X8 Pros and Cons

[Akermay]

Hi

We have looked at so many standard hex setups and now peeking at a few X8 possibilities. As far as we are aware, they don't seem very common at the moment.

The most we have gathered is that they are going to potentially be more stable and carry more weight. But what other pros and cons are there for X8 setups?

Thanks.

 

[Stacky]

My experience is more nimble and easier on orientation than a Hexa. More stable in strong winds but in normal and light winds a Hexa is possibly a little smoother.
Down side is the loss in efficiency. You will get shorter flight times than if you had a flat 8 configuration because the bottom props are always pushing dirty air.

Hi

We have looked at so many standard hex setups and now peeking at a few X8 possibilities. As far as we are aware, they don't seem very common at the moment.

The most we have gathered is that they are going to potentially be more stable and carry more weight. But what other pros and cons are there for X8 setups?

Thanks.

 

[maxwelltub]

To add my abbreviated opinion, X8 is way stable in wind, but less efficient.

 

[Bartman]

To add my abbreviated opinion, X8 is way stable in wind, but less efficient.

Less efficient hasn't really been quantified but to balance it there is much less structure and wiring. Plus, the open view out the front is a big plus that can be made even better if the arms are pushed out to sides a bit.

 

[maxwelltub]

I have a question for those more qualified then me, there has been talk of having different size/ pitch props on the bottom to help increase performance. I notice that most people just stick to the same prop on top and bottom so I assume that theory never had to much evidence to support itself.

 

[Bartman]

this is something i've been trying to get to. i've got a test stand with two eagletree monitors so it's just a matter of having the time to get both up and running.

speaking from my time flying coaxials, having the same pitch top and bottom feels like driving on icy roads. if you're gentle it might seem the same but when you give it power then it doesn't respond the same and control is less certain. when i have one to two inches of pitch more on the bottom everything feels more like it's gripping the way it's supposed to. i should really get the stand set up and settle this once and for all.

 

[tombrown1]

Most say that you lose efficiency with coaxial, but your weight is lower with 4 fewer arms, so that definitely helps to offset.

 

[jes1111]

Damn - I'm agreeing with bart again!

The science supports using higher pitch props on the bottom - the top prop is (effectively) acting on static air, the bottom prop is having to accelerate air that's already moving at speed (and spiraling). Fixed wing flyers have been using coaxial motors for some time and they've generally settled on a smaller prop behind but I believe that may only be valid when the props are within millimeters of each other (i.e. an actual coaxial motor rather than two motors on opposite sides of an arm). I also agree that the "inefficient" argument is largely cancelled by the lower weight. I, too, haven't bothered to test any of this - coax works for me and I wouldn't dream of buying/building one of those huge, unwieldy octocopter monsters.

 

[DucktileMedia]

There are a few things I would say are a small issue with the x8. Efficiency is the biggest one and efficiency is more than flight time as it is also a loss of lift. So although you can add larger motors/props on a coaxial you will be able to lift more with a comparably equipped flat octo. They are also more likely to show the lower props on a level pan. Other than that it is all advantages. then, if you take things a step further and go to Bart's XY8 you add quite a few things. You can fly fast forward and never see props. You can tell orientation LOS much better. If your gimbal can point upward you can achieve a rare upward elevator shot. And it fits in the car really well. I also dont like the "x" symmetry of the X8 as it can be hard to tell orientation especially if you have a cam op spinning the gimbal in circles. For this I would actually say the bigger the heli the better hence a flat octo. But you need a truck to move that around!

 

[ovdt]

I have tried both for years(almost 2 years) and I chose flat octo over X8. I have two simple reasons:

* Efficiency loss. Around %20-25 less battery time with the same AUW.
* Props get in the camera's view more often when panning.

No need to say the advantages of X8 that everyone mentioned.

 

[Bartman]

When I needed to carry two flat Okto's plus my gear I had to bring my Suburban. With my Xy8 I can throw one on the back seat of my car and the other in the trunk, this is with heli's that swing 14" props. I think 20-25% efficiency loss is overstating it. Using higher pitch props on the bottoms lessens efficiency losses.

 

[Benjamin Rowland]

When I needed to carry two flat Okto's plus my gear I had to bring my Suburban. With my Xy8 I can throw one on the back seat of my car and the other in the trunk, this is with heli's that swing 14" props. I think 20-25% efficiency loss is overstating it. Using higher pitch props on the bottoms lessens efficiency losses.

Bart, what props are you using? (We spoke a bit about this the other day.)

 

[Bartman]

I'm using Xoar 14x6 on top and 14x7 on the bottoms, PJN and PJN-P with the MT4008-18 motors and 30 or 40A ESC's. The 40's have the BEC which the 30's don't, otherwise the 30's are all you need.