Steve Hargreaves - Moderator Posted December 1, 2015 Share Posted December 1, 2015 The concept that an electric motor has a fixed "design speed" & will always try & achieve it & work as hard as necessary to do so is one that people unfamiliar with electric motors can get their heads around I find.... A more detailed explanation does get confusing & I find that fellow modellers I talk to tend to glaze over right at the point I mention "back emf"....... Quote Link to comment Share on other sites More sharing options...
kc Posted December 1, 2015 Share Posted December 1, 2015 Do you really need 150 watt per pound for this type of model? There is a lot of wing area. I would expect it to fly well on 100 watt per pound. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted December 1, 2015 Share Posted December 1, 2015 Posted by kc on 01/12/2015 13:36:49: Do you really need 150 watt per pound for this type of model? There is a lot of wing area. I would expect it to fly well on 100 watt per pound. I think it would probably fly quite sedately at about 80W/lb, I will be aiming for something around the 110w/lb with about 20 or 30w/lb capability in reserve if needed by simply up propping it,,,,,, also means that the motor/ESC are not being pushed towards their limits - I'll probably start off with an unreliable 60A esc I have for ground testing and replace it with a new ESC before flight Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted December 1, 2015 Share Posted December 1, 2015 Oh dear Peter ! Why oh why don't folk like your means of propulsion for which your magnificent designs are meant? Now we are bombarded with incomprehensible motor code numbers/the requirement for a box full of propellors /To going flying with several different batteries (chargers etc) all for just a very few minutes of actual flying . I''ll get mi coat & I do have a lekky Multiplex motorised glider which will virtually fly as long as I want -so there ! Grumpy grounded Myron Quote Link to comment Share on other sites More sharing options...
kc Posted December 1, 2015 Share Posted December 1, 2015 The experts all have their own views! What we need to decide here is what we should advise the complete newcomers to building to use. Bearing in mind they may well buy the laser cut complete set. If they have fuselage sides pre cut then the possible options become limited ( they cannot easily move F1 ) so what motor and Lipo do we advise for novice builders? And what method of motor mounting? Maybe this type? Quote Link to comment Share on other sites More sharing options...
kc Posted December 1, 2015 Share Posted December 1, 2015 Myron it's because the public don't like the noise! Restrictions on power flying sites and developments in brushless motors and Lipo batteries have coincided. Electric flying is taking over. It's called progress! As for number confusion, that's what we are clarifying here. Great to have Myron speaking his mind though! Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 1, 2015 Author Share Posted December 1, 2015 They're at it with the I.C jobbies as well Myron, what's the world coming to Johbn Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted December 1, 2015 Share Posted December 1, 2015 KC that sort of motor mount would work, but we need to find somewhere for the Lipo too and a hatch..... And now that I am armed with the plan..... Between F1 and the nose ring is 100mm, lots of room for a motor.... I am tempted to make a motor mounting/battery box from lite ply running from F2, through F1 and extending into the cowl... I will have to choose a motor before I know how far forwards it should extend, the motor box will also form the mounting for a cowl which will slide over the box and be a tight fit perhaps a couple of magnets on what remains of F1 for peace of mind....... The hatch would be from F1 to F2 giving access to the open top of the battery box..... as long as the box is deep enough a decent sized battery should slide in...... So the deviations from a laser cut short kit would be: Cut out in F1 for the Battery Box Sides, top and bottom of the Battery Box End cap "Firewall" for motor mount Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted December 1, 2015 Share Posted December 1, 2015 As for motor choice, for a sedate 3S or more capable 4S power train I would suggest **LINK** Costing £12.63 if you wait for the offer, With a 60A ESC and something like a 12x6 or 8 prop giving about 100W/lb on 3S and 125w/lb ish on a 4S Edited By Dave Hopkin on 01/12/2015 15:27:06 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted December 1, 2015 Share Posted December 1, 2015 Posted by Myron Beaumont on 01/12/2015 14:42:59: Oh dear Peter ! Why oh why don't folk like your means of propulsion for which your magnificent designs are meant? Now we are bombarded with incomprehensible motor code numbers/the requirement for a box full of propellors /To going flying with several different batteries (chargers etc) all for just a very few minutes of actual flying . I''ll get mi coat & I do have a lekky Multiplex motorised glider which will virtually fly as long as I want -so there ! Grumpy grounded Myron The problem is, Myron, that I don't have the brains required for electric flight I can simply say .40 FS and everyone knows exactly what is needed and I know exacty what size range I can build to suit that enngine. This doesn't take any high powered brains, just good old fashioned experience.. Now you may have noticed that basically no one has asked what size engine to use. A few have asked how much bigger to make the nodel with a bigger engine. which is fair enough. And I must add that I do fly electric. I have have a nice Great Planes Spektra built from a kit and powered with a Speed 600 motor turning an 8 X 4 folding prop and using 7 cell NmHi batteries. Not sure what size speed controller I have but it works. Quote Link to comment Share on other sites More sharing options...
