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is this overly optimistic?

zev

lumpy member
#1
firstly, sorry to be flooding the multirotor forum with questions, but you guys are so awesome and multirotors are SO COMPLICATED.

I have been fiddling about with eCalc for the past few days, trying to find the optimal prop and battery to go with my (planned) tricopter with dt700's. no matter what I tried, I couldn't seem to get the hover time much more the 15min. but then just today I tried it with NTM 28-30A 750kv and esc's/prop to match, but the same battery. the lighter motors make up for the heavier esc and prop. now I am getting 18 min flight times!

now, to be perfectly honest I would be happy to get 15min flight times. but I am assuming that this eCalc thing may just be very optimistic, or I am entering some information wrong.


what is your experience? how does your flight time compare to the calculated one? is this a trustable tool?


Screen Shot 2013-02-22 at 4.31.26 PM.jpg
 

PaulT

New member
Mentor
#2
"All values are calculated and may deviate from the real."
How did you calculate the dt700's?
I cannot see any listing on this site for these motors.

Bear in mind 18 minutes (if you are able to get this) is an awful long time in the air, assuming that you are airborne that long.
A shorter flight time enables you to check on things that come loose and they will. And it will allow your motors and esc's to cool off too.
 

Ak Flyer

Fly the wings off
Mentor
#3
I was wondering the same thing. 18 minutes is a looooong time to fly in one shot. If you aren't doing long range FPV or something anyway. I find that after 8 minutes I need a break but that's doing 3D flight with planes and helis so maybe it's apples vs oranges. Still seems like a long time though. I would be happy with ten unless it's long fpv or photo missions.
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#5
A little off topic, but that's what I do...

When you get up and flying, I insist you get some footage at Hemlock Gorge Reservation, right there in Natick. I used to love that park, both in the winter and in the warmer months.
 

zev

lumpy member
#6
PaulT: I found tests online in which no load current, resistance and number of mag poles were all calculated.
FlyingMonkey: I have never actually been there. I looked it up on online though, and those bridges look amazing! I might actually go later today.

well guys, I figure that the longer the flight time the better, because that means I can have a smaller (lighter!) battery, and have more weight in fpv and arial photography gear. I see it as the less efficient the setup, the less stuff I can put on.
so no, I probably wont be flying it for 18 mins, but I see no reason why I shouldn't build in the capability to fly longer with a bigger battery, if I want to.


anyway that wasn't really my question, I was asking how accurate have you found eCalc. is it optimistic, or pessimistic?
 

PaulT

New member
Mentor
#7
anyway that wasn't really my question, I was asking how accurate have you found eCalc. is it optimistic, or pessimistic?
There are so many variables that you are dealing with that the eCalc is just a guideline.
It's a good starting point.
 
#8
ecalc is pretty safe to use, i do my calculations and its right on the spot !

the props you are specifying have too much pace. thats why you got that ridicoulous amount of time.... type in 11x4,7 or 12x3,8 and you will get credible numbers for 3s

also check your flying weight, altitude, and temperature - those factors make a big difference
 

zev

lumpy member
#9
sorry, what exactly is prop "pace"? and what is ridiculous about a gws 12x6? anyway, changing from a 12x6 to a 12x3.8 doesn't change my flight time. it does change a bunch of other things, like throttle percentages, and max current.
 
Last edited:
#10
I meant prop pitch, excuse me my french ...

with 12x6 your Tri wont be as stable as with a lower pitch propeller, since it will spin slower to maintain hover, spinning slower means slower gyro adjustments.

your Tri wont fly as smooth as with lower pitch props, but it will be fast and powerful; you need to weight the Pros and Cons.
 

zev

lumpy member
#14
one more question, eCalc says that I wont be pulling more then 8.4c from the battery, so do I really need a 50c battery, or could I use a 25?