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RCM&E April 2013 issue preview!

RCM&E April 2013 issue preview!

in the shops 8th March

Pete B - Moderator04/03/2013 17:31:35
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Quick off the mark again this month - mine's arrived! Just a brief glance so far but the Panther article is going to get a good reading and I'll drool over the Nuremburg offerings and that big Monsun at my leisure....smile

Pete

Doug Ireland04/03/2013 17:42:16
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Mine arrived this morning and after a quick inventory of the wood pile I think I might build Peter Miller's new model.

Kevin Fairgrieve04/03/2013 18:24:33
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On the doormat when I got home.

Will take it to the library later.

Kev

Terry Walters04/03/2013 18:44:53
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Got mine this morning too Pete but been busy re-arranging the internals of my own Monsun (it's bit nose heavy!!) to read the article about the new ones yet!!

Looks like a good read again.

Terry

Danny Fenton04/03/2013 19:01:42
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Great issue really enjoyed my copy

Mr.B.04/03/2013 19:34:35
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Hey hey I've got my copy first for once!

One thing, in the letter responding to the flying start series it is stated that if stalled, an electric motor will still exert torque. Now this comes up from time to time in the elec V IC debate (and I really have no desire to start that again, neither do I have a view one way or the other) but while this is true of brushed motors it is not true of sensor less brushless. Once a sensor less brushless is stalled it will not restart unless the throttle is closed then opened as the ESC is no longer receiving the back EMF pulses. So why does it keep getting repeated?

Andy4804/03/2013 19:45:12
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Just read that too. However its all a bit academic if you fit a safety plug as the series suggests. (The wording is CAN BE MADE SAFER). I'm also still wondering how an electric motor can unexpectedly start with the safety plug removed.

Mr.B.04/03/2013 19:56:35
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Good question. Equally if the prop is obstructed when the throttle is opened the motor will kick then do nothing other than emit a horrid shriek. >>

On safety plugs, I advocate using a different pattern safety plug to that used for the battery. This is after seeing a mate inadvertently stick the safety plug he had in his hand into the battery connector instead of the esc. Boom. Singed fingers and one ex lipo.>>

>>

Andy4804/03/2013 20:07:12
1378 forum posts
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Your last point is a good one, and initially I used EC3 connectors for the safety plug. Instead of two plugs or two sockets in the safety plug, I used one pin and one socket. However, I have gone off these big time after having a lot of trouble getting the soldered pins into the plastic housing. (Before anyone asks, I'm pretty good at soldering and don't get any on the outside of the pins.). On one of my models I was having a few problems with what seemed a dodgy battery. I changed it, and had a good flight, but the plane cut out after it landed. It turned out the pin had come out of the plastic housing of my safety plug and was only just making contact. XT60s from now on.

Chris Bott - Moderator04/03/2013 20:38:17
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On the "stalled brushless motor is safe question", I would advise caution. With the huge variety of sources of motors and particularly ESC's, and the variety of qualities, then what happens with one type shouldn't be assumed to apply to all others.

I have seen a model with a brushless motor burst into flames because the throttle was left open when the prop was stalled.

I'm not about to go stalling one to prove otherwise, but I'd also think that there's a chance of the esc continually trying while a motor is stalled, if this is the case, then removing whatever's stalling the motor or even just picking a model up could cause it to start again. This is not the safest of situations either, especially if it's not expected.

Mr.B.04/03/2013 21:02:03
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I'm not suggesting that stalling elec motors is 'safe' thing to do. But then again the people that tell that a stalled IC motor is safe aren’t suggesting that you should stop an engine by grabbing the prop either!

It just the way brushless sensor less ESC works, no motor rotation, no pulses, no output. I guess it would only re start if you flicked the prop round in the IC starting fashion. Not that I'm about to test this either!

Chris Bott - Moderator04/03/2013 21:23:02
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I'm not convinced Mr.B. There are no pulses when starting up from scratch, but it manages to go then, by applying a random rotating field until it does pick up some pulses.

