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To UBEC or Not to UBEC? That is the question.

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leccyflyer25/03/2011 10:18:54
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The thread discussing the post-mortem on the dead Seagull PC-9 has been closed, with the recommendation that any further discussion on the subject of power looms, UBECS, connectors and data loggers should be in a new thread.
 
I came to that thread rather late, but in reading through it found a number of items that were clearly of a wider interest to electric flyers. Those include the fragility of the power and radio control systems being dependent upon the linkages and connectors that we fit to the various components in our models.
 
My main question is - is the use of a UBEC a case of putting all our eggs in one basket, in a safety-critical part of the system?
 
I admit that reading the original posts in the threads relating to the big dead Seagull I was drawn to conclude that it makes a great case (IMO) for a completely separate power supply for one's radio system, especially in larger models, where the additional weight isn't detrimental. In the event of any sort of serious mishap in the power train, one does not then run the risk of losing radio control as well.
 
I think it's settled the matter for me in that I won't now be fitting a UBEC to my favourite model, since the potential disadvantages would seem to outweigh the advantages..
 
The other thing that I was enquiring about in that thread, regarding the wiring up of our power looms, connectors etc concered the additional complexity of in-flight monitoring equipment.
 
The introduction of extra gubbins into the power circuitry, whilst it produces some nice, useful data, is something that IMO needs to be looked at very carefully, lest that compromise the integrity of the overall system itself. As another poster pointed out, one is left with the little niggle as to whether the fitting of the data logger contributed to the situation at all.
 
I also asked the question whether the leads for the data logger (and UBEC) were added to the connectors in a second phase of soldering, which could conceivably have reheated, and weakened the original solder joint. I asked that for the sake of clarification and it appears that the datalogger was merely added in series in the circuit and there was no second phase of soldering to the 4mm bullet connectors used for the power circuit.
 
I stopped using my trusty Wattsmater years ago, in favour of a clamp meter, precisely to avoid the considerable extension of the power loom that results from using adaptors to fit that equipment in series, between battery and ESC. I could have lopped off the fitted ASTRO zero loss connectors. which would have shortened the extra cable length a bit, but there is still a fair length of extra cable to introduce into the circuit.

The other, similar, though opposite question is - in the interest of accruing data, are we in danger of over-egging the pudding and introducing extra points of failure in our models?
 
Both questions are egg-related, funnily enough. Hamlet and eggs - what more could you wish for?
 
Happy Easter.
 

Thoughts?

Edited By leccyflyer on 25/03/2011 10:23:09

Craig Carr25/03/2011 10:28:51
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Posted by leccyflyer on 25/03/2011 10:18:54:
My main question is - is the use of a UBEC a case of putting all our eggs in one basket, in a safety-critical part of the system?
 
I admit that reading the original posts in the threads relating to the big dead Seagull I was drawn to conclude that it makes a great case (IMO) for a completely separate power supply for one's radio system, especially in larger models, where the additional weight isn't detrimental. In the event of any sort of serious mishap in the power train, one does not then run the risk of losing radio control as well.
 
Im sure others may have different points of view LF but I for one always fit a seperate RX battery on big electric projects. Just sort of makes sense to me personally not to have another electrical component in the works that can go wrong.
 
With a seperate rx battery you do have a bit more of a chance to bring the model back in if the motor battery goes
 
If the model can accomodate a bit more weight I wouldnt think twice about it.
 

Edited By Craig Carr on 25/03/2011 10:30:02

leccyflyer25/03/2011 10:53:34
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Those are pretty much my thoughts on the matter.
 
Reading that particular post-mortem thread has only served to reinforce them, since I had a loss of power in the air on Sunday and was able to recover the model to a straightforward deadstick landing in the middle of the field with no more damage than one "How can you have a deadstick with an electric?" in my ear having called it.
 
I don;t think that loss of power would have led to loss of battery power to a UBEC (or an internal BEC) as it happens, and I do use BEC on several of my smaller models and am happy to do so. The equation there is a bit different though, where the extra weight of a receiver battery comes into the equation and where onboard integrated BEC on an ESC on 3s1p power makes sense to me.
 
The particular model in question needs a receiver battery to balance, with the 6s1p Lipos mounted on the CofG, enabling different packs to be used. The main disadvantage is that of keeping the RX battery charged, which is just the same as for an IC model. I usually fast charge the RC pack at the field, on arrival.
 
