BEC vs separate battery for receiver

[BoneDoc]

What do you guys think? I was thinking of putting a dual BEC since I'll be running 2 x 6S 5000 in series. That will sure keep the weight down, and it will have the redundancy of having 2 systems for backup.

Any input is greatly appreciated.

Thanks
Josh

[Ed Lyerly]

IMHO .... anything over 10S .... use a seperate receiver pack.
Ed

[BoneDoc]

it's 6S x 2 really :). So each 6S connection will have a BEC piggyback on it, hence the redundancy. Any particular reason why it should use a receiver pack? And if he does, he'd need two, plus two switches, and two regulartors.

[GordonTarling]

If you want true redundancy in your system, you'll need to supply each BEC from its own 6-cell pack rather than both BEC's from the one 12 cell ( 2 x 6S) pack. You'll also need to be careful about connecting two BEC's to the same receiver. Personally, I'm not a great fan of such a system, as you're relying entirely on BEC's to supply the current and have found from experience in my Tiger Moth that sudden servo commands can cause momentary glitching. The system I run uses the best of both worlds IMHO and comprises a BEC and a receiver battery fed to a battery backer and then to the receiver. Under normal flight loads, the battery provides most of the current and is a low-impedance source for those sudden servo demands, while the BEC will still be sufficient to fly the model should the battery fail for any reason.

[BoneDoc]

That's what I was planning on doing. Each 6 cell will have its own BEC. What size Tiger Moth are you talking about?

So you have tried successfully to put a receiver battery and a BEC together?

Thanks
Josh

[pentaxman]

I would be tempted jut to go for the Rx pack only & not use the BEC at all.

I assume it is a large plane due to the forum it is in, so a Rx pack is hardly going to make much impression on the flight manners of sucha machine.

[F1 Rocket]

I would not depend on the main packs to provide power for the control system in a large plane. I demagged a motor once in my DPM Clipped Cub and the packs were stressed to the point of failure in a very short amount of time. If the control system was powered from those same packs I would have lost the airplane. Used one of these in that project, powered with a separate 2s 1500 pack.

http://www.espritmodel.com/index.asp?PageAction=VIEWPROD&ProdID=5710

This setup is good for 7.5 amps and is what I am currently using in my 74" EF Yak as well. The Yak is has 5 JR 8611A digitals but is a bit smaller than your project so you may need something that can handle more power. For light weight redundant setup check out Gary's post (#5) here:

http://www.rcgroups.com/forums/showthread.php?t=681634

What ever way you end up going I would keep the main and control power systems separate.


Danny

[BoneDoc]

It's a 35% Dalton Aviation 260.

The reason for the BEC is that after all the hard work I've done to bring the weight down to sub 20 lbs RTF, why add an unnecessary 1/2 pound to the weight of the frame?

F1, when you demag your Cub's motor, did you notice immediate power dropout? At any rate, a BEC works to bring voltage down to 6V, and less than that, it'll just act as a conduit. The reason why I initially feel that it's just as safe is because I'm using two separate 6S packs, hence true redundancy.

[staggerwing]

I picked up several 2100 MAH NIMH RX packs awhile back AA size----always use one seperate for the RX in HV elecs ----too much of a risk to lose a larger plane w/ a BEC & the extra weight is not a problem----use it if possible to gain proper CG.
I do however understand your particular need not to add weight

[F1 Rocket]

F1, when you demag your Cub's motor, did you notice immediate power dropout? At any rate, a BEC works to bring voltage down to 6V, and less than that, it'll just act as a conduit. The reason why I initially feel that it's just as safe is because I'm using two separate 6S packs, hence true redundancy.


When the motor demagged everything went south very quickly. There may have been enough to run a BEC but it could have fried everything and I would have lost control. As it was I was able to make an uneventful landing.

Even though you plan on connecting a BEC to each pack both packs are tied to the same ESC and motor. If something fails upstream of the packs you could still lose both packs and control system power. Granted, there are a lot of other things that can fail and cause a crash but what you are planning on doing is relying on the most stressed system in the plane to provide additional power for control.

[BoneDoc]

Does anybody have actual experiences with running dual BEC from the main pack?

[kmp647]

I use a 2 cell 2100 lipo with a voltage reg, 10 amps
small light and reliable, and seperate from the powersystem
its about 4 oz tops

[pentaxman]

Does anybody have actual experiences with running dual BEC from the main pack?

Tested such a system on my Mosquito (74" wingspan), but I found one ESC to run much hotter than the other. With 1 of the 2 BEC's wired out, the temps dropped back to normal so I now use the BEC on 1 ESC only.

I believe others have found similar issues running 2 BEC's although I seem to recall CC stating that with some of their ESC's you can run the setup you are talking about with no problems.

[FlightAddict]

I've got 10S4P 8000mah and 2 Koolflight 6v UBECs - one to receiver, one to servos (via an ElectroDynamics EDR-111) - in a Chip Hyde Double Vision. Has worked well for about 50 flights so far. Was originally aiming for redundancy, but there were some special things you needed to do with the BEC's to allow this, and I never pursued it. You can check for further info with the Koolflightsystems.com guy at jsmeyers@earthlink.net if you are interested in going this route and no one who has done it chimes in.

