Brown outs and Grey areas - the truth!

[Frank Skilbeck]

Maybe you could put a small heater in as well and check the temperature effects

[Lee Burke]

And when you have finished these tests, Timbo.  Please do them all again on a Futaba  2.4Ghz.  

Ducking and running very fast 

[Tim Mackey]

Another thing..... I am going to create more controversy now with the following statement

" BECS are actually safer than a  separate battery" 

Let me explain why I think this could be so.  BECs ( whether separate or part of the ESC ) rely on getting their power from the main flight battery - a relatively meaty great big powerful beast. The ESC also features a low voltage cutoff circuit ( LVC ) designed to give visual but safe indication that the battery is running low. However even if the battery approaches this low level, it will still have more than enough juice left to continue powering the BEC / UBEC which in turn powers the receiver and brown out should therefore not happen. A seperate Nixx battery pack on the other hand has the following potential problems.

1) It needs to be capable of supplying the correct voltage and current necessary - and many are not.

2) It needs charging ( and by different means to that of the flight pack ) and this could be / has been forgotten.

3) Nickel based cells have a bad reputation for black wire disease - which most decent evidence seems to point to the chemistry of the electrolyte used. No such BWD has been found in Lithium cell based packs.

4) Perhaps most critically of all - if, for whatever reason, the seperate pack runs low, or stops altogether due to a bad connection etc there will be no prior warning via the motor stopping / slowing / pulsing or whatever the ESC would normally do. The first signs of trouble will be the receiver stopping working altogether - including the flight controls! This will not be a failsafe situation - that can only occur with RF signal loss / interference

This of course is dependant on the BEC / UBEC being reliable and capable enough for the job...which frankly these days the majority of them are. 

Timbo dons his hard hat and retires to a safe distance.

[Tim Mackey]

Blimeys Jet....the wedding could be back on at this rate

[Tim Mackey]

Frank Skilbeck wrote (see)

Maybe you could put a small heater in as well and check the temperature effects

Errr. no!

Lee Burke wrote (see)

And when you have finished these tests, Timbo.  Please do them all again on a Futaba  2.4Ghz.  

Ducking and running very fast 

Gladly Lee. The address to send the donated fuby gear to is....

11 tester place

Im not getting much else done drive 

Information overload city

Hell Hell 66 2Bseen

[Brian Parker]

I have been following this thread (and the related thread) and with interest. The conclusion must be loss of signal.

If one studies the limited performance of transmitting omnidirectional vertical/stub antenna at 2.4Ghz the fact that the system works at all is down to the extreme sensitivity of the receivers and quality of the transmitters.

With regard to the so called ‘doughnut effect’. Current flows up and down the antenna-causing a magnetic field around the antenna-radiating outwards at right angles and falling to zero along the axis of the antenna-the electromagnetic wavefront expands, decaying in intensity as it moves outwards. More of a sphere than a doughnut. The sketch is an attempt to highlight the critical angles. At 90degrees(ie. pointing directly at model)…no signal.  75degrees virtually no signal. 45degrees...poor signal.  Antenna parallel to model and its receiver antenna…full strength signal (if in range!).

Note the small increase in signal if one turns their back directly to the model.

This all assumes that the receiver’s aerials are correctly oriented.

This is greatly simplified; propagation of radio waves is extremely complex especially at these frequencies.

Anyone for 35Mhz?

(I have yet to make the plunge to 2.4Ghz).

[Lee Burke]

Timbo - forum moderator wrote (see)

Gladly Lee. The address to send the donated fuby gear to is....

Hmm,  Think I'll have to pass the hat round then . . .  Come, who's first?

Otherwise your remarks on BECs being safer than separate Rx battery seem to make a lot of sense.  Isn't a UBEC the best bet in the end, I mean doesn't a UBEC keep cooler - when all around are loosing their heads, to quote our old chum Kipling.

[Alistair Taylor]

Hi all

 Been following this thread with much interest as I'm thinking of going 2.4GHz. Hats off to Timbo for the tests. Very revealing.

Sounds to me like there's a niche in the market for remote stub antennas mounted on sun hats/baseball caps

Normal practice among the RC flyers I've seen (and indeed my own way of flying) seems to entail moving only ones head when flying for the majority of the flight. The result (I would suggest) is that the TX signal, as seen by the RX, is constantly varying in strength as the position/orientation of the moving plane to the (largely static) TX aerial changes.

This might be what did for Shaun's Fury.

Positioning the TX aerial on top of one's head would ensure that the aerial was oriented at right angles to the plane and RX as the pilot's head followed it around, ensuring maximum signal (as per the diagram above) at all times.

Right then - where's the sewing kit.

Can't help feeling that some people might feel compelled to compare RC fliers to small garden birds if they start wearing baseball caps with small stubby aerials on the top.....

