Max Amp

[Phil Robinson]

Hello people

                      I am a born again modeller after a 25 year absence only this time I am going electric. and here is the first of many ( no doubt ) problems that I would like your help with if you wouldn't mind.

I have put together a a power pack that consists of a cf2822 outrunner motor a 25A esc and a 1500mah 15C li-po battery.

According to the motor spec it will run with a 10x5 prop at 10A and give approx 600+g of thrust , which on testing is true ( tested using a watts up meter } the problem I have is that the stick on the transmitter is at about 70% of travel when running at 10A, and so it will definitely go faster but with more power usage. What I would like to happen is that when the throttle stick is at full travel I would like that position to be my 10A  max. Now all you clever people out there how do I do it ?

Thanks

[Tim Mackey]

As Jet says, you could just use a smaller prop, although that will of course reduce your thrust as well as current.

Alternatively you could always adjust throttle travel throw so that you only acytually achieve 3/4 "throw" at full stick deflection ?

Frankly though, I have NEVER found this necessary on any of my electric models, and as Jet also pointed out the Amps will be quite a bit less as the prop unloads in the air....sometimes as much as 20% or more.

Do you make a habit of always flying with the go stick on full ?...if not, then WHY do you want this goal ? 

[Steve Hargreaves - Moderator]

Hi Phil & welcome back to the hobby.

I suspect you will find not much increase in current for the last 30% of stick travel. I had exactly the same problem recently....I'd prop'd a motor as per instructions which should pull just over 20A...it hit 16 at half throttle & 20 at about the three quarters mark & like you I thought there was something wrong. Screwing up my courage I went to full throttle & it hit.................21.2A!!!!!!! As the lads say this will unload in the air & you don't fly at full throttle all the time do you........

Having short arms & deep pockets I tend to use budget ESCs & I suspect they are not perfectly linear in their response....take a stiff drink & open that throttle.......I suspect you will be fine.

If it goes way over then your only option is a smaller or less pitchy prop......electric flight is very dependant on the prop used & you can spend many a happy hour finding the prop that gives the best thrust for the least power....even different makes of the same size are hugely different. I went through a load of props testing them on a particular motor & just for a laugh stuck an ancient Top Flight 9x7 nylon IC prop I had found at the back of the drawer....guess what.....?? It gave the best static thrust for the lowest current of any of the props I'd tried (measured subjectively!!!!) Interestingly it was completely rubbish in the air!!!!!

What does this tell us (apart from the fact that I like to ramble on a bit too much)?? It tells us you should always experiment with yer prop size to find the best one (although the best ones are usually APC E props but with an honourable mention to the Master range too!!)

[Tim Mackey]

Justifiably of course...

[Phil Robinson]

Hello again people

                                  what can I say but a big thankyou for your speedy responses and valued advice and information, the ideas floating around in my head seem to  be right  but you kind people have just confirmed them for me which is very reassuring.......( my partner is always telling me I think too much and am too cautious ) but as we all know the easiest thing to do with a model aeroplane is to trash it.  Once again people Thankyou for your help

Regards Phil Robinson

[Steve Hargreaves - Moderator]

You can never think too much about this wonderful hobby of ours....there is always some problem to be overcome or worked through....oops did I say "problem"?? I meant "learning opportunity".......!!!!

 IMHO the people who have the most problems are the ones who do the least thinking!!!!

[Steve Hargreaves - Moderator]

PS so what current does it pull at full chat then?????

[Tim Mackey]

And...how are you measuring this ? -  take it you have wised up and purchased a proper "whattmeter" or similar?

[Tim Mackey]

It is in fact the correct item description, and is available from West London models amongst others.

Made by Astro Bob ( he of astro flight fame in the US ) - got mine direct from him a few years back when they were expensive....now much more reasonably priced.

WHATTMETER

Old Grumpy wouldnt know where to stick it

[Steve Hargreaves - Moderator]

Yep... Timbo is correct. The spelling threw me at first too but Whattmeter it is....I know cos I've got one!!!!!

[Phil Robinson]

Hi Steve

              on full throw of the throttle its pulling 18 to 19 amp and the spec on the motor rates it at  16amp max for 60 sec., hence my reason for trying to limit the max current plus the bonus of extending the duration.

Regards Phil Robinson

[Steve Hargreaves - Moderator]

Aaarrgghhh!!! That sounds a bit high to me...I think you might be risking the motor there. I would suggest you prop down a bit (APC9x4.7 perhaps). A slight overcurrent at full throttle is OK but you're way over........

