Dominic Posted June 20, 2015 Share Posted June 20, 2015 I'm still fairly new to the hobby and have a Bixler 2 which I'm learning to fly with. I've just picked up a cheap (ie less concerned if I crash ) diesel high wing trainer off ebay as my next step but want to convert it to electric. The prop that it came with is 10x6" & wingspan is 48". My calculations to convert to electric are... Weight with battery, servos, rx = 1150g Plus 100g (estimate) motor = AUW = 1250g = 2.76lb Power needed = 100w/lb = 2.76 x 100 = 276W (lets say 300W) I've got a 3s 2200mAh battery from the Bixler that I think is about right, so ESC = 300/11.1 = 27A = 30A ESC (= 40A for safety) After some research I think I need about 1000Kv So I think this motor is going to be about right **LINK** Am I in the right area? Thanks Quote Link to comment Share on other sites More sharing options...
Phil Green Posted June 20, 2015 Share Posted June 20, 2015 Thats quite a powerful setup you've chosen - what model is it and what size diesel engine? Cheers Phil Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted June 20, 2015 Share Posted June 20, 2015 I ran your numbers and motor choice through Ecalc I assumed a rather mean wind area of 400 Square inches on a 10x6 Prop it gives 102W/Lb Stall Speed 20mph, Max Speed 43mph (subject to my assumed wing area) with a max current of 25A on a 10x5 Prop it gives 92W/lb Stall Speed 20mph, Max Speed 39mph (subject to my assumed wing area) with a max current of 22A Dropping the prop to 9" gives far too low a wattage Increasing it to 11" would give you too much power and be to much current for the motor So I reckon you are pretty close... Quote Link to comment Share on other sites More sharing options...
Phil Green Posted June 20, 2015 Share Posted June 20, 2015 It really depends on the model - for instance the similarly-sized DB Tyro could be described as a 'diesel trainer' and would be massively overpowered and nose-heavy with the proposed setup. Edited By Phil Green on 20/06/2015 14:22:39 Quote Link to comment Share on other sites More sharing options...
IanN Posted June 20, 2015 Share Posted June 20, 2015 Posted by Phil Green on 20/06/2015 12:27:29: Thats quite a powerful setup you've chosen - what model is it and what size diesel engine? Cheers Phil Yep, tell us what diesel engine it came with, Dominic Quote Link to comment Share on other sites More sharing options...
Dominic Posted June 20, 2015 Author Share Posted June 20, 2015 Unfortunately there are no markings on the engine at all - no make, size, nothing.... However, here is a pic of the plane if that helps? I'm looking for a setup that is going to be fairly slow - not sure if that needs a change in prop? Dave, I did take a look at Ecalc but very little of it made sense . Any advice/pointers gratefully received. Quote Link to comment Share on other sites More sharing options...
Bill_B Posted June 20, 2015 Share Posted June 20, 2015 The model has a short-ish nose so the battery could always be pushed rearward to compensate for motor weight if it's too much. Also, if there seems to be too much power, simply make good use of the throttle, or prop down. Quote Link to comment Share on other sites More sharing options...
IanN Posted June 20, 2015 Share Posted June 20, 2015 A pic or two of the engine would be good. No rush - whenever you get round to it Quote Link to comment Share on other sites More sharing options...
Dominic Posted June 20, 2015 Author Share Posted June 20, 2015 And here is the engine... Edited By Dominic on 20/06/2015 18:31:32 Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted June 20, 2015 Share Posted June 20, 2015 Oh and (you probably already know) it will need a lot more rubber bands than those shown in the picture Quote Link to comment Share on other sites More sharing options...
IanN Posted June 20, 2015 Share Posted June 20, 2015 A P.A.W. Excellent! Sometimes there are numbers inside the backplate recess re the capacity, sometimes not Quote Link to comment Share on other sites More sharing options...
Dominic Posted June 20, 2015 Author Share Posted June 20, 2015 Ian - The numbers 1 9 are stamped in the recess - does that help/make sense? Quote Link to comment Share on other sites More sharing options...
Phil Green Posted June 20, 2015 Share Posted June 20, 2015 A PAW 19 is 3.1cc so an electric equivalent would be about 250 to 300 watts. So your initial choices look good Cheers Phil PS Dont know what you paid for the complete model but cleaned-up the PAW will fetch 40-50 quid Edited By Phil Green on 20/06/2015 22:59:54 Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted June 20, 2015 Share Posted June 20, 2015 Posted by Phil Green on 20/06/2015 22:56:19: A PAW 19 is 3.1cc so an electric equivalent would be about 250 to 300 watts. So your initial choices look good Cheers Phil Edited By Phil Green on 20/06/2015 22:58:00 But the throttle control will be far far better Quote Link to comment Share on other sites More sharing options...
