To Coax or not to Coax
- Thread starter Cheshirecat
- Start date
Steve Townsend
Member
Dave, I'm going WKM. Just trying with a Naza on a Y6 at the moment but will go X8 with a WKM.
Would like more flight time, but not at the expense of stability in the breeze.
Would like more flight time, but not at the expense of stability in the breeze.
FerdinandK
Member
Some month ago I was running different props at top and bottom and I argumented that with the "already accelerated air" the second prop runs into. For now I am using the same size at top and bottom, since (if you think twice) the "massflow" through the two props is the same, since (in the range we are dealing with it) air is incompressible. So you cannot see the two props independent, or the second working "after" the first, the are working "together". Also the radial-speed of the airflow is of minor order, and if you run the lower prop at same rpm but higher pitch, this additional massflow must enter the second prop beside the airflow through the first prop.
In my practical tests, I could only get less efficiency on the prop (significant). On the other hand, if you compare a flat okto with an X8 you can build a much lighter frame for an X8 which of course increases the efficiency of the whole copter. So there is no winner, if you go for records (in flight-time) I think a flat-setup is superior to a coax-setup, but for "standard" applications the coax plays it´s advantages, you have have much smaller frames, bigger props (X8 compared to Flat Octo), and your frame has typically less weight. The coax is considerably more stable (e.g. if a fast descent, or in windy conditions).
Until now I have tried the following combinations:
12x3,8 and 11x5
11x5 and 11x5
14x8 and 14x8
14x7 and 14x8
15x4 and 14x7
17x5,5 and 17x5,5 (top secret for now
)
Here some of my coax setups:
best regards
Ferdinand
In my practical tests, I could only get less efficiency on the prop (significant). On the other hand, if you compare a flat okto with an X8 you can build a much lighter frame for an X8 which of course increases the efficiency of the whole copter. So there is no winner, if you go for records (in flight-time) I think a flat-setup is superior to a coax-setup, but for "standard" applications the coax plays it´s advantages, you have have much smaller frames, bigger props (X8 compared to Flat Octo), and your frame has typically less weight. The coax is considerably more stable (e.g. if a fast descent, or in windy conditions).
Until now I have tried the following combinations:
12x3,8 and 11x5
11x5 and 11x5
14x8 and 14x8
14x7 and 14x8
15x4 and 14x7
17x5,5 and 17x5,5 (top secret for now
)Here some of my coax setups:
best regards
Ferdinand
Lanzar
Member
Answers on the props sizes
Until now I have tried the following combinations:
12x3,8 and 11x5 If dji normal mixer this is spining in one direction
11x5 and 11x5
14x8 and 14x8
14x7 and 14x8 this one is also spining so flyable in carefree or with jaw stick to one side
15x4 and 14x7 spining to insanity
17x5,5 and 17x5,5 (top secret for now
FerdinandK
Member
All my copters have "mixed" props (CCW and CW) on top and bottom and I am using the dji "normal" mixer (it might be stated, but it is not necessary to have CW on top and CCW on bottom, just plug the CW and CCW to the correct channels) . There is no yawing on any setup in any mode, the FC (Naza and WKM) takes care for this. Here a video of 12x3,8 and 11x5:
https://vimeo.com/47266306
best regards
edit: does your frame for the 17x5,5 props also have not more than 100gr?
Ferdinand
https://vimeo.com/47266306
best regards
edit: does your frame for the 17x5,5 props also have not more than 100gr?
Ferdinand
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Lanzar
Member
Dodeka does not count since this is normal hexa with dubble output on 1 motor out from naza. So this is not DJI mixer. If you can show me original dji mixer on okto x with different pitch on bottom and upper props without spining then i will take my words back.
Normal DJI mixer does not allow different pitch on bottom and upper motors since upper motors spin in 1 direction and bottom on the other direction.
Well out bird with 17 inch props lifts 30 kg or more so 100gr frame wouold brake. We made it big and not small.
FerdinandK
Member
The dodeca is a Y6rev so in my opinion that counts ..
If you mix (CW CCW) top and bottom props, it works with different prop types also with the standerd dji mixer, but I see this is your arena.
best regards
Ferdinand
If you mix (CW CCW) top and bottom props, it works with different prop types also with the standerd dji mixer, but I see this is your arena.
best regards
Ferdinand
Great info guys. I'm also curious to know if I'm actually gaining any more thrust power moving from a flat hexa to a X8 coax? I know you loose some (approx15%) thrust going coax. My thinking is a flat hexa running 13x6.5" props will have similar thrust to an X8 running the same props (rpm faster for lower props)...am I crazy for thinking this?
Another question regarding MK mixer for X8. In the mixer setting pic below I see the the lower motors are set to spin at 71 and top at 64 but uf you read the text in the top portion of the window (red arrows) it reads "(100%-64)" my question, is 100% the max rpm as it says? or by inputting 71 the RPMs are actually increased? has this been confirmed or tested?
View attachment 9431
Another question regarding MK mixer for X8. In the mixer setting pic below I see the the lower motors are set to spin at 71 and top at 64 but uf you read the text in the top portion of the window (red arrows) it reads "(100%-64)" my question, is 100% the max rpm as it says? or by inputting 71 the RPMs are actually increased? has this been confirmed or tested?