Steve McIntosh Posted December 1, 2015 Share Posted December 1, 2015 Posted by kc on 01/12/2015 14:48:37: The experts all have their own views! What we need to decide here is what we should advise the complete newcomers to building to use. Bearing in mind they may well buy the laser cut complete set. If they have fuselage sides pre cut then the possible options become limited ( they cannot easily move F1 ) so what motor and Lipo do we advise for novice builders? And what method of motor mounting? Maybe this type? Exactly. I am planning on buying the laser cut set. This is a first build(after 3 ARTF's) and whilst I would eventually like to get to the point of just a plan and a stock of wood lets take it in baby steps. I need to know EXACTLY what to do to differ from the plan to make an electric set up. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted December 1, 2015 Share Posted December 1, 2015 In answer to KC's earlier point - no you don't need 150W/lb for this model - but that's what I want! I did make that point in the post! T he purpose of showing the calculation in detail was so that if you wanted less - say 100W/lb - you could simply follow the method through and you'd end up with your particular values. The trouble with just saying "buy this motor and this ESC" is that it teaches people absolutely nothing! OK they can buy those things - but they don't know why they are the appropriate items. The point of the MB is help people reach a position where they can do this for themselves. By showing how to calculate this for yourself I believe I have at least tried to improve knowledge. I'm not saying "buy the same motor as me", what I am saying is "I've told you you need 100W/lb or so minimum now here is a method for calculating what you need - I'm going to illustrate it with a value of 150W/lb (because that's what I want) you use your own values". Simple! BEB Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted December 1, 2015 Share Posted December 1, 2015 Hello to all, I'll second BEB on his reply. I'm a total newbie myself (RC, modelling, IC, EP, EPP, ESC, Gorilla stuff, PVA, GF, CF, TMA, AUW, BRU Airport & a lot more acronyms to master ...). But if you tell people what they 'have' to do - ie. motor A, combined w/ ESC B & prop C -, obviously they 'll not be learning a lot, just 'copycatting' what as been said (ordered?). No learning phase there, I'm afraid. Explaining W/lb, max current, KV, prop pitch & so on, seems to be the right approach in a learning curve. One's knowledge 'll only improve if he/she understands how & why things are happening. Since more than one year I'm daily visiting this forum as we don't have this kind of 'wealth' in the country. And some members here are really dedicated to 'help' the newcomers. Great pedagogy, thanks to them. So, I'm buying a Wattmeter right away... Chris Brussels, Belgium ps: ... the easiest way to calculate the lateral offset of your motor mount is to use the sine of the thrust angle... Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 1, 2015 Author Share Posted December 1, 2015 I dare say those going the I.C route will fit a variety of engines, no different for lecky flyers, each to his/her own, by the time we start building there should be enough set ups mentioned, for us to choose one that suits our own particular style of flying. I like a bit of grunt myself but that don't mean it'll be a pylon racer, just means loops will be big and i'll be throttling back and getting longer flights. John Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 1, 2015 Author Share Posted December 1, 2015 Posted by john stones 1 on 30/11/2015 17:15:29: Always a conundrum for myself choosing the motor prop combination, I have a Turnigy SK3 3548 1050kv it's a little on the powerful side but my thinking is prop it down on a 4c 3300mah lipo and 60 amp esc? then i'll get longer flight times and cooler running, prop will be figured out using the watt meter, I have some APC 14x7 and am guessing a little over 620w ? all guess work so far though. I have been using these SK3 for a while now and they've been very good. Feel free to chip in if my thinking's wrong. John My prop thinking was way out, I've been reliably informed on a 10x6e apc i'll get 153w/lb..46 amp max and 7 minutes flight time on this set up, these figures are from ecalc and it's been my experience so far, that I get better flight times than predicted without pushing the lipo's John Quote Link to comment Share on other sites More sharing options...
