Sounds like the title of a detective story, as a matter of fact, this story is a search for something missing. Before jumping to conclusions, we have to be clear about the word missing. There is a possibility of something being really absent, but it might be equally true that we simply percieve something to be absent, when in fact it is not. It all depends on the method of observing. And that brings us straight to the core of the problem.

If we decide we want to know the value of something, we usually have a gadget to measure that something. (Bless the 21st century)

To be more precise, when one wants to measure voltages, one uses a gadget called a Voltmeter.

When measuring Amperes (Amps in newspeak) one uses an Ampere meter.  And to join this duo, we might as well introduce the 3rd illustrious cousin: the Ohm.

And since they all depend on each other, and are often used together, some smart kid decided long ago, that it would be a neat idea to stick gadgets to measure those three friends in a single box. (I’m simplifying, hope you will understand that!)

Fast froward to the digital age, and we figured out a way to get rid of that Meter-thingy ( The nice big box with the moving needle) and replace it with something ‘digital’, a chip. And so the DVM was born. (Digital Volt Meter) .

But first, lets talk about the Volts and Amps and Ohms a bit.

It all started because some bloke in ancient Mesopotanie decided to put some bits of metal in a jar (http://en.wikipedia.org/wiki/Baghdad_Battery) and call that a battery. We still are not 100% sure wheather they actually used these batteries to fly their model airplanes, but judging by the hieroglyphics discoverd, one would not be too surprised if they if fact did. But that’s another story.

 So the fellow (lets call him Ahmed, because he likely had a name, and it could well have been Ahmed), Ahmed then, was wondering how strong the juice was that his batteries produced. The tongue test was ok, but when you put 20 jars in series, this test resulted in some strange effects: his wife was unable to talk for days or weeks, depending on the amount of jars used for the test. (Yes, dear reader, of course Ahmed asked his wife to be the tester, since she had a far better ‘feel’ for these things.) Needless to say, eventually the misses decided she had enough of Ahmed’s bat-ter-eeeeh tests, and left him for a rich merchant. Ahmed being the inventive soul, decided that something more reliable was needed to measure the properties of the the jar-juice.

He had by now worked out that there were actually 2 main properties involved with his juice-jars. The one that determined how long the missus would be quiet, he called Voltage (this word has of course been translated from ancient Mesopotania-speak for the benefit of you, dear reader), and the one that decided how many of her sisters would be knocked out at the same time he called Amperes. History has not quite revealed what Ahmed discovered, but we can be sure of the results!

Skip forward a few centuries…

Since we live in a different country, and don’t have too many volunteering wifes/girlfriends available for our tests, we have to invent a different way of testing and explaining the Volts and Amps.

Imagine my surpise, when I discovered that we have such examples right here, in the Mourne Mountains. As I was travelling through said mountains the other day, I was observing the melting snow (in April!) and the little waterfalls that the melting snow created.

Eureka, the perfect example!  The amount of water flowing down is equivalent to the Amps, and the speed of the flow is determined by the height difference between the location of the melting snow and the final destination. So if you have loads of water (Amps), and a very small height difference (Volts) you can see there will be a relatively low current. (No need to translate that). Then take the same amount of snow, and put it on top of the hill and the water rushes down, because the Voltage is now much higher. On the way down the water encounters Resistance (Ohms) in various forms. See, it’s all easy!

The moral of this story is that there is a relation between Volts and Amperes and Ohms.

Ohms = Volts divided by Amps.

Amps times Ohms = Volts and

Volts divided by Ohms = Amps.

If you think about it for a bit, it will make sense! Just replace the Amps with amount of water, the Volts is the height the water is falling, and the Ohms the obstacles the water encounters on it’s way. You will never be confused about the Volts and Amps again!

However, we are still none the wiser about How Much any of these things is. Big, bigger, loads, tiny bit??

Luckily, beeing a pint loving nation, we soon have that sussed. We all are aware of the extreme importance of getting a pint that is the same, no matter which pub serves you this heavenly brew. To make sure we all had the same pint we invented the pint glass. (No use having the pint without the glass,  right?) So now we had a pint glass and went about making sure the landlords served the right amount of fluid to each of us punters. Great. We are happy. One universal pint, no quibbles. Until…

The owner of the glassworks decided that it would be cheaper to have someone else make the pint-glasses. He simply asked them ‘send me a load of pint-glasses’. And you will already have figured out, that things from far-away-places are usually different from what you make yourself. Some time after the new pint-glasses were sent to the happy customers, trouble started. Landlords were accused of ‘you served me short’. The opposite cry was probably never uttered. But honesty requires we mention te possibility that someone cried ‘you served me long’. (Of course this language was never actually used, however since this is a nice story, I can not quote the actual words used).

