 channel rudder and elevator control to teach my son to fly! Its now teaching my grandson!

The only mods I made for 2 channel was to slightly reduce the dihedral. It looks better like that, I think! The elevator is a tooth-pick like affair cut into the trailing edge. Full down gives excellent penetration, but is not enough to "tuck under"!

And yes, it was me who invented the mixer....!



02/09/2008 17:27:00

A few years ago I actualy made a 35 MHz FM single channel set to work an Elmic escapement! Worked beautifully! I installed it in a Sub-Mini - a half size Super 60 that was a free plan in RCM&E many years back.

 Its still sat in the shed - hasn't flown for a while and probably needs the nicads replacing, but still otherwise in good order!



Thread: From the Archives
01/07/2008 09:55:00

If I remember right, the free plan in the January issue (the one with Maynard Hill on the front) was a thing called the "Sub-Mini" -  half size Super 60, for 0.5-0.8 cc engines.

 I built several of these for single channel - powered by Cox .049s, and still have one, complete with Elmic escapement! However, it now uses an own design 35 MHz single channel system to replace the original MiniMac!

I also built a lightly modified one (reduced dihedral) with 2 channel propo (rudder and elevator) to teach my son to fly RC. That one must be 20 years old now, and still flying! Its currently powered by a PAW .80, and on its last outing was used to introduce my grandson to the joys of RC flight!

Not bad for a forty+ year old free plan! Boddo should be proud!



Thread: Are all the 2.4GHz the same?
01/06/2008 09:57:00

The point is that ALL systems are at risk of "dropping out" if the volts drop as far as 3.5 volts, and that includes 35 MHz, be it PCM or PPM! The difference is the time it takes the system to recover when (and if!) the volts come back up.

I have to say I believe the problem has been seriously exaggerated! The only people I  have heard of suffering from it are extreme 3D helicopter pilots! A digital servo can draw a few amps under load. A typical 3D helicopter set up will have 5 digital servos plus a gyro. The instantaneous current draw could be as much as 10 amps - maybe more -  all going through a single little plug between the nicad and receiver!!!

 At that kind of current draw, it only takes a resistance of 0.1 ohm to reduce the voltage at the receiver by 1 volt!

Think about an old car starting in winter. Quite often it will refuse to crank or start, even though the battery is known to be good, because of corrosion where the earth lead connects to the chassis making a poor connection. It is exactly the same problem!

So for most fixed wing pilots - and even sport helicopters - it shouldn't be an issue at all.

But if you are into extreme 3D with helis, and insist on running a full house of digital servos, make sure your nicads and wiring harnesses are in tip-top condition - WHATEVER radio you use!



31/05/2008 16:08:00

Most integrated circuites used in consumer goods are only guaranteed down to 3.5 volts. That would include ALL radio gear, be it PCM, PPM or 2.4 GHz. Go below that at your peril. It may well continue to work - many Spektrum receivers do, but it is NOT GUARANTEED to work!

 Nicad manufacturers recommend that cells should not be discharged below 1.1 volts per cell, otherwise permanent damage may be caused.

If your volts are dropping below 4.4 volts, then either your Nicad is inadequate or knackered and needs replacing, or your switch harness is knackered and needs replacing!

If you are suffering brown outs it is because of POOR MAINTENANCE!

Having said all of that, should a brown out occur, the Spektrum receivers were rescanning the whole band to try and re-locate their "parent" transmitter, which could take some time. The quick connect feature makes it check the last channels in use first, where it should find its parent tranny immediately.

Quite what happens to a Futaba, which is hopping all over the place in a pseudo-random sequence, I don't know! But it too will have to relocate its parent transmitter somehow. This is unlikely to be instantaneous!

Brown outs are a symptom of a deeper problem, not the problem itself!



Thread: From the archives
25/05/2008 11:40:00

Gosh! My first ever RC unit was  Terrytone2, which I built from a kit! I couldn't afford a tranny as well, so I used to turn up at the field and look hopeful until someone lent me one, for what was usually a very short attempt at aviation!

 The one I borrowed most was a valve Reptone, but another one I borrowed quite often was a "Windy Kreulen" transmitter one of the club members had built from a magazine article!

