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Old Jan 28, 2013, 10:47 PM
KlonWarz
Joined Dec 2012
455 Posts
:-)

Wow!
Haven't heard THAT in quite a while, i !

IIRC, the Coandus Effect has been determined to be pretty much in-effectual, or un-necessarily difficult to implement for the actual return.

Do you know of any practical implementation of the coandus effect, in use today?
Cute hobby UFO you showed, and I'll agree it's fun stuff, yet most improved thrust devices I've seen use a simpler venturi inlet and thrust vectoring for control.

And, if you look at the DT booms, they are a rectangular beam, with would both block thrust, and create turbulence, spoiling lift. Also, his monolithic foam motor holder is also larger than factory methods... possibly lighter, yet still infringing upon a minimal amount of the thrust created.
In an attempt to place a label, the squared off bottom of the foamie booms and motor mounting portion might possibly exgibit some Kamm effect, or, if you will, something along what KFm hopes to achieve with the stepped airfoil wing.
All told, I feel DT would have been better off using the boxwood spars, alone, with perhaps a laminated cellulose motor holder.
Fun stuff!
:-)
rc
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Old Jan 29, 2013, 12:34 AM
wrong descision, wrong time
United States, WA, Maple Valley
Joined Sep 2010
520 Posts
Thanks everyone for your input, I had to try a foam frame just to see if would work. It definitely was a really easy way to get the motors mounted and lined up. I usually have one or two failed air frames for every good air frame when I'm scratch building. I wasn't born with the building gene like my brother (he builds everything perfect first time, even without plans). I have a bamboo stick frame already built, I just need to get down to the home improvement store and get some PU, and make some paper tubes.

The other way I thought to easily mount motors was to either just buy the mounts and legs from banggood (which I will probably do anyways when I get some extra money), or design something that could be 3d printed. While I did CAD back in high school (autocad 13 on DOS), I need to spend some time coming up to speed on modern 3d modeling programs. Don't know when I will get that time, between family, work, and the fact that DLG contest season is coming up (and I have a glider to build still).

On my next one I'll make sure the motors are all right, and make sure I have the rates set on my radio properly (I found settings for er9x on a 929 thread).

Heath
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Old Jan 29, 2013, 03:54 AM
We can rebuild it!
djdavies83's Avatar
United Kingdom, Wales, Swffryd
Joined Apr 2010
3,686 Posts
No worries dumb_thumbs, interesting little thing I found out about motor locations and wire colours is that with the V929 board the motors and wires are in the same place for direct drive and though a gear set, I don't have a V929 but I put the board into a S026 tandem chinook which has a similar single stage gear set, because the motor is rotated 180' on its Y axis (shaft pointing down) it changes the direction of rotation then the gears change it again so gear driven blades of that location will spin the same as a direct drive for that location.

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Old Jan 29, 2013, 04:45 AM
Registered User
Joined Jan 2012
1,594 Posts
Quote:
Originally Posted by midelic View Post
I tested myself an hybrid with Syma X1 board.The conclusion is....big s**** ever, waste of money.I have no control on full 100% rate, the quad is not moving, ail/ele full stick, only throtle up down....and that's it.
I made same experiences but could happily sell the board.
This hybrid was a fail.
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Old Jan 29, 2013, 06:03 AM
Tri-Quad-Hexa-Octo-copters!!
United States, TX, San Antonio
Joined Feb 2007
14,668 Posts
Hi I,
The airflow from a specially designed fuselage for Coanda effect is quite different from a flat arm under a prop. The square arm area under a prop on a multicopter is one of the causes of vibrations to the flight controller. You can test this effect by holding a piece of the arm material under the prop thrust and feel it beating and vibrating. No lift effect is present there

Cheers,
Jim
Quadrocopter and Tricopter Info Mega Link Index
Quote:
Originally Posted by ilektron View Post
The foam underneath may not affect thrust as much as you may think, as long as the air can flow around it. Coanda effect!