Attached photo shows the 2 BEC's peeking out from under the 2 5S packs. The BEC's aren't attached each to a 5S, they're attached at the 10S point.

[FlightAddict]

Another recently updated thread - http://www.rcgroups.com/forums/showthread.php?t=681634 - addresses the issue I brought up. See GWRIGHT's post #5...

"Jeff will modify a matched pair of U-BEC's with extra circuitry to eliminate the "backflow" from one to another."

[BoneDoc]

Thanks for the pic,

So what do you connect your BEC to in order to route the power to the servos only?

[AmpAce]

I've had excellent reliability with separate BECs. I've never had one fail.

I think that in striving to provide redundancy in your feed system to the flight controls, you are just introducing more risk into the system. Running two live systems
to the flight controls at the same time just doesn't make sense. That's why ESC manufacturers recommend disconnecting the current feed wire to the reciever when using a separate BEC. Even with the modifications mentioned in post #15, I would still be concerned about reliability.

If you can find some kind of reliable switching device that will sense when voltage drops below a certain point in one system, and automatically switch to another system, you might be O.K.

Apparently you are dealing with a twin engined model, where each 6S power system is completely separate. If not, and your two 6S packs are wired together in any way, you aren't really gaining anything by using two BECs, except for any possible advantage in the BECs themselves and the wiring to and from them.

I think your safest way is to use a separate pack to power your flight control system. If you don't want to add that much weight, then get the best BEC you can find, and use it.

I have never used a separate pack, and in the event of a motor failure, or short, or anything downstream of the ESC that reduces the voltage in the battery, the ESC will shut the motor system down, with still enough voltage remaining in the battery to provide control of the plane through the BEC.

My $.02.

AmpAce

[BoneDoc]

Ace,

So you're only using 1 BEC? In my position, I'll be using 5 x HS 5955, each capable of several amps at full stall.

[AmpAce]

Yes, I've never used anything but a separate single BEC. I don't have a plane flying that is large enough to need that much amperage.

My biggest one flying now is a Senior Telemaster that uses 6S-2P lipo for power. I use a single UBEC to power the flight system for it. The servos are only standard sized servos, and I don't really know the amp draw spec's for them.

You haven't said what plane or power system you are using, and anything larger than what I am using is out of my range of experience. I would check out what some of the pros are using in their big (30%+) 3-D electric planes. These things tax flight systems to the utmost. I suspect that most of them use a separate pack for the radio/control system.

Even though your servos draw several amps when stalled, in normal use, if your linkage isn't binding, etc., they should never draw that much amperage, and usually only two or three of them at a time would normally be working at maximum load.

Probably for the lightest, safest system, not requiring reduncancy, I would use a 2S lipo pack with a regulator to reduce the voltage going to the flight system. I'm not sure how much amperage a regulator will handle, though. Also there has been quite a bit of development and improvement made in separate BECs lately.

I don't really know just what is available, but I'll guess that with all of the large 3-D electrics gaining popularity, someone is making a separate BEC that will handle substantial amperage.

Good luck with your quest, and keep us posted.

AmpAce

[BoneDoc]

The problem with dual 2S lipos + regs + switches, is that they add close to 1/2 lb to the whole plane. Why waste all that weight, especially since I've gone through pretty heroic measures to get the plane to be as light as where it's at right now?

Check out my 35% Dalton Aviaton Extra 260 thread

Dalton Aviaton 35% Extra 260 (http://www.rcgroups.com/forums/showthread.php?t=694403)

[sun.flyer]

I picked up several 2100 MAH NIMH RX packs awhile back AA size----always use one seperate for the RX in HV elecs ----too much of a risk to lose a larger plane w/ a BEC & the extra weight is not a problem----use it if possible to gain proper CG.
I do however understand your particular need not to add weight


I agree here with staggerwing. I personally would much rather run my rx off of a seperate pack then off of a BEC/UBEC. For me to many eggs in one basket is not always a good thing. Saving weight is great but being able to land my plane should something happen to the motor/main packs is much more important to me.

I am working on an 85" electric now that will be run off of a seperate rx pack.

Tim

[GWRIGHT]

Although I understand your concerns,..they're not based an real-life data. I'm using these systems in things now, and have used them in others in the past and they provide redundancy and reliability far above a single regulator setup. The two "live systems" as you put it are simply paralleled input power, which has been done for many years. Back as early as the late 80's and early 90's we were using two batteries and switches that were smaller than normal, in helicopters, to provide redundancy in rx power, wiring, and switches, so it's nothing new, just accomplished now with U-becs and lithium packs. Also,..the reason ESC manufacturers recommend cutting the feed wire from a BEC equiped ESC when using a seperate power source is not because it "just doesn't make sense",.. it's because of the risk of "back-feeding" the ESC,..and that issue is eliminated with the redundant U-bec option when you get the modified ones.