View attachment 9431
Attachments
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DucktileMedia
Drone Enthusiast
It takes 16 motors to lift a gopro? kidding. I only argue with the concept that the lack of the 4 additional arms would make an X8 equally efficient as a flat octo. There is no way that 400 grams of weight will equate to 10-15% power loss. You still have the same amount of motors and wire. Now if you are smart like our forum owner Bart, you start thinking about sharing a common power lead to both motors on a coax. now we're talking weight savings.
Droider
Drone Enthusiast
I am still not getting this thread.
So I have a Y6 carrying a 550D. The guy next to me has a flat 6 with exactly the same camera, gimbal, batteries ect ext.
What will he gain over my Y6?
What will I gain over his flat?
From my experience I can fly in better in winds, but I guess thats just my opinion.
Easier to transport? undoubtedly..
The flat may fly for longer but in reality and in the real world of earning a wedge how much longer?
Would that sell the services of the flat over the Y6?
Dave
So I have a Y6 carrying a 550D. The guy next to me has a flat 6 with exactly the same camera, gimbal, batteries ect ext.
What will he gain over my Y6?
What will I gain over his flat?
From my experience I can fly in better in winds, but I guess thats just my opinion.
Easier to transport? undoubtedly..
The flat may fly for longer but in reality and in the real world of earning a wedge how much longer?
Would that sell the services of the flat over the Y6?
Dave
I recently built both a UAP1 flat hex and a "beater" Y6. . . There is a fair chance that my UAP flathexa will become a Y6 this spring.
It seems to me If I can figure on tuning that he Y6 will be more maneuverable as long as I can still lift my Nex5, I won't care if I lose 1 minute of flight time as long as the minutes of flight are more productive.
I actually have a similar question that I think may have stumped us all..
I'm curious to know if I'm actually gaining any more thrust power moving from a flat hexa to a X8 coax? I know you loose some (approx15%) thrust going coax. My thinking is a flat hexa running 13x6.5" props will have similar thrust to an X8 running the same props (rpm faster for lower props). Could it be possibly a flat hexa running 13" props has the same power as a X8 coax running the same props? am I crazy for thinking this?
I'm curious to know if I'm actually gaining any more thrust power moving from a flat hexa to a X8 coax? I know you loose some (approx15%) thrust going coax. My thinking is a flat hexa running 13x6.5" props will have similar thrust to an X8 running the same props (rpm faster for lower props). Could it be possibly a flat hexa running 13" props has the same power as a X8 coax running the same props? am I crazy for thinking this?
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I just answered my own question. I feel kind of silly for asking in the first place. Just did a thrust bench test using a single 13x6.5" prop/motor combo controlled by the MK motor test tool. I raised the throttle up to 150 which gave me a thrust amount of 1740~ grams as seen on my g/kg scale. Next I tested a single coax arm fitted 13x6.5" props for top/bottom. Bottom motor set to spin 11% faster than the top (64/71). Thrust amount: 3286~ @150 throttle setting in motor test tool.
Not a bad return at all and not what I expected. Very little loss it appears. So to anser my own silly question: YES a coax octo is more powerful than a flat hexa using the same motor/prop combo. My test results showed that thrust results are similar between X8 and flat octo with only 7-8% loss in thrust for coax setup. Now I have to confirm all that I've been reading regarding better wind stability for the coax setup. If so, the slight loss in efficiency is worth it IMO.
Not a bad return at all and not what I expected. Very little loss it appears. So to anser my own silly question: YES a coax octo is more powerful than a flat hexa using the same motor/prop combo. My test results showed that thrust results are similar between X8 and flat octo with only 7-8% loss in thrust for coax setup. Now I have to confirm all that I've been reading regarding better wind stability for the coax setup. If so, the slight loss in efficiency is worth it IMO.
Lanzar
Member
Well you are also correct that if you know what you are doing you can also use different props with original mixer but then you need to know a lot. If you just use normal mixer and if you connect the motors as shown in manual it will not work on x8. Tried it and it did not go well.
almost crashed. So this is kinda a warning to non experienced users off this forum.
Lanzar
Member
Yes on 13 insh props the loss is as you said around 8%. On bigger props the number can go down to 6%. So coax is
Yes on 13 insh props the loss is as you said around 8%. On bigger props the number can go down to 6%. So coax is
:nevreness::nevreness: I'm very happy Lanzar! Coax is the best!
RyanMcCrae
Member
Has any one tested the difference between running coax with short booms and long booms. Does motor spacing effect stability?
Hi all,
I'm also a Y6 addicted, i have 2 now on Arducopter 2.9 and i'm trying to shorten to max the booms and it could seems hard to have it stable with short booms but i'm now working hard on the PID to see what i could do.
I've already read about Y6 to be sensible to gain settings in the PID and to the motor alignements.
What's your idea about Y6 more sensible in comparison to non coax setup?
I'm also a Y6 addicted, i have 2 now on Arducopter 2.9 and i'm trying to shorten to max the booms and it could seems hard to have it stable with short booms but i'm now working hard on the PID to see what i could do.
I've already read about Y6 to be sensible to gain settings in the PID and to the motor alignements.
What's your idea about Y6 more sensible in comparison to non coax setup?
RyanMcCrae
Member
Do people like short booms with coax, just for transportability?
Steve Townsend
Member
Read somewhere I think Lanzar wrote that a WKM coaxial performs better with not so long booms.