Receiver Drop-Outs

[Lee Burke]

An interesting article written by Marck Krief in a French magazine, RC Pilot.   According to his tests on flight packs that were charged to 50% of their nominal capicity, a 4,8V 1050 mA NiMH flight pack can drop to 3,46V under demand from 3 servos loaded at 1kg each.  This will cause the Rx to switch off and reboot resulting in a nasty, and probably disastrous, moment for the pilot.  He found that 6V pack dropped to 3.48V.  He lists various types of receivers and gives their susceptibility to brown-outs - the most modern variety - 2.4Ghz being the most delicate and slowest to recover.  He mentions also, of course, the threat of overheated ESC's switching themselves off.  Then he gives some solutions.

1) Use 0.5mm wire (instead of the ususal 0.3mm) to connect the battery to the Rx and keep the wire as short as possible.

2)Use 5 element packs if the servo's can take them.

3)Use only packs designed for propulsion.

4)add a supplementary capacitor external to the Rx (which has its own inbuilt).

This supplementary capacitor is aimed at providing enough power to keep the Rx alive when the battery-pack voltage dips.  He suggests using a condenser with a service tension of 10V (or 6.3V), an internal resistence of <0.4 ohms and a capacity between 2000 and 6800 microfarads.  The condenser is connected to the Rx via servo plug to a free channel.

 This may be old hat to many, and the author remarks that such condensers are available on the modelist market ready wired. 

[Tim Mackey]

And according to HH themselves....using a capacitor to buffer the volt drop is useless in an airborne system - these are marketed by HH for the ground based systems only where it is alledged that early ground based receivers ( IE cars ! ) had no input capacitors fitted and were more likely to suffer a voltage drop out due to the lower cell count used in their powertrains - the jury is still out on whether they have any benefit at all in the modern airborne receivers.

Using sensible guage wires to connect the power source to the receiver is a wise move - however, I doubt that most everyday systems require anything more than the standard guage multistrand wire supplied as standard on the battery pack.

To say that the modern 2.4Ghz sets are the most delicate and slowest to recover is simply wrong. Providing that Spektrum users have ensured their receivers have been "quick connect" enabled they are probably the FASTEST of all to recover following a brown out. Futaba 2.4 also have a lower brown out voltage than nearly every other receiver on the market - around 2.75V I believe - if you are using a battery that is likely to dip this low in any circumstances, then you need your head examining - well your battery at least

Use only packs designed for propulsion - what does that mean ?

If your ESC is overheating then you have either used an ESC not suitably rated for the job, or it is badly vented - or both! Also be very wary of using ESC BECs in any model with more than 4 or 5 servos.

All BECS are NOT equal!

I am sorry...... but all this talk about brown outs and receiver voltages dropping or disappearing altogether is something which has NEVER happened to me once in any of my models...and I have been flying various types including many many all electric powered variants for almost 30 years. I dont need to touch wood as I type this, because... I SIMPLY ENSURE MY RADIO BATTERY IS UP TO THE JOB - HERE ENDETH THE LESSON.

[birdy]

By prepoltion packs I think he means a pack designed as a flight pack or simular, designed to be able to take a few amps without significant voltage deducton. i.e: You wouldn't expect a lipo flight pack to lose two volts because you were using full throttle would you.

[Lee Burke]

It is interesting and reassuring to hear your take on this, Timbo.  I do not pretend to be in a position to make any judgement here.  I thought the article of sufficient interest to mention.  It is, in fact a two-page spread complete with oscillograph readings and tables.  Marck Krief writes for a number of magazines which have an interest in electronics in Europe and reviews for example for Topmodel. I have no idea of his credentials but assume that the editors of these publications considered them authorative.  He might, for all I know, be the Marck Krief who is the head of engineering and electronics at the France 2 TV channel,.

The "packs designed for propulsion " is my fault, it is a more-or -less direct translation from the French text: "Elements destines a priori aux propulsions electriques"  and by that I understand the author means those battery packs which have the characteristics required to supply power to an electric power train - as against one suitable as a purely Rx pack.

The table he gives showing relative parameters of various types of receiver lists the range of acceptable voltage their current consumption, their tolerence to electrical disturbance and their recovery time.  Copywrite considerations prevent me from reproducing it, of course, and again there is no mention of sources for the material -a woefully common habit, so one cannot judge, if one were able to, the value of the figures. 

Clearly bad news always makes interesting reading even in hobby magazines and its possible the article is simply a "filler", but Mr Krief seems to be considered an authority.and his opinions of some value.

But again, I just put it there.  Don't shoot the messenger.  Personally it is the first I have heard of this particular problem, should it be one.  But then I am new to this and like a lot of us - still learning. 

[Tim Mackey]

No one is shooting anyone Lee, and I did not mean to sound as If I doubted Mr Krief's technical knowledge... I was just giving my response in my own way. I guess the only one I did contradict was the one about 2.4ghz being slow to re-connect - and this WAS true until HH announced a fix in the form of QC.

