Why coax?

[Motopreserve]

I would love that! But this little "backseat" is not really a backseat at all (I've never seen someone stuff a human in here anyway).

Foldability is key. And if I need to update the center plates anyway - might as well go for it and bump up to the X8 config.

 

[Hexacrafter]

Well... This subject has come up sooooo many times here ..... and sooooo many times the same things come to light....
The typical responses here are OPINION and SUBJECTIVE......including mine.....
If you look in previous threads with facts & reports
http://www.multirotorforums.com/thr...ver-the-other-chime-in.8446/page-5#post-94250
...when it comes to Coaxial there is a loss of thrust from the inline motor.....this is fact.... the amount of loss has been debated for years, but according to NASA's tests it is in the 20-30% loss range....for the inline pair.
Is this a BIG deal??? It depends on an individuals goals, experiences & opinions....
With the advances in flight controllers, I really cannot see much difference in flight stability whether Flat or Coaxial.....if tuned properly...
The real question is what best serves your needs.....or which do you prefer.....
Sleepy prefers Coaxial.... I prefer Flat.....
Some Prefer Hexa... Some Octo & Some Y6......
At the end of the day, it is all about what works bests for your needs and your preferences...

 

[crayfellow]

Thanks @Hexacrafter , the common thread, I think, is dimensional efficiency since a larger prop can fit on a smaller airframe. So you end up with something that is more portable per load potential. But that explains why flat hex and octo are still prevalent. Maybe the next evolution will be experimentation with angled arms and other modifications, which again will bring both benefits and detriments.

In the meantime I'll use all of the info you all have provided so generously and figure out what is the ideal airframe for this application! Thanks all.

 

[Hexacrafter]

Cray...
Do your homework on the entire aircraft before stepping off....so your not struggling to make all of the components work together after you buy...
The biggest challenge for me with X8 or coaxial is to get the entire "system" to work together.....
Consider the Battery location, Gimbal location, Landing Gear and aircraft electronics and get a plan before stepping off.
Coaxial can present challenges for mounting landing gear and gimbal (as well as all of the above mentioned)..... as you have those "rotating knives" hanging down about 5" below where most are accustom to.... and getting in the view of the camera....and blowing down on and shaking the landing gear or gimbal....
These must be carefully planned for as the platform decreases in diameter, other issues can arise...
Best of luck..... Keep us informed...

 

[Pumpkinguy]

The other night I read a 18 page post on another forum about how the A2 flight control is having major issues with coax config. Loss of altitude... Something to do with the vacuum created by coax tricking the barometer. I believe the pixhawk has similar problems from that thread as well. Like Andrew said, do your homework. Or better yet, build based on someone elses successful design. For example, if sleepy has a rig running like a fine oiled machine, copy it.

 

[crayfellow]

The other night I read a 18 page post on another forum about how the A2 flight control is having major issues with coax config. Loss of altitude... Something to do with the vacuum created by coax tricking the barometer. I believe the pixhawk has similar problems from that thread as well. Like Andrew said, do your homework. Or better yet, build based on someone elses successful design. For example, if sleepy has a rig running like a fine oiled machine, copy it.

yes. that is great advice. Whatever we decide on, I have nothing to gain by trying to 'innovate' in the platform itself, others are already doing a great job of that. What we need is a proven platform upon which to build a unique solution.

 

[Pumpkinguy]

yes. that is great advice. Whatever we decide on, I have nothing to gain by trying to 'innovate' in the platform itself, others are already doing a great job of that. What we need is a proven platform upon which to build a unique solution.

I thought I was a smart guy and designed my own rig. I have since changed the frame, motors, esc's, FC...lol So basically the whole thing @ a total cost of $5000-6000 loss by the time I sold the components at a loss and the frame was crashed. lol

 

[crayfellow]

haha! well, for the record I did that too. And I'm having a blast although it may look like "failure" to some, it's all a smokescreen for progress

 

[Vermiform]

The other night I read a 18 page post on another forum about how the A2 flight control is having major issues with coax config. Loss of altitude... Something to do with the vacuum created by coax tricking the barometer. I believe the pixhawk has similar problems from that thread as well. Like Andrew said, do your homework. Or better yet, build based on someone elses successful design. For example, if sleepy has a rig running like a fine oiled machine, copy it.

When you get time, would you mind linking me that thread, here or via PM?

 

[Rattler]

are you suggesting it is better than a flat layout? if so, in what way? and what ratio do you suggest for upper/lower prop? Cheers.

Yes that is exactly what I am suggesting. I read this in one of the RC Mag.s and as a Pilot it made sense to me that the X8 instead of a flat 8 is more efficient. This is because instead of having 8 props cutting through the air by them self's you have the top prop on an X8 braking up the air for the bottom one. With the FX-8 Pro Elite (See Link) they get an hour of flight time. They also use a smaller prop on the top and a bigger one on the bottom.

https://cdn-aerialpixelscom.netdna-.../2015/05/AerialPixels-FX8-Pro-Elite-ER-MM.pdf

 

[Str8 Up]

In forward flight the coax design, with props closer to center, allows more dirty air to disturb the camera gimbal. I think this is part of why Freefly sticks with flat designs.