Question about running 5 cell vs 6 cell

[929freak]

My current set-up is 170 main gear with 16pinion,my head speed calculator gives me 2450...
I'm switching to the 112 main slant tooth gear with a 13 pinion,if I run that gearing on 5 cell it's says headspeed of 2620. So 5 cells are cheaper and lighter,anyone have a reason this isn't a good idea?
I do have the pinion to use with the slant and 6 cell but was considering the 5 cell for a weight reduction.
All things being equal,if geared right performance wouldn't suffer on 5 cell would it?
Thanks guys!

[GlobalHawk]

If you wanna run 5s I suggest you get a 500. You're gonna kill that 5s battery!!!!! It'll puff after 1st flight.

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[Nko15]

There is also a 12t slant pinion from the 700.

[929freak]

What am I missing? A 5000 MaH 40C 5 cell is good for how many amps? 200, correct? And a 6 cell 5000MaH 40C battery is also good for 200 amps,right? The only change is the voltage, 22.2 vs 18.5. So if geared correctly for the Kv of the motor shouldn't it work?
Or am I WAY off base here?

[krobinson103]

The LHS owner is running a beam 600 on a 5s. He changed out the pinion and main gear to compensate for the decreased power. It flies well, but the best way to describe it is docile. Very stable and docile. He calls it boring.

[929freak]

Thanks Krobinson...I just can't figure why....amp draw is amp draw,and all things being equal if geared accordingly it seems like it should fly the same...or better with the weight reduction..
I'm pullin' my hair out here!!!!

[chakotay]

Originally Posted by 929freak

What am I missing? A 5000 MaH 40C 5 cell is good for how many amps? 200, correct? And a 6 cell 5000MaH 40C battery is also good for 200 amps,right? The only change is the voltage, 22.2 vs 18.5. So if geared correctly for the Kv of the motor shouldn't it work?
Or am I WAY off base here?

Power is (voltage x current) so by going to 5s battery, you will lose power or increase the current draw (please don't take the C rating too seriously, there's a lot of marketing in that number, most importantly don't expect to be able to pull 200 continuous Amps out of a 40C battery!).

That being said, this helicopter is a very versatile machine. I can run through a pack (6s by the way) in 4 minutes or in 8 minutes depending on headspeed, blade length, and flying style. If you go to 5s, you just have to expect less power and make sure that you won't over amp it. It's all just common sense really - run lower headspeed (mine is a great sport flier at 1900-2000 RPM) and shorter blades (the stock 520's are not bad), keep the weight down if possible etc. I think it's doable. Good luck!

[Chris DeSain]

18.5v x 200A = max watts 3700
22.2V x 200A = Max watts 4400

So the load voltage drop will be greater on the 5S than the 6S

There is more to it also but your not going to get equal power at the same amp load or even a greater amp draw on the 5S.

You can gear it like it should be equal but it will not be. If you are running way below spec of the batts they will be closer but when the pack is loaded it will be noticable.

[Wynn1427]

I always run the calculation based on the motor output.

Motor output watts / Voltage = Amp Draw

Stock 600mx it will be

Cont. = 2000 / 22.2 = 90amp
Peak = 3000 / 22.2 = 135amp

Now on 5s

Cont. = 2000 / 18.5 = 108amp
Peak = 3000 / 18.5 = 162amp

Saving on weight is a good thing but at the expense of two more critical items of flight time and stress on electronics is the reason to not go with a 5s. Going to a 5s setup could decrease flight time by up to (1 - (90 / 108)) = 17%. And with only a weight savings of maybe 140g on a 2800g+ setup, probably won't even notice it is gone.

Take a look at my post here in regards to the actual stress on lipos. Even though they both have the same stated amp draw one is more stressed and results in a lower voltage under load.

Wynn

[jonp]

Originally Posted by Wynn1427

I always run the calculation based on the motor output.

Motor output watts / Voltage = Amp Draw

Stock 600mx it will be

Cont. = 2000 / 22.2 = 90amp
Peak = 3000 / 22.2 = 135amp

Now on 5s

Cont. = 2000 / 18.5 = 108amp
Peak = 3000 / 18.5 = 162amp

Saving on weight is a good thing but at the expense of two more critical items of flight time and stress on electronics is the reason to not go with a 5s. Going to a 5s setup could decrease flight time by up to (1 - (90 / 108)) = 17%. And with only a weight savings of maybe 140g on a 2800g+ setup, probably won't even notice it is gone.

Take a look at my post here in regards to the actual stress on lipos. Even though they both have the same stated amp draw one is more stressed and results in a lower voltage under load.

Wynn

What an excellent, clear and concise reply to a good question.

[929freak]

Wynn,thank you for the clear answer...it really helped
Jon,thanks for the "good question" comment...I felt a little embarrassed to be asking it as a builder!