However.... his message and mine are really both the same but I perhaps put it in simpler less scientific ways ( I am NOT a scientist, or even an engineer...just an experienced modeller ) and that message is

USE A POWER SOURCE WHICH IS UP TO THE JOB REQUIRED.

PS I apologise for not thanking you for the post - it was a useful and stimulating one 

AS for the "propulsion thing" well I hadn't realised that he was discussing electric flight particularly....and even now... I am not sure he was. Probably as you say a little language translation mismatch - In which case he is absolutely spot on, EG: USE THE RIGHT BATTERY FOR THE JOB  

[Lee Burke]

Fairy Snuff   Did I get it right this time?   No, Marck Krief wasn't talking exclusively about electric flight, he simply meant, as you say, use the right battery for the job of powering the Rx, and that this is not necessarily the one proposed by the LHS.

There was, inevitably, something "lost in translation" and it was a fairly long article so of course I didn't put everything in my post.  For instance, his figures show that increasing the wires to 0.5mm can result in a saving of up as much as to 0.4V on 5 servos which is a surprise to me at least.   But maybe only worth fiddling around changing wires on a "full house" set up. 

The most contentious feature of his article remains the statement that 2.4Ghz receivers are the most "delicate".  Perhaps this is a question of just what is being assesed.  He lists types of recievers among which are these  :

PPM    requires 3.6 to 9V.  Consumes < 10 mA.  Has excellent  tolerance of electrical disturbence (spikes and power-outs) and recovers immeadiatly from a tension dip.

PCM                  3.6 to 9V                      <30 mA      Good tolerence           Recovers quickly

PPM Synt          4 to 8V                         <30 mA      Average tolerence      Recovers  quickly to moderately quickly

2.4Ghz               4 to 9V                         <70 mA      Weak tolerence          Recovers slowly

Now, as I said, I don't know on what these conclusions are based,  perhaps his own research.  I know these are not academic papers but it would be nice to have that kind of information as well.

I didn't mention it, but his oscillographs show that the addition of a condenser buffer smooths the voltage drop on servo demand  and, for example, in the case of the 6V 2100 mA NiMH pack reduces the drop from 3.48V to 3.96V.

Personaly I can't see myself bothering with most of that stuff (apart from the batt pack) just yet   But I did find it interesting.

Thanks for your comments, Timbo.

                                  

[Frank Skilbeck]

I think the message here is as Timbo and Marck both point out, make sure your battery pack can deliver the amps with out losing too many Volts.

Some of the cheaper high capacity mah AA cells that are appearing and havge been made into Rx packs seem to have more internal resistance than others and when asked to provide a high load the voltage can dip.

If you have a 6 servo plane, or are using high power digital servo's than you should check that the Rx battery (and switch harness etc) are upto the job, also make sure you have a charger that can handle the batteries you are using. 

[Tim Mackey]

Here is the official statement from HH ( which I have linked to before in other threads )
Receiver Power System Requirements  - Horizon Hobbies. With all radio installations it is vital the onboard power system provides adequate power of 4 volts or more without interruption to the receiver even when the system is fully loaded (servos at maximum flight loads). This becomes especially critical with giant scale models that utilize multiple high torque/ high current servos. Inadequate power systems that are unable to provide the necessary minimum voltage to the receiver during flight loads have become the number one cause of in flight failures. Some of the power system components that affect the ability to properly deliver adequate power include: the selected receiver battery pack (number of cells, capacity, cell type, state of charge), switch harness, battery leads, regulator (if used), power bus (if used).
While Spektrum’s receivers’ minimum operational voltage is 3.5 volts, it is recommended the system be tested per the guidelines below to a minimum acceptable voltage of 4.8 volts during ground testing. This will provide head room to compensate for battery discharging or if the actual flight loads are greater than the ground test loads. Recommended power system guidelines:
1. When setting up large or complex aircraft with multiple high torque servos, it’s highly recommend a current and volt meter (Hangar 9 HAN172) be used. Plug the volt meter in an open channel port in the receiver and with the system on, load the control surfaces (apply pressure with your hand) while monitoring the voltage at the receiver. The voltage should remain above 4 volts even when all servos are heavily loaded.
2. With the current meter inline with the receiver battery lead, load the control surfaces (apply pressure with your hand) while monitoring the current. The maximum continuous recommended current for a single heavy duty servo/battery lead is three amps while short duration current spikes of up to five amps is acceptable. Consequently if your system draws more than three amps continuous or five amps for short durations, a single battery pack with a single switch harness plugged into the receiver for power will be inadequate.
It will be necessary to use multiple packs with multiple switches and multiple leads plugged into the receiver.
3. For really large aircraft or complex models (35% and larger or jets) multiple battery packs with multiple switch harnesses are necessary or in many cases one of the commercially available power boxes/ busses is recommended. No matter what power systems you choose always carry out test #1 above making sure that the receiver is constantly provided with 4 volts or more under all conditions.