I think that in striving to provide redundancy in your feed system to the flight controls, you are just introducing more risk into the system. Running two live systems
to the flight controls at the same time just doesn't make sense. That's why ESC manufacturers recommend disconnecting the current feed wire to the reciever when using a separate BEC. Even with the modifications mentioned in post #15, I would still be concerned about reliability.
AmpAce

[BoneDoc]

Gary, so do you think it's feasible? What have you put these dual UBECs in so far? What's the largest plane you've had them in and what kind of servos were they powering? AUW?

Thanks for your input and expertise.

Josh

[GWRIGHT]

Reading further, I see the comment about being able to land should the power system pack fail, and the comment about weight. In the setup I'm talking about in the Yak,.. I didn't worry about weight, so I'm using two 910mah 3-cell packs and two u-becs,.. that's two ounces of battery and one ounce of ubec,..and I could easily use 480's or even 350's and save a couple more ounces,.. down to 1/4 lb total instead of the 1/2 lb mentioned. I use about 200mah total in 3 flights, the the smallest packs you can find would actually work. If something happens to the ESC and takes out the flight packs, I can still land, since the radio is using the seperate 910 packs and not the 12S/5000 pack. In another plane that's only 10S instead of 12S, and low current at 50 amps peak instead of close to 100,.. I'm using the dual U-bec's straight off the flight packs, without any seperate packs.
If you'll remember the first of the "large electric aerobats" that was on the cover of S&E modeler a few years ago. It was a 33% extra with a dual C-50 setup, on two 10S/8000mah packs. I did the test flights on that plane, and it had FOUR U-becs in it,.. Two on each of the 10S power system packs, with the extra circuitry in them for backflow.Never a problem with it either. Many people are skeptical of things they've never used,..but be carefull about saying something is "wrong/bad/doesn't make sense" and giving advice on something you've never actually done yourself ;)

[GWRIGHT]

I did the first few flights on Rob's large extra mentioned in an earlier post. It had some hefty digitals in it, although I don't know which ones. It was a 30 lb plane and 6000 watts.
My Yak is smaller, at only 16 lbs, but I have 4 9155's and a 9152 in it,..thats close to 200 oz/in per ail and elev, and a little shy of 300 oz/in on rudder. All digital. Plane has a little over 4.2Kw on cold packs, and has been as high as 4.4Kw on really warm packs fresh off charger.

Gary, so do you think it's feasible? What have you put these dual UBECs in so far? What's the largest plane you've had them in and what kind of servos were they powering? AUW?

Thanks for your input and expertise.

Josh

[BoneDoc]

So do you think that 2 UBECs with the backflow circuitry tapping off each of the 6S is pretty safe? I've yet to blow an actual flight packs before.

[Tipover]

Do the motor power source batteries actually fail often on these larger planes? You guys are scaring me :D Or is the concern more of a single U-BEC failing under to much servo load?

Kevin

[Smash McCrash]

I haven't seen it mentioned here, but, if you run one off of the "lower" 6S pack and the other off of the "upper" 6S pack, the grounds will be at different voltages, unless there is something in the BEC's that I don't know of to isolate the output grounds from the input grounds. If there is nothing to isolate them, you will short one out just connecting them into the circuit. If there is, I don't see a problem with it. I would talk to KFS and get the matched ones.

Mike

[AmpAce]

The main problem with Doc's proposed system, as I understand his description, is that he is treating his power system batteries as being two separate packs, when in effect it is one.

I agree that two small battery packs with separate BECs and wiring systems to feed the flight control system, should be very safe, provided that he uses "no backfeed" modified BECs.

I didn't even realize that this type of BEC was available. I've never had cause to need such a system. My budget dosen't allow this kind of sophistication in my models. Obviously, I've been talking 'way over my head.

Just trying to help. I had not way of knowing what type of model BoneDoc was building.

I"ll now bail out and shut up, as I should have done before I even posted to this thread.

AmpAce

[F1 Rocket]

Josh,
Here's some info on how much current your servos are likely to draw. When I built my 74" Yak I checked the current draw on the JR 8611A servos. I used the completely unscienific but practical method of loading up one of the elevators until the control horn was about to break off. The highest I saw was 1.6 amps (grabbing hold of the servo arm and back driving the servo a bit pushed the current to 2.1 amps) so five of these puppies would be pushing 8 amps (plus a bit more for the rec) in this condition. I don't think it gets anywhere close to that in flight so I'm comfortable with the single 7.5 amp rated BEC I'm using. The HS 5955's you are planning on using shouldn't draw any more than the 8611's.

After reading through all the input so far I think I would use a pair of the matched UBEC's and a single pack sized for the amount of flight time you want between charges. You could probibly get by with a 3s 800-900 sized pack. These are only around 2.5 oz. Seems like a small amount of weight on a 20 lb airplane.

One last thing. I wouldn't use a switch as it's just one more thing to go wrong.

One more last thing. All of the above is for a 6 volt system.


Ok I'll go now


Danny

[BoneDoc]

I haven't seen it mentioned here, but, if you run one off of the "lower" 6S pack and the other off of the "upper" 6S pack, the grounds will be at different voltages, unless there is something in the BEC's that I don't know of to isolate the output grounds from the input grounds. If there is nothing to isolate them, you will short one out just connecting them into the circuit. If there is, I don't see a problem with it. I would talk to KFS and get the matched ones.

