Here is a practical example. I'm finishing an Alfa Models P47. I put an AXI 2212/34 outrunner brushless motor in it. What lipoly battery will work? Checking the manufactor"s data:

AXI 2212/34


Small and very robust but light weight (57g with 14cm long power wires) brushless motor with rotating case suitable for all models of 300-400 size wich surprised you with very high power can deliver. Hardened steel Shaft have 3,17mm and is supported by two large ball bearings wich ensure very good mechanical stability. Thanks to using newest materials this motors achive in their weight category extremely high efficiency and high load possibility. A new future in AXI design is a provision for radial mounting.


Specification
Voltage range 6-10 cells
2-3xLi-Poly
RPM per Volt 740 RPM/V
Max. Efficiency 77%
Max. Efficiency Current 4-8 A (>70%)
Max. loading 10 A / 60 s
No load Current / 12V 0,4 A
Internal resistance 345 mohm
Dimensions 27,7x30 mm
Shaft Diameter 3,17 mm
Weight 57 g
Recomended model weight 300 - 700 g
Propeller range 2xLi-Poly prop 12"x8"
3xLi-Poly prop 10"x5"
10 cells prop 10,5"x7"



Recomended speed controller:
ModelMotors 0810-3
ModelMotors 1210-3


Accessories for AXI22xx/xx.

Radial mount set for AXI22xx/xx.








Examples of use - AXI 2212/34 Motor Prop. w/o gearbox Battery I/A RPM U (V) P- OUT (W) P- IN (W) Efficiency (%)
2212/34 9x6 APC Slow 3xPi-Pol 7,2 5770 10,2 58 73 79
2212/34 10x4,75 APC Slow 3xPi-Pol 6,9 5850 10,2 56 70 80
2212/34 10x7 APC Slow 3xPi-Pol 9,4 5170 9,9 69 93 74
2212/34 11x4,75 APC Slow 3xPi-Pol 9,4 5160 9,9 69 93 74
2212/34 11x8 Gr. CAM gear prop 3xPi-Pol 9,3 5200 9,9 69 92 75
2212/34 10x7 Aer Glas elektro 10x N500AR 7,7 6030 10,8 64 83 78
2212/34 10,5x7 Aer Glas elektro 8x N500AR 6,2 4990 8,8 43 54 78
2212/34 10,5x7 Aer Glas elektro 10x N500AR 8,3 5810 10,6 68 88 76
2212/34 10,5x8 Aer Glas elektro 8x N500AR 6,7 4840 8,8 45 59 77
2212/34 10,5x8 Aer Glas elektro 10x N500AR 8,9 5610 10,5 70 93 75
2212/34 11x8 Gr. CAM gear prop 8x N500AR 7,5 4620 8,6 49 64 76
2212/34 11x8 Gr. CAM gear prop 10x N500AR 9,9 5350 10,3 75 101 74


I'll be using a 3s lipoly pack and an APC 9x6 prop. The data says 7.2 amps (Sorry, I know its hard to read the table, but the current draw is listed after the prop size).

I have 3s Kokam 1500 packs that can handel a 8c draw or 12 amps (8x1.5=12).

I can use this pack.

2nd case. I have a Multipex twinjet with 2 mega 16/15/4 motors in parallel with APC 6x4 props. I measured the current draw at 40 amps. With the same packs, I used 3 in series (a 3s3p). They can handle 36 amps (3x12=36 amps) continuously, so I used this battery, but I knew that I could only use full throttle in short bursts. Well, I liked doing full speed passes so I changed props to 5x5 to drop the current to 34 amps and I can now fly all the high speed passes that I and my club mates can stand.

Sorry about the long post, but I hope that I answered your questions.

John