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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: Future balsa supplies in UK
22/09/2020 16:14:10

Thanks for that, Robin! Yes, you could be right! It was a long time ago!

But as I say, not the first time this has happened, and I doubt it will be the last. I do recall being horrified by the quality of the very expensive balsa being sold after the last round of shortages...!



22/09/2020 07:56:27

This isn't the first time this has happened! Those of us of "a certain age" will probably remember the last balsa shortage - back in the 70s IIRC!

Back then, it was blamed on a new generation of massive oil tankers which required balsa for "insulation" of the tanks. I've no idea if that was fact or fiction!

I do know that it was followed by a sharp rise in the cost (and drop in the quality!) of balsa!

In the last seven years (since I retired!) I've built a few models from plans, mostly 5-footers and designs from the 60s. I was staggered by the cost of the wood alone! Were it not for the satisfaction factor of flying something I've built myself, I would stick to ARTFs, which are much cheaper than building your own!

If only most of them weren't so fragile and UGLY....!!!



Thread: How do you clean your glow engined models after flying?
18/09/2020 09:47:58

Muc-off - followed by mechanics paper towels.

Muc-off is also good for cleaning trannies without affecting the plastic!



Thread: To stabilise or not to stabilise - the gyro question
12/09/2020 09:01:59
Posted by TonyS on 12/09/2020 08:18:42:
Isnt that a bit like a Ford Pop driver poo-pooing a paddle shift gearbox and saying that anything other than double de-clutching isn’t really proper driving but is cheating?

Well, a paddle shift gearbox may well be perfect in a Formula One car (less than one turn on the steering, lock to lock), but is absolutely abysmal on a road car. Its simply a gadget for wannabe racing drivers.

I was racing with sequential gearboxes decades ago, and if anyone had suggested a shift mechanism like paddle shifts, he would have been laughed off the track!

We used something akin to a column-shift, moving it one way to change up and the other to change down. It was always at your finger-tips, regardless of the position of the steering wheel. Paddle shifts are just ergonomic insanity in a road car.

The occasions when I've had to drive a car with them, I've just left it in full "auto" mode. Absolute nightmare devices!

And don't get me started on electric handbrakes!

Bah! Humbug!



Thread: Researching the ancient Ripmax Futaba M6
09/09/2020 12:06:20

The digital vs analogue argument is not completely clear cut. Many early proportional sets were genuinely analogue, and operated in a variety of ways. One common method was to transmit two audio tones alternately. The frequencies of the audio tones provided two channels, the mark/space ratio between them a third channel, and the rate at which they alternated a fourth.

Other systems used a sequence of four different audio "tones".

At the receiver, the signals were decoded into a varying voltage that was fed to the servos as a control signal, eg: 1V = left, 3V = right.

Analogue systems provided very good interference protection, but suffered terribly from drift, poor resolution and slow response. It was also difficult to re-use circuitry for different channels, and almost impossible to implement more than four proportional channels.

The first digital system (designed by Don Mathes and Doug Spreng) was an attempt to overcome these issues. It was digital in the sense that the signal was either "on" or "off", but sort of analogue in the sense that it was a pulse width that represented the control signal. However, even in the servo, there were no varying voltages, the drive to the motor being either "on" or "off" (0 or 1, so in a sense "digital".

Some early digital systems did convert the "digital" signal to a true analogue one, as at the time, the digital servo amp devised by Doug Spreng was a spin-off from military technology, and some manufacturers were worried about being prosecuted by the government! This didn't last long, though, and after short time everyone adopted the Spreng design. It was so successful that it is still in use today!

The original Mathes/Spreng Digicon did transmit the full control pulse of 1-2 mS per channel. However, back in the days of AM rather than FM, this caused problems in the design of the Automatic Gain Control - AGC being an essential part of an AM receiver. It was Frank Hoover of F&M (a major American manufacturer at the time) who is credited with suggesting that rather than transmit the whole pulse, it would be better to transmit a short "marker" pulse to indicate the beginning and end of the actual control pulse.

With the introduction of digital integrated circuits a few years later, this had the added benefit of making a "digital" decoder extremely simple in the receiver.

So you see, the digital vs analogue argument is not clear cut! Early "digital" systems were neither truly analogue nor truly digital. However, the fact that we still use the same system to this day to drive our servos, added to the fact that the control signal is either "on" or "off" (0 or 1) leads me to believe that it is more digital than analogue!




Thread: To stabilise or not to stabilise - the gyro question
09/09/2020 11:34:46

I learned to fly helicopters before gyros were invented. Never really gave me any problems. I've never really understood why they would be needed on a fixed wing model, other than in exceptional circumstances!

To me, the enjoyment comes from the challenge of flying smoothly and realistically - whatever the conditions. However, I am getting older, and my eyesight and reactions are not what they once were, so I now - reluctantly - fit tail rotor gyros on my helis.

