Engine Doctor Posted May 2, 2008 Share Posted May 2, 2008 Hi to all the electric guru's out there .I am conversant with ic powered models but have only dabbled ,quite successfully ,with smaller electric models but this is my first electric multi motored job and would welcome some input . It is a 72 " lancaster bomber , not sure of plan as i bought it in a moment of madness. Weight without motors and radio gear is 5 1/4 Lbs. Watt ( excuse the pun ) I would like to know is Do you think this model would fly on four 120 watt bell motors turning 9x4 props? Any suggestion would be welcome ,but please consider cost as exotic motors will be out of the question. Thanks.E.D Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 2, 2008 Share Posted May 2, 2008 Cost is not a factor these days ED - I just purchased a 1200 watt outrunner motor for a shade over £20 brand new.At 5.25 lbs less powertrain you need to add around 30% so AUW will be approx 6.8lbs, lets call it 7For reasonable scale flight aim for around 70 Watts per pound or so minimum, thats 490 so again lets keep the number simple - 500 Watts. Your 4 X 120 watt motors should be just about OK, but not much in reserve there, and it may just lack the thrust for a good take-off especially on 9" props, a 6 foot span lanc is not a small bird is it !Please also consider how exactly you are goung to control these 4 motors - seperate ESCs mean the possibility of one motor cutting before others, perhaps arrange the 2 inboards to be paired up, with their own battery a nd escs together with a DPM and the 2 x outboard likewise, then at least if the LVC kicks in they will stop in pairs and not affect the torque too much.Personally ( if you have the ground clearance ) I think I might go for a 10" prop and motors such as these which have a little morer power 200watt motor for 10 quidOr if budgets are REALLY tight and you keep the smaller prop and lower power these combos maybe ? Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 2, 2008 Author Share Posted May 2, 2008 Hello Timbo Thanks for the input. I had decided to pair the motors (two out board and the two inboard ) as you suggested . The motor combos you suggest are what I had been looking at but didn't want to go down that road without getting another opinion ; although the other motor you suggeted, would be better with 10 inch props ,which I recon would just about be posible . Decisions ! RegardsE.D. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 2, 2008 Share Posted May 2, 2008 Better to a have a little MORE power rather than not enough! Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 4, 2009 Share Posted June 4, 2009 Hi, Lancaster fans! I am just starting out on a 96ins wingspan Lanc and have been thinking about going electric. Don 't know any figures for it yet ie: weight etc. but the advice above has given me a guide and I'm very grateful for that. WhenI last built a RC model things were very different! Materials were different, building techniques (looking back) were really quite basic compared to today, and the thought of electric motors had never been heard of! Like ED I had already decided to pair the outers and the inners, not only because the plans recommended it but for the same reason given my Timbo above too. At least I got that bit right! I should be starting it within the next 2-3 weeks so you may see quite a bit from me for advice etc. Hope nobody minds. Apart from the complication of using IC, the Lanc would never sound like the real thing which is why I have been considering electric motors, but from what I've been reading here over the last few months it is, in itself quite a complicated field and not being any good at all with electrics with regard to working out the figures etc. advice is always welcome. The practical side is not a problem but I don't know enouigh about elecs to work out the requirements. Se you all later!! lol Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 4, 2009 Share Posted June 4, 2009 Hi scuba.... no problem mate, we will help you all you need. Why not consider an onboard sound system for her too - I have one going in my Hangar 9 camel. Quote Link to comment Share on other sites More sharing options...