This was a nuisance of major proportions. But the clever blokes we are, we soon got around that one by inventing the %, which simply is a shorthand way of saying: my pint is the same as yours. (The two little circles are symbolic pints, I don’t need to explain.)

That was all great, but what if my pint was smaller then his? mmmm…. Some pints later, after mulling over this problem, (in fact, rumour has it, that it was 100 pints later) it was decided that it would be a good idea to say that if two pints contained exactly the same amount of beer, (lets skip the method of measuring ‘exactly’, since that involves even more beer) we would say they were 100% the same!

Hah! now we’re drinking. And a whole new mathemathics was born, jobs were created, life was good. And kids soon figured out it was a lot easier to ask their parents for a 50% pint. All they had to do was ask twice, to get the same amount..

Due to the enormous amount of pint-glasses around, it soon became a bit impractical to test each pint-glass. And truth be told, most customers could not really tell the difference between a 95% pint and a 105% pint, als long as the lights were low and the craic was great. For the landlords it did not really matter, because on average the pint was a pint, and each cask more or less contained the same amount of pints, and because of spillage they could never be sure how many pints were in the cask to begin with, and they did not really care anyway. After a while they did not really want to pay for expensive 100% pint glasses, when cheapy 95-105% glasses would be acceptable to the punters. (And the reader will observe, that it soon became custom to shorten the 95-105% notation to 5% in order to save ink.) Next time you have a drink, you can ponder about that question, is this pint a pint?

Can we pleeease go back to Volts and Amps, I hear you cry…  Ok, I’m just having a great time, and since the interweb is down anyway, I might as well write a good story..

Lets recap: You just learned about the Volts and Amps and about tolerances right? Yes you do, say yes please. I don’t want to repeat all this!

A Volt is only a Volt if we can measure it with something accurate. A Volt measured with a 10% meter is not the same as a Volt measured with a 0.1% meter. That’s actually not true, the Volt is the same, what you think it is (measure), is something different.

And so we enter into the murky world of: Is What I See Really What It Is?

Or more precise: what I measure is only as accurate as the tolerance of my measuring instrument. And to shatter a digital myth here and now: Just because it’s digital does NOT mean it’s accurate! True, compared to pint-glasses, our measuring devices are unbelievable accurate. But, not as accurate as we like to believe!

Typical DVM’s have an accuray of 1% (DIY-Maplin range). Many, gadgets we use have an accuray of 3%. That bad huh.. Yup. Because standard components used in electronics have a 5% tolerance in their values. And that’s because we are so good! 10% is what you buy in the shop, but within a batch of components, the spread is probably 5 % or better.

I got 10 pcs 1% resistors the other day, their values as measured by my 1% DVM were:

99.7 99.9 100.2 100.3 100.4 100.4 Ohm. (the others were worse)

All within specs. But are they any good for what I need? (What do I need them for anyway?)

Lets build ourself a Circuit. (This involves soldering wires together, and in general having fun explaining to the hotel manager that you are only trying to test a theory. All I can say is that hotel managers in N-I do not seem to understand, and as a result I was banned from accessing the interweb.)

My circuit was nothing more then 6 resistors glued end to end. Or to put it more precisely, wired in series.

Now if I were to connect the ends of this string to a Voltage producing Gadget (A bunch of Ahmed’s bat-ter-eeeeh’s or if available, a 5 cell Lipo) a certain current will flow through these resistors. The higher the value of the resistors, the lower the current and vice versa.

Since I had the equivalent of 20.6 Volts handy and the bloke at Maplins only had 10 pcs of 100 Ohm resistors, we can calculate some important things.

6 resistors of 1% 100 Ohm, wired in series creates the same value as 1 resistor of 600 Ohm. I can calculate the current running through this string by dividing the Voltage by the resistance (Ohms). 20.6 (Volts) devided by 600 (Ohms) = 0.0342 (A). So the total current through the string of resistors is 0.034 Amps. (A common way of writing this would be 34 milliAmps. )

Ah, but this is only true is the total of all resistors was indeed 600 Ohm. Yup, and it was not! Remember, the total added up to 601.1 Ohm. You are so 100% absolutely right, but let’s keep the maths simple, just pretend for a minute it was 600, ok?)

We do remember that Voltage is Current times Resistance. V=A*Ohm. (Most tesxtbooks will show this as U=I*R, since that is the official way of expressing a Voltage, current and resistance)

We know that the current throught the string was exactly 34.2 mA. not 34.01, or 33.99, but 34.2, because our 1% accurate meter says so.