And this is the recommened prop...???? Is it the "correct" 10 x 5....? (not all 10 x 5s are created equally you know!!!) A slow fly wide blade jobbie will move a lot more air (& take more current!!) than a slim blade of the same size.

With the greatest respect I would suggest looking at the instructions again (you've not read off the wrong line or the wrong battery have you) for a motor that should pull 10A on a 10x5 to actually pull 18-19A.........something not right there methinks!!!!

Plus you're getting close to the battery limit there (15C equals 22.5A on your battery) which will shorten its life.......

[Tim Mackey]

Is he using a 3s battery when the specs were for a 2s ? Just a thought....

CF2822

3S

950

10X5

6800

10A

685g / 1.4lb .

CF2212

3S

1534

7X6

11000

15.5A

730g / 1.61lb

Taken from a quick google just now...I reckon they have got the figures wrong. How can they claim  a 7 X 6 prop will pull  15.5A , yet a 10 X 5 will only draw 10A ON THE SAME BATTERY !!

I reckon the 10" prop is for 2s. 

[Steve Hargreaves - Moderator]

The 950 & 1534 numbers are interesting......might these be the kv figures?? a 10 x 5 on a 1534kv motor with a 3S battery  would pull some amps!!!!! Probably a lot more than 18 or 19 though to be fair!!!!

[Tim Mackey]

they are alledgedly the RPM !

I reckon its DEFINATELY that the 10" prop will be for a 2s Pack only, and as is unfortunately the case all too often.....the info supplied is WRONG!

PHIL  - DO NOT USE THIS LITTLE BELL OUTRUNNER ON A 3S WITH A 10 X 5 PROP!

[Steve Hargreaves - Moderator]

Thought I'd heard of these motors before........Giant Cod sell 'em

http://www.giantcod.co.uk/product_info.php?products_id=53&osCsid=e5c2e5ab3b29f18bdaf3c79690c64804

They give props 8x3.8 to 10x5 & 2-3 cells but don't define which prop goes with which battery......Like you Timbo I bet the 10 x 5 is for 2S!!!!!

[Phil Robinson]

Hiya people

                       once again thanks for your input, what my next move will be is to conduct a little test with the set up  I have but with as many different props as I can. I think the moral of this story is " Don't believe all you read "

Oh, and you guys may have "whattmeters" but I have a "watts up meter" and it probably tells me the same information as yours does but whatever the meter is called it is definitely the best bit of kit that I have bought so far

Thanks again

Regards Phil Robinson

[Myron Beaumont]

Just a quicky -but a  serious question .! 

  I bet a few dyed (died) ( dai'd) in the wool non -welching  old timers like me foolishly thinking of following the trend of subscribing to this new dodgy technology  are beginning to wonder how many PROPELLERS you must carry around in your" flight box  plus whattmeters (in the field ) to cater for changes in the ambient pressure /temp/type of cowling /connectors /fire extinguishers/no of batteries in series or parallel /ad-infinitum,,when all I have is  fuel containers & my small battery 7 AH primitive but reliable lead/acid /gel power source charged by my dual system on the mobile home/campervan as I drive--- for glow plugs( & the hand held one as well ! ) I REPEAT I would love to try 'lectric flight ,especially edf's & multi-engine set ups -BUT .  Well the real answer is that I can't afford to gamble on me having a stress free flight having read all the horror stories .on quite a few threads  .I do however feel that Timbo (traitor) has mastered the technicalities & is on a very steep & obviously enjoyable learning curve ,possibly ending up with an MBE for his services to Specktrum & all explosive flying machines

Grumpy

[Steve Hargreaves - Moderator]

Hi Phil... a Whattmeter does preftty much the same as a Watts Up Meter....the important parameters are current & voltage under load. Testing with different props is obligatory for EF set ups.....to help you fine tune the settings.....its a bit like holding the nose of an IC aircraft vertically to make sure the needle is set right!!!!

 Myron, the props live in your workshop drawer...once you've picked the right one it stays on & all flights are exactly the same......no fiddling with the needlevalve or changing the plug cos waethers' a bit hotter than last week like you do with yer IC jobbies !!!!!