iawnski Posted June 4, 2009 Share Posted June 4, 2009 my lancs got no motors shes a glider ,will do loops, rolls , shall i go the elecy way ,naaaaaa i love her as she is lol ,but good luck to you guys will read with interest maybe ill be tempted someday Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 4, 2009 Share Posted June 4, 2009 Hi Timbo. Thanks for the offer. To be honest, that was one of the 1st things I thought about seeing as it will be almost silent! I'm going to have a look around the web to see if I can download it somewhere. As I said, the theory of elecs leaves me cold! There's not much I can't turn my hand to but I've never understood the theory side of it. So most of the advice and help I'm going to need is advice on which motors and which batteries and which props etc. and I'm sure there will be quite a bit of other stuff too. Will look forward to working with you! lol I've seen quite a lot of 3 letter abbreviations in your replies to others questions.... like: ESC, LVC, IMO,WOT,AUW & DPM. These might as well be in chinese as apart from guessing at a couple they are acomplete mystery to me!! No doubt when the time comes all will be explained. cheers jon Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 4, 2009 Share Posted June 4, 2009 I was tempted to go elec because of all the complications of IC and now I've fouind I'm going down another road with something I know almost nothing about.; Elecs were not even a twinkle in my dad's eye when I last made model planes! I'm impressed with the glider bit though. That must be some sight without motors! Isn't it a bit heavy for gliding? Unless it's only a small model of course. I don't think I could make my 96" one a glider...it would take something to get it into the air! lol j Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 4, 2009 Share Posted June 4, 2009 For starters..... ESC electronic speed control - self explanatory i think LVC Low voltage cutoff ( it shuts the motor off but leaves enough juice to control the radio as the battery gets low ) IMO In My Opinion WOT Wide Open Throttle AUW All Up Weight DPM Discharge Protection Module - prevents a lipo from discharging too low which can be very baaaaaad HTH ( Hope that helps ) Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 5, 2009 Share Posted June 5, 2009 LOL Nice one Timbo! I guessed right for only two of them. Thanks for that, it will help me considerably. Do you know where or if I can get a wiring diagram for this project? I have a good friend who is an electrician so I will get some advice there but if anyone has already built a multi engined model they may have a diagram that will suit my application. Most of it will, no doubt, be basic and straightforward but as I said earlier a lot has changed since I last built one! lmso (laughing my socks off) Hey....we could start an all new thread here...guess the meanings of the letters!!! lol Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 5, 2009 Share Posted June 5, 2009 Its not so much a wiring diagram you need TBH ( to be honest ) more a case of deciding exactly how you will set things up as far as control and supply is concerned. For instance, you have to choose things like... What physical size batteries of what type, and what capacity will you use? Where will they be fitted - in nacelles or fuselage /other? Will you have a seperate battery for each motor or run two batteries in parallel or indeed just one larger capacity pack? where will the ESCs be fitted - and will use be using BEC or UBEC or separate battery for radio What about cooling of the packs and the ESCs Will you fit isolation switches or digiswitches IF LiPo is used then they should ideally be removable for charging, whereas A123 cells can be left fixed and charged in situ. what provision if any are you making for simultaneous LVC of each ESC - such as a DPM etc etc etc..... As you can see, there is a lot to plan for before you even think about the actual cabling. As far as the cabling is concerned, the type of wire used will differ depending on run lengths - as determined by the above choices as well as likely power to be carried. You really could do with estimating first and foremost the likely AUW ....then at least you can start selecting likely props motors and batteries and ESCs. Once ou have some basic ideas of this lot, the rest will be easier to plan. Edited By Timbo - Moderator on 05/06/2009 15:05:45 Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 5, 2009 Share Posted June 5, 2009 I knew it was going to be a prob. will have to discuss it with you when i get that far, although I will need to decide some things before i actually need them to make places for them in the aircraft. I was thingking LiPo was the best idea but i'm not sure now! BEC & UBEC? Don't understand the bit about cooling the packs. What is the difference between isolation switches and digiswitches? All this will have to be sorted out as I build the fuselage I know so I had better ask now or i will forget. will print out all your answers and comments so i got a record when i need it! Have copied and pasted all the previous posts we have had so i got continuity, hope you don't mind me doing that. With my memory what it is, i forget so easily these days! now where was i? Money is not an problem and i want to do the best i can cos this will most prob. be the last model i will build and i want to go out on a high! lol i estimate it will take between 1 & 2 yrs to build. