Author Topic: Lipos - Selection  (Read 1934 times)

Online Matt Hoyland

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Re: Lipos - Selection
« Reply #15 on: 27, January 2018, 12:30:04 PM »

On the previous point, my Dads view of his practise flights are a little idealised.  My recollection of normal practise is him having to repeat the first few manoeuvres because they went wrong so the flights and usage are rarely consistent.


The point being (at my Dads expense as is often the case  ??? ) the cells are robust to real world usage.  With this inconsistency and often breaking the rules they still deliver.


I am not one for over analysing and checking stuff, I just want to practise.  I glance at my Tx after a flight, if the voltage is over or equal to 37v then I think that's ok, if they're under 37v then I probably pushed them a little more than preferable.


Matt

Offline Yoda

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Re: Lipos - Selection
« Reply #16 on: 27, January 2018, 12:43:41 PM »
Mike, when flying in good conditions, sometimes never.


Matt, no, not using the wrong cells. Re throttle control, I'm doing ok thanks  ;)


1) I can't answer for you, AC or anyone else, but I do know Jason Shulman and the Thunder Power pilots are using the new 6000mAh batteries for F. I let you read between the lines. Why not ask Chip about doing the unknowns at a windy US Nats a few years back when using electric or Seba in the finals in South Africa 2013? They will have very different stories. BTW, if you are at or under 37V then you have basically emptied your packs so I'm not sure how you can say 5000mAh cells are not marginal. You have just proved that under certain circumstances they are.
2) Your models might be, but not everyone flys multi thousand pound models using the latest technology. Yes budget models can be light as well but not everyone can easily make the weight limit, especially when using larger cells. F3A is slowly but surely dieing, adjusting the weight limit to make it easier for people to compete would be a good thing for our sport. Remember, it isn't all about the guys flying at "the top".
3) Shortening the schedules may not be required, but it would have other advantages besides addressing the mAh issue.
4) Our opinions differ
5) We won't but as you correctly point out, other industries will and I'm looking forward to the day when my electric F3A aeroplanes have the same endurance as my IMAC aeroplanes



Offline Andy Shutt

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Re: Lipos - Selection
« Reply #17 on: 27, January 2018, 01:01:37 PM »

Thank you for the very interesting comments.


I think for the first of packs I will buy both economy and premium packs.


Andy

Offline Mike Wood

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Re: Lipos - Selection
« Reply #18 on: 27, January 2018, 01:07:43 PM »
Thanks Yoda

I think you made a good summary of where we are and the criteria for deciding how much to spend.

As you say, if we were only taking 50% on normal flights, then any brand of cell would not be being pushed.

I'm guessing the best packs will be those where, out of a batch of cells manufactured, the ones that show up as better when first
tested are binned as best and then matched to each other to make up a pack. Much in the way that Intel produces identical chips,
then bins them, with the better ones getting a higher clock
rating ( see binning in first paragraph: https://en.wikipedia.org/wiki/Clock_rate).

One advantage of a fuel motor was that one could easily complete a schedule, then practice a few manoeuvres and then some and
then land.

Mike

Online Stuart Mellor

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Re: Lipos - Selection
« Reply #19 on: 27, January 2018, 06:27:57 PM »

Angus hit on the real problem - the weight limit is now too low for current technology. It's ok for sponsored pilots who can simply throw away stuff & replace it & don't see the problems. For other punters (the vast majority) it just gets more expensive to be competitive. That's not in anyone's interests.
I know people who like to keep to the 5kg limit (in the belief their models are designed to fly at that weight), so won't fit the bigger capacity batteries.
The real answer is to increase the weight limit, but keep to the 2m rule. This would cheapen things by increasing longevity & add to flexibility of design and power sources.
I know some fervently defend the status quo & always will - but sometimes need to move on as problems are found. The FAI are notoriously slow in that department.If you were to ask anyone why 5kg's I doubt there's a sensible answer - and the overweight bombs of the past will never return.....
« Last Edit: 27, January 2018, 06:30:20 PM by Stuart Mellor »

Offline Mike Wood

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Re: Lipos - Selection
« Reply #20 on: 27, January 2018, 06:41:53 PM »
Weighing electric models without the battery would help and also simplify weight checks and perhaps the
5kg rule could be kept (for the time being).

It seems that pilots already have more than enough power, but not, especially in high winds, flight time length.

m
« Last Edit: 27, January 2018, 06:46:47 PM by Mike Wood »

Online Stuart Mellor

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Re: Lipos - Selection
« Reply #21 on: 27, January 2018, 06:54:50 PM »


Hi Mike - scale models are weighed without battery! -so why weigh aerobatic models with battery?
Re 'the time being'  - there is always scope for changing a rule in n years time to give designers time, but it never happens.....
Its not about power - its about reducing costs to be competitive - if we are to survive.


ps - max. weight for scale models is 15kgs, but models are weighed without battery. Looking at the Sporting code - can't see any mention of pre fight battery checks or max. voltage for scale. Assume that the max voltage is the FAI voltage limit for any model - I think is 72 volts. (Anyone looking at the FAI site - good luck at finding the relevant information. What a minefield.)
« Last Edit: 27, January 2018, 07:47:12 PM by Stuart Mellor »

Online Phil Lewis

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Re: Lipos - Selection
« Reply #22 on: 27, January 2018, 08:29:03 PM »

I'd pretty much agree with Stuart and Angus, it will just never make sense to me that IC is weighed without fuel whereas electric is weighed with, why? There might well be a good rationale but I don't know what it is.


