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Electric conversion


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I built this Stolp Starlet during lock down. It has only flown once. It is72 inch span  and weighs about 6 lbs with an SC 70 FS. The problem I have Is I can not get the engine to idle. It is mounted sidewinder and will reach peak RPM,  but when I lower the revs to idle it hunts and cuts out. I originally had an OS 70 surpass which had the same problem. I thought it was the engine and changed it for an SC which I used previously in other models, but same problem. I can only assume it is a fuel tank problem as it sits well behind the engine but on the same level. To this end I decided it would be an Ideal opportunity to convert it to electric.

Now I have asked this question before on this site and asked not to be blinded with science. All I got was blinded with science. There must be a way someone can tell me this motor is equivalent to an OS70 FS, you will need this battery and this speed controller and this prop. It is a scale model and will fly at scale speed. Am I expecting too much.438198970_20200826_1508512.thumb.jpg.d42beec31eaa1568b9a1526aa566c391.jpg

 

Edited by Richard Acland
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The decision on motor, battery/prop is less of a problem than the more practical one of how you install the system in an already built model - particularly battery access.  For practical use, the battery hatch needs to be easily accessible and, as it will be a major part of the CoG because of its weight, its position.

 

Start with the propeller.  It doesn't 'know' what's driving it so the set up you fit should drive it at the same rpm as you OS70.  Aim for approx 100 watts /lb (600) and approx 9000 rpm.  It's similar in weight/performance to my DB S&S Gipsy Moth which flies well with up to 10 minutes duration  on a 4S 4AH LiPo with a GT3526 710 rpm/volt motor with 13x6.5" prop IIRC.  The current draw is (theoretically) 47 amps, so fit an esc capable of coping with 60 amps.

 

As I said, your main problem is not specifying the drive train, but accommodating it neatly in the model.  It would be a shame to spoil should a nice looking aeroplane. 

 

I bought a 1/4 scale one on eBay some years back for very little because it needed a lot of work done on it.  I fitted a Zenoah 26 and it was my first big model.  The hard bit was working out the CoG because of the unusual wing plan. 

 

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Edited by Geoff S
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Geoff is right - access to the battery and space to connect up without putting your fingers near the prop is the tricky part.   I suggest you consider the way Chris Foss advises fitting the lipo for Wot4 electric conversion   - shown here.  Basically a ply tray with Lipo inserted underneath and secured with a wing bolt.  The slightly differnt way Chris Foss uses for the UnoWot is also worth looking at.   Might solve the battery access without cutting the cowl.

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Having had OS70's in numerous models back in the dark days of my IC flying, my go-to electric equivalent is:

AXI4120/14 (5055 660kv)

13x6 APC prop

70A esc

5S1P 4000 mAh LiPo

 

This combination gave me the same performance as the 70 (about 1.1 hp) for 8 minutes of spirited flying.

 

The AXI motor is rather expensive now, but you can get similar Chinese motors cheaper - search for 5055 660Kv motors. RCLIFE.CO.UK has some nice equivalents.

 

Tom

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43 minutes ago, Tom Gaskin 1 said:

Having had OS70's in numerous models back in the dark days of my IC flying, my go-to electric equivalent is:

AXI4120/14 (5055 660kv)

13x6 APC prop

70A esc

5S1P 4000 mAh LiPo

 

This combination gave me the same performance as the 70 (about 1.1 hp) for 8 minutes of spirited flying.

 

The AXI motor is rather expensive now, but you can get similar Chinese motors cheaper - search for 5055 660Kv motors. RCLIFE.CO.UK has some nice equivalents.

 

Tom

Thanks for that, most unscientific answer I have had which makes it easy to undrstand.

 

Richard

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