I suppose another option would be to fit a Lipo RX battery with a regulator, or the UBEC, but I'm not mad keen on keeping a Lipo permanently in the model and I don't charge my lipos at home anyway.
Danny Fenton25/03/2011 11:26:51
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On the face of it this seems an obvious conclusion, however you are now introducing a second battery, the looms associated with it, the switch harness, the need to charge the battery (correctly). and you could easily suffer black wire corrosion which would take out your Rx. I use a good high powered UBEC and feed it fromthe ESC connectors as Tim does and have not had an issue.
I also only use 4mm bullet connectors but would probably go up a size if the current was going to average more than 50A. Bearing in mind my 14lb Hurricane, capable of more than 2Kw averages only 30A.
 
Cheers
Danny
Tim Mackey25/03/2011 11:51:20
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Almost the same title HERE lads, however I may be rethinking my original preferences
leccyflyer25/03/2011 11:51:34
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Hi Danny
 
Agreed on the connectors. With 6mm connectors readily available these days I'd probably do the same. As you know I've seen your lovely Hurricane in action and it's prototypical flight pattern on just 30amps shows the advantages of a high voltage system (over one that is frying eggs on the motor casing).
 
As regards the introduction of a second system,
 
To my mind it's really just exactly the same as in every IC model that I've ever flown. With a very large one of those - which are not in my sphere of interest - then redundancy of RC systems, especially batteries, is a common feature.
 
Yes you do introduce extra equipment, but you also offer redundancy in that, in terms of a back-up.
 
That would be the ideal for very large models, but in lieu of that a well maintained conventional power source for the radio gear would seem to avoid the loss of all radio control, in the event of a failure in the rive-power chain.
 
cheers
 
Brian
leccyflyer25/03/2011 11:54:52
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Posted by Tim Mackey - Administrator on 25/03/2011 11:51:20:
Almost the same title HERE lads, however I may be rethinking my original preferences
I only noticed that thread was there after I had created this thread, or I'd have given this one a different title.
 
I don't actually enter the site through the individual forums and hadn't seen that when I posted this thread. I use the View Latest Posts options and refresh that page.
Steve W-O25/03/2011 11:57:44
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I don't think the answer is so clear cut.
 
Each way has pros and cons.
 
I usually take more than one model flying, but several of them use the same size lipo, so one bag of batteries to charge and change.
 
 
I think if I was convinced to use a seperate battery, I would set the BEC to 6V, and have a 6V battery wired in parallel with blocking diodes, with two diodes on the battery. That way I could use a small AAA receiver battery, and fit it to the model I was flying at the time.
 
That way the battery would not normally be supplying any power, and would solely be a back up.
 
In the lst year, I have damaged two planes, both small depron plane, one I ran out of talent rolling 6' off the ground, the other suddenly lost power at 30' just after take off, as I took off with full flaps and down elevator, it wasn't really flying in the true sense of the word, so it just fell to the ground. Had I have done a stick reset of the ESC, it would have regained power, so both times it was pilot error.
 
I have yet to be convinced that going to any extra trouble like having a seperate RX battery with its associated problems, is going to give me any real advantage.
 
The electronics, when used correctly are very reliable.
Tom Wright 225/03/2011 13:09:45
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Hi all.
This thread seems to to miss the main point when it comes to the reason for fitting a ubec .the usual bec built into the esc is prone to destruction when the esc is subject to over heating ,if a ubec is fitted the esc can be destroyed and the the ubec will continue to function if the supply is taken from a well considered point.
 
TW2.
 
Steve W-O25/03/2011 13:19:31
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Posted by tom wright 2 on 25/03/2011 13:09:45:

Hi all.
This thread seems to to miss the main point when it comes to the reason for fitting a ubec .the usual bec built into the esc is prone to destruction when the esc is subject to over heating ,if a ubec is fitted the esc can be destroyed and the the ubec will continue to function if the supply is taken from a well considered point.
 
TW2.
 
 
 
If the ESC overheats, the drive to the motor mosfets is cut/reduced, not to the BEC.
 
Of course if it smokes, it may stop the BEC from working, if it shorts out the battery, but then thay may stop anything connected to that battery from working.
 
Any ESC over 30A, I use a seperate BEC anyway, but it is still powered by the same battery.
Tom Wright 225/03/2011 13:29:43
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Yes Steve a good esc should go into thermal shut down and leave the bec ok,but i have often seen other peoples models downed due to the cheaper esc types smoking.i have at least 40 ep models most with ubecs never had one fail.
 