And yes, I have two flybar-less models that I fly quite happily without any electronic stabilisation of the main rotors!

None of my fixed wing models have gyros, save one. That is a tiny UMX Pitts Special. I am told (by someone who managed to figure out how to disable the gyros!) that it is unflyable without them. With them it flies very well, to the point of being BORING!

To me, gyros are a training aid - a bit like the stabiliser wheels on kiddies bikes - and something that should be dispensed with at the earliest opportunity!

For heaven's sake, learn to fly the aircraft - not a computer flying it for you!




Thread: Farm vehicle interference on 2.4?
07/09/2020 22:20:12

I refer you to what I said earlier: This smacks of radar or microwave link interference. Such interference is not on 2.4 GHz, and won't show up on a 2.4 GHz scanner. It works by directly interfering with the processor in the receiver, which also prevents the failsafe from operating.

I would suggest contacting Ofcom, copying in the BMFA. If I am right (and I think I am) finding the source of the interference will not be achieved with the kind of equipment most people can afford!



Thread: Wanted: Super Tigre GS 40/45 exhaust manifold, gasket, bolts
07/09/2020 08:53:51
Posted by Jonathan M on 07/09/2020 08:17:59:
Posted by Peter Christy on 06/09/2020 23:26:05:

Forget gaskets! Use 5 minute epoxy! Never leaks, never comes loose, but can be removed easily when required.

How about silicone sealant?


It sets soft, so doesn't help with vibration loosening the silencer. 5-minute epoxy sets hard, provides a good seal and prevents any loosening because the silencer is bonded firmly to the engine block.

Yet, the 5-minute epoxy seal can be broken by using a sharp tap from something like the handle of a large screwdriver, making removal of the silencer quite easy.

Use 5-minute epoxy and you will never have a silencer come loose or leak again!



06/09/2020 23:26:05

When I broke mine a while ago, I replaced it with a BCM Sport universal silencer from Just Engines: **LINK**

Not cheap, but quiet and well made! (They also do a larger 60-90 size one)

Forget gaskets! Use 5 minute epoxy! Never leaks, never comes loose, but can be removed easily when required.

The BCM works a treat on my ST 45 in a SpaceWalker.



Thread: Kraft Series 70 Radio Equipment
06/09/2020 15:36:36

Tosh: I'm sure there are plenty of people over on mode-zero that would love to give your Kraft a new lease of life!





05/09/2020 15:25:12

Phil: The NE 543 was 3 wire IIRC. I think it was the introduction of IC amps that allowed the use of 3 wire setups. All the 4-wire servos I've seen had discrete amps, all the 3 wires were ic.

Another complication may be the decoder used in the Kraft (never owned one, so I don't know!). A lot of sets from that era uses SCS devices for the decoder, and these didn't like driving servos with low input impedances. SCS decoders were pioneered in the RCM "Classic" system, and for a short period became very popular as they were cheap and easy to implement. Unfortunately, SCS devices were very temperature sensitive, as I found out one day flying in sub-zero conditions!

After that disaster, I went a bought a bag load of them from a local supplier, and spent a few evenings going through my two Sprengbrook receivers with a can of freezer spray, and replacing SCSs until I had both working well below zero!

SCS shift registers were rapidly replaced once integrated circuit shift registers became available!

No idea if Kraft used these or not, but IC servo amps generally have a high enough impedance not to load SCS decoders.

Some systems also used negative going pulses instead of the usual positive. I think Kraft were always positive, but EK Logictrol and OS were negative going. Long time ago, now....! wink



05/09/2020 09:13:35

No! The way the servo operates requires the use of a centre tap. Without it, the servo won't work at all!

Whilst it may be possible to modify the servos to work on a 3-wire system, the cost / effort involved simply isn't worth it. Changing the amplifier isn't too difficult (if you can source them these days!), but you would also need to change the motor as well. Finding one that would fit your casings, and accept the matching pinion gear would almost certainly be problematic.

In any case, modern servos of much better performance are readily and cheaply available.



Thread: Farm vehicle interference on 2.4?
04/09/2020 12:40:49
Posted by martin collins 1 on 04/09/2020 11:35:29:

...most problems have been reported at this end.

Sounds to me more like a microwave link or radar, and inadvertently flying through the beam. It might not be active all the time.

Remember that 2.4 GHz is an unlicensed band, which means we have no protection against other users - as long as they are operating legally! Proving they are not operating legally could be tricky. In any event, pure RF interference on 2.4 GHz should still allow the failsafe to operate normally.

The incidents you describe seem to indicate that the failsafe did not operate. That indicates either 1) power loss to the radio or 2) something breaking directly into the processor.

1) could explain a single incident, but not multiple ones, which leaves 2). That is likely to be either a radar signal, or other high powered microwave transmission.




