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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: Upgrading Windows7 to Win10 for free
24/01/2020 08:49:24

Exactly! I ditched windoze decades ago, and have never had a problem since!



Thread: New old stock - SC30FS - just purchased.
21/01/2020 16:54:30

Never had a problem running an OS20FS inverted in an Attila. Just be careful not to flood it and cause a hydraulic lock when starting.

I've got an ASP30FS as well (running upright), but it seems a bit gutless. It seems happier on straight fuel, rather than the recommended 5%. On 5% it sometimes sounds like its tightening up in flight, which it doesn't do on straight. Maybe it just needs a lot more running in....



Thread: Theory of the operation of a servo
21/01/2020 16:49:14

True enough, Mike!

The problem is that I'm old enough to remember *real* analogue systems - Space Control, Sampey 404, Orbit (all American), and in the UK, Flight Link and Staveley.

They offered good interference rejection, but were inferior in every other measurable way - though the Staveley was probably the best of the bunch.

These were genuine analogue systems where the servos were controlled by a varying voltage, not by pulse width, and thus really deserved the name "analogue". We mis-use the terms "analogue" and "digital" for our current generation of servos, because in reality, they aren't really either, but have some characteristics common to both.

Sorry, but this terminology is a pet hate of mine! devil



21/01/2020 14:34:42

Nigel: Yes, all quite true!

I really didn't want to get into concepts like velocity feedback and damping because I would imagine many readers eyes would have been glazing over already! wink

Its actually not too difficult to apply a crude form of velocity damping to a conventional "analogue" servo by feeding some of the back emf from the motor (during the "off" period) to the pulse stretchers, and most amplifiers do this. It helps in controlling overshoots on light loads.



21/01/2020 12:53:29

Any properly designed servo amp will apply FULL and CONSTANT voltage across the motor if the error is more than about 10% (typically). This is true of a genuine analogue servo, a PWM "analogue" servo or a "digital" servo.

True analogue servos have not been available since the demise of Flight Link and the Staveley analogue system.

On a true analogue system, when the error is less than 10%, the voltage across the motor is reduced, and becomes proportional to the error. This is why true analogue systems suffered from poor centering that varied with load.

On a PWM "analogue" servo, or indeed a "digital" one, when the error is less than 10% (approx) the motor gets a pulsed drive, still at full voltage, but with a mark/space ratio proportional to the remaining error. This provides full torque for brief periods, improving the centering under varying loads.

The main difference between a PWM "analogue" servo and a "digital" one is the rate at which the motor is "pulsed" at low errors (less than 10% typically). On an "analogue" servo, the rate will be around 16-20mS (50-60Hz). On a "digital" servo it will be higher, maybe as high as 300Hz. However, the "digital" servo will still only receive updates from the transmitter at around 50Hz, unless it is either connected to a high-speed gyro, or the receiver has been programmed to a high frame rate.

In short, the main difference between any of the 3 different types of servo is only noticeable when the error is less than around 10%. If the error is greater than 10%, all will behave the same - all other factors being equal.





Edited By Peter Christy on 21/01/2020 12:55:23

Thread: Synthetic instead of caster oil?
19/01/2020 13:07:22

I see a number of people here differentiating between "old" and "new" engines, when specifying which oil to use. I think we need to be careful here. If by "old" you mean "vintage" (Frog 500s and the like), then there may be a case for some castor - but I'm not convinced.

To give an example, I'm running a pre-Blackhead Webra 61 dating from late 67 / early 68 (can't remember exactly when I bought it, but it was around then!) on Bekra - pure synthetic - with no issues at all. Similarly I'm running an old OS Max 40 from around 1973 on it. No problems at all. And then there's all the Cox .049s.

Basically, my experience is that anything made in the last 55 years is fine on full synthetic! And I wouldn't dream of allowing castor anywhere near them, nowadays!



18/01/2020 11:53:11
Posted by Jon - Laser Engines on 18/01/2020 11:00:06:
I say two oils, but so far the only comparison has been between one oil and one manufacturer. Klotz make a number of different oils and some, like super techniplate, are very much inferior due their castor oil content.

Quite correct, which is why Bekra uses plain Techniplate, which contains no castor.

IIRC, it also contains small amount of other synthetics as well, as each synthetic has a working temperature range. I was told that these small amounts of other synthetics (may well be ML70) provide some protection outside of Klotz's range - for example during a prolonged lean run.

Certainly, my experience had been that with standard size motors (ie: up to .90 size), nothing compares with Bekra. Clearly larger motors may need less oil, and for bigger engines I have no direct experience.



Thread: FrSky Major Update for most TX and RX
18/01/2020 10:22:23

Thanks for the update, Mike!