So whether it continues trying when stalled is up to the whim of the software designer. He either does the sensible thing and stops it trying, or, for whatever reason, makes it continue trying.

Tim Hooper04/03/2013 21:31:57
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Never mind all the techy talk - I'm still laughing at the pic of Young Whittaker!

tim

Mr.B.04/03/2013 21:36:45
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Hmmmm. It starts the motor initially by applying and random rotating field because the throttle is advanced from 0%. In my experience (caveat!) if the motor fails to pick up and spin, for example you open the throttle very very slowly or if one wire is disconnected, the motor just stops and you have to shut then re-open the throttle. I’m not going to stick my neck out and say that there are no ESCs intelligent enough to automatically try to re-start the motor. So I shall withdraw my opening statement and slink off to the shed.>>

Danny Fenton04/03/2013 22:30:35
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Posted by Tim Hooper on 04/03/2013 21:31:57:

Never mind all the techy talk - I'm still laughing at the pic of Young Whittaker!

tim

I thought my hair was long in my yoof, but Alex really does look like one of the "Young ones"

Adrian Day04/03/2013 22:38:19
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351 forum posts
101 photos

nice one this month .. got my one this morning wasn't thinking it was going to be here till mid week but very happy .. and so far at a glance some great reading to be had.. great cover shot too..

keep up the great work

Prop Nut05/03/2013 15:34:07
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Excellent letter from Andy Blackburn.

Edited By hellcat on 05/03/2013 15:34:33

Prop Nut07/03/2013 16:19:11
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Very tempting advert in 'Market Place':

"Black Horse Chipmunk, 64" span with SC91FS, seven servos, working flaps and oleos. Ready to fly, just add crystal. As new - £240."

And... no seller contact details!

ken anderson.07/03/2013 16:34:42
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772 photos

the final part of the panther is worth waiting for.......and AW's look back at the old engines's is as usual good entertaining reading......made me laugh as i remember the good old days with the diesel's(sore finger ends from getting nipped by the engine)...and of course the ether.....circa...early 60's...

ken anderson....ne..1.... diesel days...dept.

Biggles' Elder Brother - Moderator08/03/2013 12:48:06
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I was reading through the letters page when I came across the one about buddy leads. To save you the trouble the writters basic argument is "don't use them because if you do you either learn bad habits such as attention lapses - because you know the instructor will always bale you out - or alternatively you'll never learn to recover from tricky situations because you never get to do it." He finishes with some pretty strongly worded advice - "you'll never learn how to regain control with the safety net of a buddy lead".

I'm not at all sure I accept this argument. Personally I think the problem - if he has one smile - is not with the buddy lead, but with the way his instructors have used it with him.

The buddy lead system needs intelligent use by the instructor. Yes, initially it is very much an interventionist policy. The early stage beginner often needs lots of "rescuing" - even if only to keep the model more or less in the circuit. But a good instructor works to wean the student off the buddy lead. Gradually taking him to a situation where it is clear to the learner that the instructor will only intervene if:

1. There is a real safety issue

2. The student asks him to.

Other than that - the student flies the model.

The aim surely to get the student to sucessfully complete flights where the instructor can truthfully say "I never took control once". Then this is used to give the student the confidence to go without the lead.

The lead has another use I believe which is precissely to do with the difficult situations the letter writter refers to. How is a student pilot supposed to learn to recognise the signals of an on-coming stall if you don't allow him to stall the model? How is he to learn stall recovery without deliberately stalling? Surely the safest way - both physically and for the model - to learn this sort of thing and how to recover from the "tricky situation", is on a buddy? If the student freezes in the stall recovery and will not push the stick forward then the instructor can intervene. But then you go round and do it again - this time emphasising the need to do the counter intuitative thing - and push down on a falling aeroplane!

I personally believe that the buddy lead was the greatest invention ever for helping people learn to fly. Its probably saved countless models and, used intelligently, bred thousands of good pilots. Advice against its use is I think not helpful - advice to some instructors on how to avoid students becoming over dependent on it - now yes, that might be helpful.

Just my view....

BEB

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