Mike

If that were true, then Gary would've short circuited his 10S 8000 mah packs already on that 33% conversion. Do you have evidence / real life data of such, or is it a theoretical speculation?

Btw, I appreciate ALL of your inputs, whether I agree with it or not. One of the things we tend to do is to be skeptical of new things. So please don't take offense when I debate your opinion. I simply want to get to the bottom of it.

[F1 Rocket]

Btw, I appreciate ALL of your inputs, whether I agree with it or not. One of the things we tend to do is to be skeptical of new things. So please don't take offense when I debate your opinion. I simply want to get to the bottom of it.


Playing with new toys and trying new ways of doing things keeps the hobby interesting. However, after a while (my addiction started in '75) you tend to let others be on the bleeding edge of things........... sometimes........ :rolleyes: well maybe once.............well........gee that extra battery in the Yak is just dead weight. Why I bet if I........................................just went to bed I'd wake up in the morning and go fly :D

[BoneDoc]

lol, true, true.

[GordonTarling]

BoneDoc - sorry for delay replying! The system I described is installed in a 1/4 scale Tiger Moth weighing 19 pounds. I am using a Powerbox 40 to handle power redundancy and both UBEC and receiver battery feed separately into this. I decided to do it this way because I have another large model which I very nearly lost when the receiver battery went flat. I did consider using two UBEC's, but didn't want to put all my eggs in the one basket!

[BoneDoc]

Thanks Gordon,
Who makes the powerbox?

[Smash McCrash]

If that were true, then Gary would've short circuited his 10S 8000 mah packs already on that 33% conversion. Do you have evidence / real life data of such, or is it a theoretical speculation?

It's just speculation on my part. If the UBEC's isolate input grounds from output grounds, you should be ok. If they are not, there will be problems.

Gary used 2 completely separate packs to power his system, they weren't put in series to power the plane as well. When they were connected to the system the grounds were referenced to each other.

Mike

I will try to get a drawing up to show, I just can't get it converted here at home. :P

[BoneDoc]

It was a 33% extra with a dual C-50 setup, on two 10S/8000mah packs. I did the test flights on that plane, and it had FOUR U-becs in it,.. Two on each of the 10S power system packs, with the extra circuitry in them for backflow.Never a problem with it either.

Looks to me that he had 2 x 2 setup, each of which has 2 UBECs that is mated to the same pack. What do you think?

[GordonTarling]

BoneDoc - Powerbox is made by - http://www.dual-power-control.com/e/powerbox_systeme/produktuebersicht/start.php

I see that the one I'm using has been updated and had a name change - now called the 'Powerbox Basic'.

[GWRIGHT]

Two 5S packs in series to make a 10S/8000 pack,.. two U-becs off there,.. repeat for the other side (second C50 setup),.. so, no shorting from the two negatives coming off different spots in the 10S pack, since it's basically two different power systems, they just happened to be geared to spin a single prop. I can see where you get that,.. the negative is at cell1, and the other negative at cell 6,.. so there could be a short,..unless the circuitry they put in the duel setups prevents backflow on both positive and negative, and I'm not sure of that. On my 90" E3D, I fly with 10S (two 5S packs) and have the duel U-becs running off all ten also. On my dearly departed Pitts, I had the duel setup running off one of the 5S packs in the 10S setup (wasn't paying attention making up the "Y" harness for power and put the u-bec leads on one side rather than the whole 10S pack). This worked also for a couple years before I tried to pull out of a flat spin too low with that plane (crash was not u-bec's fault, was idiot thumbs' fault <G>). The only issue with that is that you're drawing a bit more from one of the 5S packs in a 10S series setup (on recharge I'd see from 50 to 60mah difference in the two packs), but if you only run out 80~90 percent of the pack as you should anyway,..it's not an issue.

[BoneDoc]

I see your point, so I probably will have to go off the 12S pack if I do that...

[GWRIGHT]

Actually, they're only good for 10S input, so you'd have to go only on one side (6S) for input,..which really isn't a concern,..just something I think you should be aware of.

Also,..sent you PM

[feathermerchant]

BoneDoc - Read my blog. I set mine up to run off of one of the three 4S packs. Works great. As a bonus I can connect one pack and check the controls before I fly with no danger of the motor starting. Like Gary said the extra draw on the one pack doesn't seem to matter much. For redundancy you could set yours up like mine than add another small 3S battery and second UBEC.

[BoneDoc]

I may do as you said Bruce. Just out of curiosity though, is it not possible if I go with 2 x 6S wired in series with each UBEC coming of each pack?

[GWRIGHT]

would need to have Jeff confirm or deny that the negative leads are also in the blocking circuit. If only the positives, then you would create a short as someone mentioned earlier.

[feathermerchant]

Right Gary I fear it would let the smoke out.
BoneDoc if you're that concerned about weight, you might have to build another from scratch. Good balsa is a big part of a light build. Most kits have pretty heavy balsa.
My 1.5X Stevens Edge ended up at ~9lb. For a 75" Edge that's not too bad.

