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suggestions for a motor/prop/esc combo

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richard cohen24/02/2015 22:46:52
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289 forum posts
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evening all. While an experienced pilot and LMA member, i have only just started playing around with electric flight. My first forays have been with a HK Skipper and it is a hoot but it does come with the hardware supplied so i didn't have to think about the setup. Some years ago, i bought a parkzone spitfire (again it all came complete in a box) which i kept in my workshop for a lunchtime flying fix in the local park. I never considered it a proper model as it was 3 channel and on 27mhz but it served its purpose and then got shelved. Well now i am looking at electric flight in a new light i thought that it ought to come out to play again but instead of the brushed motor/gearbox and Nimh set up i ought to see if i could cheaply change to brushless/lipo. My problem is choosing the set up. I have read lots of threads, articles and the like but my failing is numbers ....they just don't gel in the old bonce. (which is why i prefer oily items). I emailed 3 leading electric flight specialists but have never had a reply so what i am looking for is advice on a motor/esc/prop combo which will provide adequate power. The model is 36 inch span and currently weights 1 pound without a battery. If i could utilise the 3s 1500 lipos from the skipper that would be helpful. I don't want to spend a fortune and don't want a pylon racer, just enough go to perform scale flying and basic aero's.

any help would be very much appreciated

Cheers

Richard

Frank Skilbeck24/02/2015 23:09:45
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Richard, you are probably looking at something around 120 watts which on a 3s battery would be around 11 amps, so your 1500 3s lipos would be perfect. Do you have any preferences on where you will shop for the bits, if so it would be easy to suggest something from their range.

Note that you'll probably be looking at an outrunner motor which will not fit the existing motor mount, is that an issue?

Pete B - Moderator24/02/2015 23:17:58
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Views may vary but I think the AUW is the start point for looking for a suitable system as the weight of the model will dictate the wattage required. In the broadest terms, power in the region of 50-70 Watts/lb will be fine for vintage-type models, around 100W/lb will give a sport or scale model respectable performance, whilst for vertical aerobatic performance, 150W/lb+ is needed.

On that basis, your Spit would probably be very satisfying on 100W/lb, so let's say that with battery it will be, for simplicity's sake, 1lb 8oz at the outside, allowing for a bit of overhead in the power department and the use of the throttle. 1.5lb x 100W = 150W/lb.

BRC Hobbies have a useful page of motor/ESC combos graded by maximum watts output. Looking at that list, there's a 160W combo. Following the link on the page brings you to the motor spec.

You'll see from the table on that page that on a 3S pack, a 7x4 prop should give you about 150W.

If you want a little more in reserve, you could consider going up to the 220W combo, although personally I think a 30A ESC would be plenty.

Pete

richard cohen24/02/2015 23:33:24
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289 forum posts
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Hi Frank. thanks for the reply and good to know i can standardise the lipo packs. with regard to where to buy, i have tried emailing Robotbirds,BRC and Puffin but with no reply i kinda think 'how rude' and why should i use them but maybe i am cutting off my nose etc. my only other experience was with hobbyking for the Skipper purchase and prices seemed keen but i'll be guided by the forum if you have suggestions.

richard cohen24/02/2015 23:41:58
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289 forum posts
37 photos

Hi Pete. thanks for the info. the BRC page is useful (even if they didn't reply my emailsarcastic)

The power combo certainly seems to match your 100-150w per lb and if the weight comes out lower then i can always throttle back !

one thought has occurred to me. as the model lands on its belly, the current prop is quite flexible and has never broken on landing (i guess it flexes enough and then the motor rotates till horizontal). Will an APC prop have some 'give' or is it going to break, or do i need a folding affair like the glider boys use

Rich

john stones 124/02/2015 23:48:59
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11688 forum posts
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I have a few leckys Rich never broke one landing yet

John

Dave Hopkin25/02/2015 00:20:47
3672 forum posts
294 photos

George at 4-Max has a very good list of suggested set ups **LINK**

Had a quick look and the only spits are the 42" Cambrian and a 48" Ripmax versions, but I have always had brilliant help via email from him - and while their motors aren't the cheapest they are solid and reliable units

I would think the 850Kv version of this **LINK** would be a pretty good fit

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