Lucky Escape !

[RaySky]

I'm with dog on this, one battery for everything.
You say that if the vtx battery fails you can fly los. Have you ever tried taking the goggles off and try and find the plane in the sky. If the brightness of the sky doesn't blind you the sheer panic will!
The other problems are, remembering to charge all those batteries, human nature dictates that we will forget stuff.
And how do you monitor the second battery in flight? Most osd's will only monitor 1 voltage. If that voltage starts dropping fast you won't know till it goes dark... cue the panic!
In this video, I was monitoring the voltage and current, all of a sudden the current drops to 0, I had to assume the motor had stopped, which it did. Immediately turned for home and saved the plane. Without that info I would of wasted time and altitude trying to work out what was going on
http://youtu.be/zgvQRvi11_c

Brucey, Brill return to base and live another day  :D

To answer you question of "Have you ever tried taking the goggles off and try and find the plane in the sky. If the brightness of the sky doesn't blind you the sheer panic will!"
YES and very recently lol  ;)  and on my first FPV maiden flight of a new design over water, have a read if you wish... Got the T-shirt too  :+ http://www.fpvhub.com/index.php/topic,21339.0.html

I get the concept of reducing items that will fail to a minimum but by powering all the equipment by one power source means you have more critical catastrophic components, by that I mean items and components that may/will result in total loss of every system needed to perform all of the tasks they are intended to do!

If the dodgy soldered bullet connector had been on the battery instead of the ESC motor connection you would have had a blank screen with no OSD, Motor, Vtx or control... basically a bin bag job  :(
IF you powered the Rx and Vtx from a separate pack you could still have flown back to base  :)
If the ESC connection had melted and made contact to the other motor connection I would say the current flow would have fried the ESC and bottomed out the pack voltage and caused a total brown out of the Rx and Vtx.. result bin bag,
I could write loads of what ifs  ;)
The "what ifs" given as a rebuttal is humans make mistakes and can forget to charge battery packs and I agree  :) but I haven't done it yet, the cheapest OSD from HK monitors 2 voltages but not Amps  :(

I don't like single catastrophic points of failure so until I learn an expensive lesson I am gonna stick with separate packs powering separate systems,
I agree having an OSD with motor amps is a brill idea, I have to go with the much lower tech solution of listening to a AV until I have a full monitoring system,
When the screen goes blank and I have no idea what's happening I will turn of the TX and hope the RTH/failsafe Rx kicks in with power from either the ESC,Pack1 or Pack2 AND Prayer lol

[krikey]

raysky, if youre willing to check each battery prior to launch, including connections to each piece of kit, then the redundancy of three batteries is a good one. For this to happen and always happen, presumably you would make up a pre-flight checklist?

Im on the fence with this one as there are also some good reasons to have a separate battery for VTx to reduce noise too, however, youre also carrying extra weight.

Perhaps ask yourself, whats most likely to fail, the battery(s) itself or the connections in some way. The more connections you have the more likely a failure due to bad soldering/disconnects after hi G manoeuvres including takeoff and landing.


Sent from my iPad using Tapatalk

[RaySky]

raysky, if youre willing to check each battery prior to launch, including connections to each piece of kit, then the redundancy of three batteries is a good one. For this to happen and always happen, presumably you would make up a pre-flight checklist?

Im on the fence with this one as there are also some good reasons to have a separate battery for VTx to reduce noise too, however, youre also carrying extra weight.

Perhaps ask yourself, whats most likely to fail, the battery(s) itself or the connections in some way. The more connections you have the more likely a failure due to bad soldering/disconnects after hi G manoeuvres including takeoff and landing.


Sent from my iPad using Tapatalk

Krikey, that's a well balanced posting ;)
I think we have come full circle on this topic as it started with a badly done battery connection at the manufacturing stage of which non of us has any control over other than to purchase the best packs we can afford... and even then can we be completely sure?

I am going down the low cost route to enjoy FPV but even if I had hundreds or even thousands of pounds to spend I still would not be happy putting my complete and utter trust in one single battery connection and pack!
In no way am I trying to re-invent FPV or change anyone's personal choice of how to power FPV equipment,
I too am still on the fence as you say  ;) a lot to be said for one pack system... Plug and Play  :D Enjoy

I have a feeling that most who prefer a One Pack System are the same who may also fly quads and multi rotors!
With a fixed wing craft the weight of an additional pack almost becomes a secondary thought in my mind.

Yeah its a pain charging the HK HD wingcam and the Vtx packs AND the Main Packs TOO Grrr
All I need is the RTH kit in the form of the T1000FC and I will be out there  :D
And an OSD would be nice too but that's for later on once I have enjoyed my first complete FPV flight of more than 5 mins lol

[skyscraper]

The usual reason to have 2 batteries each powering a separate system is to try to stop noise getting in to your video feed.  However the reason noise gets in in the first place is usually down to poor layout anyway. (Ive expounded my ideas on using a power hub several times so wont go into it again here) But batteries powering separate systems isnt redundancy.