O dear, the meters accuray is 1% so it could very well be 34.543 or 33.858 and still be ‘accurate’. (And my meters scale was 0 to 20 Volts, it would be 1% of the full range. Usually the scale is not 100% linear either)

But let’s not worry for the moment. I have the only 100% accurate DVM in the universe. Honestly. And we are not really interested in absolute values, we want to know the relation of the values to each other!

So, lets say, I have exactly 34.2 mA through my resistors.

And I have exactly (as measured with my 100% accurate DVM) 20.6 Volts connected to the end of the string of resistors.

Lets do something funny. Let’s measure the voltage accross each resistor. Each resistor has a slightly different value ( my meter tells me so) Lo and behold, I measure approx 3.4 volts accross each resistor.

Wow!! so which on is accurate? The second one? Because we thinks it is 100 Ohm?

Remember, this was a test circuit with resistors that have a value that is within -0.2/+0.4% of 100. (or so we think)

And the casual observer will cry: But you started out with 20.6 Volts!! True, my meter says so, but to measure something in the lower voltage range I switch to a different range on the meter, and now I have no idea what I measure Yes, my Friends, that’s Life in Electronics. It all works on grey smoke, and no one has a clue how it manages to work at all! And I am not joking. Electronics is all about trying to make the tolerances of parts work in your favor and at best stop them behaving badly.

Using an 18 Volt supply (giving me a 30 mAmp current) to make the maths easier I can see that:

Above is what you measure if you use standard 5% resistors. Shocking, right? Yes, indeed.

Below are the values you can expect using standard unselected 1% resistors.

It gets worse. In the above example I use a 100% accurate Voltmeter.

What happens if I use a meter that has an 1% accuray (as in: value could be +/-1%)

So, worst case: my 3.000 volts could actually be somewhere between 2.95V and 3.07V and still be within 1% specs.

3% components give me anywhere between 2.83 and 3.19Volts. And so far I have only used a single voltmeter.

If you use a circuit that has to scale voltages to be able to be measured,.it really gets exciting.

Scaling is often/always needed, because most voltmeters only have a certain range they can measure. In our world of digital wizardry, a common range would be 0-5 Volts. To measure higher voltages, one would introduce a voltage devider, (as the names suggests, it divides one higher voltage to a lower one, that fits into the range of our measuring device. ) Of course all these components have a tolerance)

I’m sure by now you see that we actually have no hope at all of measuring anything at all with any amount of accuray.

But to return to the beginning of the story, the Missing Volts.

This whole ramble was caused by one of our esteemed clubmembers mentioning the fact that one cell in his LIPO’s always indicates a higher value on his measuring thingy.

Since it happens on all packs, my suspicion is the measuring gadget. And without feeding it with some accurate voltages to test it, we do not know what it measures!

To be continued, errors fixed, and story completed with more results!

Kees

Below is a speed estimate taken from a recording of Brian McCartan’s Dara 20 at the field, as you can see, the figure comes out at 240km/h or in old money a hair under 150mph!!

What have you got??

Measuring the Doppler effect (change in sound frequency) during a low pass to give a speed reading

Brian’s Dara 20, not a lot to keep an eye on at 150mph!

With the weather improved from what it’s been for about 18 months, Climb & Glide was fine if you stayed out of the low cloud patches (Me!) and your engine quit when asked (Sean!),  but with the field still wet, touch & go’s were out, as was the Tripple Thrash. So some alternatives were sought and the old favourite of one minute of loops was settled on and for a change one of the mystery rounds used at the Nats, Roops.

What are Roops I hear you cry!

Roops consist of a one minute flight including a countdown for the pilot in which to complete as many sequences of one roll followed by one loop as possible, with the plane to touch down before the minute is up. For every second over one minute, the pilot looses two points. In my case, I performed 11 sequences but went three seconds over so lost six points, in Paul’s case a score of nine with a penalty of -22 would have resulted in a score of -13, but we were generous and gave him zero!

The comp finished as usual with the Limbo, with some good scores, some not so good scores and one buckled undercarriage (ask me how I know!)

Final positions were

1st Mathew   3713

2nd Alistair  2937

3rd Brian       2912

4th Sean         2414

5th Iain          2178

6th Paul         1440

Soaring

After lunch, with conditions favourable, and the experience gained from last years highly unpredictable weather, it was decided to run the e-soaring competition scheduled for the following weekend. Fair notice had been given to be prepared for this, so  suitable models were on hand. Unfortunately I had to leave early so I can’t provide a very detailed report, only the results. Two rounds were flown, with a 20 second climb followed by a glide, with bonus for spot landing, which nobody got!