[GWRIGHT]

9 lbs for a 75"er??? The 90"er in my avatar was 9 lbs with 20 sub-c roundcells in it <G>

[GWRIGHT]

Bonedoc,..where are you at in your ortho training?
I'd like to get your cv to our recruiter.

[feathermerchant]

Yup your 90"er was fabulous. I remember looking at it many SEFF's ago.
My Edge was just a scale up of a Stevens Aero Edge. It was to come out at 7lb but cubic scaling took hold... Then on the maiden I found out my tail was too thin.... So after the beefed up tail it needed a larger motor and batteries for CG. Anyway when I see the 12-15lb planes in this size, I know they can be done a lot lighter. Ben has an ARF Extra that is 72" and ~8lb. Can be flown on an AXI 4130 and 6S and the inexpensive JR DS 821's easily. Makes a very affordable setup.

[pentaxman]

Sorry still off topic but had to add this post fter seeing the last couple.

How about an 74" twin, brushless powered, running on twin 3S 2100mAH all coming in under 6lbs?

Or maybe a 74" single, brushless powered running on a single 3S 2100mAH coming in at 4.5lbs?

Sounds affordable because they are to me, and they fly just beautifully.

[BoneDoc]

Right Gary I fear it would let the smoke out.
BoneDoc if you're that concerned about weight, you might have to build another from scratch. Good balsa is a big part of a light build. Most kits have pretty heavy balsa.
My 1.5X Stevens Edge ended up at ~9lb. For a 75" Edge that's not too bad.


How about a 35% at sub 20 lbs? Since I've gone through heroic measures to get it down this low, that's why I'm scrutinizing everything I do / put inside the plane.

http://www.rcgroups.com/forums/showthread.php?t=694403

[blucor basher]

Since I've gone through heroic measures to get it down this low, that's why I'm scrutinizing everything I do / put inside the plane.

I can vouch for the "heroic" part. I was in his house. There's a fine layer of vaporized Carden all over everything...

[desert_flyer]

I run 2x VHVBECs from dimension engineering in a 74in extreme flight YAK on 12S powering 5 high torque MG servos. I use 3 flightpower 4S packs in series and both BECs tap off the full 45-50V.

With a Neu motor, this bird weighs 3oz less than it would with a YS160 and no fuel. It flies like a dream and I'm not going to change that by adding half a pound of li-ion cells. Have about 20 glitch free flights so far.

[BoneDoc]

So I guess the conscensus is that I can't tap off each of the 6S cells. That's fine. I'll just have to go either with VHBEC or add a small receiver 3S cells.

[desert_flyer]

Bonedoc,

No you absolutely cant go off the two packs separately. That would be an instant meltdown. The VHVBECs are rated for up to 14S lithium and after some discussion with the manufacturer, we decided to shoot for 2.5A peak on each.

You should read the following page:

http://www.troybuiltmodels.com/Servos.htm

They suggest shooting for 10A peak on a 35% model, in which case you would need 4 x VHVBECs :eek:

With that in mind, perhaps a lithium pack makes more sense

[BoneDoc]

That's a 35% model weighing 27-31 lbs. Mine is almost 1/3 lighter. UBEC is rated for 5A peak each, so two will give you the necessary 10A Peak.

[desert_flyer]

Is UBEC good for 12S (50V)?

[Steve H.]

I have been using a single UBEC in my 10s planes for a while, never thought twice about it till now. :)

[BoneDoc]

The HV version is.

Steve,
It's totally up to your level of comfort. I've put a lot of hours into this project, and I'm not going to let a possible battery failure throw it all away. Had it been a 50cc ARF conversion, no problem.

[feathermerchant]

A bud just crashed his heli Sat. Flew it twice. Checked batt both times. Midway thru flight, it quit responding altogether. Wire broke in battery (factory JR) harness. Cells are OK. Helicopters don't free flight well.
Redundancy is a good thing.

[GWRIGHT]

Off topic here,..but I found a heli can actually fre-flight very well. Was late 80's, hirobo shuttle,.. I kept wondering why the tail trim was changing in flight, was in hover, and it started slowly pirouetting, which accelerated to a medium speed, maybe 3/4 pirouette per second, slight climb, and I had nothing. Had to be the rx battery, as I was "pushing" it for just one more flight that day (yes, very stupid). I chased it for a mile or so in the car till I lost sight as it was climbing and spinning. Never saw that shuttle again.

[desert_flyer]

Bonedoc,

Which VH UBEC is rated for 5 amps? I could use one of those...

[F1 Rocket]

As I've said before. If you power your BEC from the main packs you are relying on the most stressed system in the aircraft for basic control. I do it myself in planes below 1.5KW but over this I don't feel the risk vs reduction in weight is worth it. I tend to prop my stuff for max power. There is a lot of power going through these systems and all at takes is being a little over zealous with the "go" lever and bad things can happen.


Danny

[feathermerchant]

OTOH with so much $ at stake I tend to be careful about propping up too much. A failed ESC or motor is going to cost a lot more to replace. So I guess it deopends on your preference. I have no flight packs in any of my planes but that's my preference.

