WINDSOCK

NEWSLETTER OF THE READING & DISTRICT MODEL AIRCRAFT CLUB

July 2007

Musings from the Model Shed

The summer’s gone, well at least the calendar says it has, but I an not sure it ever arrived!

Firstly let me extend my apologies for the lack of Windsock’s this year – truth is that work hours have been getting longer and longer and having spent 10 hours staring at a computer in the office, lets just say my motivation for sitting at one when I get home is low. But as work pays the bills and grants us more models, which is why we’re all in this, it has to take priority.

The AGM is fast approaching – 4^th December – so make sure it’s ringed in your diary’s/calendar’s . If anybody would like to take over the editors job I would be happy to stand down, otherwise I will continue with best efforts!

Idea’s and articles are always gratefully received.

Back to the weather - I think we had better flying weather in the winter, I have only been into modelling for a relatively short period of time, but the weather has not been playing ball at all this year. Having said that, over the last year I have developed an interest (obsession) with gliders and all this windy weather has presented many opportunities to go slope soaring. I have spent most of my flying time soaring and become thoroughly hooked! While I would never think of giving up things ‘oily or lectric’ there is just something about watching a glider come howling down from on high only to magically swoop back up into the sky from whence it came with out assistance from an engine of sorts.

For those of you that have never tried it, I can thoroughly recommend it – it is a very different discipline to power flying and quite probably teaches you to be a better pilot as you need to fly as smoothly as possible to conserve energy and you can’t rely on the big fan at the front to get you out of trouble. Trekking up the hills is good exercise too and you get to see some magnificent views.

So I am currently building (installing the radio) my first moulded glider – a Mirco Floh XL from www.GoGliding.net and really looking forward to flying it in the near future. The kit is of fair quality, but considering its half the price of similar size mouldies, that’s to be expected. My only gripe is that there are no instructions with the model, just a photo copied 3 view drawing with rough radio positions and a C of G. Luckily the model was reviewed in Quiet and Electric Flight some time ago and that give some clues! On the plus side I had excellent service from John Marsh at Go Gliding. I rang him Monday morning to order the model, apparently he only takes cheques, so a cheque was duly posted Monday lunch time and large box arrived at my desk on Wednesday!

With all this gliding, I have done some power flying this year. Allowing a friend to fly my WOT 4 earlier this year with left me with a bag of bits and an opportunity, that has now been filled with a Great Planes Extra 300. The model is suitable for 60 size 2 stroke or as I have fitted, a 72 4 stroke. Building is progressing slowly but surely and I’ll do a quick summary of the build and any comments on the kit and flight characteristics as soon as its finished, but so far it looks fantastic.

Let us know what your up to – write a review of your latest model, engine, battery charger or what ever, send it to me by post on paper or e-mail I don’t mind which. :o)

Happy landings.

Paul Joslyn, 8 Fairfax Road, Chalgrove, Oxon, OX44 7RS.

01865 400603, 07771 963200 paul.joslyn@xerox.com

Field charger power supply

Firstly let me say that all the usual disclaimers against the club and author apply and if you are not sure of your abilities with regard to things electrical seek help or just don’t go there!

Having said all that this provides a cheap or indeed in some cases virtually free, fairly high current desk top PSU for your 12v field charger.

What you will need is:

· an old (working) PC power supply unit (PSU),

· some 4mm terminal posts (if you’re going to make a nice job of it)

· a 10 ohm 10 watt (that’s important) resistor

· a switch – low voltage on/off type.

Modern power supplies are what are called ‘switch mode’ power supplies which operate at a much higher frequency than PSU’s of old, consequently transformers are much more efficient and therefore much smaller, lighter and cheaper that the great big lumps of yesterday. One small down side of this is that they will not run without an electrical load, this is where the 10 ohm resistor comes in – it provides a small load to keep the PSU running when nothing is connected. Basic ohms law 5v across 10ohms equals 0.5A.

Note: if the PC you are taking the PSU out of is still functional and you have a volt meter, its worth checking that the colours / voltages from the chart below match – there is nothing like the computer industry for producing non-standard parts!!! I will say again, if you’re not used to dabbling with things like this take great care.

Function	Ind Std PSU	Dell PSU
+3.3v	Orange	NA
+12V	Yellow	Yellow
-12V	Blue	Blue
+5V	Red	Red
-5V	White	White
Ground	Black	Black
Power on	Green	Gray

So what do you need to do? With the mains power removed, leave it an hour or so, so that everything is discharged, then take the cover off. What you need to do first is to get rid of some of the wires as there are multiples of most going to different parts of the computer. The table above shows what the colours mean.

What you need left is (colours are for industry std PSU – amend accordingly if yours is different):

· 3 Ground wires (black)

· 1 +5v wire (red)

· 1 +12v wire (yellow)

· 1 Power on line (green)

This will give you a +12v power supply – if you want to add some of the other supply lines e.g. 5v you will need to add the appropriate wire for that supply, red in the case of a std PSU for +5v.

Mount the resistor (make sure the wires cannot touch the case) to the case, preferably some where in the air flow from the fan, mount the terminal posts and the switch.

Connect the ‘power on’ (green) to one side of the switch and a ground (black) to the other so that they are electrically connected when the switch is thrown – this will be your on/off switch.

Connect +5v (red) to one side of the resistor and ground (black) to the other, and finally the remaining two wires +12v (yellow) and ground (black) are to the terminal posts.

Attached are some shots of the one I made.

Double check everything thoroughly and switch it on. Test the polarity and voltage are correct with a meter before you connect your field charger.

Then you should be good to go. Mine’s been running for about 6 months now, and it makes charging batteries at higher currents much easier, I no longer have to lug a car battery around the house, especially for LiPo’s that have to be charged at 1C (their capacity – a 2100mAh LiPo must be charged at 2.1A’s)

If you have any questions or are not sure of something, don’t hesitate to give me a call on 01865 400603.

My finished PSU – I have opted for adding extra terminals for other supply voltages

Inside the lid – I could not get a suitable 10ohm resistor so used 2 x 4.7 ohm in series – note my PSU was a Dell so I needed the gray wire not a green for the on/off switch

The rest of the power supply – note for future options I kept one of each supply wire curled up on the back. Never know when you might need a –12v supply

Hints and Tips from Dave Belcher

Earlier on this year Dave gave us an excellent talk on covering models adding a wealth of hints and tips to boot. I did my best to make notes and you can find them here.

And Finally,

congratulations to all (left to right) Dave Belcher, Ron Perkins, BMFA instructor, Martin Dance and Dave Grey who are all BMFA approved flying instructors

Comments, suggestions or articles to:

Paul Joslyn, 8 Fairfax Road, Chalgrove, Oxon, OX44 7RS. 01865 400603 – 07771 963200 or paul.joslyn@xerox.com