As for overweight bombs of the past well wouldn't a two litre coke bottle filled with fuel get you there? After all, it's IC so weighed without any fuel.

Offline Mike Wood

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Re: Lipos - Selection
« Reply #23 on: 27, January 2018, 10:05:28 PM »
Hi Stuart

That's very interesting about scale models, which means there is a precedent set and
perhaps getting electric f3a models weighed without the battery would be a first step.

Hanno wanted to help with simplifying things when he designed, as some called it, his
'trainer' model, the Calypso and being the pilot he is, won with it  8)  in .... 1983!

One thing to ponder, is what the unintended consequences of such a change could be,
that could possibly lead to increased complexity / cost, the opposite of the desired
outcome?

Mike

Online Phil Lewis

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Re: Lipos - Selection
« Reply #24 on: 27, January 2018, 11:00:20 PM »
Purely out of interest can anyone say what a current IC F3A plane weighs when it's fully fuelled for a schedule?

Offline Mike Wood

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Re: Lipos - Selection
« Reply #25 on: 27, January 2018, 11:40:12 PM »
Hi Phil

If a 20oz tank holds 0.568 litres of Methanol and 1 litre of Methanol weighs around 791g
then that's about 450 grams.

So a 4,999g model would take off at 5,449g.

If one is only weighing the model, then the battery could weigh as much as you like, just as
one could fill the entire fuselage and wings with fuel today, which would give a longer flight, but
I'm not sure it would fly too well  :)

Mike
« Last Edit: 27, January 2018, 11:43:07 PM by Mike Wood »

Online Phil Lewis

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Re: Lipos - Selection
« Reply #26 on: 28, January 2018, 12:23:32 AM »

Hi Mike,


thanks for the answer but what I was looking for is the actual weight that a competitive IC plane actually does take off at which of course depends on what it weighs when it is empty (accepting that that is of course less than 5KG.

Offline Bill Michie

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Re: Lipos - Selection
« Reply #27 on: 28, January 2018, 12:15:19 PM »
I might be out of order here, but:
Doesn't starting Temp have a significant effect on how well your LiPo's perform? eg if you start with a stone-cold pack & "floor it" at high throttle for the first couple of minutes, does that not shorten their life? Additionally, if you charge them when they're stone cold (eg stored in garage) does that not affect their longevity?
What I'm trying to say is that LiPo's can be treated very differently and their chemistry MUST suffer from temp & charging regimes as well as how we use them................ :-X
I'll get me coat............. ::)

Bill

Online Stuart Mellor

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Re: Lipos - Selection
« Reply #28 on: 28, January 2018, 05:03:53 PM »


Hi Phil - on the right track, as Mike says  - but the max weight of an ic model (FAI) is 5050grms  (without fuel)  - plus fuel for flight, @ say 450 grms gives a probable take off weight of  5500grms. As there are now  many designs that are either ic or electric, there is no reason why an electric model  couldn't also weigh 5500grms with equivalent safety. This would allow an extra 450 grms of battery 'capacity' to be used for the same take off weight i.e kinder on batteries. Therefore probably cheaper in the long run.
Although don't forget, an ic model gains performance as fuel burns off!


ps - As Bill says -there are all sorts of ways of abusing batteries!





« Last Edit: 28, January 2018, 05:06:32 PM by Stuart Mellor »

Offline Adrian Mansell

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Re: Lipos - Selection
« Reply #29 on: 07, February 2018, 09:05:40 PM »
Hi All,


Just skimmed through this thread.


I have used Zippy compact 25C 5000mAH 5S for the last 5 seasons.  I fly FAI P&F in all weathers with a 4.75kg model with C50-13XL + Jeti Mezon.  I look after my LiPos:
  • All batteries get two 2C discharges before flying
  • Batteries are balance charged in parallel pairs at 0.9C to 4.2v per cell using Fusion Emperors. (On occassion at 1.5C when I'm in a hurry.)  I only charge to 4.19v per cell in the winter.
  • Batteries are never left fully charged for more than 36 hours, and never left in a very hot or cold car when charged.
  • Generally, a schedule uses 3500mAH to 4100mAH depending on conditions and schedule being flown. On occassion many of my packs will have taken a right kicking, usually a big F schedule in appalling conditions, sometimes down to as little as 5%.
  • Used batteries are not storage-charged unless I know they are not going to be used for 10 days or more
  • I try to ensure batteries are between about 15degC and 25degC at the start of a flight

I generally get around 130-150 flights per pack before performance degradation starts to become noticeable.  Very, very rarely I will get a single 5S pack that will fail noticeably earlier, usually within 30 flights.
I have used Optipower batteries as well from time to time and can confirm Matt's comments about them - their after sales service is also excellent.  But for me, I find the zippies an excellent solution at a very good price.
« Last Edit: 07, February 2018, 09:11:12 PM by Adrian Mansell »