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Spec a Tri-Copter for long flight time

#1
As the title suggests, I want to build a tri-copter based on a Bat Bone frame with a GoPro and an FPV setup to have the longest duration flight time you can squeeze out of it. I am still new at this, but I have been reading and researching as much as I can. Sometimes research doesn't replace good old experience. So, I wanted to bring my questions to those that have real world experience in this.

How long can you normally fly on a single charge?

Prop size, motor KV, amp draw, wattage, 3s, 4s, milliamps per hour, weight...it can be a little challenging for a new guy to figure out. I know there are trade-offs for everything you do. That is why I ask what would you do in my situation?

Help me spec my build please!

Mark
 

Tritium

Amateur Extra Class K5TWM
#2
Many things come into play when determining flight time but as a general rule 8 to 10 min is probably average flight time with MOST multirotors with single batteries, the longer time being an exception in most cases.

Thurmond
 

vk2dxn

Senior Member
#3
This is the million$ question.
My first tri had a total weight of 1.6kg and flew for 10:50 on a 4500mah 4s drawing close to 110a WOT.
Although it flew great I wanted longer flight times so I have gone back to the drawing board and redesigned it (closely copying Dave's design) and will post about it soon. Lets just say that so far without motors and esc's the frame comes to a total of 285g.
Keep an eye out for my post soon as I get some time.
I am learning by experimentation. :)
 
#5
Keeping weight down will be important. More weight means more thrust needed, more thrust means more amp draw, and more amp draw means shorter battery life per X amount of battery capacity. Battery capacity is a double edge sword; if gives you more available power, but it is heavier and requires more lift to carry around.

600 grams of all up weight, with a 3300mah 3S battery (~250 grams), spinning 8x4.5" props on 1000KV motors could give upwards of 15 minutes of flight time with moderate maneuvering. At full throttle somewhere around 85 watts per motor (<8 amps) to extend battery consumption. Medium size props spinning relatively slowly limits your lift capacity, and is crucial to keep the overall weight down. The heavier you get from 600 grams could mean stepping up to 9x4.7" props for adequate lift and more current per motor and less flight time per charge.

Edit: It would be just about impossible to do a FPV copter less than 700 grams. Even when going to light weight 1400kv motors swinging 10x4.5" props, with a 3000mah 2S battery, on a Bat Bone body it is just a nudge over 600 grams. 15 minutes of flight time, but adding 300 grams of FPV gear and there isn't enough trust left for maneuverability and it drops flight time in half.

From experience, building a high power/trust setup to lift big heavy batteries to get longer flight times isn't a good solution either for the Rotor Bones components. They're just not up to handling 5.5Lbs of thrust and 3Lbs of all up weight; motor mounts break from torque, the extra weight tears up frame parts on crashes, and getting a good CG on the Bat Bone body is impossible without mounting the battery forward of the body itself. High power/trust setups need heavier duty frame parts which adds to the additional weight and where you start getting into multiple batteries to negate the additional power again from the additional weight for more air time; it is a never ending cycle.

In the world of automotive enthusiasts there is a saying: Fast, Reliable, and Inexpensive; pick two. It means to be fast and reliable will be very expensive, to be fast and inexpensive means it will not be reliable, and to be reliable and inexpensive it will not be fast. There is a trade off to be made. Weight, Power, and Flight Time; pick two.
 
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Cyberdactyl

Misfit Multirotor Monkey
#6
You guys have seen my version of David W's 'V2.6HV' several times, :rolleyes: but it is pretty much as light as I can make it using the fairly large DT750s. All CF, including the props. I did hold out on CF legs as I wasn't sure just what look I wanted, so I made them out of 3/16" plywood in case I wanted to change later. I put the ESCs out with the motors to save on having another 15" of heavy 16g wire inside the booms. But I probably offset that savings by having more planform obstruction, although the ESCs are turned vertical and fairly close to the motor, away from prop's largest bite of air. Anyway, it's AUW is 714g using a 3S 2200 45-90c.

Mustang's right, I doubt you can get a tri much lighter and still have any sort of decent lifting platform for a GoPro-ish cam and Vtx and still have any sort of prolonged air time. One thing about using larger CF props on a light tri is it is very quiet. I have to strain to hear it in a hover at 40 or 50 feet.

 
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#7
Thanks for the replies!

I am certainly aware of the trade-offs, hence my question regarding the setup. Maybe I should narrow down my question a little bit:

What MOTOR, PROP and BATTERY combination will yield the longest flight time possible on a Bat Bone Tri-Copter setup up with a Go Pro and FPV?

As I mentioned previously, this is all new to me and I want to start experimenting, but I want to do so wisely with a proven recipe to begin with to help my understand all of the dynamics involved.

Information such as what Mustang7302 provided is the kind of stuff that new people should be paying attention to:

From experience,...getting a good CG on the Bat Bone body is impossible without mounting the battery forward of the body itself....
@Cyberdactyl....I really dig your set up! Keep us updated on your progress! I like the clean look of the airframe.

Mark
WL7NI
 

vk2dxn

Senior Member
#8
With my mk1 I ran gws 13x6.5 props and ntm 35-48 900kV 815W bad boys turnigy plush 60 esc to give me total of 10:50 in the air.
My mk2 will be running 12x6E props and ntm 28-30 800kV 300w Afro30 esc. Lift should be similar but smashingly less weight.
I'm still waiting for my new motors and esc's in the mail, I will let you know how I go.

@Cyber
My mk2 is based on Dave's 2.6HV as well

@every one in this thread
Sorry I have not put a thread together as yet, most on my forum surfing is done with my iPhone on the way to work and don't get much time at night because of the rug rats. I will get to it soon with pics :)