[wrenwright]

I prefer the separate Rx pack over a BEC that has been added on.

[F1 Rocket]

OTOH with so much $ at stake I tend to be careful about propping up too much. A failed ESC or motor is going to cost a lot more to replace. So I guess it deopends on your preference. I have no flight packs in any of my planes but that's my preference.


I'm pushing over 3KW on 12s on a motor rated by the manufacture at 2.2KW on 10s so yes there is the possiblity something could go pop. But at least I'll be able to guide the smoking hulk :D The highest temps so far are:

motor- 140
esc-110
packs-120

Max current is around 83 amps, well within the spin 99's spec.I love the power but I do have to be carefull who I let fly the thing. If someone were to motor around at full throttle for too long things would most likely start getting hot.

[GWRIGHT]

Is that why i've only flown it once Danny? <G>

[edoc]

I am reading everything I can find, but I am still at a loss...
This size Electric is completely new to me.

I am converting an Aeroworks 120 size Yak 54 to electric. 10S 1.5 KW or more. About 10 lbs.
I had to replace the servos I had from an old Glow 1/4 scale project with 5 higher torque digital servos. Four, HS-6975HBs for aileron and elevator (140 0z-in at 6 V) and one Metal gear HS-5985MG for rudder (170 oz-in at 6 V).

I have a 6 volt UBEC that I originally was going to use before I recieved the Yak and found they recomended stronger servos than I was planning on using. Now I am concerned it will not handle the Amp load. I also have an inexpensive MPI 10 amp 6 volt voltage regulator (not swithching type). I am trying to decide how to go.
1. Would just one UBEC work with 5 high torque digital servos? Seems that it could be overloaded. Have any of you had problems with this setup doing aggressive 3D and really loading them?
2. Would a 2s Lipo with Voltage regulator be better? Hate the extra weight and the bother of charging an extra pack.
3. Can I just plug directly into my reciever or will the amp load be to much?
4. Do I need a seperate reciever battery? IF I need to, what is the safest, most cost effective way to isolate reciever from servos?

The cost keeps going up. Originally I chose this size Yak as the most cost effective way to have a larger 3D plane. I hadn't planned on the cost of these new servos and multiple UBECs etc.

Thanks for the help
Tim

[F1 Rocket]

Tim,

See my comments below in blue.


1. Would just one UBEC work with 5 high torque digital servos? Seems that it could be overloaded. Have any of you had problems with this setup doing aggressive 3D and really loading them? You could be pushing things a bit on a single UBEC.
2. Would a 2s Lipo with Voltage regulator be better? Hate the extra weight and the bother of charging an extra pack. This is what I run in my 74" EF Yak and it works great. I use a 2s 1500 mah but a 900 mah pack would work just as well.
3. Can I just plug directly into my reciever or will the amp load be to much? You can plug direct to rec.
4. Do I need a seperate reciever battery? IF I need to, what is the safest, most cost effective way to isolate reciever from servos? No need to separate the power.

Thanks for the help
Tim

[Tipover]

I personally feel the need for all these very high torque servo's on 10 lb birds is industry driven, in an attempt to sell more "stuff". I see so many over equiped and over weight planes being flown. They blast vertical, but not that much fun otherwise. It becomes a pile-on effect. Mores stuff...more weight...need more power. I've flown a YS 110 powered Funtana 90 with HS-645MG for two seasons with not an issue. I also have been flying my E powered Funtana 90 for close to a year now with only 4-JR9411. Only one servo on the elevator with a joiner wire(the old fashion way). These are only 82 oz/in servo's. There are no issues with blowback on these size planes that I can detect. I also use a single HV Ubec on the electric version on 10s A123 cells with no issues. For me, the attraction to e power is not needing to mess with all the extra stuff conventional to glow or gas setups...just charge and fly. I say live on the edge a bit and enjoy the lower weight. Sure, there's a small chance something will fail and cause a crash, but odds are I will be cause and not the equipment. All JMO

Kevin

[feathermerchant]

I have flown 5 HS5985MG's on several different planes on one BEC with no problem. One was a UBEC and one was a Medusa 3A 5/6V BEC. Both handled the load fine.

[BoneDoc]

I say live on the edge a bit and enjoy the lower weight. Sure, there's a small chance something will fail and cause a crash, but odds are I will be cause and not the equipment. All JMO

Kevin

If it were a 200 dollar ARF, I would agree with you. However, when it's an 800 dollar kit that takes 1 month to build doing it at a rapid pace, I think not.

I'm going with 2 UBECs, one off a 6S pack, the other, a separate 3S battery.

[Tipover]

If it were a 200 dollar ARF, I would agree with you. However, when it's an 800 dollar kit that takes 1 month to build doing it at a rapid pace, I think not.

I'm going with 2 UBECs, one off a 6S pack, the other, a separate 3S battery.

Agreed. On your 35% thats a smart move. The extra weight will be a small penalty.

I was replying moslty to edoc and his 120 size plane. Sorry, didn't mean to hijack your thread.