https://www.youtube.com/watch?v=CBbPVB11Wis
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Old Jan 29, 2013, 07:23 AM
Registered User
Joined Apr 2012
6 Posts
Quote:
Originally Posted by rastsaurabh
ANYONE TRIED WITH mjx200 FC ??
a friend has built a diy quad using that board and it flies very nice. be aware it only works with the stock tx though. not 9x or any other quad radio. in fact the tx is not even compatible with his brothers mjx.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------

Thanks dave 1993.
The TX is unique and no is GR146. the point is that i have bought MJX f47 Heli which has exactly the same remote .... so wanted to make quad with MJX 200 ( which is also sold with GR146 TX)

So assume that the heli TX would work for MJX200 FC board. Anyone with the same though or tried ?
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Old Jan 29, 2013, 12:04 PM
KlonWarz
Joined Dec 2012
455 Posts
Very kool graphic presented by Hank's barrister, J!

I always enjoyed all those presentations in Popular Mechanics /Science and other mags...
I first read of Coandas as a reverse cone with center extractor used on a 4 cycle mc exhaust pipe, with great claims, of course! :-)
Then, it seemed all the dragster were running zoomies, and mc's went to tuned length.
Coandas fell by the wayside...

Possibly the best evidence .against. Coandus would be the small hovercraft designs that are built, today. Lot's of interesting dsigns actually built and flown, and I haven't seen Coandas yet.

Fun stuff!
:-)
rc
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Old Jan 29, 2013, 12:23 PM
Will fly for food
ilektron's Avatar
United States, CA, Carlsbad
Joined May 2011
532 Posts
Quote:
Originally Posted by jesolins View Post
Hi I,
The airflow from a specially designed fuselage for Coanda effect is quite different from a flat arm under a prop. The square arm area under a prop on a multicopter is one of the causes of vibrations to the flight controller. You can test this effect by holding a piece of the arm material under the prop thrust and feel it beating and vibrating. No lift effect is present there

Cheers,
Jim
I admit, I was being facetious. However, you could easily estimate the drag force from the frame. If you know the velocity of the air (which can be estimated by the pitch of the prop and the rpm), you can figure that the arm is a flat plate perpendicular to airflow, calculate the area under the airflow, use a little wikipedia, and Bam! You can have a rough comparison of the drag caused by the arms.

I've never thought of the airflow as a cause of vibration, though. Interesting thought.
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Old Jan 29, 2013, 12:35 PM
Tri-Quad-Hexa-Octo-copters!!
United States, TX, San Antonio
Joined Feb 2007
14,668 Posts
Hi I,
Yep. We went through a similar multicopter discussion and testing on this about 7 years ago. It is one of the reasons the better multicopter frames are based on round tube designs. The round tubes also have more torsional strength and of course are easier to replace than some of the other designs out there. See the TIPs in the Arm materials section of the Quadrocopter and Tricopter Info Mega Link Index for more info.
Cheers,
Jim
Quadrocopter and Tricopter Info Mega Link Index
.
Quote:
Originally Posted by ilektron View Post
I admit, I was being facetious. However, you could easily estimate the drag force from the frame. If you know the velocity of the air (which can be estimated by the pitch of the prop and the rpm), you can figure that the arm is a flat plate perpendicular to airflow, calculate the area under the airflow, use a little wikipedia, and Bam! You can have a rough comparison of the drag caused by the arms.

I've never thought of the airflow as a cause of vibration, though. Interesting thought.
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Old Jan 29, 2013, 03:04 PM
Registered User
Canada, ON, Merrickville-Wolford
Joined Jun 2012
835 Posts
Quote:
Originally Posted by ilektron View Post
I admit, I was being facetious. However, you could easily estimate the drag force from the frame. If you know the velocity of the air (which can be estimated by the pitch of the prop and the rpm), you can figure that the arm is a flat plate perpendicular to airflow, calculate the area under the airflow, use a little wikipedia, and Bam! You can have a rough comparison of the drag caused by the arms.