That's a pain, stopping X series receivers binding in D8 mode! I've got at least one set up like that, so that I can fly it with my single-stick Tx, using a "hack" module. Of course, if FrSky brought out a D16 hack module, it would solve all my problems, but I suspect that if they were going to, we would have seen it by now!

I wonder how long they'll keep producing D-series receivers....



Thread: Theory of the operation of a servo
17/01/2020 16:16:21

P.S. Should have added (for the benefit of OP):

A "digital" servo will work with either a low or high frame rate system. An "analogue" servo will only work on a low (standard) frame rate, and may be damaged if used at a high frame rate.

All 35 MHz systems are standard frame rate, and most 2.4GHz systems put out a standard frame rate unless specifically instructed otherwise. Some gyros output a high frame rate.



17/01/2020 16:07:09

I hate the terms "analogue" and "digital" when referring to our servos, as neither term is strictly accurate.

Early proportional RC systems were truly analogue, and supplied a varying voltage from the receiver to the servo. Those early servos were REAL analogue, and bear no relation to anything currently in use.

Modern systems became known as "digital" because the signal was either off or on (0 or 1), however, the varying pulse width is (sort of) analogue.

The main difference between between a standard ( "analogue" ) servo and a "digital" one is that the "digital" one uses speed controller technology to drive the motor. This makes it relatively independent of the frame rate of the transmitter. The amplifier in a standard servo will only work correctly if the frame rate of the pulses it receives are within a fairly narrow window, in the 50 - 60 Hz region. Both work on a variable pulse width control signal.

The original (truly) analogue RC systems were much less sensitive to interference than the "digital" systems that succeeded them. However, they suffered from fairly slow response times, neutral drift and it was very difficult to make a system with more than four channels.

Even four channels was a challenge, and Kraft spent years trying to produce an analogue system, before giving up and going "digital".

"Digital" systems weren't so good on interference rejection, but offered better response times, better centering, little or no drift, and many channels. They were also cheaper to produce, as all the circuits for the different channels was the same. You only had to design one channel and then you could "daisy chain" the rest.

So PLEASE can we be careful when referring to analogue and digital servos, as neither term is really correct!

[Rant mode /off] devil




Edited By Peter Christy on 17/01/2020 16:08:21

Thread: FrSky Major Update for most TX and RX
17/01/2020 15:43:12

I, too, still have my original DSX-9 and its still giving sterling service. However, it doesn't have telemetry - which may or may not be a good thing - and it isn't upgradeable. Neither are the receivers.

At least the FrSky is upgradeable, and relatively easily at that. And whilst they may not be the most communicative, they do seem to react quickly to any problems that occur.

From reading a translation of the German website, it appears that most of the issues have occurred in Germany, Austria and Switzerland, countries that share a lot of common borders and geography. They are also - I suspect - countries that are more eco-friendly than many others, with a larger percentage of electric flyers. This probably means that many clubs operate closer to civilisation and potential sources of interference than is common in the UK. Lets face it, most of us fly way out in the sticks!

For that reason, I suspect that the issue is not as pressing here as it may be in other countries.

Having said that, I probably will upgrade, but not immediately. I learned long ago, never to use "Vers-1.0" of any software. Always wait for at least the first bugfix! wink

One or two of my models have rather inaccessible receivers (the downside of scale foamies!), which is an active discouragement! Also, a lot of my models are still on D8, and I want to be sure that this upgrade won't remove that protocol from my transmitters before upgrading!



Thread: Trendsetters and Iconic Models over the Years?
17/01/2020 15:26:29

Well, the "Taurus" dominated fixed wing-aerobatics for many years, and clearly influenced many other designers. On that basis, I would think it deserves to be regarded as a trendsetter, iconic AND common - at least in 60s aerobatic circles!



Thread: Synthetic instead of caster oil?
16/01/2020 08:31:43

I run all my engines - from Cox .049s to 4-strokes - on Model Technics Bekra fuel. The main oil constituent is Klotz, no castor whatsoever, and no problems.

Although sold as a helicopter fuel, it works fine in all my engines, ancient and modern! Helicopters generally run hotter than fixed wing, so if the fuel will work in a heli, it will have no problems in a fixed wing!



Thread: No Auto Rotation
13/01/2020 09:39:12

Even if the pitch is set negative with respect to the hub, it will still be positive with respect to the *airflow*, which is the important bit!

Remember, the disk is tilted back so that the air flows up through it.

My experience with autogyros is limited, but I have a lot of helicopter time! More negative pitch will accelerate the blades to speed quicker, but the rotational speed will be slower. As you increase the pitch, the blades will spin faster, but take longer to get there - bit like using a higher or lower gear on a car. Eventually, if you increase the pitch too much, the blades will slow down - like over-gearing a car.

At our sizes, autorotational forces are small, and need all the encouragement they can get! Airfoil section is fairly important, and a flat plate is unlikely to work well!