Erfolg Posted December 1, 2015 Share Posted December 1, 2015 I do have a number of models in the general range being discussed, that is circa 54" span. I do have information with respect to the motor, voltage and propeller combinations. What I do not have is the weight of the models, nor wing loading. What I am not recognising at present is the power necessary for what I had anticipated in a gut feel sort of way. You are all looking for far higher power than I had sort of guessed would be necessary. In my case I need to get the scales out and sort out my own model weights, Perhaps the Ballerina weight is higher than I had anticipated. Although my own models are pretty much the same type of structures of both Peter and Tims. In the case of the TH, CS, the model itself weighs nothing, could this be part of the issue with the IC model. The engine the extra nose weight? At present I do not know or understand. It seems for me there is some work to do. Quote Link to comment Share on other sites More sharing options...
Glyn44 Posted December 1, 2015 Share Posted December 1, 2015 Wot watt meter, excuse pun. I bought one and it arrived with three leads at one end, three leads at the other, not a connector attached to any of them! Lesson, don't forget to order some connectors, and be prepared to solder them on. Another part of the learning curve I suppose. Happy landings, Glyn. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 1, 2015 Author Share Posted December 1, 2015 Check what extra's you need when you buy the electrics as well Glyn.Hobby King do them at fair prices. John Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted December 1, 2015 Share Posted December 1, 2015 People use many different types of connector Glyn....there is little standardisation so a wattmeter fitted with say a Deans connector would not be welcomed by someone using XT60s.... But I'm intrigued by the three leads.....most only have two & fit between the battery & the ESC. Which wattmeter do you have? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted December 1, 2015 Share Posted December 1, 2015 Yes - I've not see a Watt meter with three leads? I have a nice one as it has a servo tester built in as well - very handy. BEB Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted December 1, 2015 Share Posted December 1, 2015 I've put 5.5mm bullets on mine and then made a pair of 5.5mm bullet to XT60 adapters. Most of my batteries are XT60 so the wattmeter sits in my box with the adapters on ready to be used (I won't lose them this way). When I need to measure my F3A stuff with bullet connecters, I just unplug the adapters. This logic should work with any type of connecters. Just think about what you will need, then make up the leads to suit. Quote Link to comment Share on other sites More sharing options...
Geoff S Posted December 1, 2015 Share Posted December 1, 2015 Glyn: Both my Wattmeters have 4 wires. A positive and negative in (from the battery) and a positive and negative out (to the esc). I can't think why yours has 3 at each end. One of mine does have a connector for a balance lead so that it can check the voltage of each cell in a LiPo pack but the other ( an original Astroflight one that cost a small fortune when I bought it) just has the 2 in and 2 out. There is a wide variety of connectors for electric flight. I use 4mm bullet connectors but others use Deans or XT60 etc. Annoyingly my polarity of choice is opposite from the ones HK supply. I chose mine 20 years ago, almost at random and it's too much trouble to change now. Geoff Quote Link to comment Share on other sites More sharing options...
Erfolg Posted December 1, 2015 Share Posted December 1, 2015 It is perhaps worth a few words on the different types and sizes of connectors? The aspects that concern me, and influence which ones I would consider using are: Polarity protection, and how fool proof inadvertent wrong connection is. How bulky the connectors are. How easy are they to solder and protect. At one time there was a brief period that many seem to have standardised on Lipos using Deans type (now never supplied on the Lipo), now C60's are pretty common, as are bullets in housings and so on. I am just prepared to solder, every time. Quote Link to comment Share on other sites More sharing options...
kc Posted December 1, 2015 Share Posted December 1, 2015 you mean XT60 don't you Erfolg? The Component Shop catalogue has good picture of all normal connectors if that helps anybody. They supply connectors with leads soldered on if that helps you. Just soldering the 2 wires together is easier! Quote Link to comment Share on other sites More sharing options...
Glyn44 Posted December 2, 2015 Share Posted December 2, 2015 Sorry you guys, grovelling apologies! My watt meter is still in its box unused as yet, until I fit my connectors. I never checked it and for some stupid reason thought it had three wires as per ESC I'll try to buck up. Glyn. Quote Link to comment Share on other sites More sharing options...
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