I've never thought of the airflow as a cause of vibration, though. Interesting thought.
A square, or rectangular, cross section would be a better vortex generation shape (although you can get a vortex trail behind round too). The vortex alternatively sheds from each side which can set up a vibration. The spirals you sometimes see on the outside of tall chimneys are there to disrupt the vortex generation.

Likely having sufficient structural stiffness of a tube would more than counteract the vibrations. I must admit that it's pretty tough to figure out what the actual "in-use" loadings on a multi-copter frame are ... especially in "extraordinary" event cases (aka "unplanned landings").

cheers,
Andrew
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Old Jan 29, 2013, 03:48 PM
it WILL fly! someday....
Richard_s's Avatar
Slovakia
Joined Aug 2008
448 Posts
Hey guys. My parts for DIY 939 arrived, and I hacked together bamboo/balsa 11cm M2M quad. 20 ~ 22 grams without battery, about 29 with stock one. I used wltoys 939 motors (two CW and two CCW), stock 939 battery, and stock props. I get some nasty behavior here... with fresh battery, just after lift-off, quad starts to rise pretty fast and no matter what I do with throttle stick, it just goes up to the ceiling. Only zero throttle stick stops this, quad stops motors abruptly, flips nad crashes . I use 9x transmitter, with linear throttle setting. After maybe dozen of such tries, as battery gets lower a little, I can actually fly the thing. However, it shakes - oscillates quite a bit, but flies fully controllable until LVC.

Any ideas? I'll snap some photos later.
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Old Jan 30, 2013, 09:57 AM
Gone with the Mistral
ztoon13's Avatar
France, PACA, 13
Joined Jun 2012
86 Posts
Hi Richard,
Quote:
Originally Posted by Richard_s View Post
1/ no matter what I do with throttle stick, it just goes up to the ceiling. Only zero throttle stick stops this. After maybe dozen of such tries, as battery gets lower a little, I can actually fly the thing.
2/ I use 9x transmitter, with linear throttle setting.
3/ However, it shakes - oscillates quite a bit, but flies fully controllable until LVC.
4/ Any ideas? I'll snap some photos later.
1/ that's weird... most strange is you can control it when power goes low !
2/ I suppose you use stock firmware ? not er9x ?
3/ is it a v929 or v939 board ? (I did a short test flight on my new smallest frame with a v929 board, was not as good as v939 in my opinion as it ended with lot of wobble and a broken motor due to crash...)
4/ please post some pics...
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Old Jan 30, 2013, 10:13 AM
it WILL fly! someday....
Richard_s's Avatar
Slovakia
Joined Aug 2008
448 Posts
I use radioclone fw in t9x. It is 939 board. Weird indeed, except for wobble, it flies okay with not-so-full battery...
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Old Jan 30, 2013, 10:21 AM
Gone with the Mistral
ztoon13's Avatar
France, PACA, 13
Joined Jun 2012
86 Posts
Quote:
Originally Posted by Richard_s View Post
I use radioclone fw in t9x. It is 939 board. Weird indeed, except for wobble, it flies okay with not-so-full battery...
If your quad flies ok with "notsofullbatt" , I think your 9x is guilty of strange behavior : I updated (recently) my tx to er9x so I can't help you with radioclone, sorry.
Look at your tx settings and at the same time you could take some pics to share with us
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Old Jan 30, 2013, 10:21 AM
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LittleMo's Avatar
United States, VA
Joined Dec 2006
1,494 Posts
Quote:
Originally Posted by Richard_s View Post
I use radioclone fw in t9x. It is 939 board. Weird indeed, except for wobble, it flies okay with not-so-full battery...
Having a wobble is not normal. Maybe there is too much vibration. Could be a bad prop, board is not attached securely to the frame, frame is flexing too much, motor not securely attached, etc. Re-checking all the wiring might be a good idea too. Could be a bad motor. Just guessing as I have never seen this issue.

Then of course there is always the chance that the board itself is bad. I'm assuming your TX works correctly with other models so that's probably not the problem.
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