Nearly all the kit in those days was built from magazine articles or kits! I became quite adept at making PC boards using a fine brush and Humbrol enamel to mask them off prior to etching! Only the wealthy could afford pre-built equipment, and even then, nothing would come with connectors, and everything had to be wired up by the purchaser! Bear in mind that early "reed" servos would each have seven wires to connect them to the receiver, and a "full-house multi" installation would have 5 servos, and you realise it could take you a week just to wire up the various elements of the airborne radio!

Happy days!



Thread: Aviation Funnies
25/05/2008 11:31:00

An RAF chum of mine tells a tale of flying near Yemen - formerly Aden - after the British had pulled out, and the Russians had moved in!

A Russian transport was departing, and, aware that an RAF plane was in the area, called out:

"Ah, English! You used to control Aden!"

"Er, yes?" replied the RAF pilot.

"And now we have it!", continued the Russian.

"Er, yes?" responded the RAF again.

"And now we would very much like you to HAVE IT BACK!", concluded the Russian! 



Thread: Giant Warbirds
21/05/2008 16:53:00

So who else remembers that wonderful sequence in "Spinal Tap" with the 9 inch high model of Stonehenge......???

Thread: From the archives
21/05/2008 15:13:00


My pleasure!

BTW, apologies for the typos - I'm working from a non standard keyboard today!!!

I started learning about proportional systems by devouring the "digitrio" articles in the American RC Modeller magazine, and the follow up RCM "Classic". But it was your book that pulled it all together for me, and explained many of the "missing links"!

 Sadly, EC and Ofcom regulations have pretty much killed off innovation and experimentation these days. During the late 60's and early 70's new systems appeared (and often dis-appeared!) overnight, but no-one can deny the innovation that was going on. Now we just buy our black boxes off the shelf, and there is another source of enjoyment gone!

Trust me, if you think the buzz from completing your first solo is good, you should experience doing it with equipment you've designed and built yourself from scratch! Nothing matches it!

<nostalgic sigh!>



21/05/2008 10:36:00

Ah! Nostalgia isn't what it used to be! But I do remember the Graupner Consul. One of these was my first consistently reliable rc models, fitted with the Grundig RC gear also featured! I've still got the Grundig radio - needs new batteries, but otherwise it should still be in working order!

 The cost of modelling goods back then would make a modern modeller quake in his boots! My first set of proportional gear was a 2nd hand Bonner Digimite, which I paid £200 for in 1967! Bear in mind that you could drive a brand new mini out of the showroom for just over £600 and this will give you some kind of idea.....!

Good tp hear from Paul Newell! His book on the theory of RC systems was my "bible" when I was learning to put my own systems together! I still have my 1st edition copy, and it still offers some of the best explanations of the why's and wherefores of RC that I have ever encountered!

 More from the archives, please! But is it possible to do it in a manner that we can magnify the images fot more detail?



Thread: Futaba FAAST: important announcement (from Ripmax website)
19/03/2008 15:50:00

As I understand it, all the T7CPs were modified before RipMax released them, so unless you've "grey imported" one, you shouldn't have a problem.

 However, the 6EX sets and TM-7 modules can be zeroed at any time, if mishandled. Just because you've had your set tested doesn't mean you are immune! Like the MOT on a car, all it means is that the set was OK at that moment in time!

 Having said that, the information I have is that a 6EX can ONLY interfere with another 6EX, and a TM-7 module can ONLY interfere with another TM-7. Both sets have to be faulty for interaction to occur. For club users, this just means a simple check for any interaction with other users of similar sets prior to take-off. However, for event organisers, its a nightmare!!!

I hear on the grapevine that Futaba have now issued a permanent fix, and are in the process of distributing it to their dealers. It sounds as if Robbe are recalling, and presumably RipMax will do the same once they have the repair kits. But give them a break! There will be a lot of sets to fix, and they can't do them all at once!

In the meantime, the best advice seems to be check carefully with other users of similar equipment before flying. Event organisers are likely to restrict users of the suspect sets to a "one out at a time" policy.



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