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 5, 2009 Share Posted June 5, 2009 BEC simply means will you use the BEC built into most ESCs, or use a seperate "standalone" BEC ( often called UBEC ) This is basically a regulator to drop your main flight battery voltage to feed the radio the 5V it needs. If the batteries are pushed hard, and get too hot during discharge, then you will need to arrange some cooling slots /holes etc. Ditto the ESCs. Digiswitch is a foolproof, vibration proof, superb radio supply switch with bult in BEC and is electronic rather than mechanical, and also has battery condition meter built in - not expensive either really. heres a link. I never personally use battery ( main pack ) isolation switches, preffering instead to simply unplug the battery immediately after landing. Of course with some installations, in scale models and so on, a neat switch / isolator link would be preferred. PS dont think of this project as problem - it is a nice project that will give immense satisfaction - it just needs thinking and planning to avoid disappointment. Dont worry, theres plenty of peeps here to help you. Edited By Timbo - Moderator on 05/06/2009 16:14:24 Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 5, 2009 Share Posted June 5, 2009 Right, thanks. At least i understood that bit! wjen you mentioned cooling i was thinking i might be able to leave a cooling slot or something like it in the fuselage. The only thing is, where! I will have to build it 1st to see where the balance piont is. it's on the plans but in my experience that will only be approx. cross that bridge as and when. i wasn't really thinking of this as a problem that was just a figure of speech. i'm sure there will be loads of things to sort out and you're right. it will give me a lot of pleasure and satisfaction....i've been looking forward to it for about 5 yrs and it's only now i've got the chance to do it. digiswitches sound ideal. dont know which way to go yet about isolation switches or not as the case may be, another bridge to cross later! Have built my new workbech for it in my, now empty, garage! most tools acquired, shelving up and lighting fitted over the bench. even got a radio on the top shelf! lol Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 5, 2009 Share Posted June 5, 2009 Sounds like you have been preparing in a serious way John.... Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 5, 2009 Share Posted June 5, 2009 Well, i thought so until i started delving into the wonderful world of elecs. about which i know exactly nowt! lol but with luck and following wind and you to guide me i'm sure we will pull through! I did pick up on another point you made though. you mentioned different grades of wire depending on the length. Is there a set formula for working out the correct size? I didn't think it would matter much on the low voltage and the short distance. does it make that much difference? cheers jon Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 5, 2009 Share Posted June 5, 2009 Well there guidelines available on the internet, but as ever, what you read may simply add to the confusion as theory and specs seem to vary from person to person! I use a more practical and simple approach - the heavier wire guage the better - every time - limited by the weight penalty that the model will suffer. As for whether it makes a difference...most certainly - in most cases. The low ( relatively) voltage is exactly why its important to minimise losses as far as possible. Consider this. The electric company have to send our 250V supply over a distance and do this at something like 25000 volts minimum - which is then stepped down by a local substation transformer before being passed to us. The very high voltage transmission lines allow the current we are likely to need to be transmitted without using hugely thick cables and massive currents ( which of course are air cooled also ).If they sent us 250 V from the power station, by the time it reached our wall sockets it would barely light a torch lamp. Power or Watts, is a function of volts times amps. If we need say 1kw ( 1000 watts ) for our electric bar fire, at 250V its only 4 Amps ( 1000 / 250 =4A ) so the wire does not actually have to be that huge as its current which causes motors and elements to expire. If we were fed only say....100V to our house, the same bar fire would now need wires capable of carrying more than double the current ( 1000 / 100 = 10A ) Ohms law dictates that a small drop in voltage at large currents will affect the power considerably, and we are only working at very low voltages to begin with. ( as stated earlier ...relatively ) Quote Link to comment Share on other sites More sharing options...
Scubajon Posted June 5, 2009 Share Posted June 5, 2009 Have noted all that thanks. makes some sense to me, i remember ohms law from school. will sort it out when the time comes. i'm spinning with all this info today! have noted all you've said so far and i'll get back to you when i've sorted it as far as i can go without advice and help. thanks for all so far. cheers jon Quote Link to comment Share on other sites More sharing options...
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