TW2.
Bob Cotsford25/03/2011 13:49:39
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my take on this is that if the model is too big/complex to run off a BEC, then I'd use a dedicated rx & servo battery.
I'm now having second thoughts about my Cularis with it's 6 (admittedly micro) servos running off a BEC. No problems to date, but IF there were a problem it could go an awful long way, bearing in mind that we're talking catastrophic failures here so the failsafe wouldn't work either.
Tom Wright 225/03/2011 13:50:07
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The other point not mentioned is that the most popular ESCs only have a 2-3amp bec,were as you can buy UBECS very cheaply with ratings of 7 amps ,this redundancy keeps the electronics running nice and cool , and more reliable.
 
TW2.
leccyflyer25/03/2011 13:52:56
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Posted by Bob Cotsford on 25/03/2011 13:49:39:
my take on this is that if the model is too big/complex to run off a BEC, then I'd use a dedicated rx & servo battery.
I'm now having second thoughts about my Cularis with it's 6 (admittedly micro) servos running off a BEC. No problems to date, but IF there were a problem it could go an awful long way, bearing in mind that we're talking catastrophic failures here so the failsafe wouldn't work either.
Bob
 
When we did some tests a number of years ago some microservos drew more current than standard servos. There were some real amp hogs in there with a couple of microservos drawing upwards of 1 amp.
Peter Beeney25/03/2011 14:12:46
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I’m following this thread with some degree of interest, as I think this is subject that’s been in the news before; and as I’ve been Thinking Safety for about the last thirty five years there is only one option for me. For anything other than a foam model or a smallish powered glider I would just fit a separate receiver pack. For me, the reasons are sound enough.

I have done the diode/backup battery trick a couple of times in the past, but this was i/c, when I was experimenting with some batteries, and it was backing up a receiver pack, rather than a regulator. I would consider that, whilst it is an alternative way of providing some safeguard, it’s still not entirely without it’s drawbacks. I’ve also done a lot of bench testing with battery and regulator (BEC) combinations. Here you can load the lash-up much higher and for far longer than you can in the air, all night for instance, and I’ve never seen the slightest problem. I’m a member of ORWISC (Our Red Wire Is Still Connected), but you have to consider that’s only slightly tongue-in-cheek. It’s more or less irrelevant in any case. Until you get a fault, that is!

Funnily enough, I seen a really good practical example of this, when a model was totally stuffed because the pilot changed his procedure slightly on one occasion, and on inspection of the remains it became apparent as to just how severe the conditions can get and still the electronics continue to function. As it so happened, in this little episode he’d got it connected correctly! Or, at least, conventionally! But, sadly, fatally! I’ve related this particular story before.

I’m a bit of a belt-and-braces-and-a-bit-of string man, meself! I hate watching models crash.

PB

Edited By Peter Beeney on 25/03/2011 14:15:46

Edited By Peter Beeney on 25/03/2011 14:19:00

Tom Wright 225/03/2011 14:18:17
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Here here! Peter.
 
TW2.
Tony Smith 725/03/2011 18:55:28
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I have this feeling that ESCs are more likely to fail than other bits of airborne electronics. Is there any special reason that this would be the case? Its really that feeling that made me fit a separate UBEC to my Cub, rather than any calculation about load from the servos etc.
Tim Mackey25/03/2011 19:13:55
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There is absolutely no way to guarantee that an overheating ESC will not affect the BEC circuitry - they almost always share the same PCB, and probably several tracks and components. I remember well flying my mates Ripmax Mustang on a slope session, and upon just trying the motor to check it was all working in case it was needed for the landing etc, and found no increase in speed. I questioned this with him, to be told that he had left the large rubber band on the cowl to stop the folding blades flapping around !
A superbly realistic plume of white smoke started bellowing out from the cowl, and as i was already turning back to the slope face wit full control, I thought we might get away with it. Unfortunately, controls were lost on the final approach, and the model "arrived" just short of the stone wall. Upon examination, the ESC was burnt to a crisp.
Tom Wright 225/03/2011 23:14:29
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Here here Tim.
 
TW2.
Tom Wright 225/03/2011 23:38:37
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At the field today i watched a guy landing an MX2 that promptly wiped the U/C off "not hard to do on that model" it was sat on the runway with the prop stalled ,while the pilot was making excuses , i noticed the tx throttle was still at near half way ,and promptly closed it for him ,to late that tell tale smell was already drifting across,and on investigation guess what no bec output ! I have seen this sort of thing happen so many times yet pilots just blame the esc,until i sit them down to explain that stalled motors draw horrendous currents that will often destroy the esc and the bec.
 
TW2.

Edited By tom wright 2 on 25/03/2011 23:39:49

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