My Octocopter ... MC-835

[NHSA]

... mainly 3D printed

Hi,

After presenting myself yesterday here

https://www.multi-rotor.co.uk/index.php?topic=24604.msg223101;topicseen#new

I wanted to post some images of the build but totally forgot it.

Thanks Bad Raven for reminding me.

Attached some images as well as video of one of my first flights.

Motors from QXMotor 1100KV and Gemfan propellers 1145. 30 Amp ESC and controller is a DJI NAZA v2 and a real cheapo FPV camera moavble via a Micro servo 90

Flight time is around 7.5 minutes with a 3S 5200 mAh LiPo battery. Here I am still working on it in order to increase it.

Perhaps somebody has a tip for motor KV and Propeller size which could go up to 12". It is difficult for me to source mot here in Mexico and so I order from ALI and Amazon. Here in Mexico the shops do really have nothing.

The frame size is 835mm (motor center to motor center)

best regards Rainer

Video 

[Bad Raven]

You are pretty much on a hiding to nothing with table comparing differing makes of motor/prop sizing!

Issues are that some (most??) motor manufacturers quote figures that are not comparative, some tending far more towards fantasy over fact.

Having been around electric flight for almost as long as its existed commercially, this is what I do.

Props are generally cheap items, usually not difficult to obtain.  I therefore keep stock of a wide range. Usually on a 4 prop multicopter the diameter is fixed either by duct size or prop swing frame clearance. So we are talking pitch being the only practical variable.

Thus for example for a 5" freestyle quad I have 5.0" and 5.1" diameter props in 2.8, 3.0, 3.5, 4.0, 4.5 and 5.0 pitch. And differing makes in those pitches, as some are far less accurate than others. 

Also some have even pitch, others have extreme pitch near the boss and by 2/3 span have near zero pitch.

Experimentation is almost the only way, tempered by experience.

Obviously the more motors a UAV has, the trickier this becomes!

With regards motors, size and kV are really poor measures of motor performance, even to the extent that some motors are listed by rotor dimensions, and others by external dimensions. Example, there was a period when HobbyKing 2836 motors were the SAME SIZE as Suppo 2212.

Given your situation I'd tend to fit the larger end of the size range that seems "right", then tune on the props. I'm not above trimming props to best suit a motor,for example some of my indoor planes with Suppo 2204 motors have 8x4.7 two blades trimmed to 7.5x4.7 to match rpm and torque for best efficiency!

[NHSA]

Hi,

Thanks. I use eCalc.ch for the calculations and so far this combination gave me the best result in ""   

I still have a long way to go.

I have everything in order to find out the characteristics of the motors like KV, internal resistance, current at 10 volt, etc., but of course the big incognita is still the magnets used by the motor producers as well as the air gap between stator and rotor which seems to be an imortant variable. It is a pit that most of the motor producers do not really give you the real specs of their motors. Looks like they are hiding a lot.

I think I will go back and built some Hexa- or Quadcopter.

Thanks and regards Rainer

[NHSA]

Hi,

I think another important factor in my case is that I do fly at 1950 meters over sea level (~6400 feet) at tempertaures around 28°C to 32°. The air is thin up here.

 

[NHSA]

Hi,

me again I guess for this big ones one needs lower KV and bigger props. Will test some 12" to 12.5" props and as you said buy a certain amount of different sizes and see how it comes out.

 

[Bad Raven]

Hi,

I think another important factor in my case is that I do fly at 1950 meters over sea level (~6400 feet) at tempertaures around 28°C to 32°. The air is thin up here.

 

Yup, that certainly won't make it easier!

[Bad Raven]

How's it going?