AlistairT

[Tim Mackey]

Perhaps the cake maker was worried about his head "loosening" but I am pretty sure it was old Rudyard that observed people losing theirs ! LOL

More seriously though.... yes I think you are dead right Lee -  a seperate circuit UBEC should indeed run cooler ( provided it is within cpability and has airflow around it ) than one built onto an already warm hard working ESC PCB

So in order of preference I will go for - in true miss world fashion EG: in reverse order...drum roll please.....

6th place- the seperate 4 cell NiXX battery

5th place- the seperate 5 cell NiXX battery

4th place - the ESC BEC combo unit

3rd place - the UBEC powered by Nixx battery

2nd place - the UBEC powered by seperate LiPo

Ist place -  the UBEC powered by main flight pack 

[Tim Mackey]

Brian Parker wrote (see)

I have been following this thread (and the related thread) and with interest. The conclusion must be loss of signal.

If one studies the limited performance of transmitting omnidirectional vertical/stub antenna at 2.4Ghz the fact that the system works at all is down to the extreme sensitivity of the receivers and quality of the transmitters.

With regard to the so called ‘doughnut effect’. Current flows up and down the antenna-causing a magnetic field around the antenna-radiating outwards at right angles and falling to zero along the axis of the antenna-the electromagnetic wavefront expands, decaying in intensity as it moves outwards. More of a sphere than a doughnut. The sketch is an attempt to highlight the critical angles. At 90degrees(ie. pointing directly at model)…no signal.  75degrees virtually no signal. 45degrees...poor signal.  Antenna parallel to model and its receiver antenna…full strength signal (if in range!).

Note the small increase in signal if one turns their back directly to the model.

This all assumes that the receiver’s aerials are correctly oriented.

This is greatly simplified; propagation of radio waves is extremely complex especially at these frequencies.

Anyone for 35Mhz?

(I have yet to make the plunge to 2.4Ghz).

This is very good Brian - and hopefully illustrates better than words what we mean by the "doughnut of death" as I have started calling it. More correctly of course it is the "doughnut ring of death" for it is indeed the "hole" in the middle of the ring that causes the most misery - in both the radio wave sense, and the sticky bun sense EG: the hole is tasteless! I dont quite get the diagram fully - what is the angle at the top right illustrating? and why did the signal appear stringer when you turned your back to the model?

Of course, as you say, Rx aerial orientation is also important, but by very virtue of the nature of the moving aeroplane this orientation can not be optimul at all times...which is why some of the Spekky  receivers intended for larger /more complex models have several "satellite" rcvrs allowing multi positional aerials on board.

I suppose my next trials should show the effect of jhaving the Rx aerial "inline"  with the tx aerial pointing its tip straight at it...this would presumably represent the worst case scenario for reception.

[Lee Burke]

Poor old Timbo, chained to his test bed now and forever   I like your Miss Power 2008 ranking.

Thanks for that explanation of the signal radiation, Brian.  Does the shortness of the wavelength of 2.4Ghz mean that the "hole" in the signal is narrower than that of, say, 35MHz.   I have attempted to discover just where the No Signal point is on my 2,4Ghz equipment but so far without success (maybe a good thing) but I guess proximity to the Tx means the Rx is "smothered" and bound to pick up a signal wherever the Tx antenna is pointing.  Just how far away does one have to go, I wonder?  Shaun, you seem to be the unwilling expert here   How far out was the ill-fated Sea Fury?

[260 Flyer]

"Sounds to me like there's a niche in the market for remote stub antennas mounted on sun hats/baseball caps"

Or how about we do it a la Spektrum and have one sticking out from each side!

Or you could attach them to a pair of sunglasses.

[Ultymate]

I know you guys are mainly talkin about Spektrum issues here but this photo shows Futaba's advised aerial position for best reception on their 10C 2.4 trannie

[Brian Parker]

Timbo, The right hand diagram was to illustrate that the angle of orientation is zero at right angles to the antenna and at 90degrees at the tip.

Regarding the signal with your back to the model. Microwave antenna tend to be ‘top fed’ (a generalisation) because in doing so, the ‘front’ signal strength tends to a slightly fatter even curve (ie. better) than the ‘back’ curve, this tends to fall away more steeply but less evenly, particularly when approaching 90degrees.

Lee, 35Mhz is less critical with respect to antenna orientation, the signal at this frequency behaves somewhat differently as it travels over the terrain, indeed, a reflected signal can be of sufficient strength, although at 35mhz this is less likely than at lower frequencies. However, it is still not advisable to point the antenna directly at the model particularly at distance.

Ultymates photo demonstrates the ideal position unless the model is overhead then it’s the worst (back curve).

[Lee Burke]

Thanks, Brian.

[Tim Mackey]

Thanks Brian. As to Ultymates antenna position, is this not, to a large extent due to the fact that this shows a module system where it would be impossible to have the aerial sticking "up" anyway?

Here's a shot of how David Ashby holds his dedicated futaba 2.4G and this is very close to how I hold my Spekky DX7

In either case, the aerial "as upright" is generally speaking at right angles to the model during the vast majority of the flight, and certainly not pointing the dead spot straight at it.