PatMc Posted June 21, 2015 Share Posted June 21, 2015 My vintage Veron Robot is fairly similar in size, weight & power requirements. The model is 45" span, 416sq ins, RTF weight is 52 oz. When built I made a number of mods including mounting the engine on a paxolin plate so that I could try it with various old glow & diesel engines, one of which was a PAW19. It flew with ic power for 3 or 4 years before I decided to go all electric. I modded the redundant fuel tank area to take a 30A Jeti esc with a 3s2200 lipo below accessible via a hatch underneath. The first motor I used was a Himax 1600kv inrunner with an 8x4 APC prop. With this set up the performance was pretty hot, being more like a mini Watt4 than a vintage model & far more lively than it had been with any of the ic engines. I flew it like that for a few months but at full throttle the current draw was 34A static (around 365 W) & although the esc coped OK with the overcurrent situation I was a bit concerned but didn't want to drop the prop size. Eventualy I fitted a version of this outrunner which at the time was marketed by Overlander as a Tornado outrunner. It was cheaper than the Perkins but IMO this Turnigy at around £13 would be equally capable. With a Graupner 9x5 slim prop, the Tornado outrunner pulls 26A for 297W at 10800rpm. The model isn't quite as lively, speed is down a little but the climb rate is improved over the innrunner. I'll post a couple of pics tomorrow. Quote Link to comment Share on other sites More sharing options...
Dominic Posted June 21, 2015 Author Share Posted June 21, 2015 Posted by Phil Green on 20/06/2015 22:56:19: PS Dont know what you paid for the complete model but cleaned-up the PAW will fetch 40-50 quid Edited By Phil Green on 20/06/2015 22:59:54 This plane, plus a vintage 62" high wing with OS glow engine and a Fokker biplane (no engine) for £30 off ebay - All in good serviceable condition so sounds like I got a bargain PatMc - Thanks for your specs. It would be good to see some pics of your setup. Excuse my noob ignorance and I have probably misunderstood something, but the motor you quote shows 665W power which is twice my original posting (of 300W). In Phil's first post he says that my suggestion is quite a powerful setup and you are suggesting double that? Now I am confused . Is it just down to flying experience and personal preference? Thanks Quote Link to comment Share on other sites More sharing options...
DH 82A Posted June 21, 2015 Share Posted June 21, 2015 For an E-calculator try Web-o-Calc, very easy to use. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted June 21, 2015 Share Posted June 21, 2015 Posted by Dominic on 21/06/2015 11:34:48: PatMc - Thanks for your specs. It would be good to see some pics of your setup. Excuse my noob ignorance and I have probably misunderstood something, but the motor you quote shows 665W power which is twice my original posting (of 300W). In Phil's first post he says that my suggestion is quite a powerful setup and you are suggesting double that? Now I am confused . Is it just down to flying experience and personal preference? Thanks Dominic, the wattage of a motor is a variable feast, depends on the voltage and the load. The motor PatMC quoted is rated for a max wattage of 665W with an acceptable voltage range of 2 to 4S Lipos (roughly 7 to 15V) the higher the voltage the higher the potential wattage available at the expense of a higher current drain Wattage = Volts x Current Current = Wattage/Volts But the load on the motor dramatically affects wattage and current (in any given set up the voltage is fixed) So the Motor PatMC quoted has stats like: Voltage : 2-4S (7 - 14.8 v) Max Current = 38A Max Power = 665W Sp to get 665W we would need 15v and we would pull a current of 44A (it will survive the current overload as long as its not sustained for long) If we applied a 3S Lipo we would get the lower wattage PatMC states But that can all be blown out of the water by over/underloading the motor, as brushless motors have a KV rating (revolutions per volt) and that is the speed they will rotate at (or try to) s- if we put a 5" prop on PatMC's motor (very much underloading it) the current draw would drop and so would the output wattage, if we shoved a 15" prop on it, the motor would still TRY to get to KV speed but would draw so much current trying to attain that speed it would burn out...... Quote Link to comment Share on other sites More sharing options...
