Skywalker 168cm FPV plane - Page 1059 - RC Groups
Oct 10, 2012, 10:54 PM
FPV Crash Test Dummy
Quote:
 Originally Posted by subsonic I don't want to beat the one vs two battery argument any more, as it's been done to death way too much anyway. All I want to say is that you'll just have to try and look past this "single point of failure" being a problem. Your FPV plane is full of single points of failure, the most critical and fault prone being the pilot, followed by all the hundreds of mechanical and electrical components that in series keep your aircraft in the air. If any one of them fails, you're pretty much down, so trying to avoid that by adding complexity is folly in my opinion. Sub.
I predict 1 battery vs. 2 batteries will eventually become the only remaining political parties.

Seriously though, I'm one of the folks that runs two batteries with a dedicated circuit for the flight pack. For me the decision was not so much about single points of failure. It was instead based on two rather simplistic ideas: (1) The probability of a relatively high current carrying circuit where the battery could fail or the ESC could fail and take the integrated BEC with it, compared to the probability of a few extra hardwired connections on a relatively low current carrying circuit failing. (2) Even if you assume that the probabilities are equal, I still have at least a chance of landing my plane with RTH or radio control and not suffering a total loss of the aircraft.

Obviously a large part of the premise for this logic is around the assumption that flight pack batteries are more stressed and therefore more likely to fail than a receiver/FPV battery, and/or that it would be more likely that a BEC would get taken out by an ESC failure than a standalone BEC failing by itself. Most built in BECs also do not appear to be designed to handle the current draw of a large FPV platform with lots of servos and other accessories, which would further increase this risk.

I'm not saying the logic is bulletproof and I would never try to convince others which way to go. I'm just saying that its not necessarily as simple of an argument as complexity versus redundancy. The logic is at least as valid as some of the "experts do it" reasoning I've heard.
Last edited by vewdew1; Oct 10, 2012 at 11:05 PM. Reason: i r gud spelr
Oct 10, 2012, 11:07 PM
Registered User
Quote:
 Originally Posted by vewdew1 ...and/or that it would be more likely that a BEC would get taken out by an ESC failure than a standalone BEC failing by itself. Most built in BECs also do not appear to be designed to handle the current of a large FPV platform with lots of servos and other accessories, which would further increase this risk.
It should also be noted that a combined ESC/BEC, while separate circuits, have one thing in common - the heat sink. Linear BEC's especially generate considerable heat so taking the BEC function off the ESC will lower the ESC's temperature. And because the circuits in the combined ESC/BEC are separtate anyway, you are not really adding a separate failure point by using an outboard BEC. You actually lower the likely hood of failure because of the reduced heat on the ESC. Just make sure you use really good components.

Cliff
Oct 10, 2012, 11:15 PM
Build Something
Quote:
 Originally Posted by cliffkot You actually lower the likely hood of failure because of the reduced heat on the ESC. Just make sure you use really good components. Cliff
Using a separate BEC surely is not a redundancy / reliability question is it? If my ESC's internal BEC was up to the task of 6 flight servos plus pan / tilt, I'd not hesitate to use it. Fact is, they aren't tough enough for the job, so BEC it is.
Oct 10, 2012, 11:21 PM
Registered User
Quote:
 Originally Posted by Meez i still remember an old chap told me this, 'add more stuffs and you add more evil on the plane'. Kind of agree to me.
Wellll... not always. 2 magnetos are always good. 2 engines are generally better than 1 if you've got the rating and keep your practice up.
 Oct 11, 2012, 12:50 AM Registered User The "two is better than one" argument only works if the system still functions with only one. ian
Oct 11, 2012, 03:36 AM
Flying Zayin

# BEC it is.

OK OK OK
Thank you everyone, so BEC seems to be something that a fat bird has to have, more or less everyone agrees on it.
Another dumb newbeish question comes! (I'm having more up my sleeve)...

Here is a connection diagram (shamelessly borrowed from Castle Creations).
The BEC cable is plugged into a vacant socket of the receiver, while the cable going from the ESC to the receiver has its red wire plucked out. Clear enough.

Now, the question:
Why waste a socket in the receiver, and what if there is no vacant one? Will it be a legitimate option to pluck both red and black wires out of the ESC cable and replace them with those from BEC cable? (see the second picture)

This solution seems obvious to me, perhaps a bit too obvious, so I suspect something might be wrong with it.

