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Sizing LiPo and ESC for Electric Sailplane

Old 07-01-2022, 06:02 PM
  #26  
svenyonson
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Well, looking back I can see the wisdom of using e-calc up front so you don't wind up buying motors/escs that won't work. But, I'm a gear guy and love having an assortment of parts to use on other projects.

I have now what I think is a winning combination:
- D2826 1000KV Outrunner -
Amazon Amazon
. This motor can swing a 10-11 inch prop, I am using the 9x5 folding prop
- Spektrum 15A ESC.
- Spektrum 1300mAh 11.1 3S LiPo. 30C

Measuring at full throttle, the motor is only pulling 9.3 amps and the IR temperature holds steady at around 82 degrees. I built a rig to measure thrust and it is pulling 600 grams, for a plane that should have a build weight of <= 700 grams.

The listing for the motor suggests a 30-40A ESC, but Spectrum support recommends the 15A for a (different) motor that is rated at 14A continuous, because they say the 15A ESC can handle peaks of 25A. Also I am using a smaller prop than recommended.

Am I missing anything here or does this look about right?
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Old 07-01-2022, 09:38 PM
  #27  
quorneng
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Nice thrust test rig.
As long as you are happy with the accuracy of the motor amps in static conditions with a 9x5 then a 15 A ESC should be fine. In flight the full power amps will reduce by about 10%. I would be wary of a "claimed" max amps figure for an ESC. it is most likely just a burst figure for a few seconds before the MOSFETs overheat. Heat is the killer for ESCs so it is good practise to specify the ESC so the max full power amps is only 2/3 the ESC's rated power. Like batteries manufacturers many ESC figures are influenced by 'marketing' and for maximum profit many use the cheapest components that just meet the specification.
What is important is that the max measured amps the motor is pulling is less than the motor specification. The D2826 1000kV is rated at 150W so your 9.3 A on a 3S LiPo is (say 110W) is safely within its maximum.
600g thrust will be plenty for your plane.
I wouldn't surprise me to find you can cruise and maintain height on no more than 1/2 throttle likely about 3A.
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Old 07-02-2022, 12:00 AM
  #28  
svenyonson
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Thank you, good to get a 2nd opinion. One thing that confuses me still is from what I've read a D2826 would be 28mm in diameter and 26mm in length, which it is, pretty close anyway. But an an A2212 is the same size as the D2826 - I would have expected 22mm diameter and 12mm length.
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Old 07-02-2022, 05:35 PM
  #29  
ron_van_sommeren
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It is a good practice to have some headroom built in. Motor runs cooler, slightly more efficient too, and you have some leeway should things go south a bit.
About derating motors, controllers, batteries, electronics in general:
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Old 07-06-2022, 01:23 PM
  #30  
quorneng
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svanyonson
Unfortunately there is no 'standard' for motor dimensions.
D2826 is its external length and diameter. For the A2212 the figures refer to the dimensions of the wound armature inside the out runner. These dimensions actually better determine the potential power of the motor so you can see why some manufacturers describe their motors this way. The installation dimensions will also be given in the motor's specification.
In addition a motors kV. will determines the speed it will want to run at for a particular voltage which will determine a suitable prop. Just to make thing even more complex a particular motor with a low kV will generate less power (Watts) than an otherwise identical motor with a higher kV.
The simplest is of course to use a recommended motor and prop for the plane but remember a motor with the same physical dimensions and kV will be direct substitute.

You may say IC engine selection is so much simpler but to be fair this is only because radio control IC engines are "dumbed down" to give a good part throttle performance so are all very similar for a given capacity. If you go back to the days of control line there was a considerable difference in the power and performance between engines of similar capacity. You had to choose an engine and prop combination that gave you the performance you wanted just as you do now with electric. .

.
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