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Old Nov 17, 2012, 11:29 AM
Chris Lee
United States, MO, St. Louis
Joined Oct 2005
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Balancing power between Y6 coaxial-mounted props

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
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Old Nov 17, 2012, 08:45 PM
Staying Frosty
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United States, CO, Colorado Springs
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No responses? I'm debating between a Y6 and what I call flat 6 rig myself for this very reason. I like how the y6 performs in the wind compared to flat, but don't want to buy tons of diff props to figure it out.
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Old Nov 17, 2012, 09:27 PM
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Originally Posted by Hellsiege View Post
No responses? I'm debating between a Y6 and what I call flat 6 rig myself for this very reason. I like how the y6 performs in the wind compared to flat, but don't want to buy tons of diff props to figure it out.

Y6 Cons:

Half the efficiency (half the flight time of a similar flat hexa), loud as a banshee, difficult to takeoff for newbies, Motor redundancy doesn't react as stable as a flat hexa.

Pros: Handles heavy wind better, more options for FPV cams to not have props in View.

I'm a fan of Spyder Hexa's followed by flat hexas. It all depends if you plan on using a gimbal, doing FPV or aerial video
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Old Nov 17, 2012, 10:13 PM
Chris Lee
United States, MO, St. Louis
Joined Oct 2005
324 Posts
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."
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Old Nov 18, 2012, 03:15 AM
Staying Frosty
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One other pro for me coming from Helicopters on the Y6 is orientation. The tail of the Y is similar to the tail of my heli, so where yesterday I was flying the DJI550 w/naza, there we're a few times I just let go of sticks and had to think for a second to see the two red arms and get my orientation. At least that can be done, try that on conventional heli and your picking up pieces

I was leaning towards flat hexa, what's a spyder hexa?
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Old Nov 18, 2012, 03:47 AM
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I have to disagree.

Generally a flat hexa has no redundancy, while a Y6 has redundancy as long as you have a hover throttle under 50%

The efficiency loss is 5-10 % depending on your propeller pitch.

I do agree that it's loud though =)

@lineofsight, a good pitch ratio for me has been 12x3.8 on top layer and 12x4.7 on bottom layer.

I've made a more detailed pro/con list on my blogg. I had the same questions as you had a while ago.

http://multicopterworld.com/2011/05/...acopter-frame/

Quote:
Originally Posted by daign View Post
Y6 Cons:

Half the efficiency (half the flight time of a similar flat hexa), loud as a banshee, difficult to takeoff for newbies, Motor redundancy doesn't react as stable as a flat hexa.

Pros: Handles heavy wind better, more options for FPV cams to not have props in View.

I'm a fan of Spyder Hexa's followed by flat hexas. It all depends if you plan on using a gimbal, doing FPV or aerial video
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Old Nov 18, 2012, 06:09 AM
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Quote:
Originally Posted by lineofsight View Post
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?
I have no idea how the FC handles the motor power but I would reason that the FC must give the same amount of power to both motors (on an arm) because it has no way of knowing if one prop is doing more work than another.

Alternatively if it somehow gets a reading of current draw for each motor, you would assume it tries to even it out for all motors.

So I would conclude it's not possible to do the test just by checking the amount of power going to each motor (all in my humble, non-expert, armchair opinion).
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Old Nov 18, 2012, 07:25 AM
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Norge, Vestfold, Tønsberg
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Quote:
Originally Posted by daign View Post
Y6 Cons:
Half the efficiency (half the flight time of a similar flat hexa)
I can agree on around 20% loss +/- And you gain some by lighter airframe.

Quote:
Originally Posted by daign View Post
loud as a banshee
Different sound than a flat hexa with the same props, but not loud. If it is you might have a problem with vibrations and resonance.

Quote:
Originally Posted by daign View Post
difficult to takeoff for newbies
IMO it is not. Something is wrong if it is.

Quote:
Originally Posted by daign View Post
Motor redundancy doesn't react as stable as a flat hexa.
The only thing that is stable with the motor redundancy on a flat hexa is that it is not there. Y6 with one motor out will come down level. This all depends on the FC and power/weight ratio though.
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Old Nov 18, 2012, 07:30 AM
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Quote:
Originally Posted by lineofsight View Post
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?
Only feedback it uses to balance this is yaw sensors I think.
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Old Nov 18, 2012, 09:57 AM
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A static test running motors at same rpm would be interesting to see. Curious to if 4.7 vs 3.8 makes enough difference to count, or if you rather use a 6 or 8" pitch.

Lars
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Old Nov 18, 2012, 11:27 AM
Chris Lee
United States, MO, St. Louis
Joined Oct 2005
324 Posts
That's basically what I'm trying to figure out, a way to test for the ideal prop pitch combination.

How does a same-RPM test help? The ESC doesn't know what RPM the motor is spinning (no governor), it only knows what throttle point is being applied to the motor, right? So in real-world flying, the RPMs will vary based on load.

My question is, does a constant current being drawn by both motors at the same throttle setting indicate the motors are working equally hard?

