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Old Aug 29, 2012, 09:51 AM
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Originally Posted by jihlein View Post
Good to see someone experimenting with this. Don't know how many variables you can easily change on your test rig, but I can tell you that the shape of the duct, and the position of the fan in the duct, greatly affect the total thrust you'll get.

Just thoughts for future tests.....
I agree and is one of the foundational for the tracker pull test environment. I wanted to create as close of a real application as possible to test various changes within the duct.

Examining the purchased EDF, I noticed the spacing between the blades and the tube is much greater than the cooling fan. I was to add some tape to the inside tube to reduce that spacing and see if that improve the efficiency.
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Old Aug 29, 2012, 11:08 AM
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Ducted propellers exist since 1930 and have been studied for a long time.
Have you read this 2008 study by University of Maryland funded by the United States Army Research Office ?
Hover and wind-tunnel testing of shrouded rotors for improved micro air vehicle design : http://drum.lib.umd.edu/bitstream/19...i-umd-5771.pdf
It could help you.
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Old Aug 29, 2012, 11:14 AM
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Thank you for the information however, if I had a research budget as they do, maybe I could come up with something better. Ha.
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Old Aug 29, 2012, 11:33 AM
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Don't tell me you have read 348 pages in 6 minutes, I wouldn't believe it!
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Old Aug 29, 2012, 11:59 AM
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Don't tell me you have read 348 pages in 6 minutes, I wouldn't believe it!
I read the ABSTRACT and Table of Content, that is good enough for me. But Thank you, it is much too much for what I need right now.
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Old Aug 29, 2012, 12:15 PM
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P.S. This is about using items that are normally considered TRASH that the well Educated overlooked in their quest to appear smart. Haha!

Just read a story this morning about how the US and NATO are losing the war in Afghanistan to very low tech weaponry, so don't tell me these educated people know everything. Ha!
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Old Aug 29, 2012, 12:54 PM
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I just finished a preliminary test of the Unmodified Purchased EDF and again, it is very CLEAR to me why they are inefficient. I juiced it a few time and the analog amperage meter went off the scale (more then 50 amps).

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Old Aug 29, 2012, 12:55 PM
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Quote:
Originally Posted by 2008 study by University of Maryland
"Compared to the baseline
open rotor, the shrouded rotors showed increases in thrust by up to 94%, at the same
power consumption, or reductions in power by up to 62% at the same thrust. These
improvements surpass those predicted by momentum theory...
"

Jesus, makes me wanna experiment with them too!

I'm really into that thread - been reading a lot of your post, rimshotcopter/copterritchie - since I'm designing a bicopter... Hmm, a bicopter with proper shrouds/ducts, not only very efficient, but also badass!

Ah, like I needed more challenge (bicopter itself is quite challenging, throwing in precise ducts is a bit crazy). But hey, I like challenges, and even slightly approaching those efficiency figures would be amazing.

Subscribed.
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Old Aug 30, 2012, 11:56 AM
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We encountered the same result. Most EDFs are current hogs.

Other things we found (out of the box, cheap 55mm EDFs)
a. EDFs with similar static thrust to open props are typically 3-5dB louder (unmodified EDF shroud/typical mount). Likely coming from the cheap housing/duct (not the blades)
b. Having more vectored thrust makes yaw as well as translation motion (via pitch) a bit too sensitive. It does not fly like a fixed-pitch heli as most multirotors do, so the control laws in a typical autopilot need some tweaking.
c. Blade, aka prop balancing is even more critical
d. Duct housing flex is even, even more critical since most hobby EDF ducts are designed to handle different stresses (e.g. mounted in a hull/tube) vs a rod attached perpendicularly.

What I am really interested in is EDF speed control. If you can't get accurate speed control, then all this is pointless. With the higher rpms present I though it would be easier to control rpms, but so far I have not seen it (maybe due to the ESC I'm using... and they are not flashed.... yet). That could also be a reason why the EDFs are sucking so much current.

