How to choose brushless + esc + prop + lipo

Hey guys. Thanks a lot. I was away so I did not get to see all the responses till today. To be honest, I few RTFs and that made it easy to deal with motors, etc. Then I flew glow which I honestly still love. My entirely unscientific explanation is that I like the way that heavier planes behave in the air. For instance, between the spitfire and the racer that these guys built, I find the racer and the cruiser to be exactly the kid of thing I like to see in the air. Nitro planes have a tendency to fly more heavily and for that reason, I think, to track better. With electric I am always in a guessing game. So I will try to put this thing together step by step.
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Step 1: You can determine the power requirements of a model based on the “Input Watts Per Pound” guidelines found below, using the flying weight of the model (with battery):

• 50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
• 70-90 watts per pound; Trainer and slow flying scale models
• 90-110 watts per pound; Sport aerobatic and fast flying scale models
• 110-130 watts per pound; Advanced aerobatic and high-speed models
• 130-150 watts per pound; Lightly loaded 3D models and ducted fans
• 150-200+ watts per pound; Unlimited performance 3D models

Step #2: Divide the total desired watts by battery voltage to determine necessary amps.

Watts / Voltage = Amps

Step 3: Determine the Voltage to /Currant ratio by dividing the given Amp by the Voltage.

Amps / Voltage = V/C Ratio

Voltage/Currant ratios should be fairly low; 2 or 3 to 1 being ideal.

Examples: 900w / 11.1v = 81a 7:1 ratio
900w / 14.8v = 60a 4:1 ratio
900w / 18.5v = 48a 3:1 ratio
900w / 22.2v = 40a 2:1 ratio

Step 4: Determine the battery discharge rate (C-rating) by divide the desired Amps by the battery pack capacity, expressed in Amps (A).

Required amps / Capacity (A) = C-discharge rate

Example: 40amps / 4 (4,000mAh) = 10C

Step 5: Determine the Max. full throttle flying time, full discharged battery time by dividing 60
minutes by the C-rating.

60min / C-discharge rate = Max. full power time

Example: 60min / 10C = 6 minutes

Step 6: Determine the 80% discharge flying time by multiplying the Max time by 0.8.

Example: 6 minutes x 0.8 = 4.8 minutes.

Clear as mud?

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it's a little bit on the advanced side, but I would recommend paying around with eCalc.
http://www.ecalc.ch/motorcalc.htm?ecalc&lang=en
If eCalc is all gibberish to you, then go to this article about picking props/motors.
http://oddcopter.com/2012/02/06/choosing-quadcopter-motors-and-props/
It's geared towards quads, but down lower on the page is a series of links for "understanding the science" and the articles it links to cover all the things you'll probably want to know about motor construction and ratings to set you on the right track and how to better use eCalc.
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A general rule of thumb I have seen (and use):
50-75 Watt/lb - glider or trainer
100 Watt/lb - aerobatic
150-200 Watt/lb - 3D

Calculate your total weight (battery and motor included), and figure what type of plane you want, then determine your watts. Remember, you can always throttle back, but you cannot make a weak motor give more power (when in doubt, use more power and deal with the weight).


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Hi, I don't like those fast revving motors either. Very generally speaking - the slower the motor the bigger the prop. But even more basic than that is the actual power of the motor. It all comes down to the amps and the volts - multiply those together and you'll get the Watts (energy available for a given interval of time) - forget about KV that's just the speed the motor can turn at - it's all about those watts. The Blue Wonder can handle about 8 amps (amps is current - flow of electricity) on a 3S (11.5v) battery that's 8 x 11.5 = 92 watts (in a perfect world) probably more like 80 watts. A Blue Wonder will just manage to fly a plane of about 500g, but you'll not have much performance. And if you don't want planes that sound like a fly buzzing choose a motor that runs about 1200-1500 KV and put a bigger prop on it - 8 or 9 inches. Weigh your plane - remembering to include extra for battery and motor - and choose a motor that has enough POWER (Watts) to drive it through the air. A lot of motor sellers specify the model weight range of their motors "suitable for planes 200-600gms" etc. The one your holding up will probably come in about 500-600 gms so you want a motor of about 12-14 amps or a little bigger. That should give you plenty to get it moving. Trawl through the Flite Test articles on prop adventure etc. and you'll start to get the hang of things. At the end of the day, there's no hard and fast rules, but there are combinations that work. Check out the Flite Test builds and compare them to your model - there's some motor/prop/battery/ESC combinations they advise for these builds - they're as good a guide as any. Is yours a light model or will it need the 'beef' combo? Hope that helps. Regarding those fly-buzz motors, they tend to go on pushers that don't have much room to swing a prop, or on smaller scale models where a larger prop would just look ridiculous, and probably hit the ground if the model has scale landing gear.
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