Current should vary based on load even at the same throttle setting, is that a correct assumption? If so, at the same throttle point, the lower motor with the same prop should draw less current. So my theory is to find the prop pitch that matches the current draw at the same throttle point.

Is this a valid method?

@multicopter: Can you describe how you settled on 12x3.8 and 12x4.7 combination? That 1" pitch difference concurs with other values I've seen, 12x4 and 12x5, but I'm not sure if it's based on testing, real world flying or just doing what others have recommended.
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Old Nov 18, 2012, 10:29 PM
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United States, CA, Los Angeles
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Quote:
Originally Posted by Multicopter View Post
I have to disagree.

Generally a flat hexa has no redundancy, while a Y6 has redundancy as long as you have a hover throttle under 50%

The efficiency loss is 5-10 % depending on your propeller pitch.

I do agree that it's loud though =)

@lineofsight, a good pitch ratio for me has been 12x3.8 on top layer and 12x4.7 on bottom layer.

I've made a more detailed pro/con list on my blogg. I had the same questions as you had a while ago.

http://multicopterworld.com/2011/05/...acopter-frame/
Generally? I've had a 100% success rate out of the 3 I ownThe following flat hexas passed the test in my stable flying indoors next to my TV...:
Flyduino Flyduspider Hexa
Xaircraft DIY CF Hexa
BlueskyRC Spyder Hexa
Openpilot BlueskyRC Mini Spider Hexacopter with one motor out Coptercontrol (1 min 44 sec)


Using the exact same motors you see in that video on a Y6 of the same size produced 6 minute flights times vs 12-13 minutes in Spyder config...

Could be the mini factor...

I just have't liked nor had very good luck with my Y6's...

The fact that people need to bandaid them with prop size and pitches/motors up top and down below says a lot I think.

I know a lot of people have good luck with expensive Y6 setups... My experience hasn't been that great.
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Old Nov 18, 2012, 10:39 PM
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Originally Posted by JanHenning View Post
I can agree on around 20% loss +/- And you gain some by lighter airframe.


Different sound than a flat hexa with the same props, but not loud. If it is you might have a problem with vibrations and resonance.


IMO it is not. Something is wrong if it is.


The only thing that is stable with the motor redundancy on a flat hexa is that it is not there. Y6 with one motor out will come down level. This all depends on the FC and power/weight ratio though.
Then perhaps I'm doing something wrong. My build threads are still lying around here on both these... '

Videos > words.

Bolt Y6 Motor Test. Loudest Multi I've ever built.
Shrediquette Bolt Clone Y6 Hexacopter Motor Test (0 min 53 sec)

Bolt CC3d tuning Flying:
Bolt Y6 Hexacopter Shrediquette Openpilot CC3d (2 min 44 sec)


Bambucopter Y6 during PID tuning with CC3d. I was able to dial out the tail wag with COG adjustment.
Bambucopter Y6 Hexacopter Openpilot CC3d RC: 20120725-f9eb8247 (1 min 18 sec)


For comparison here is a Bambucopter Quad running the same props and motors as the Bambucopter Y6 above. Notice the difference? Same camera...

If you give a newbie a Y6 he'll have a hard time just jamming the throttle to get off the ground. I've had other Y6 owners admit that taking off is different than any other platform. It requires more confidence in the throttle and build. You have to give a lot more throttle to get them off the ground to comparative multi designs IMO. I've had a couple Y6 owners agree.

I wanted to like the Y6 design. i really did. The Bolt Y6 is one of my favorite designs. If you have a theory of what I've done wrong with my builds, I'll bust out the frames and try what you think.

The bolt Y6 is hanging on the wall ready for your input on how to fix the loudness and takeoff issues. It requires over 50 % throttle to take off. The bambucopter did too...

As far as flat hexa redundancy? Watch the video in the post above above.
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Old Nov 18, 2012, 10:53 PM
Chris Lee
United States, MO, St. Louis
Joined Oct 2005
324 Posts
Thanks for your comments, but I'm not asking which is better between a flat hexa and Y6 configuration. I've already made up my mind for a variety of reasons which suits me best. I'm looking for the best way to optimize the set-up.

The fact that the upper and lower motor pairs require different props is not something I'm going to hold against the design and I don't think direct comparisons can be made between a flat hexa and Y6 without changing props.

It is what it is, it makes sense that the lower motor requires additional "pull" since the air it is working with is already partially accelerated by the upper motor. The question is how much additional? If it helps narrow the discussion regarding scale, I'm looking at 12x4 props to start and going up from there, not the really small stuff that may have other inherent instability issues.

Thanks!
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Old Nov 18, 2012, 11:01 PM
Z06 Tony's Avatar
United States, NY, Rochester
Joined Sep 2008
7,107 Posts
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

Rc-Drones KongSix XL-6S 950mm Y6 Hexacopter Shot w/GoPro Hero3 Action Camera Vid #2 (1 min 56 sec)


Rc-Drones KongSix XL-6S 950mm Y6 Hexacopter Shot w/GoPro Hero3 Action Camera (1 min 59 sec)
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