[Brian Parker]

Timbo,

You might like to try a simple diode probe to explore the output along the length of antenna.

Make up a small probe with a detector diode across a meter (or ‘scope) held close to the antenna it should show the voltage distribution pattern.

 I’m not on 2.4Ghz so am unable to try it (it works for 35Mhz).

 

[Tim Mackey]

Well found an old germanium diode in my box of electronic bits and bobs ( god knows why I still have an old cat's whisker in my collection of stuff ) which is the closest thing to a schottky or tunnel diode that I could find - it just about works by simply putting across the DVM voltage measurement range - and showed around 20mv or so when held close to the tx aerial. It could be seen altering in differing positions. Its definately higher toward the tip than the base, especially after the "knuckle joint"

Can be filmed if any one is sad enough / geeky enough to want to watch the movie!

[Yorkman]

all this talk about antenna outputs and the doughnut of death-as the spektrum tx aerial is bent halfway up its length, doesn't this remove said confection? Aren't there two 'tubes' -for want of a better word-of transmission waves? (you can tell I'm no expert on this!) overlapping and cancelling any 'blind spot'?

[Tim Mackey]

Well the doughhnut ring of death could still apply as it merely refers to the effective / non effective radiation area of the antenna - be that 35 Mhz or 2.4Ghz - pointing the tip of the aerial at the receiver is a dodgy thing to do with any radio system. The Spekky aerial is indeed HINGED to ALLOW the user to bend it upwards as it were, and this is definately the preferred angle....assuming the user holds the tr "flattish" which most do. However, some users do NOT take advantage of this hinge or knuckle joint and use the aerial straight....much as they did with the old 35Mhz sets they were weaned on.

The two frequencies will only provide redundancy in the event of one signal being lost / weakened and in that case the receiver should happily continue working on the remaining good signal....until hopefully the second one returns.

None of this matters of course if the Tx is simply not sending out its signal strongly enough in the first place....due to amongst other potential problems...the aerial orientation being incorrect as described above. HTH ?

[Yorkman]

thanks Tim-just looking at my Tx and thinking-if it was possible to angle the aerial 45dgress away from oneself, and assuming, as you say, holding the tx flattish, that puts the DOD either in the ground about 30 feet away, or somewhere behind your head...neither places one intentionally flies ones model...

[Tim Mackey]

Not quite sure I can picture that yorkman....not your fault - I am just suffering from information and testing overload syndrome

As I understand it...the transmission radiates strongly "around" the aerial rod as it were... but very little if anything actually eminates from its "top" EG: not up to Brians superior knowledge or graphics of earlier, but heres my version

[Yorkman]

[Brian Parker]

Yorkman, The lower (‘unbendable’) part of the unit is more than likely a series resonator (coil) with a tapped series capacitor and will have no effect on the actual radiation pattern of the antenna. The effect is to make the antenna behave better than it physically is. Again this is an assumption but more or less confirmed by the diode ‘test’.

 

Timbo, nice to know that there are other collectors of germanium semiconductors around, you see they still have their uses (don’t throw anything away).

 

The diode ‘test’ is clearer with an analogue meter rather than a DVM, as the swing is easier to follow. (I bet you still have an AVO8). Your diode test indicates/confirms a ½ wave antenna, but not being on 2.4Ghz I am unable to measure it. Is the antenna proper, i.e. not including the lower unbendable bit, around 70mm allowing for any protective covering at the ends?

 

Are we moving away from the spirit of the thread?

[Tim Mackey]

Brian Parker wrote (see)

Yorkman, The lower (‘unbendable’) part of the unit is more than likely a series resonator (coil) with a tapped series capacitor and will have no effect on the actual radiation pattern of the antenna. The effect is to make the antenna behave better than it physically is. Again this is an assumption but more or less confirmed by the diode ‘test’.

 

Timbo, nice to know that there are other collectors of germanium semiconductors around, you see they still have their uses (don’t throw anything away).

 

The diode ‘test’ is clearer with an analogue meter rather than a DVM, as the swing is easier to follow. (I bet you still have an AVO8). Your diode test indicates/confirms a ½ wave antenna, but not being on 2.4Ghz I am unable to measure it. Is the antenna proper, i.e. not including the lower unbendable bit, around 70mm allowing for any protective covering at the ends?

 

Are we moving away from the spirit of the thread?

Hi Brian...you are absolutely spot on with one assumption, and dead wrong with the other I dont have an AVO 8 anymore one of those caualties of divorce / house moving / gebneral life trauma type things I am afraid.... bit like my vinyl record collection - where did that grand funk railroad album get to etc
The "live" section of the Spekky aerial is indeed exactly 70mm.

As for drifting off topic... well 2 things to consider...

1) "Grey areas" sort of fits - after all..... people are a little uncertain about this subject

2) I am the moderator so we can do whatever I like on my thread LOL