With regard to the explosive LiPos issue then you must remember the thousands of people flying around who DON'T set everything on fire every flight. Compare this to the few fires you hear about & you'll see how safe it really is. Like everything in life you will get a few numpties who get their fingers burned but used correctly within the parameters (measured on yer Wattmeter) & with the correct charger not a resistor & a 12volt battery you won't have any problems with LiPos....do you have a mobile?? A laptop?? a new cordless powerdrill?? Ever thought what the batteries are??? Yep they're LiPos!!!!

Don't get me wrong I love ic & it will always be my first love cos I like fiddling with the engines but you can't argue with the fuss free & clean operation of the electric stuff.....plus its something new to learn & mess about with....isn't that why we all do this????

I reckon the forum members could put a good electric flight package together for you Myron.....literally everything including the model, motor, ESC, battery, prop, charger...even the connectors.... that would fly on yer 35Mhz kit & guarantee success...in fact it would make a great thread!!!!! How about it Myron........tell us your budget & the sort of model you'd like to fly & I bet we could come up with a set up to put a smile on yer face...........

PS don't expect a 1/4 scale EDF Sabre for under 100 quid!!!!!!!

[Tim Mackey]

Oh no...now you've gone and done it Steve

[Bruce Richards]

I put my first electric model in the air for about £45 and it has been great.

Fokker III foamy from Ebay       £15 (this includes a brushed motor but I did not use it)

emax CF2822 bell motor         £5

Emax 18A ESC                         £10

2 Micro servos BDM 3.7g     £3

2 2S 900ma Lipos                    £10

Prop                                             £2

Total                                            £45

Then theres a lipo charger     £40

Total                                            £85

If you want to add a whattmeter £35 then the total is £120. Not bad I think and the larger cost items are one offs.

Bruce                     

[Myron Beaumont]

Timbo    Yep !

Steve     Thanks for revealing your real feelings about "power plants "I realise that Timbo is biased 'cos he only flies off the Great Orme Where they don't like any nice sounds apart from the gnashing of sheep &sticky buns from ASDA  (Association of Seriously Dedicated Aeromodellers)   and the whoosh of a glider heading for his cliff top retreat.  You mentioned 1000's of fliers on Lipos- Well I have not met a single one !     I have 35 mghz  kit  Optic 6 + Futaba 2.4 kit by the way !

My budget is not important .It's what I can not afford to loose that bothers me.    OK   I said I would like an EDF or twin (or more ) engined model ,obviously a problem with I.C.'s!  You inferred that I "fiddle " with needle vales etc . NO only on the bench before installation.No probs .

I do have a few plugs in my flight box drawer -just in case (2 for each motor I use )  Never used even one "in the field".          Told you I feel like sticking to what I know  ! Maybe I'm just too old to change BUT to repeat    I AM interested  as long as it doesn't cost more than another divorce .!

To get back to your suggestion about a "package deal".OK  & not just for me it seems  ! criteria coming up.

#1  Must smell of  aeromodelling chemicals I've used for at least 50 years.Not that electrical burning transformer type nasty odour

#2 Last more than one season

#3 Be around 60 " span (failing eyesight )& look like a proper A/C & fly like one too ( Cap etc.)

#4 Appeal to 'er indoors for obvious reasons (-she loves my  Sopwith Puppeteer & all biplanes)

#5 It's a Hawker Hunter 'cos I loved one I built in the 50's (Jetex 100)

#6 & If It's not    -an Islander (Norman Brittan) The A/C I looked after at St Just aerodrome !( I.O.S  Steamship company based in Penzance

#7 Flight time of at least 15 minutes each time I fly for 5 or 6 times each session & some left in spare

#8 Big box to carry all my props( & me if I  get incinerated)

#9 More " Amp hours" than I can manage at the moment Without Lipos  ( I'm very drawn to NiMh 's batteries 'til we all know as much as Timbo ).

#10 £100 & I'll build the aeroplane at my own expense

[Tim Mackey]

1. Just silly..thats half the reason to use leccy !
2. that depends on your piloting and maintenance skills
3. plenty available
4. she will love it 'cos its clean and quiet - unlike the pilot
5. available - its just a model aeroplane remember
6. see above
7. possible if you have a generous accountant and 'er indoors is wealthy
8. how big a box would you like us to find for you myron?
9. depends on how much you can manage now - not sure I understand your question - but then whats new.
10. not really...and anyway d'ya think we would be daft enough to let you near an electric aeroplane

   

[Myron Beaumont]

er indoors isn't interested - she wants a holiday, not another plane.

Chrisy

[Tim Mackey]