Redundancy is a different matter. In that situation you would have 2 or more batteries powering the whole system ( or one powering the system and a small one as a backup etc), but the batteries running the system are being monitored continuously for failure. If a failure is detected, then the system routes around the bad battery to another or others and alerts the pilot what's happened, while continuing hopefully on your way back to base.

I can visualise a compact backup system with a small battery which fits legal requirements ... In the event of main battery failure, power would be disabled to the the motor but  power would go to RC, and Video giving time to land and then powering RF beacon to find the model... This is also more in line with legal requirements of failsafe from CAA

regards
Andy

[jamesb72]

I can visualise a compact backup system with a small battery which fits legal requirements ...

You can get battery backup systems for RC, like the scorpion Backup Guard which is used widely in RC Heli's, it has a small internal 2S lipo and regulator, and monitors receiver voltage (typically 6v), and if this drops it switches in to provide power (at 5v, so enough to run your FBL unit, receiver and servo's to provide control). Obviously with an RC heli if the flight battery, or ESC/BEC fail, this will allow you to autorotate and save the model - your telemetry will alert you immediately when receiver voltage drops etc, so its a good solution and fairly cheap - around £20. Also and importantly it doesn't reduce your reliability as this is completely separate to your primary power setup (no extra connections/switches etc are needed), so only cuts in when that's already failed.

The extra complexity to do the same for FPV is you need 12v and 5v outputs (for vtx and rc gear) but if you could come up with a similar concept (a backup system independent of primary power setup which only cuts in when that has failed) you could be onto a winner.

Having something which runs multiple batteries for backup normally means you would need to route your primary power through this single backup/switching unit, which then becomes a single point of failure (on output side), also to make this reliable it would be expensive and that puts people off, which limits sales which makes it even more expensive.

Replacing a battery and a bit of wire, which are both fairly reliable passive components with anything more complicated to provide resilience is always going to be a hard sell, but a backup box I think would be easier to find a market for.

Large RC planes I understand run two separate RC systems with seperate power/receiver/servo's etc to provide some chance of recovering (or safely ditching) a model in the event that one system fails, but again thats a lot of extra complication.

[krikey]

Forgive my naivety but could you not build in redundancy by supplying 2 batteries in parallel to the system. If one battery were to fail, would the other not simply take over? Could diodes be used to ensure that the flow of electricity were always to go in the right direction and perhaps not back into the failing battery?

Sounds too simple to me :)

[jamesb72]

Diodes have a voltage drop and cannot cope with a lot of current ie 40amps or higher typical motor power.

Parallel batteries only add capacity if one fails short it would take out the other so your potentially doubling your risk of failure.

[Charliewalker]

Diodes have a voltage drop and cannot cope with a lot of current ie 40amps or higher typical motor power.

Parallel batteries only add capacity if one fails short it would take out the other so your potentially doubling your risk of failure.

I'm no electronics bod but surely if you run two packs together like I do (simply to double the capacity) for quad & plank with power leads on both going to the esc, if one fails then surely the other would keep working wouldn't it? 

[jamesb72]

...surely if you run two packs together like I do (simply to double the capacity) for quad & plank with power leads on both going to the esc, if one fails then surely the other would keep working wouldn't it?

It might and it might not, if a wire fell off the second pack and didn't short on anything - yes, the first pack will carry the load.

If a cell dies in one of the packs and that pack drops from 11.5v to 7.5v, it will pull the other one down, possibly get hot or worse.

Also running two packs you have some kind of splitter so potentially your adding extra joints/connections which potentially are extra failure points.

Lastly if you always run two packs they are sharing the current load, over time packs get weaker as IR increases, so it may be that one of your packs couldn't actually keep a quad flying, which you won't know about until one of the packs or joints fails. Also unless you have telemetry, if one pack failed, your flight time would half, and you may not realise until 2/3 through the flight when it falls out of the sky.

You can worry too much about these things, modern packs are pretty reliable, so whilst bad things can happen, thats true of pretty much everything we use so spending a lot of time or money on one single point of failure will never guarantee something else won't fail anyway. An ESC or motor failure (probably much more likely) will take out a quad and some hex's. A flight controller failure or glitch will take out pretty much anything.

[Charliewalker]

jamesb72

Yes I understand what your saying, Maybe an esc or motor failing, but a wire joint breaking, then coming out of the shrink sleeve, then finding something of the opposite polarity (if that's the right term) to short on I don't think so, as I said I'm a electro numpty, but wonder would/could a lipo pack loose a cell just like that or would it happen gradually.   

[RaySky]

Hi All,

Some very interesting points made by everyone, I think if you are personally happy with your own setup then and trust the equipment installed then you've done more than enough  ;)

Some say the zippy compact packs are rubbish and some swear by them...
It shocked me the wire came away and hadn't been soldered,  fortunately I wasn't in full FPV mode so it didn't cause any hassle,
On the flip side of the coin it was in a Delta... and if one of the 2 servos failed you have only 2 options... Screw it into the ground Clockwise OR Anticlockwise LOL

Everything mentioned is in my thoughts for the MK2  :D I know it will be much bigger and therefore much more cost of which I want to keep in one piece,

Ray