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Electronics explained

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Glyn4425/12/2016 09:55:07
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701 forum posts
92 photos

If you would like a clear and detailed of model electrics I have come across this, which is just a beauty, and simply explained.

Ok it comes from a boating forum, but it is still mostly applicable to us flyers.

**LINK**

Geoff Sleath25/12/2016 11:36:14
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3363 forum posts
272 photos

At a quick glance through this seems to be an excellent primer for the electrically ignorant (and we're all ignoramuses about something)

One thing I noticed was that the the writer attributes the number of charge/discharge cycles for a LiPo as >1000 which I would have thought somewhat optimistic in my experience. Another thing to be aware of is that models boats are anything but weight sensitive (in fact a lot of ballast can be required to get the displacement needed) so the reduced weight/increased efficiency of brushless motors and LiPos isn't an advantage and heavy lead acid batteries and brushed motors are common.

Well spotted.

Geoff

Simon Chaddock25/12/2016 12:02:13
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5442 forum posts
2853 photos

This is quoted as an example

"an electric motor having a resistance of 30 ohms and connected to a 12 volt battery will draw 12/30 amps = 0.4 amp".

Whilst the figures are technically correct they are wrong when applied to an electric motor. The resistance of an electric motor has little impact on the current it might draw when it is actually running.

It would have been rather better to have used as an example something with a simple resistance load like a car side light bulb where the current it draws and the power it uses is controlled by its resistance.

Edited By Simon Chaddock on 25/12/2016 12:04:16

Geoff Sleath25/12/2016 14:11:21
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3363 forum posts
272 photos

Well, Simon, it will draw that current if the motor's stalled Having said that, 30 ohms is a pretty high resistance for a small brushed motor likely to be used in a model boat. But you're right, of course.

Geoff

Peter Beeney25/12/2016 14:35:01
1554 forum posts
59 photos

Simon,

Whilst I would agree that if this is an example to illustrate Ohm’s law it might be somewhat confusing; however, to be a bit pedantic I’d also consider that the resistance still has everything to do with the current that would flow when the motor is running. It doesn’t change in value; because of the way an electric motor functions it’s the voltage that actually changes; generally within a circuit if the resistance stays constant to vary the current it requires the voltage to vary.

Also, in all honesty, in terms of electric motors for models (aeroplanes) at least, 30 ohms does seem rather a bit high, 0.3 ohms would be much nearer the mark. Or better still, 0.03 ohms… In fact, in power terms the lower the total resistance of the complete power train can be made the better - but undoubtably the monetary cost will also grow proportionally…

I’ve not seen the link yet, so maybe I’m talking out of turn here, but it seems to me it does need something more of an explanation; using a motor to explain electrical principles might be a bit tricky!

PB

Mike Blandford25/12/2016 16:53:25
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530 forum posts
22 photos

Simon, actually a car side light bulb is not a simple resistance either! When cold, the resistance is much less than when alight and hot.

Mike.


eflightray25/12/2016 18:50:31
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575 forum posts
128 photos

Sorry, but once I realised that the writer loves writing, and writing, and writing, I just gave up on the link in post #1.

I have never been to keen on written 'technological explanations' by experts, yes they have a place, but I rarely find it is with some people who are generally looking for a little help.

Plus generally, knowledgeable writers also then get critiqued by other knowledgeable people, which confuses the lay person even more.

Electric flight has so many 'variables' that many of the 'e-flight calculator' are just general information, and often with calculated data, not real world actual physical test data. Even 'thrust test' data is static data, i.e. only 'accurate' when a plane is not flying.

Sorry if I appear to be stepping on toes, (but I do it a lot), but electric flight is not something that can easily be fed into a formula and give the answers people hope for.

There is basically a simple 'rule of thumb', the prop does all the work, choose what you hope is the right prop, then find a power system to drive it at the hoped for rpm. And that could be quite a range of different motors, and battery voltages.

Currently I am 'playing' with a KK stability system. 'Playing' as the 'instructions' run to 90+ pages, obviously written by someone who just loves writing, and writing, and writing .......

KISS is not something 'experts' understand. wink

Ray.