As can be seen the MINIMUM operating voltage is 3.5 as I originally stated. I believe ( but have no hard evidence from the manufacturer, and as a non user, have not researched it myself ) that the Futaba receivers on 2.4Ghz have a minimum level of 2.75V.  No wish to be argumentative - just clarifying this particualr point

[Lee Burke]

Great, thanks for reposting that info, Timbo.   I'd never seen that before, and even if I had it never hurts to drum things in,

[Capt Kremen]

Picking up on point #4 in the French article (i.e. use of a capacitor plugged in a spare rx port).

I see Multiplex have had such a ready wired (plugged) item in their catalogue for some time (MPX Part No. # 8 5180 Peak Filter cost £4-99 approx). Is this item worth considering (at all), for 2.4 GHz users?

Also ...

With reference to NiMH cells, the latest variants (AA cells as may typically be used in Rx packs), are of the ready charged/long shelf life type (e.g. eneloop from Sanyo and similar 'badged' product from SONY, GP etc.

I picked up a (SONY/eneloop) set of 4 x AA for use in my Spektrum DX6i Tx in the local Sainsburys at £7-99 (plus Nectar Points of course!). I've topped these up via my Schulze and 'load' tested, they seem good for Tx duties. Any one any thoughts, comments, long term experience of these 'new' chemistry NiMHs?

[Lee Burke]

I am not sure what the answer to your first question is, Captain, since our good guru Timbo has never experienced the Rx blackouts described in the article and his information on 2.4Ghz receivers and the use of buffer capacitors is at odds with that of the author of the article, it looks like the jury is out on it. 

I guess its up to you if you think the £5 is worth spending,  You would need to know if it at least complied with the parameters set out by Marck Krief in my first post.  If I had a big expensive model and were flying it anywhere loss of control could injure spectators I think I would adopt the all precautions in Marck Kieif's article.  They surely can't hurt.  On the other hand just buzzing around in a light powered glider, say, I'd probably not bother too much.  But that's just me

[260 Flyer]

" They surely can't hurt "

Be very careful plugging large capacitors into your Rx, at power-up they are effectively a dead short and could fry your PCB. It would be better to wire them into the switch harness.

[Lee Burke]

I can't find the Multiplex capacitor Capt Kreman mentions, it would be interesting to know its specs, one would think Multiplex, at least, knew what they were doing

[Always broke]

I am one of those non Tecy sort of people but I have been using Spectrum radio since it was introduced into the UK and now have upgraded to the JR9X  TX . I fly models fitted with Petrol engines of 62cc, Electric models with 3KW 10S set ups , down to shock flyer's. I have never had a single instance with the radio in all that time , BUT I do use power supplies that are up to the job. All the big models are fitted with sub C 5 cell packs,Smaller modes are fitted with 5 cell AA packs. I never use 4 cell packs now and this gives me the safety margin I feel is needed using this radio. Some of my Digital servos needed changing to do this . I always check the voltage before flying with a decent meter that puts a load on the system..On  Electric models using the ESC to provide the power for the radio I only use Switch mode Becs ,and again this has given no problems at all. Good quality switch harnesses are also a must and a lot of the cheap copies are going to fail. I only use heavy duty unites . All these thing cost very little to be sure of and is nothing compared to the cost of a model.

Maybe what I do is overkill but As I said I have not had a single radio fault with 2.4. If you have a radio loss due to low battery voltage at the RX it IS YOUR OWN FAULT AND NO ONE ELSES in my book. I can't see it needs to be any more technical than that.

[Capt Kremen]

The Multiplex 'Peak Filter' (Part No. # 8 5180) is on page 77 of the MPX main catalogue with discription of use (the 'voltage collapse' bit is toward the end), or see this web page:

http://www.modelmaniacsonline.co.uk/products.php?ProductID=5436&CatID=12&SubCatID=355

I don't disagree with all the valid points raised by 'Always Broke' however it makes me wonder about the many, many years 'we' were all (merrily) flying our 27 then 35 Meg sets using anonomous 4 x AA Rx pack NiCads, of less developed specification and without cycling and general TLC we all give our precious cells these days!

[Lee Burke]

Thanks for providing the link to the Multiplex Peak filter, Capt.  Kreman.  It seems designed to preventing damage from spikes as well as power drops.  Pity they don't give any specifications, but it looks like just the sort of accessory that Marck Krief  recommends. 

I also agree with most of what Always Broke writes, and he says much the same thing as Timbo; and obviously we all hope we are installing adequate equipment and should blame nobody for ourselves for our own cock-ups.  The problem is knowing just what one can rely on, and taking nothing for granted is a good policy in any pursuit, I guess. 

Your second point about earlier electronic equipment not suffering power fluctuation problems is interesting, but so far nobody seems to have had any problems attributable to power fluctuations with the new stuff either, well, not that I have read of anyway.  Perhaps it is just hard to nail a problem down to that particular weakness.  There are so many imponderables, not least the magnetism of trees. 

I understand that over the years as electronic equipment has become more sophisticated it has also become more susceptible to fluctuations in current., and it is possible that earlier equipment, while less complex, was also more resilient to this, although no doubt it had other irritating flaws.  But I have absolutely no expertise in this area and just offer my two cent's worth, or maybe not even that. 

[Former Member]

[This posting has been removed]