1st Matthew  2000

2nd Brian       1559

3rd Paul          1207

4th Alistair     1207

Happy Landings,

Iain

I  want  rid  of  the  lot  ASAP !

No  Time  Wasters  or  Haggling !

If  you  buy  and  don’t  like  it – bring  back  in  SAME  condition  for  FULL REFUND .

Peter  R  Anderson

Ph:02897565521  .

e-mail : pranderson9@hotmail.com

With the kind help of Horizon Hobby UK you will have the only chance in the UK to come, fly & explore the latest products from Eflite, Parkzone, Blade & Spektrum. We will have demo’s throughout the day and plenty of products for you to have a go.

There will be a large raffle of Horizon Products to raise money for Cancer Research UK, a very worthwhile cause. I’ve set a fundraising page up on their website which i’ll update shortly, http://www.justgiving.com/ComeandFly

The details are;

Date : Saturday 17th November 2012
Time : 1pm – 6pm
Venue : Queens University PEC Sports Hall. (BT9 5EX, Stranmillis Embankment, Belfast)
Cost : £2 per head
(This includes entry into a separate raffle to win a Horizon Hobby Product)

You will need valid BMFA insurance to fly, this will be checked on the door.

I think that’s all for now, more details will follow closer to the time. If you have any questions just drop me an email.

Please pass this info onto anyone who may be interested, everyone is welcome.

Thanks,

Matthew

Pilots & Spectators at the 2012 area Funfly

I’m glad to say that the Area Funfly postponed earlier in the “Summer” ran on the 22nd of September and was once again organised by the Banbridge club and this year was hosted at the Craigavon clubs very well maintained Cranny road site, which provided an excellent venue. Also excellent was the weather, which i’m glad to say behaved itself all day.

Pilot numbers were well up on the last couple of years, with eight pilots in class 1 and three in class 2, and also in a change to recent years there were not only several clubs involved, but several countries!, so the first ever international funfly took place. I’m glad to say that by very fortunate co-incidence Simon McNeill was home from Scotland for the weekend & so Dennis’ Limbo dancer found itself with higher rate than normal, while our good friend Kees Blokland was also back on the auld sod for a short break. To help Kees out Sean stepped up & volunteered his recently completed Limbo Dancer for Kees to take part, and take part he did, in two rounds, until the electric wires at the edge of the field jumped up & bit him! shearing the wing very neatly in two.

A slightly embarassed Kees with “modified” limbo wing, a very forgiving Sean & Dennis glad to have finised in one piece!

Sean completed the comp with Matthews spare plane, while Kees declined the offer for some unknown reason!

The remainder of the competition provided the usual thrills and spills of cut limbo strings & caught wing tips, it was great to hear the spectators shouting every time a plane managed a pass under and the ooh’s & aahh’s when it didn’t quite make it!

The mystery round which both classes took part in was loop’s & Spots, a 30 second climb, engine cut & perform as many loops as possible before landing as close to the centre of the strip as possible. Believe it or not 30 seconds makes a plane very small & they carry very quickly downwind as I found out. I also found out that just because someone suggests you could squeeze in another loop, doesn’t mean you should!

The competition was definitely in the traditional funfly spirit and big thanks are due to the Craigavon club for their hospitality and willingness to join in.

Scores are below.

Thanks,

Iain

Matthew is posting a daily blog HERE where you can follow his progress.

Good luck Matthew, You can do it!

Kees: Well, he did!  14th (out of 33)  in a very tough competition, in which Gernot Bruckman took the top honours. Trevor and Matt hit the road tonight, I’m starting off tomorrow morning, so see you all next weekend

Old Friends (not that old!)

Matts Extra in the Pits at the Acromasters

For once the weather behaved, the wind was manageable and most surprising of all given the summer we’ve had, was the sunshine.

I’m very glad to say that Matthew retained his Unlimited IMAC title for the 3^rd year in a row, came second in the freestyle, and won the Breitling trophy for overall champion in IMAC. Simon also placed well at 7^th in Unlimited & 3^rd in Freestyle.

As for how much fuller Sean’s car was coming home, I’m not sure, no doubt some new toys will appear at the field sometime soon!

Matthews report & some Pics can be found HERE, also keep an eye out for his article in an upcoming Radio Control Model World.

For those of you with a Facebook account have a look at the 500 or so pictures taken by Thomas Bakon HERE, they give a great flavour of a day at the Nats and made me wish I’d gone!

Iain.