 

Edited By eflightray on 25/12/2016 18:51:54

Edited By eflightray on 25/12/2016 18:53:44

Peter Beeney25/12/2016 21:22:12
1554 forum posts
59 photos

So can we now now consider bringing ourselves right up to date here, just for fun lets change that car side lamp bulb for a modern LED type and then perhaps we may be able to shine a whole new non-linear very efficient white light on the dark, dusty and mysterious pronouncements of electrickity…

No? Oh well, perhaps not then; I shall therefore just continue to motor on rewardless (or resistless, maybe?) in the gloom…

Happy Landings in 2017.

PB

eflightray26/12/2016 14:53:58
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575 forum posts
128 photos
Posted by Peter Beeney on 25/12/2016 21:22:12:

.............................................

No? Oh well, perhaps not then; I shall therefore just continue to motor on rewardless (or resistless, maybe?) in the gloom…

Happy Landings in 2017.

PB

Perhaps your 'reluctance' regarding 'resistance' is an 'impedance' to your quest. Maybe more 'reactance' could help. wink

Ray.

Peter Beeney26/12/2016 16:38:18
1554 forum posts
59 photos

Thank you for your very kind thoughts and considerations, Ray, but perusing this from my usual sort of upside down/sideways angle I feel that my ‘permeance’ regarding my ‘conductance’ may well be of an adequate sufficiency… However, I do agree that my ‘susceptance’ is now certainly showing signs of flagging (as it often does nowadays!) but fortunately the hour is fast approaching when I’ll have some pleasure in taking a small ‘measure’ to ‘rectify’ that situation…

I’ve now read the link at last and I’m rather of the same opinion as yourself regarding the amount of information; but by the same token I’d tend to think that some areas at least are worthy of some sensible discussion, if only to make a token point; but nevertheless motors will continue to turn props and models will continue to fly regardless…

PB

eflightray26/12/2016 19:48:09
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575 forum posts
128 photos
Posted by eflightray on 26/12/2016 14:53:58:

Perhaps your 'reluctance' regarding 'resistance' is an 'impedance' to your quest. Maybe more 'reactance' could help. wink

Ray.

Sorry, that was a throw back to my introduction to electrickery back at college in the early 60's. Still don't remember how resistance, impedance, reluctance, and inductance related to each other, or how you used them.

For the electric beginner, an explanation about electrics for RC models really could fill a book if someone went into it in depth. There are some model 'calculators' that are quite useful, but like most things, you put rubbish in, you get rubbish out, so you need to know what to feed in. Car manufacturers quoted mpg figures come to mind.

As e-flight has now been going for many many years, there is already a load of very useful user data on the web. Even the Hobby King motor pages occasionally have useful user information under the 'Reviews' tab, (though not always).

It's often easier to copy/use someone else's experience regarding a motor, prop, battery, combinations, than try to start from scratch, or try to learn all about electric power. At least it should give a new user some confidence a model will fly.

There is quite a difference between selecting an IC engine, (each one having a fairly limited prop range), and an electric power system where a much larger range of props are capable of being used.

I have tried writing a 'simple' explanation of electric power myself, but all I did was write more and more explanations that got more and more complicated the deeper I went. So I gave up, and now just try to answer individual questions in forums where I can help, (not as often as i would like).

So for the electric beginner asking the usual, "what motor should I buy ?", I would recommend looking for similar models to see what they used. Then you can ask about that specific set-up if a problem occurs or if they want for information. To gain experience and knowledge, learn by copying first, then you have a basis to ask 'why', 'what'. Read a book if it helps, go on electrical/electronic courses if it helps.

See, now I am writing too much for many to bother reading.

Ray.

Tim Mackey29/12/2016 08:07:38
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20919 forum posts
304 photos
15 articles

FGS this stressed "keep it simple!"

Graham Moore 115/09/2019 20:08:15
12 forum posts

Is there anybody out there who can help me with this question?

I have a JP Power panel on my field box with a 12v Pb gell battery. Can I charge the said battery through the starter banana plug sockets or will this fry some of the circuits in the panel. I would like to do it this way if possible as I think that repeated removal and refitting of the 4.8 faston connectors at the battery will shorten their life.

Tim Flyer15/09/2019 20:32:42
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1047 forum posts
185 photos

I also have a JP starter panel and charge it through the 12v starter motor sockets. Have done it for years and it’s fine 😊

Graham Moore 120/09/2019 19:38:25
12 forum posts

Thanks for that Tim. I thought that would be the case but did not wish to tempt the smoke.

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