Kevin

[callen]

I have been using a single UBEC in my 10s planes for a while, never thought twice about it till now. :)

I use Kool UBEC 6 volt on my 10s 74" yak for over 50 flights with no problem. I use the Park 6 volt 3.5 amps also on lipos up to 8 cells.

[callen]

I prefer the separate Rx pack over a BEC that has been added on.

I've seen more crashes on 4 cell nicad packs than with a ubec. Seems most push the rx packs or forget to charge.

[edoc]

Thanks all for the great comments and help. I am still not decided, but I feel more comfortable with going either way.

Josh (BoneDoc) Your plane has 2x the weight and Watts, so I guess if I use one UBEC to your 2, I may be OK.

Even a little 120 size Yak is not close to a $200 ARF. I have over $2,000 spent already with motor, battery, servos and the least expensive part, the kit for $400 plus with shipping. So there is alot of incentive to keep her from crashing from a UBEC or Battery failure.

Tim

[edoc]

F1, I believe the 2S lipo with voltage regulator is the safest solution as long as I remember to charge and test the battery. I do have a history of a crash from a weak (properly charged) reciever battery, so I guess there is no perfect solution.

Thanks fmerch and callen, It is good to hear of others using the Kool UBEC with 5 high torque servos on 10S, this is exactly the kind of information I need. Can you do Blenders or Consecutive violent snaps with this set up?

Tim

[edoc]

finally, I personally feel the need for all these very high torque servo's on 10 lb birds is industry driven, in an attempt to sell more "stuff". I see so many over equiped and over weight planes being flown. They blast vertical, but not that much fun otherwise. It becomes a pile-on effect. Mores stuff...more weight...need more power.
Kevin

Kevin, I think you hit it right on the head. I have a set of older 80 oz inch plain resin servos that were the ones recomended for a 12 lb 150 plus size Cap 7 years ago. Why did they work then, but now we need 2 x the torque and MGs or at least Carbonite gears? Is it the need to sell more expensive servos?

Tim

[feathermerchant]

I never give power to the servos a second thought. I had te reatractable gear hang on my H9 P-51 (6 servos total) on maiden. I had it high and did not rrealize until I git it trimmed and a bit lower so the UBEC powered everything happily though the retract servo was bound. No problems. I would use your wattmeter to identify any binding in your linkages though.
As far as servo torques go, #1 they need to cover themselves. #2 Most things now are '3D' this or '4D' that and want 45deg or more throws. That requires a much stronger servo to work. #3 Seems like control surfaces are much larger and that requires larger servos.

[GWRIGHT]

When that cap was out 7 years ago (I think you mean the blue one that H9 had) we didn't have power systems yanking things around like we do now,.. we didn't fly with 45 to 60 degrees of movement like we do now, and control surfaces were generally smaller. Will lower torque servos work?,..usually yes,..however, they may not have the torque to hold full deflection during certain maneuvers. For instance,.. I once flew 69 oz/in servos all around on a large 90" span plane. I thought they were fine,..however, if I did consecutive rolls and increased throttle to increase speed, the roll rate would actually slow down. I didn't think much of it because that was rarely the case with that plane, it was always flown slowly in 3D. On one of it's successors, I put 132 oz/in digitals in place. Man, what a difference. Roll rate would increase from 1/8 throttle (level flight) to about 60~70 percent throttle, then remain the same. Roll authority was far better also,..almost like installing power steering. In another successor, that I'm flying now, I have 192 oz/in servos in it, and it's another level of improvement. From level flight at low speed, all the way to level flight at full throttle, doing consecutive rolls,..the roll rate increases the entire time. These servos have literally transformed the plane. Control is IMMEDIATE and responsive with authority. Did the $29 servos at 69 oz/in fly the plane?,..most definately. Do the $110 192 oz/in servos work better?,..YES,.. WORTH EVERY PENNY of the difference in my opinion.

[BoneDoc]

Well, I'll be using 5955 x 5 on my 35%, so I definitely would need the extra juice :D.

[blucor basher]

I have had good success with a single UBEC on 5 X 150 oz/in servos in my 2kW 74" Extreme Flight Yak. Also had good success in an identical plane for a customer with the MPi reg on a 2S 2000 lipo. I do enjoy not having to charge a battery on mine, however.

[Tipover]

finally,

Kevin, I think you hit it right on the head. I have a set of older 80 oz inch plain resin servos that were the ones recomended for a 12 lb 150 plus size Cap 7 years ago. Why did they work then, but now we need 2 x the torque and MGs or at least Carbonite gears? Is it the need to sell more expensive servos?

Tim

I think pilot arms are getting weaker ;) All kidding aside, I thing better servo's will always make a good pilot look better. But there needs to be a practical limit determined buy the weight, size, speed, and skill the aircraft is being flown.

I know a local guy that wanted to buy a 14MZ because he needed his control inputs to get to the plane faster. I'll never be able to keep up with that kind of flying :D

Kevin

[kilimaro]

I can give you my sad and empiric experience.
A battery failure means loss of every control over the plane.
My $100 extra 300 plane crached, my $70 esc burned, the $100 lipo battery, two servos, the propr, etc.
All above for saving a $5 rx battery?
Now I have different circuits for the control and the Engine.