Quote:
Originally Posted by rimshotcopter View Post
I just finished a preliminary test of the Unmodified Purchased EDF and again, it is very CLEAR to me why they are inefficient. I juiced it a few time and the analog amperage meter went off the scale (more then 50 amps).

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Old Aug 30, 2012, 12:05 PM
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Originally Posted by recharged95 View Post
We encountered the same result. Most EDFs are current hogs.

Other things we found (out of the box, cheap 55mm EDFs)
a. EDFs with similar static thrust to open props are typically 3-5dB louder (unmodified EDF shroud/typical mount). Likely coming from the cheap housing/duct (not the blades)
b. Having more vectored thrust makes yaw as well as translation motion (via pitch) a bit too sensitive. It does not fly like a fixed-pitch heli as most multirotors do, so the control laws in a typical autopilot need some tweaking.
c. Blade, aka prop balancing is even more critical
d. Duct housing flex is even, even more critical since most hobby EDF ducts are designed to handle different stresses (e.g. mounted in a hull/tube) vs a rod attached perpendicularly.

What I am really interested in is EDF speed control. If you can't get accurate speed control, then all this is pointless. With the higher rpms present I though it would be easier to control rpms, but so far I have not seen it (maybe due to the ESC I'm using... and they are not flashed.... yet). That could also be a reason why the EDFs are sucking so much current.
I agree with the greater percentage of your statement however I believe the present EDFs are designed for air speed and not static thrust which is vital for a multi-rotor. I was just looking at the following picture from Change Sun 12 blade 90mm and the Pitch of those blades are HUGE. What we need is a fan similar to the APC Slowfly props with low pitch but as many blades as possible. We want volume of air passing through the tube, not speed.

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Old Aug 30, 2012, 05:47 PM
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Quote:
Originally Posted by rimshotcopter View Post
I agree with the greater percentage of your statement however I believe the present EDFs are designed for air speed and not static thrust which is vital for a multi-rotor. I was just looking at the following picture from Change Sun 12 blade 90mm and the Pitch of those blades are HUGE. What we need is a fan similar to the APC Slowfly props with low pitch but as many blades as possible. We want volume of air passing through the tube, not speed.

Very good observation. I have been following your thread and wanted to chime in, but you beat me to it! A custom designed rotor is the only thing that will ever work for this. EDF's made for a jet would give you about 2or 3 min flying time. Twin EDF planes are amp hogs, so 3 or 4 EDF units would be insane amp usage.
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Old Aug 31, 2012, 04:44 AM
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you may want to look up verax computer fans.
They spent a lot of effort in optimizing the blades.
http://www.noisemagic.de/home.php?nr=2217
I am not sure if it would benefit the thrust issue?
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Old Aug 31, 2012, 04:55 AM
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and why it it supposedly better (and different) in german http://web.archive.org/web/200201202.../www.verax.de/
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Old Aug 31, 2012, 11:27 AM
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Originally Posted by UNABLE2SURF View Post
Very good observation. I have been following your thread and wanted to chime in, but you beat me to it! A custom designed rotor is the only thing that will ever work for this. EDF's made for a jet would give you about 2or 3 min flying time. Twin EDF planes are amp hogs, so 3 or 4 EDF units would be insane amp usage.
Thank you and Chime in at anytime.
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Old Aug 31, 2012, 11:32 AM
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Here are a few pictures of the BEST candidate for conversion I have founded to date. The cooling fan sticker reads: Model AFB0812VH DC Brushless.

In my opinion, it is actually structural stronger (integrity) than the purchased EDF and the pitch appears to be right on the money for the Multi-rotor. On this conversion, I am going to leave the magnet ring on because I strongly believe it has a function like a flywheel and helps to keep the fan running smoothly.
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Last edited by rimshotcopter; Aug 31, 2012 at 06:02 PM. Reason: Fixed Grammar
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