IanN Posted June 21, 2015 Share Posted June 21, 2015 Posted by Dave Hopkin on 20/06/2015 22:59:04: Posted by Phil Green on 20/06/2015 22:56:19: But the throttle control will be far far better But the lovely noise and gorgeous aroma will be sadly lacking Quote Link to comment Share on other sites More sharing options...
IanN Posted June 21, 2015 Share Posted June 21, 2015 Posted by Phil Green on 20/06/2015 22:56:19: PS Dont know what you paid for the complete model but cleaned-up the PAW will fetch 40-50 quid Edited By Phil Green on 20/06/2015 22:59:54 I'd say that's a little rich - very much towards the upper end for a plain bearing .19 r/c with obvious signs of use. But, on the right day, anything's possible - who knows! Quote Link to comment Share on other sites More sharing options...
Phil Winks Posted June 21, 2015 Share Posted June 21, 2015 Your initial thoughts ain't so far of though I'd go for a 3300Mah 3s lipo and this motor don't forget by the time you've added the battery the weight will have gone up a tad, also when fitting the battery try to get it some where near the COG or a little forward of it, usually right where the fuel tank was. That motor will be somewhere close to the weight of the diesel engine you've taken out so getting the battery under the front of the wing will help keep the balance right. I run one of those motors on a 11 x 6 prop I think, and she pulls just about 350W which isn't that much more than you need for that trainer and you can always not use full throttle plus the extra power helps with what is almost certainly a draggy airframe, mines fitted in an E-Pioneer and is just about right as a basic trainer the nice thing with that set up is the ability to step up to a 4s setup (with a slightly smaller prop) as you get better giving you slightly more in the tap for loops and the like and a shorter take of run mostly, though the added weight of a 4s does mean faster landing speeds, something best kept for a little way down the line. Quote Link to comment Share on other sites More sharing options...
Phil Winks Posted June 21, 2015 Share Posted June 21, 2015 As a ps and not quite on thread did those early diesels not have a locking arm on the compression screw ?? Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted June 21, 2015 Share Posted June 21, 2015 Some did Phil but by no means all. I never had one that did. I still have a number of diesels. Quote Link to comment Share on other sites More sharing options...
IanN Posted June 21, 2015 Share Posted June 21, 2015 All my smaller P.A.W's (and all my Dad's and Uncle's too) without exception needed a comp lock screw. That said, this one may well have run well without. Indeed, I'd suggest it probably did, otherwise it would have one No great miss either way. P.A.W. sell them as spares, if needed Quote Link to comment Share on other sites More sharing options...
PatMc Posted June 21, 2015 Share Posted June 21, 2015 Posted by Dominic on 21/06/2015 11:34:48: PatMc - Thanks for your specs. It would be good to see some pics of your setup. Excuse my noob ignorance and I have probably misunderstood something, but the motor you quote shows 665W power which is twice my original posting (of 300W). In Phil's first post he says that my suggestion is quite a powerful setup and you are suggesting double that? Now I am confused . Is it just down to flying experience and personal preference? Thanks Dominic, the power quoted for an electric motor is meaningless unless qualified by the voltage used to obtain the figure. The meaningful data are the max current, the KV & the weight. For example - the max current of the Turnigy is 38A. Now it doesn't matter what voltage is applied so long as the current is held below 38A the motor will heat up to the same extent. This means that using a 2s lipo (7.4v) the max power will be 38A x 7.4v = 280W ; with a 4s lipo the power will be 38A x 14.8v = 562W & of course max power with your 3s lipo will be 422W . However to keep within the current limit the load on the motor must be reduced as the voltage is increased, the load is of course the prop. Once the prop size becomes the smallest to be practical with the type of model then the voltage limit has been reached. This is where the KV is important. I won't go in the any detail on that other than to say that the lower the KV the bigger the useable prop for any given voltage. My policy with sports models is to use the weight of the motor to help get the right cg. Using a heavy motor with a relatively low load means that whatever power is needed can be achieved without stressing the motor. This is why the current draw of the outrunner I use in the Robot is loaded well below the max amps. There's still plenty of power but if there wasn't a larger prop, or alternatively the same prop with a 4s lipo, could be used to increase the power but then the motor would be running closer to it's max current therefore running a bit hotter. Here's some photos of the Robot first with a couple of glow motors (sorry I didn't take any when it was diesel powered) then electric: With a Fox15. Enya 09 With the inrunner ... and a couple with the outrunner. The battery compartment... covered up. Edited By PatMc on 21/06/2015 23:40:54 Quote Link to comment Share on other sites More sharing options...
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