Motor selection need-to-know basics:
Thrust= Static (on the bench) pull or push of motor in oz.
Amps = (A) current used by motor at a given throttle setting
Volts = (V or Vt) For the LiPos (Lithium Polymer)packs we use;
7.4vts for 2 cell (2S) pack
11.1vt for 3 cell (3S) pack
Watts = amps times volts
Winds = (T = turns)12, 15, 17, 20, 25 etc. Generally the following applies:
More winds, able to turn larger diameter prop at same current
More winds, more efficient and better for higher cell count, higher volt packs
(exception is the new 12 pole 15 turn Komodo motors - they perform like 20 turn 9 pole CDRoms)
Diameter = length of prop (larger = more torque)
Pitch = amount of travel in inches of prop through air (used with RPM to figure pitch speed)
RPM = revolutions per minute of prop rotation
With even just some of the above information (and some on-line calculators) you can know everything you need to pick the correct combination of motor, prop, pack, etc.
We've done the research, here's the ball-park specs on the typical 9 pole CDRom brushless outrunner motors available:
2S, 7.4 vt pack:
17T w/ 8x4 = 5A - 9.5 oz thrust
20T w/ 9x5 = 5.5A - 11 oz
25T w/10x6t= 4A - 9 oz
3S, 11.1 vt pack:
20T w/8x4 = 7A - 16 oz
25T w/9x5 = 5.5A - 13 oz
NOTE: these < 1oz CDRom motors are prone to heating up fast at over about 6 amps. They can be run higher with momentary bursts of full throttle however.
Here's the specs for the 15 and 17 turn Komodo 12 pole outrunners we now carry:
2S, 7.4 vt pack:
KH2204-17T w/8x4 = 3.5A - 8 oz
KH2204-15T w/8x4 = 4A - 9 oz thrust
KH2204-17T w/9x5 = 5A - 10.6 oz
KH2204-15T w/9x5 = 6.3A - 11.9 oz
3S, 11.1 vt pack:
KH2204-17T w/8x4 = 6A - 15 oz
KH2204-15T w/8x4 = 7.5A - 17 oz
KH2204-17T w/9x5 = 8.3A - 18.25 oz
The CustomCDR brand of motors as well as the Komodo's are more robust and can handle more current for getting even more thrust from the same size power plant. Figure about 9 amps max continuous from these.
1000 mAh (milli-amp-hour) capacity = 1A current consumed in one hour
1250 mAh pack (1.25 Amps per hour)
3A average current draw from motor
1.25/3*60(minutes)= 25 minutes motor run
ESC (Electronic Speed Control)
10A rated - choose higher value than peak motor current plus .5A per servo. (Phoenix 10 is fine with CustomCDR and Komodo motors)
LVC (Low Voltage Cutoff)
Voltage selection programmed into speed control to pulse or cut motor to save remaining volts for radio operation to land safely.
LiPo cells can not be discharged below 3 volts per cell (2S pack= 6 vts minimum, 3S pack = 9 vt minimum) without rendering them useless. Be sure ESC is set correctly for the size pack you are using.
10C rated pack:
C = Max current discharge capability of pack
Example, a 1000 mAh (1A) pack that is 10C rated can be run at 10A (10*C) continuously (in theory) without sagging in voltage or overheating.
Max charge rate of LiPos is 1C. You can not charge the pack at more than its rating - 1000mAh = (1A)1000mAh charge rate - 700mAh = (.7 A) 700mAh charge rate, etc.
Power to Weight ratio needed for 3D -
.5:1 (ex. 10 oz thrust for 20 oz plane) sedate performance - no 3D
1:1 (ex. 10 oz thrust for 10 oz plane) hangs on prop at full throttle
2:1 (ex. 20 oz thrust for 10 oz plane) hangs on prop at 1/2 throttle with plenty of vertical climb available
Picking the right combo:
1) largest prop size recommended (ex- CK = 8x4, CF = 9x5, CTC = 8x4 on 3S or 9x5 on 2S)
2) pack size and capacity for desired weight - Less weight = higher power to weight ratio.
Higher capacity = more weight but higher C discharge capability and/or longer duration.
3) power or duration trade-off - Can't run a motor more than it's max thrust but you can run higher powered motors at lower throttle settings for more duration and have extra power if needed.
Still confused? Choose a pre-configured system for guaranteed results. Still have questions or want to have a custom package put together? Send an email and we'll get right on it!