How to decide whether to use 5s or 6s

[chasers]

Hi all,

Is there a website where its shows us how to calculate whether to use 5s or 6s, like the headspeed calculator? I do understand that the more cells there are, the lower the amp draw, therefore i am trying to calculator how much amp draw if a recommended setup is to use 6s but instead use 5s... Just so that I do not exceed the amp for the esc...

Formulae will also be good....

Thank you all

[johndyl]

the simple way

u can try to take the peak amp draw for 5s x the peak 5s voltage

eg 65A x 21V = 1365W

then for 6s peak voltage is 25.2V
peak amp draw should be = 1365W/25.2V = 54.17A

to know for sure, u'll have to search eagletree charts for similar setups to yours and look at their peaks

[johndyl]

but then again different flying styles(of different pilots or even the same person) can cause more than 20A difference in peaks

[Super-Hornet]

Apart from ampere... there is one thing u also need to aware of also:
Between 5S and 6S, the voltage different is 4.2V. If your motor is rated as 2000kv for example, running at 75% throttle curve will have:
6S => 6 x 4.2V x 2000kv x 75% = (6*4.2*2000) * 0.75 = 50400 * 0.75 = 37800RPM.

5S => 5 x 4.2V x 2000kv x 75% = (5*4.2*2000) * 0.75 = 42000 * 0.75 = 31500RPM.


Suppose your Main gear teeth is 150 and your pinion u use is 13Teeth, then the division gear ratio is 150/13 = 1:11.5


Thus, for:
6S
Your main rotor RPM at 75% = 37800RPM / 11.5 = 3286RPM

5S
Your main rotor RPM at 75% = 31500RPM/ 11.5 = 2739RPM


U see the different in RPM? Thus, if u want to run the same RPM that was intended to run on 6S, your 5S have to set the throttle curve higher or u increase the pinion teeth or change the motor to higher KV. Increase all those, and your current consumption increase higher.

Thus, it is normally easier to go from low voltage to higher voltage than from higher voltage to low voltage.

SH

[chasers]

Apart from ampere... there is one thing u also need to aware of also:
Between 5S and 6S, the voltage different is 4.2V. If your motor is rated as 2000kv for example, running at 75% throttle curve will have:
6S => 6 x 4.2V x 2000kv x 75% = (6*4.2*2000) * 0.75 = 50400 * 0.75 = 37800RPM.

5S => 5 x 4.2V x 2000kv x 75% = (5*4.2*2000) * 0.75 = 42000 * 0.75 = 31500RPM.


Suppose your Main gear teeth is 150 and your pinion u use is 13Teeth, then the division gear ratio is 150/13 = 1:11.5


Thus, for:
6S
Your main rotor RPM at 75% = 37800RPM / 11.5 = 3286RPM

5S
Your main rotor RPM at 75% = 31500RPM/ 11.5 = 2739RPM


U see the different in RPM? Thus, if u want to run the same RPM that was intended to run on 6S, your 5S have to set the throttle curve higher or u increase the pinion teeth or change the motor to higher KV. Increase all those, and your current consumption increase higher.

Thus, it is normally easier to go from low voltage to higher voltage than from higher voltage to low voltage.

SH

Thanks for the explanation, makes me understand more how all the stuff works.. Knowing all this, how do I apply it to calculate whether the batt that i will be using will be able to take the amp draw, as well as whether the esc will be able to take it, and also how long will the estimate flight time be?

Scenario is the Trex500... from using 6s, I am thinking of using 5s as I have 5s batt to be shared wif my eraptor... I know i gotta change the pinion to higher pinion, but just trying to figure wat my flight time will be like using the 5s 3200mah batts and whether the esc or batt will run hot....