Thanks again,
- Mark -

### Images

Oct 11, 2012, 03:50 AM
Build Something
Quote:
 Originally Posted by Cathay Stray Will it be a legitimate option to pluck both red and black wires out of the ESC cable and replace them with those from BEC cable? (see the second picture)
Yep, that will work. You don't need the black wire from the ESC servo plug as all the grounds are common, and all the +ve and -ve pins are connected in parallel inside the receiver.
Oct 11, 2012, 04:01 AM
Flying Zayin
Quote:
 Originally Posted by subsonic Yep, that will work.
Thank you. What made me wondering was that it appeared too obvious, and why don't everyone just do it this way? It seems more simple than traditional way and doesn't jam the receiver with an extra plug.
Oct 11, 2012, 06:38 AM
Build Something
Quote:
 Originally Posted by Cathay Stray Thank you. What made me wondering was that it appeared too obvious, and why don't everyone just do it this way? It seems more simple than traditional way and doesn't jam the receiver with an extra plug.
Well it would mean that your ESC and BEC would be permanently Y'd together at the receiver plug which might me inconvenient. If I have a spare slot in the RX, I just plug in BEC power there.
Oct 11, 2012, 08:49 AM
Crash=start of next project
Quote:
 Originally Posted by Meez i still remember an old chap told me this, 'add more stuffs and you add more evil on the plane'. Kind of agree to me.
Keep it simple. Also, the biggest single point failure in my experience is the pilot.
Oct 11, 2012, 09:02 AM
Crash=start of next project
Quote:
 Originally Posted by Cathay Stray Thank you. What made me wondering was that it appeared too obvious, and why don't everyone just do it this way? It seems more simple than traditional way and doesn't jam the receiver with an extra plug.
Take a look at the ground loops page too. We tend to forget about these but in certain cases, they can be problematic. We are always chasing them on satellites.
Oct 11, 2012, 10:20 AM
I tell her RC is cheap !
Quote:
 Originally Posted by subsonic Well it would mean that your ESC and BEC would be permanently Y'd together at the receiver plug which might me inconvenient. If I have a spare slot in the RX, I just plug in BEC power there.
Most of us use UHF receivers with 9 or 12 channels, so there is mostly a spare slot available. If you use an OSD, some od them use a PPm connection so you don't even use the servo slots on the Rx.
Oct 11, 2012, 10:39 AM
Flying Zayin
Quote:
 Originally Posted by CN I Dawg This may help you, http://fpv-japan.com/technical-info/...r-for-the-bec/ Take a look at the ground loops page too. We tend to forget about these but in certain cases, they can be problematic. We are always chasing them on satellites.
Thank you
 Oct 11, 2012, 11:01 AM Mini Obsessed Well I look at other systems. For example, a car. 12V system. There isn't some 5V stuff thrown in there and then a different battery. Once you add another battery you of course add weight. You also have a second battery that you need to make sure was charged. Kind of like people who use the gopro for their video out. If they don't wire up power from the main system into the usb, they have the worry of a battery fail on the gopro which wipes out their video. I built the system I use by reading over other successful systems. I also did a lot of research on fpvlab as that seems to be where more of the hard core fpv guys go who have been doing this for a lot longer time. I went with product that works together so I could have as close to plug and play simplicity as possible. I have only been doing this (fpv) for over a year, and started with a Twinstar II. My problem on that plane was that there really isn't that much room for all the gear and you can't get great separation without a lot of work. Also, 2 motors, and 2 ESC's mean another potential issue if one of those goes. I changed to a skywalker in july of this year. I simplified my system to keep the wiring to a minimum, as well as trying to keep away from cheaper product made by companies that didn't have a lot of support. I also asked a lot of questions of both the owners and designers from Immersionrc, and fatshark. Since some of the more notorious fpv guys use their equipment, I looked at how they put their systems together and tried to keep close to that. Outside of bad elastic bands, and a bad motor mount, I have had no issues. Usually, the issues are on the electronic side. So I do think that there are ways of making your chances better in this hobby and there are a lot of ways to do the same thing, but just because they work doesn't mean they are the right way to do it.
Oct 11, 2012, 11:07 AM
Mini Obsessed
Quote:
 Originally Posted by carguy1994ca Most of us use UHF receivers with 9 or 12 channels, so there is mostly a spare slot available. If you use an OSD, some od them use a PPm connection so you don't even use the servo slots on the Rx.
Most of us? CG....you must have left Montreal FPV too early to see the consensus at the end of the event.
Ummmmmm no.
I think a lot are going to the 8 channel diversity.
That still gives you lots of channels.
you can use a servo y connector.
I have my bec and my rudder plugged into a Y cable and then into the rudder channel.
In my case my rudder is just the signal as the autopilot unit provides the power to the servos.