[Smash McCrash]

Same thing happened to me, but all I lost was the $200 arf.

Mike

[callen]

If it were a 200 dollar ARF, I would agree with you. However, when it's an 800 dollar kit that takes 1 month to build doing it at a rapid pace, I think not.

I'm going with 2 UBECs, one off a 6S pack, the other, a separate 3S battery.

What kind of drop out diode and filtering will you use with two UBES's so they will work together and not against each other?

[callen]

F1, I believe the 2S lipo with voltage regulator is the safest solution as long as I remember to charge and test the battery. I do have a history of a crash from a weak (properly charged) reciever battery, so I guess there is no perfect solution.

Thanks fmerch and callen, It is good to hear of others using the Kool UBEC with 5 high torque servos on 10S, this is exactly the kind of information I need. Can you do Blenders or Consecutive violent snaps with this set up?

Tim

I do lots of blenders and inverted flat spins but I stay away from violent snaps just for the sake of I'm chicken. One or two and thats it. Gene Payson flew my Yak and did continious low level rolling circles. Not nary a problem.I'm not very good at rolling circles.

[GWRIGHT]

The ones that come with the duel u-bec system when you order it.

What kind of drop out diode and filtering will you use with two UBES's so they will work together and not against each other?

[BoneDoc]

Yep, I ordered mine from Jeff. 95 dollars shipped.

[desert_flyer]

Is anybody concerned about the disclaimer at the bottom of the koolflight page:

"*22 gauge wire and universal servo connectors are not designed for 5 amps current"

[edoc]

(I think you mean the blue one that H9 had)... These servos have literally transformed the plane. Control is IMMEDIATE and responsive with authority. Did the $29 servos at 69 oz/in fly the plane?,..most definately. Do the $110 192 oz/in servos work better?,..YES,.. WORTH EVERY PENNY of the difference in my opinion.

Thanks, I am feeling much better about the money spent on my new digital servos.
Yes it was the old H9 Cap sold NIB after I fell in love with Electrics. Converted my last glow plane this year. I am still looking for a home for the Cap's servos.
Tim

[GWRIGHT]

None of the wire we use is designed for the peaks we put through it. With the duel setup, you halve the load on each one anyway, so you essentially double the capabilities of a single plug and 22g wire. This is another reason I prefer the duel u-bec setup over some of the others that claim redundancy with two inputs, two regulators, feeding through one plug and connector.

Is anybody concerned about the disclaimer at the bottom of the koolflight page:

"*22 gauge wire and universal servo connectors are not designed for 5 amps current"

[desert_flyer]

What is the best way to connect the two UBECs. Should one be plugged into the battery channel and another into an unused receiver channel?

[tommy321]

Hey BoneDoc,

Might be too late since you said you already ordered your BEC, but...

Since you are using 5955's and sizing power systems, I figured I'd make sure you saw this thread on FG:

http://www.flyinggiants.com/forums/fg29/2927-hitec-5955-jr-8611a-actual-torque-measurements.html

According to his test, the 5955 on 6.0V maxed out at 270oz-in while pulling ~3.1A. (His point was that they were not 333oz-in).

Something to keep in mind.

Tom

[Tipover]

While on the subject, does anyone know what the most common failure mode of a switching type BEC would be?

I know Kool Flight has a disclaimer stating that "failure of this unit could also cause raw battery voltage to be applied directly to aircraft electronics, causing damage or failure". How would this factor in with dual no backfeed (isolated) BEC's? I'd think if one output shorted to the pack voltage, that the no feedback isolation diodes would be of little use. Your receiver and servo's would see whatever pack voltage comes though the shorted regulator. Scary thought.

Kevin

[feathermerchant]

You're right Tipover. Full 6 or 8S to the radio gear would render them null and void.
I have not seen or heard of that happening though.

[Tipover]

You're right Tipover. Full 6 or 8S to the radio gear would render them null and void.
I have not seen or heard of that happening though.

I'm hopeing no one's heard of it as well. Still the possibility exists...hence the disclaimer.

Kevin

[edoc]

I will be using 2, 5S packs in series. If my UBEC is overloaded will it be less likely to fail if hooked to 5S rather than the full 10S voltage?

If a UBEC is overloaded does it overheat and fail catastrophically or does voltage rise or drop prior to failure? Has anyone changed from a single UBEC to a double UBEC and found that the servos were more responsive?

Thanks again,
Tim

[Tipover]

I asked Jeff of Kool Flight about the possibility of raw pack voltage being applied to the radio and servo's. He said he's never heard of it in the last 6 years.

It would be an interesting test to set up a dummy load on a UBEC and see how it fails under overload conditions, as no one seems to know. Anyone have a good UBEC they'd like to sacrifice? :D



Kevin

[feathermerchant]

edoc - I'd ask the maker (Jeff) that question.

[Carlyle Harper]

Will a 12s1p pack of A123 cells have enough juice left to power the receiver and servos through a UBEC after the cells have dumped to the point of not being able to run the motor?