John Gleeson Posted November 10, 2016 Share Posted November 10, 2016 Hi, I have a Goldberg Cub 78inch wingspan that I built some time ago but never got round to fitting the 4 stroke motor that I originally intended to use. I now want to go down the route of electric power but have no idea as to what size motor, esc or batteries to fit. In fact help avoiding the pitfalls that this may entail would also be useful. I would really appreciate any constructive advice that might be offered to help me achieve this. Many thanks. John Quote Link to comment Share on other sites More sharing options...
Pete B Posted November 10, 2016 Share Posted November 10, 2016 Hi John, Just found your post from 2014 regarding flaps on the Cub - I see you build as the same sort of speed as I do... I've refreshed my memory from my original build thread and the motor info is towards the foot of the first page. Finally settled on a 4250 700Kv on a 5S 4000mA pack, with a 12x8 prop. 5S is, I've found, of limited use across my stable, so you may want to consider either 4S or 6S, with a suitable adjustment to prop size. With a 60A ESC, a bit of experimenting with props and 4S should be OK Pete Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted November 11, 2016 Share Posted November 11, 2016 Just to sort of confirm Pete's figures, I converted my DB Sport & Scale 1/5 Cub (84" wingspan) to electric a few years ago using an AXI 4120/14 which has a Kv of 660. I initially flew it with a 6S pack -- don't remember what prop -- but thought it was too lively, so I then changed to a 3S pack and 16x10 APC E prop, which gives about 550 watts at 51 amps, and 123 watts per pound. I had had problems flying it with an OS91FS, often cartwheeling during takeoff, due to trying to get off the ground too quickly I think. With this setup I just let it fly itself off the ground as speed builds up, and it's a beautiful flyer. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted November 11, 2016 Share Posted November 11, 2016 John, why not invest in November's issue of the magazine (RCM&E) - out now. I believe it has a rather useful article in it showing exactly how to calculate this for yourself - and the example used is,....a 1:5 Piper Cub! Could be what you're looking for! BEB Quote Link to comment Share on other sites More sharing options...
Tony Richardson Posted November 12, 2016 Share Posted November 12, 2016 Don't have one myself John but one club member has a cub that size and it fly's very well on a E-flite power 32, 4s lipo and a 14x7 prop if you have access check out E-calc it will give you really close numbers. There is a free demo version you can use to try, if you plan on investing in electric models totally it may be worth the purchase. Quote Link to comment Share on other sites More sharing options...
John Gleeson Posted November 12, 2016 Author Share Posted November 12, 2016 Many thanks guys for your helpful and quick responses. I am going to review them and hopefully I will be able to proceed based on them., I will keep you informed. Quote Link to comment Share on other sites More sharing options...
John Gleeson Posted November 13, 2016 Author Share Posted November 13, 2016 Pete, many thanks for your responses, your build thread looks great and I will be following your ideas regarding the servo layout. Is the unit on frame at the rear of the cockpit the receiver? Never having ventured into electric flight I feel like `i have opened a can of worms . I have found a number of very informative sites regarding LiPos and there safe use etc, but how does the power train all fit together. I'm thinking here of location and weight distribution. Is the ESC on your build under and behind the motor? Yet another question I notice that you mention the Emax BL3526/05 685Kv with 60 ESC, what battery would I need with that combination and what sort of duration would be likely? Many thanks in advance for any advice I do feel a bit out of my comfort zone here, and do not want to make any costly mistakes. John Quote Link to comment Share on other sites More sharing options...
John Gleeson Posted November 13, 2016 Author Share Posted November 13, 2016 I've just taken a look at eCalc which may answer some of my questions although it does look at first glance somewhat complicated. Quote Link to comment Share on other sites More sharing options...
John Gleeson Posted November 14, 2016 Author Share Posted November 14, 2016 Posted by Pete B - Moderator on 10/11/2016 15:31:33: Hi John, Just found your post from 2014 regarding flaps on the Cub - I see you build as the same sort of speed as I do... I've refreshed my memory from my original build thread and the motor info is towards the foot of the first page. Finally settled on a 4250 700Kv on a 5S 4000mA pack, with a 12x8 prop. 5S is, I've found, of limited use across my stable, so you may want to consider either 4S or 6S, with a suitable adjustment to prop size. With a 60A ESC, a bit of experimenting with props and 4S should be OK Pete Hi Pete I have bought an EMAX GT3526/05, 60A ESC, an Overlander 4S 5000 mAh 35C/65C battery and a 12 x 8 prop, eCalc seems to think this OK, but I'm not sure what all of the data means. What do you think? I'm having second thoughts on putting flaps on it at the moment because of the extra weight of the servos, too much change too soon maybe. John Quote Link to comment Share on other sites More sharing options...
Pete B Posted November 14, 2016 Share Posted November 14, 2016 That doesn't sound too far off, John. I can't run that motor through Ecalc as I only have the MR version paid-for () and can't find a similar c.700Kv motor to substitute. I see the Emax motor is listed - anyone else with Ecalc who can crunch some figures? I would urge you, if you haven't already done so, to acquire, beg or borrow a wattmeter - they are the leccy flyers salvation (and ESCs!). A wattmeter will give you all the information you need in respect of the power output of a particular motor/ batt and prop combination. The important figures are the all-up-weight of the model and the output power of the combo in watts. Divide the watts by the model weight in pounds and you'll get a watts/pound figure. Anything over 80W/lb for the Cub should be fine. If you're further up the scale with, say, 120W/lb, you'll still be fine. You'll have some performance in hand and, after all, that's what the throttle is for.... Right now, the wattmeter will answer most of your questions. Pete Quote Link to comment Share on other sites More sharing options...
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