Aeronavics / Droidworx Need more flight time!

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RTRPLT

Guest
Anyone have any idea how I can extract more flight time from this setup?

Skyjib8
Cinestar 3 axis gimbal
MK Multi
2826/12 motors
14x7 props
70amp escs
2 x 6s 8000mah
estimated AUW 12-14kg. (need to weigh it some time)

flight time 6 min, about 30% left on packs.

Is 6 min the norm with the big rigs?
 

E

Electro 2

Member
I'd venture a guess props are waaaay too big for a 2826. I haven't seen the curves for this motor, but I can't imagine anything over a 13 would be even close to OK on the efficiency scale. With 12 motors I'd SWAG it in for about 11s to start, concievably 10s. Dunno about 6 cells either, what's the K-sub-V of these turners ?? 6 cell land begins at about 600 Kv and goes downward to 350 or so.
 

R

RTRPLT

Guest
Thanks for your reply. Could you clarify your statement a little please as I don't know what SWAG means. From what I have read and understood is that your saying that my smaller motors need to turn a smaller prop at a higher rpm to be in the right efficiency range so as not to draw so much power.
 

E

Electro 2

Member
LOL, old engineering-speak phrase (S)cientifc (W)ild (A)ss (G)uess. And yes, you understood absolutely correctly. If you have curves for this motor look for a Grams-per-Watt figure. This is the amount of electrical power, (measured in Watts), required to yield a particular amount of thrust (Lift). As one progresses through ever larger prop sizes at a given operating voltage, there will be a peak figure reached and passed. A five second rule of thumb is you can go one prop size either way and still be OK. 2 prop sizes, maybe. Three prop sizes, probably not. On my little quad whizzer, at 4 lbs AUW, I have 2810s. Kv is 750, so we're pretty much in 3 or 4 cell land. Curves show peak efficiency with a 11 X 4.7, and decent with a 12 X 4.7 and that's what I run.
 

R

RTRPLT

Guest
LOL awesome, cool phrase, will remember that one.

I am not sure where to get performance curves for this motor. Will search the net and see what I can find, they are AXi motors. Thank you for your help.
 



R

RTRPLT

Guest
Hmmm according to that calc I am running things way out of spec, past the spec of the motors, battery's and ESC's. Have to bring the prop size down to 10x5 to get it within spec. Seem a bit odd to me.
 

E

Electro 2

Member
Nope, like I implied, 11s or so, would be spot on, I'd also be sure your motors are speced for 6 cell packs. Would have to know the K-sub-v figure. Many brands of 2826 size motors are wound for 3-4 cells with a Kv figure of 700 to 800. 6 cell land is below 600 or so. Some, not all, motor manufacturers use a suffix tacked onto the armature size number to indicate operating voltage. Such as a 2826-11 would be a 3 cell wind, a 2826-22 would be a 6 cell wind. Some other maufactures use the suffix to indicate god-knows-what, too, so it's not a hard and fast rule.
 

R

RTRPLT

Guest
760 kv and rated to 5s LiPo. I have some 5s here. Going to try them and see what happens.
 

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