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Old Nov 19, 2012, 04:44 PM
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Chris Lee
United States, MO, St. Louis
Joined Oct 2005
330 Posts
Z06 Tony,

Yes! Very nice platform you built there. And running 6s, very cool, I take it those MT motors are working well for you? I was leaning toward the Avroto 2814 on 4s that I saw you also carry. I'm sure you've got a very happy customer.

So, are you running the same blade pitch on all the motors, or did you vary the pitch on the lower props? And if so, did you go through a phase of trial and error or more the TLAR method?


Chris
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Old Nov 19, 2012, 09:14 PM
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Quote:
Originally Posted by lineofsight View Post
I question the notion that a Y6 configuration is "half" as efficient as a standard hexacopter, can you offer some evidence for this claim?

No one would be doing Y6 conversions of the DJI F550 frame (or making Y6 configurations at all) if that were the case; 50% efficiency is a major loss for an aircraft propulsion system where power-to-weight ratio is at a premium. I've seen numbers reported from 10-40%, but no indication if any optimization was done for "balancing" the motor thrust between each coaxial pair. Hence this thread.

I'm willing to do the tests myself, as long as some of the experts out here can verify my logic that there should be a connection between amp draw and a "balance of powers."
yes. Bambucopter quad and bambu copter y6 frame. Exact same motors, props, escs. 7 minutes vs 12
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Old Nov 19, 2012, 11:17 PM
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Chris Lee
United States, MO, St. Louis
Joined Oct 2005
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Thanks for your thoughts, 7/12 is a 42% efficiency loss, right on the high-side of what I've heard. Not really the scale I'm looking at though.

Also, you didn't vary prop pitch, which is what this thread is about: determining how much more prop pitch is best for efficiency. It's a foregone conclusion that increased pitch on the lower motor is necessary.

I will try some tests with an amp meter and see if I can learn a bit more about how the two ESCs and motors work in combination. I've considered building a thrust meter as others have done, but that gets a bit more complicated/time consuming than I really wanted.

Chris
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Old Nov 19, 2012, 11:33 PM
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Very true...

One of these days maybe I'll try a heavy lift Y6. I still have those avroto 2814s I bought a while back from you. I just haven't found an airframe worthy of them yet.

Perhaps my Flyduspider or a rusty frame.

-D

Quote:
Originally Posted by Z06 Tony View Post
I am assuming he wants to build a camera ship not a micro Y6.

Big difference.

Your Y6 is loud as you are prolly running 5" props with 2000kv motors.

As far as efficiency its def not 50% with a typical Y6.

I have built many Y6's and they are my favorite platform for AP.
They cut through the wind better than a flat hex.

Here is 1 I just finished for a customer running 6s spinning 14" props.

I dont think its loud at all

http://www.youtube.com/watch?v=g9ieKB_bz-Q

http://www.youtube.com/watch?v=_KZNs10KQrE
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Old Nov 20, 2012, 02:33 AM
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Quote:
Originally Posted by lineofsight View Post
Z06 Tony,

Yes! Very nice platform you built there. And running 6s, very cool, I take it those MT motors are working well for you? I was leaning toward the Avroto 2814 on 4s that I saw you also carry. I'm sure you've got a very happy customer.

So, are you running the same blade pitch on all the motors, or did you vary the pitch on the lower props? And if so, did you go through a phase of trial and error or more the TLAR method?


Chris

Yes same pitch/prop size top and bottom on every Y6 and X8 I have built.
I have yet to see "proof" that a coaxial setup will fly any better with different size/prop pitch for upper and lower.

I am 100% confident that if I put 2 exact same coaxial setup in the air and 1 had all the same props and 1 had diff prop pitch on the bottom you would never ever tell the difference.


If this is true is it really worth the effort worrying about it?
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Old Nov 21, 2012, 12:18 AM
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Chris Lee
United States, MO, St. Louis
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Quote:
If this is true is it really worth the effort worrying about it?
If it were true, then the answer would be no.

But I don't know that for sure. I hope to know more after some experiments.
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Old Jul 06, 2015, 11:33 AM
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Bumping a terribly old thread, but I'm building a very similar Y6 setup (2814 motors, etc.).

I do believe there's evidence for better efficiency with properly mismatched pairs of propeller.

Consider -

I first built this Y6 swinging APC 12x6 props on top and bottom. Graphing the RCOUT from Pixhawk for motors 5 and 6 (left arm, top and bottom), I found:


I believe that is showing me the bottom motor (channel 6) is working harder than the top one. This was captured during a simple hover, and while not pictured, the measured current draw was fluctuating around 21 amps.

Then I changed the top propellers to 11x4.5, and left the 12x6 on the bottom. Creating the same graph of hover flight, yielded this:



That looks more like the motors working the same or, at least, requiring a similar output from the flight controller. The measured current draw in this configuration fluctuated around 18 amps.

I assume that's the definition of efficiency gain, no?
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Old Jul 06, 2015, 12:06 PM
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United States, WI, Hayward
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Quote:
Originally Posted by lineofsight View Post
I'm trying to determine the proper prop pitch to use between coaxial-mounted motors on a Y6 configuration.

If the props were the same pitch, same diameter, I understand the lower prop would be working against air already accelerated by the upper prop and thus would not be doing as much work.

So people have been using higher prop pitch and/or prop diameter to compensate. But what amount increase and how to determine the best efficiency?

What about measuring current going to each motor in the coaxial arrangement? At a given throttle setting, say half stick = roughly hovering throttle, measure the current draw of each motor, then vary the prop pitch of the lower motor until the amp draw is the same.

Would this be a good way to balance the props in a coaxial arrangement? One variable I don't know is how the flight controller (say the popular Naza) distributes power to a coaxial-mounted pair. Do they get the same throttle setting or does it vary throttle to each motor based on what it sees the motor drawing? Is there a feedback to the flight controller so it even knows the motor current draw or does it only know the throttle setting it's commanding to each motor and are they always the same?

On a related note, is there an advantage to varying prop diameter between the upper and lower prop (larger diameter on the bottom)?

I suspect it's also feasible to build a thrust tester and optimize for most thrust between the pair, but that's a more complicated setup, would measuring current draw on a static stand achieve the same thing?

Thoughts?

Chris
I think this Dronecon presentation is really good to understand the dynamics between the upper prop and lower prop and the question of prop lengths, motor speed and pitch.
DroneCon Talks: Robert Lefebvre, "Introduction to Rotorcraft Dynamics" (23 min 6 sec)


This thread might be helpful too at drones-discuss:
https://groups.google.com/forum/#!se...A/DYRvRK54ZlAJ
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