Mouldy Posted October 5, 2007 Share Posted October 5, 2007 Hi Guys!First post on this forum for me, but Im guessing it wont be the last! I am new back to this hobby after a 15 year lay off and have gone mad and bought a Katana S50E with a Hacker A50-14s and S70 SBec-pro.My question is this:- what Li-po's should I look to be fitting for the sort of performance that Im used to? (And to quantify this I used to fly F3A!)Cheers peeps!Ian Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted October 5, 2007 Share Posted October 5, 2007 Hi Ian, welcome and welcome back to flying. Cor, what a model well I'd go with what they recommend - seems to be a 5S Li-Po and 15" prop. Go easy on her .... Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 I believe this particular variant is for helis ( extra cooling fan I believe ) but should still be OK for you fixed wing. It is a powerful motor, and capable of up to almost 2KWatt input, so if you are gonna keep the amps manageable, then you should probably be looking at using something like an 8S pack which will give around 29 Volts under load, and if you want to wring all the power out of the motor, that means propping it to give around 60A plus. This in turn means batteries capable of 60A steady capability, so assuming you want reasonable flight times, then be looking for around 3000m/a cell capacity with 25C rating. Not cheap!Also, dont know of the S70 Sbec-pro thingy....is that the ESC? If so, is it capable of running 8s lipos ? A seperate BEC or even seperate R/C battery altogether might be wise for this ship.EDIT! Specs I have just seen indicate nmax Amps for this motor is only 55, therefore with an 8s pack, you are going to shoving too much current in ( 60A if you want the max power )Either prop it down to 50A ( gives 1450 Watts ) or increase pack to 10s which gives 36V and at 50A this would equate to approx 1800Watts. Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 The S70 is indeed the ESC and it has a bec, see here:-http://www.hackerbrushless.com/x-pro-controllers.shtmlSeems capable of running up to 6 cells and 70A continuous rating.Thanks for the details and the welcome! Second question is this:- Wheres a good place to buy batteries? Have found threads discussing makes and to be honest found them farily inconclusive! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 Incidentally, you dont state the expected AUW of your ship, but assuming around 6 -7 lbs, then 1000watts should give you sprightly performance @ around 150 watts per pound.In this case, you could reduce the battery down to 6S ( maybe 2 x 3s in series ) and prop to get 50A ( 21 X 50 = 1050 ) Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 AUW should be around 2.25KG's.Gotta say bud that your loosing me a little with the tech! Am I right in saying that by loading the motor with either more pitch or more diameter, (or both), that more current is drawn? How do i avoid overloading either the motor and/or the ESC? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 You mean X70 ?? Not S70 ???I would still worry about using an ESC-BEC in a unit using 6S Lipos. The ESC may well be happy at 70A continuos, but your motor is NOT! As I said, specs seem to say maximum 55A so go for 50 as a realistic figure, in which case the setup above I suggested would be best ( 6s propped to 50A ).IMO the best packs are still F/Power, and google for a retailer near you, or buy online. Having said that, Als hobbies are doing some very good Dualsky packs at the moment, and they are proving very capable. Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 Sorry! Typo! Yup your right, I did mean X70 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 yep, prop selection is VITAL with electric flight. If you go up just a little bit too much in pitch or diameter, current will increase, and with 6s pack, this will show a big increase in current. you really ought to invest in a wattsmeter or similar, and then experiment with props to get the current just right. I think you ESC is gonna be Ok ( 70A capable ) but the motor is only rated to 55A absolute MAXIMUM, and therefore would be happier with higher volts and less amps to give the rquired wattage. Welcome to electrickery flight ! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 keep asking away buddy....we are here to help Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 http://www.alshobbies.com/shop/lookupstock.php?pc=7366&Desc=Well you did kinda hint that you wanted top performance, and as you can see, this does not come cheap. You COULD do it a fair bit cheaper if you settle for less performance...but then thats not really your criteria is it? Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 Cheers my friend!!! So to try and clarify my muggy head!! I should be lookng at 4270 5S evolites from FP?? I have already got a charger and a balancer and although the latter will go to 6 cells, the charger will only go to 5! Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 Posts are crossing over a bit!!! