YelKiteFlyer
New to GSN!
[H=1]LUCIEN MILLER'S WAY[/H]
(Taken from ATTF podcast # 207)
Note:
An electric motor is a constant rpm machine. As you put on a larger prop the motor will try to spin the prop at the higher constant rpm but the current will increase. The propeller determines how much power the electric motor produces.
[H=1]Watts Needed[/H]
I picked a 3DHS Super Vyper to do the calculations.
Super Vyper = 1000 grams = 2.2 pounds
2.2 x 250 = 550 watts needed
80% Rule with electric systems
Always use only 80% of an electric systems.
If you use more, you are shortening the life cycle of that system.
(watts with 80% rule)
550 / .8 = 687.5 watts
[H=1]Picking the Battery[/H]
Picking the cell count of a battery
# of cells = 2 to 5 times voltage, preferably 3 to 4 times.
3 cell = 11.1 = 22 to 55 amps
4 cell = 14.8= 30 to 74 amps
5 cell = 18.5 = 37 to 92 amps
6 cell = 22.2 = 44 to 133 amps
Watts / volts = amps
3s battery
550 / 11.1 = 49.5 amps (a little to close?)
49.5 / 11.1 = 4.46 (a little to close?)
4s battery
550 / 14.8 = 37.2 amps
37.2 / 14.8 = 2.51 (that is between 2 to 5 times)
[H=1]How Big a Battery?[/H]
Amps pulling from motor / capacity of battery = C rating
4s 2700
37.2 amps / 2.7 = 13.8 C rating
60 minutes / C rating = minutes of flight (full power, total discharge)
4s 2700
60 / 13.8 C rating = 4.38 minutes of flight.
80% Rule
4.38 minutes x .8= 3.50 minutes (full power, total discharge)
REAL LIFE (Usually fly at 2/3 throttle = 1/2 current)
3.50 minutes x 2 = 7.00 minutes flight time
80% RULE
Never pull 80% of C rating out of a battery. Personally Lucien does not like taking out more than 1/2 the C rating out a battery. This saves the battery's life cycles.
C rating of battery: Our calculated C rating / C rating of battery = %
25C: 13.8 / 25 * 100 = 55.2%
30C: 13.8 / 30 * 100 = 46.0%
45C: 13.8 / 45 * 100 = 30.7%
[H=1]Picking a Motor[/H]
Prop recommended by 3DHS with watts;
3s = 14 x 7 or 13 x 6.5 with 500 watts
4s = 12 x 6 with 700 watts
So what I need is a motor with a 12 x 6 prop on 4s producing 687.5 watts weighing in the neighbourhood of 130 to 150 grams.
[H=1]Picking the ESC[/H]
The speed controller should handle the highest number of amps the motor will put out, with the prop you pick out, plus the 80% rule.
Max amps (of motor with prop) / .8 = Number of amps your speed controller should have.
(Taken from ATTF podcast # 207)
Note:
An electric motor is a constant rpm machine. As you put on a larger prop the motor will try to spin the prop at the higher constant rpm but the current will increase. The propeller determines how much power the electric motor produces.
- Find out how many watts are needed.
- Pick the battery
- Pick the motor
- Pick the ESC needed
[H=1]Watts Needed[/H]
- Motor Glider = 50 watts per pound
- Trainer = 75 watts per pound
- Sport flight = 100 watts per pound
- Pattern or warbird flight = 150 watts per pound
- 3d planes = 200 to 250 watts per pound
- Scale Helicopters = 150 watts per pound
- 3d helicopter = 400 to 500 watts per pound
- Speed flighing helicopter = 700 to 800 watts per pound
I picked a 3DHS Super Vyper to do the calculations.
Super Vyper = 1000 grams = 2.2 pounds
2.2 x 250 = 550 watts needed
80% Rule with electric systems
Always use only 80% of an electric systems.
If you use more, you are shortening the life cycle of that system.
(watts with 80% rule)
550 / .8 = 687.5 watts
[H=1]Picking the Battery[/H]
Picking the cell count of a battery
# of cells = 2 to 5 times voltage, preferably 3 to 4 times.
3 cell = 11.1 = 22 to 55 amps
4 cell = 14.8= 30 to 74 amps
5 cell = 18.5 = 37 to 92 amps
6 cell = 22.2 = 44 to 133 amps
Watts / volts = amps
3s battery
550 / 11.1 = 49.5 amps (a little to close?)
49.5 / 11.1 = 4.46 (a little to close?)
4s battery
550 / 14.8 = 37.2 amps
37.2 / 14.8 = 2.51 (that is between 2 to 5 times)
[H=1]How Big a Battery?[/H]
Amps pulling from motor / capacity of battery = C rating
4s 2700
37.2 amps / 2.7 = 13.8 C rating
60 minutes / C rating = minutes of flight (full power, total discharge)
4s 2700
60 / 13.8 C rating = 4.38 minutes of flight.
80% Rule
4.38 minutes x .8= 3.50 minutes (full power, total discharge)
REAL LIFE (Usually fly at 2/3 throttle = 1/2 current)
3.50 minutes x 2 = 7.00 minutes flight time
80% RULE
Never pull 80% of C rating out of a battery. Personally Lucien does not like taking out more than 1/2 the C rating out a battery. This saves the battery's life cycles.
C rating of battery: Our calculated C rating / C rating of battery = %
25C: 13.8 / 25 * 100 = 55.2%
30C: 13.8 / 30 * 100 = 46.0%
45C: 13.8 / 45 * 100 = 30.7%
[H=1]Picking a Motor[/H]
Prop recommended by 3DHS with watts;
3s = 14 x 7 or 13 x 6.5 with 500 watts
4s = 12 x 6 with 700 watts
So what I need is a motor with a 12 x 6 prop on 4s producing 687.5 watts weighing in the neighbourhood of 130 to 150 grams.
[H=1]Picking the ESC[/H]
The speed controller should handle the highest number of amps the motor will put out, with the prop you pick out, plus the 80% rule.
Max amps (of motor with prop) / .8 = Number of amps your speed controller should have.