Edited By Peter Christy on 04/09/2020 12:41:17

Thread: Kraft Series 70 Radio Equipment
04/09/2020 12:29:30

P.S. Should have added: A number of people have had great success converting these radios to 2.4 GHz!

Checkout some of the conversions here: **LINK**




04/09/2020 12:18:45

The centre-tap on the pack provides two lots of 2.4 volts, and was connected to one end of the servo motor. The other end of the motor was connected via switching transistors to either the positive end of the battery or the negative end, allowing the motor to be driven in each direction as required.

Later servo amps did away with this and used a "bridge" configuration to switch the motor direction.

3-wire servos use a different motor to 4-wire servos as the driving voltage is significantly different. You can't just put a 3-wire amp in a servo designed for 4-wire unless you change the motor as well.

Strangely, initially 3-wire servos seemed to suffer more "connector" failures than 4-wires, despite the extra simplicity of 3 wires! This was largely cause by the habit we have of pulling the connectors out by the leads, rather than the actual plug. 4-wires spread the load more!

The introduction of crimped connectors to replace soldered ones restored earlier levels of reliability...



Thread: Farm vehicle interference on 2.4?
04/09/2020 09:43:24

All equipment operating on 2.4GHz is subject to the same rules and regulations as we are. Compliant signals should not cause any interference.

Having said that, if someone is using illegally high powers, or something like the old analogue video systems at high power, then it could - in theory - block "our" signals.

However, even in these circumstances, the "fail-safe" should still work.

A more likely scenario is that a new microwave link has been set up in your area. These are very narrow beams providing point-to-point communications for various telecoms applications. Inside the beam, the signal level can be very high indeed, quite possibly enough to disrupt the micro-processors in the receivers, and thus prevent the failsafe from operating.

This has been known about since the days of 35 MHz! The solution then was to wrap the receivers in silver foil, which proved remarkable effective!

Note that I said wrap the receiver in foil, NOT the aerial! Not so easy on 2.4 GHz.

Did all these failures occur in the same patch of sky? If so, you've probably strayed into a microwave beam!

It could also be the someone operating a new high power radar system. This would have a wider spread. Any airports nearby? There have also been reports of the government testing out "anti-drone" measures, though these are often announced before hand - though not necessarily in places where we would see them! SteveJ of this parish seems to have some insight into these tests, so maybe he will be along shortly to comment.

In short, it is unlikely to be a problem caused by any legitimate users of the band, but more likely a high intensity (and out of band) signal that your club members had the misfortune to stray into.

All model control equipment is built "down to a price", and is unlikely to be able to deal with a highly disruptive out-of-band signal, should you be unfortunate enough to encounter one. If you want equipment hardened against such (rare!) interference, be prepared to pay a LOT more money for it!



Thread: ESC cutting out on one type of battery?
28/08/2020 13:43:36

Matty: My point is that if you carry out the test as I describe, it will quickly determine whether the problem is in the connector or in the pack itself.

If it is in the connector, it should be a quick and easy job to fix. If it is in the pack, it doesn't matter if its IR or a poor connection between cells, it needs returning.

Without checking both the voltage at the ESC simultaneously with the cell readings at the balancer while under load, it is impossible to guess where the fault lies.



Thread: Learning to fly on a large trainer
28/08/2020 11:09:48

BenB: I agree! The full size Tiger Moth was considered an excellent trainer because whilst it was easy to fly, it was difficult to fly well!

A trainer can be too stable!

To my mind, the best trainers of the "Golden Age" were the Veron Robot and the Frog Jackdaw. The Robot was fairly compact, and stable, but not too stable! Similarly, the Jackdaw - similar in size and appearance to a Super 60, but a lot less "floaty" and again, not too stable. Both these models were pretty robust when covered with nylon, and would take a lot of abuse.

Plans for the Jackdaw are available on Outerzone. Although designed as a single channel contest machine, the plans also show optional elevators and ailerons.

In my humble opinion, it was (and still is!) a much better flying machine than the Super 60!




28/08/2020 08:28:12

Lots of very valid points above, to which I would add:

If you learn on a big, stable machine, you will find the transition to smaller (sometimes twitchier, but not always!) models difficult. If you start with a small model, you'll find big ones much easier to fly!



Thread: ESC cutting out on one type of battery?
28/08/2020 08:20:50

I've got 4 Overlander 2900 3S packs. They are used in pairs to provide 6S for my "Lama" helicopter. Not had any issues with them in nearly two years of operation:

I'm using XT60 connectors.

I still think the most likely explanation is a poor connection somewhere at the battery end - maybe the connector itself, or possibly internally in the pack.

The ONLY way to settle this once and for all is to measure the voltage arriving at the ESC UNDER LOAD. Simultaneously checking the voltage on the balance lead would give an indication as to whether it is the connector or the pack itself at fault.

Until this check is carried out, discussion is just speculation.



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