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I Need Help

#1
I am still a little new to this world and I want to build a plane using a coaxial motor set up. Where I am having a problem is learning battery needs for the motor. I will put the specs for the motor down below.

Is there anyone who can help me understand what I need for a battery. I am hoping for a couple hours of fly time or at least as much as I can get.

Any help where someone can help me learn to extract the information needed would be greatly appreciated.

Weight: 275g, (9.7oz) with prop adapter
Max Power: 800W, (This is dependent on several factors)
Max RPM: 12,000 RPM
Diameter: 35.3mm, (1.39")
Length: 64.3mm (2.53")
Shaft Diameter: 4.73mm (3/16") front shaft, 9.48mm (3/8") rear shaft
Motor Mounting Holes: 4 holes, 3.17mm through, on 43mm, (1.7") bolt circle
Maximum Case Temperature: 65oC, (149oF)
KV= 1030, Rm = .0.035, Io of front motor = 4.8A/10V, lo of rear motor = 2.3A/10V
Efficient Operating Current =30-36 A per rotor, 40A Max 15 seconds per rotor.
Suggested Props: For 3-cell operation APC 12x6P front prop, APC 11x8E rear prop
Battery: 3-cell Lipo that can sustain 70 to 80 amp continuous draw.
ESC: Two 35 Amp ESCs or equivalent. Also needs a MPI 2160 or 2460 Y-harness to join the two ESC to throttle channel.
 

rockyboy

Skill Collector
Mentor
#2
It sounds like you're already set on the voltage and prop size (which will determine amp draw) so the only variable left to play with is mah capacity. And mah capacity is directly tied to the weight of the battery.

So what you're looking for is the weight trade off for flight performance - if the plane has the space and ability to handle lots of extra weight, you can drop in a massive 3s4000mah battery. But with that heavy of a battery, unless you have a lot of spare lift capacity, it's going to really drive up the stall speed and cut down your flight times.

Going the other direction, if you put in a little lightweight 3s800mah battery the plane can have a much lower stall speed and need less forward kinetic or upward thermal energy to have positive lift. That battery won't last as long running a motor like yours - but if the plane is more like a hotliner design where you power up to height and then glide around searching for thermals, it could be a perfect fit.

So what are you trying to fly? And how are you trying to fly it?
 

ElectriSean

Eternal Student
Mentor
#4
This is actually really simple math. You want 70-80A for 2 hours. 70A x 2hrs is 140Ah, or 140,000mAh. That is a HUGE bank of batteries. Not really realistic... Luckily you probably don't really need 70A continuous, or 2 hours in the air at a time. I can't imagine flying any plane for 2 hours straight unless I was sitting in it :) Maximizing flight time is about finding the most efficient setup and balancing your battery weight with the performance of the airframe and power system.
 
#5
Thanks everyone for the input. Even though this stuff is simple to many, for those who are still new, just having a bit of a hand explaining it helps put the numbers straight and helps to get a grasp on things. There is just so much to learn and when I say learn, I really mean to comprehend and know.

I am one who wants to know the why and not just the what.