Edited By Peter Christy on 13/01/2020 09:39:38

Thread: Upgrading Windows7 to Win10 for free
13/01/2020 09:30:48

I ditched Windows years ago in favour of Linux - readily and legally available for free! Never looked back or regretted it!

If you are a technophobe try this: **LINK**

If you are familiar with computers, I recommend Slackware - but get the -current (development) version, which although marked as a development version is far more stable than windoze!



Thread: Dog harassment while flying!
11/01/2020 10:03:35

This happened in the mid to late 70's: I was teaching myself to fly helicopters (very few others could fly them back then!) and as I worked on shift, I often had days off during the week. There were some large, local playing fields where a heli club used to meet at week-ends. These were usually deserted on weekdays, so I would find myself a quiet spot, and start practising.

I'd got to the stage where I could hover okay-ish, and just about stagger around a circuit, so I was practising "circuits and bumps".

Fuel was starting to get a bit low, so I decided to land, shut-down and re-fuel. As I was approaching and coming back to the hover, a dog appeared out of nowhere, and started jumping up, trying to grab my heli!

I opened up the throttle and flew round another circuit, hoping the dog would lose interest, but no, as I set up for landing, there was this dog again, still trying to grab the heli!

By this time fuel is getting worryingly low (fixed pitch heli, so no chance of autorotation - even I had been capable of it!). I decided to fly off slowly up wind, hoping the dog would follow, make quick turn, and land before the dog could get back!

This worked, and finally I got the heli down and shut off the motor. However, this heli had a very free transmission, and the blades would keep whirling for some time. By this time the dog was running back towards the heli, so I ran to put myself between dog and heli to prevent a gruesome accident!

As I stood there trying to stop the dog getting at the heli, I was struck from behind by an umbrella, and heard an angry female voice shouting "Get that thing away from my dog!", and how she was going to call the police, etc!

I replied to the little, old lady that she was welcome to call the police, as there was nothing illegal in what I was doing. However, I pointed out that there WAS a bye-law that said that all dogs had to be kept on a lead in the playing fields, and that if she didn't keep her animal under control, I was going to call them myself!

She stormed off in a huff, muttering that it shouldn't be allowed.

I never saw her again, even though I regularly went up to those playing fields to practice.




Edited By Peter Christy on 11/01/2020 10:04:38

Thread: Selling vintage kits question
10/01/2020 16:09:36

Good advice from Don, there!

Like anything second-hand - even if never opened - its basically worth what someone is prepared to pay for it. Some items can go for more than expected, some for less.

Kits can be difficult. Unless stored in ideal conditions they can (and do!) deteriorate. However, some are classics and a competent builder should be able to sort them out.

As has been said, without knowing what you've got, its difficult to advise, and I would be wary about giving out too much information too early!

Don's advice about contacting a local club is particularly sound. If you don't know where your local club is, the BMFA should be able to help.



Thread: Tufcote / Furniglass
03/01/2020 12:41:03

Has anyone tried this: **LINK** ?

It appears to be a polyurethane varnish. The reviews claim a smooth finish and doesn't yellow.

Back in the day, we used to use Kingston Diamond Polyurethane paint, which seemed to be proof against virtually everything. Sadly, it seems to be no longer available, but maybe this is as tough?



Thread: Taurus retro aerobatic build
28/12/2019 18:25:03

Very nice job, and what an understanding missus! laugh

I remember when I did mine - foam cores, but still the same bending issue for the LE - it was quite a struggle! I did manage it, once an "old hand" had taught me the water trick, but I didn't have the benefit of the steam cleaner - or an understanding assistant! I wonder how Ed Kazmirski did it with the original? Sadly, he passed away only a few years ago, so we're no longer able to ask him....

They do fly really well though, so well worth the effort! Should be more than "adequately" powered by a modern 55!!!



Thread: Probable scam?
21/12/2019 12:26:02

As a follow up to my original post:

Yesterday I happened to be in town close to the Currys branch where I purchased the TV. My phone call to customer services had indicated that "Black Friday" refunds could only be made at the store from which the goods were purchased. However, the assistant in the store - who tried to be helpful, but clearly had not been trained for this - said that claims had to be made online, and that looking at the email on my phone, it appeared genuine!

Left hand - meet Right hand!

I have decided that for £20 its not worth the risk!

I normally avoid Currys and PC World like the plague, because the staff seem more interested in selling unnecessary warranties and usually have little knowledge of what they are selling. However, my preferred supplier (Richer Sounds) was out of stock at both local branches, so I had little choice.

In her defence, I have to say that the young lady assistant did try to be helpful in this case, but was clearly unprepared for the question put to her.

I'm still not convinced that the email was genuine - and even Curry's own front line staff can't tell either!

Be careful out there!



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