3 mins from 8000mah???

Macsgrafs

Macsgrafs

Active Member
Hi guys,

Got a slight problem I think. I'm using 2 x 4s 4000mah (35-70c) lipos in parallel on a droidworx SJ8 octo running MK firmware etc.
The motors are emax GT 2830/07 & 60A ESC's (yes Im running I2C-PWM). I flew her for the first time properly today & managed a few circuits...but landed at 3mins as its a new ship & I didnt want to discharge the lipo's to low. The voltage in each cell was 3.85 which is what I would call fully discharged...for 3 mins????
I have 12x6 props & was wondering if bigger props might help in this case?

Regards
Ross
 

Bartman

Bartman

Welcome to MultiRotorForums.com!!
ross,
what was the % remaining in the batteries when you put them on the charger? how many mah went back in when you charged them? i think most people consider lipos good to 3.3 volts before ending the flight.
are your esc's set to HIGH timing?
bart
 

Macsgrafs

Macsgrafs

Active Member
Hi Bart, I put back in 1780ma in each pack give or take a few mah's ;) I have the low voltage cutoff set at 3.3v, I was being careful if you get my drift. So basically I took 50% of pack for 3 mins....maybe I will get about 4 1/2 mins but that would be really pushing it I think.
ESC's are ALL on high timing.
Here's something else thats very strange. When I do the motor text in koptertools on just 1 motor...he goes like a belt fed wombat & thats on about 170...yet when I'm actually flying her, the motors dont sound half as powerful....strange? Maybe I should make a video to show you what I mean?

Have been speaking to Craig & he thinks I might have had AH on??? He could be right by the way. Im not sure if 254 is on & 0 is off?

Ross
 
Last edited by a moderator:

matwelli

matwelli

Member
3.85 volts is the 60% mark, so you have used 40%, if you take them to 20% left (double the time) terminal voltage will be in the high 3.6's

the in-flight voltage will be lower during flying due to the current load and battery internal resistance
 

Macsgrafs

Macsgrafs

Active Member
matwelli said:
3.85 volts is the 60% mark, so you have used 40%, if you take them to 20% left (double the time) terminal voltage will be in the high 3.6's

the in-flight voltage will be lower during flying due to the current load and battery internal resistance
Click to expand...

Cheers Mat, so I will be on with 5 1/2mins max I would think, so maybe I will need to run 4 lipos.

Ross
 

matwelli

matwelli

Member
Hey Ross, what does she weigh minus the battery ? and what flight time do you need ? can do a quick calc for you
 


R

RTRyder

Merlin of Multirotors
CineStar 6, AXI 2814-22 motors, Graupner 11 x 5 props, single 4S 8000 pack, RTF weight 4.2 kilos with Nex 5N = 10 minutes flight time to 80% discharge

The emax GT 2830/07 must suck up a LOT of electrons...

Ken
 

Macsgrafs

Macsgrafs

Active Member
RTRyder said:
CineStar 6, AXI 2814-22 motors, Graupner 11 x 5 props, single 4S 8000 pack, RTF weight 4.2 kilos with Nex 5N = 10 minutes flight time to 80% discharge

The emax GT 2830/07 must suck up a LOT of electrons...

Ken
Click to expand...

That's quite impressive Ken, though I think my main problem today was taking off & flying with AH on :(
The 3 minutes could well have been 5 mins, thats 8 motors as well & 2000ma less than your pack......Though I hope a change of props might help!

As it stands I agree, the emax are greedy, hopefully my stupidity wont be repeated again & my next flight will give more accurate times & current draw.

Ross
 

R

RTRyder

Merlin of Multirotors
Macsgrafs said:
That's quite impressive Ken, though I think my main problem today was taking off & flying with AH on :(
The 3 minutes could well have been 5 mins, thats 8 motors as well & 2000ma less than your pack......Though I hope a change of props might help!

As it stands I agree, the emax are greedy, hopefully my stupidity wont be repeated again & my next flight will give more accurate times & current draw.

Ross
Click to expand...

The AXI motors on the CS seem to be more efficient than the Avroto I was using, then again they ought to be for the price difference! Using A/H shouldn't effect the flight time, only the altitude ceiling if you have it set to fixed mode rather than vario. I fly my MK in vario from the time it leaves the ground to just before landing and really don't see any difference in flight times. The video I posted earlier 'MK Sport Flying' was done entirely with vario A/H turned on.

Ken
 

Macsgrafs

Macsgrafs

Active Member
RTRyder said:
The AXI motors on the CS seem to be more efficient than the Avroto I was using, then again they ought to be for the price difference! Using A/H shouldn't effect the flight time, only the altitude ceiling if you have it set to fixed mode rather than vario. I fly my MK in vario from the time it leaves the ground to just before landing and really don't see any difference in flight times. The video I posted earlier 'MK Sport Flying' was done entirely with vario A/H turned on.

Ken
Click to expand...

That's my main problem Ken...lack of funds & of course lack of knowledge. The Mrs set me a finacial target, which I passed some time ago now ;)
What is the main difference between the 2 AH's? Also what advantage is there to having vario AH on during normal flight?

Thanks mate

Ross
 




Macsgrafs

Macsgrafs

Active Member
She's skinny enough & I prefer them to have a bit of meat ;)
Here's the results of todays flight. 3 mins & it drew 1450mah from each 4000mah pack...so thats 5 1/2 - 6 mins I would have thought? Problem was cured that I had yesterday..I had AH enabled :)

Ross
 

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