8x vs octo

[R_Lefebvre]

Originally Posted by Ben Kenobi

The Octo X uses one motor to drive two props, it isn't often you see one with two motors per arm and even if they do they tend to both be controlled from the same motor channel. These suffer more from vibration and are less stable.

This is so completely wrong, I don't even know what to say.

[Ben Kenobi]

Whether it is wrong or not (and I have seen both kinds) still misses the point - OctoX is not the equal of an Octocopter when it comes to stability with high payloads and low centre of gravity.

I actually agreed with pretty much all your posts, and that people design these things back to front, I don't see how an OctoX can ever match a properly designed Octo for its combination of lifting power and stability. I've had high payloads under a quad and under an Octo (and a Hex for that matter). The Octo ate them both for breakfast as a stable platform / heavy lifter, OK I couldn't throw it around the sky but it wasn't designed for that.

Many seem to throw a quad / hex / octo together without really matching purpose / battery / esc / motor / propeller - then bitch and whine when they get brown outs or burnt out ESC's, destroyed motors or 3 minute flight times when the GoPro and gimbal are added - if they get off the ground at all.

The vibration on my quad has always been worse than the others but the drive system is balanced. I think it could be just down to the shorter arms / harmonics / resonance - who knows, maybe even turbulent air from the props as they pass over the arms. I did notice a noise reduction on the X650 with the propeller mounted higher, I had to mount standard 12x6 on collets because the propellers for it are no longer available, I tend not to fly it much though the motors aren't exactly state of the art any more.

So I stand by my opinion that a well built Octo is better than an OctoX - which was the original posters question.

Incidentally - I use Arducopter (pixhawk) on both my birds - may even put it on the T-Rex at some point - best FC available.

[R_Lefebvre]

Where have you seen a machine with one motor driving two props? I've never seen that anywhere. I'm not even sure how you could do it, mechanically.

Most people state that OctoX are more stable in winds, due to lower "windage". I can't confirm that at all.

Performance comparisons between different machines are very difficult. You really need to try to control for all factors. If you wanted to compare stability of an Octo vs. X8, would you use the same motors? The same props? I'd think an X8 with the same frame wheelbase and same props and motors, would be more stable in wind than an Octo, due to the stated lower "windage". But that wouldn't be a very good X8 design, it should take advantage and use larger props. Larger props with more inertia, so harder to stabilize...

So, I won't prognosticate on that.

But what is clear is that an X8, with the same wheelbase frame dimensions can have much more disk area than an Octo, and thus capable of lifting more, or flying for longer, or some combination thereof.

[Ben Kenobi]

Saw a guy with it at an music festival of all places, it was a 450 frame and I believe it was using Jem motors, the motor had a spindle on both ends, one end passing straight through the mount. It was fitted with a CW or CCW pair on each motor, one top, one bottom in '90 degree' opposition - like an 'X' if you looked from the top it looked like a 4 bladed prop.

[desertstalker]

Originally Posted by Ben Kenobi

Saw a guy with it at an music festival of all places, it was a 450 frame and I believe it was using Jem motors, the motor had a spindle on both ends, one end passing straight through the mount. It was fitted with a CW or CCW pair on each motor, one top, one bottom in '90 degree' opposition - like an 'X' if you looked from the top it looked like a 4 bladed prop.

Not an 8 anything then, just a normal quad using 4 bladed props.

[Ben Kenobi]

How do you work that out ?? - it had TWO propellers per arm - how is 2 separate and distinct propellers a 4 bladed prop.

[R_Lefebvre]

I agree with desertstalker. It was a quad with a weird prop arrangement. But we're dealing with semantics. And the end of the day, it is not at all a normal X8, and only had 4 control outputs, so nobody should characterize it's performance to apply to X8's.

[desertstalker]

Originally Posted by Ben Kenobi

How do you work that out ?? - it had TWO propellers per arm - how is 2 separate and distinct propellers a 4 bladed prop.

The two props were connected to the same motor, turning at the same speed and as far as control over the aircraft is concerned there is no difference between this arrangement and a single 4 bladed prop.

[helicek]

Hi folks,
A standard octo is going to be efficient (when compared to X8) in a no wind case.
In gusty air X8 with smaller wing area it is going to get less wind disturbance and with shorter arms and powerful motors will nimbly execute FC commands. This assumption (to me) sounds correct.
A big octo is very large, not easy to handle too. I am sure X8 has much less foot print and will be more user friendly for that matter.
I follow fellow pro multicopter users comments and it is 50/50 so far. That means, octo owners think theirs are very good and X8 owners think theirs are better.
I have invested in AP machines so much (read too much) I guess I need to be sure I get what I need (not 8 pieces of escs, motors, props and what not that are no good)
It was very informative to have read all your comments.
Thanks,
Ahmet