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 Mouldy. Sorry about the techie blurb.......but really there is no alternative.In general terms, electric powered craft are matched powerwise by WATTS not horsepower / CC like IC.Average performance for an average model is achieved with approximately 75 -100watts per pound, but slow floaty glidery thingies will get away with less. Powerhouses like you are doing, really need closer to 200Watts per pound (AUW ) so simply speaking.....Plane weighs say 6.5lb6.5 X 200 = 1300 Watts.Then work "backward" from certain constraints IEMax Motor current is 50A. You need 1300 watts, ( which is a function of Amps times Volts )1300 / 50 = 26... so you need around 26 Volts. Now a 6s Lipo pack will supply around 21V+ under load, so not far out........HTH Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 5S LiPo pack ( even a good un like F/P ) will only give around 18V under load.heres the maths agin.......18V X 50 A = 900 Watts.900 / 6.5lb AUW = 138 watts per pound....not exactly stunning, but "adequate" Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 No worries dude! Gotta try and get my head around what is very new tech to me! Should have done a little more homework before I bought into the bigger plane! Might have to compromise on the performance a little in the short term on the grounds Im also building a kit car at the moment!!!! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 Ah...Kit car fan too......you and me will get along fine my friend Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 AUW 2.25Kg - thats pretty good...but how do you KNOW that if you have not decided on the battery pack ?? !!Anyways....assuming that is the AUW then at the previous calcs ( 6s pack with prop to give 50A )21V X 50A = 1050 Watts / 5lb = 210 Watts per pound . BINGO Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 If you MUST drop down to a 5S pack to suit your charger ( which seems to me a little arse about face IYSWIM ) then more maths shows us....5s pack = 18V X 50A = 900watts / 5lb = 180 Watts per pound I reckon that should be nice. Not ballistic, and if you really need F3A performance , you may be a little down on that, but 'twill still fly nice. Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 Excellent!http://s114.photobucket.com/albums/n251/vm1451/ Ongoing project which is funnily enough at the stage of fitting electrics!!!! 2.25kg's is the suggested AUW from Sebart, but of course you are right. I have no idea what avionics or battery are fitted to get that weight. So it looks like a new charger as well then! Any recomendations for this?Thanks for all the advice so far Timbo. Appreciate it! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 A plethora of chargers around at the moment, not really up to speed on them all as i have 3 different ones, all LiPo capable but been in my possession for years as I went exclusively LiPo years ago, when such things were expensive !!try Als and the like, BRC, Robotbirds, Puffin etc..... best advice I can give is ensure the following as a safeguard futureproofing.Try to get a chrger / balancer combo unit - balancing the packs WILL be very advisable on such packs / useage.At least 8 cell capable - you WILL need it one day At least 8Amp charge rate - otherwise you will be waiting 2 hours between charges Good clear LCD readout of what the charger is doing .Mains /12V power supply - otherwise that battery you are planning on using will be depleted pretty quick ! Google about, and post here when you narrow it down - we will advise on final choice. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 http://aircraft-world.com/shopexd.asp?id=4901Just one example of course....maybe the 8amp charge rate I suggested is a bit too high, and perhaps 6A may be a better criteria ? Quote Link to comment Share on other sites More sharing options...
Mouldy Posted October 5, 2007 Author Share Posted October 5, 2007 Another thing I need to clarify!The mah rating. The higher this value, the longer the battery will last for a given current draw?e-station BC8 any good? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 Yes, but also the higher the capacity, the better the pack will be at holding its voltage under load.Charger seems a nice bit of kit, but would need a seperate mains PSU to run off mains, but this is not a deal breaker. You might want to consider this below, as I did suggest that a wattmeter is essential for your type of setup, this charger includes one, but you will needa seperate balncer ( which are not expensive these days )http://www.modelflying.co.uk/forum/forummessages/mps/dt/4/UTN/1460/last/1/V/6/SP/ Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2007 Share Posted October 5, 2007 http://s114.photobucket.com/albums/n251/vm1451/Took the liberty of correctly posting your kit car build link....yours did not appear as a hyperlink Quote Link to comment Share on other sites More sharing options...
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