Andreas' Slow Rotary Sub build - Page 8 - AVS Forum
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post #211 of 227 Old 12-23-2011, 12:26 AM
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Quote:
Originally Posted by digital desire View Post

Just to give an idea on how strong and precise the rc hele hardware can be:
http://www.youtube.com/watch?v=17lme...ature=youtu.be

Jesus, that's amazing!!

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Originally Posted by AndreasMergner View Post

If you can find a way to mate it with a driver, it would likely work. Note that RC Helis blades are much higher aspect ratio and meant for high RPM. The weight of a rotary blade may be more than it is designed for.

Actually, why do you need a driver; couldn't the controller be modified to send the audio signal?

It looks like the blades are of sufficient diameter as is.

As for rpm, a slower motor could be used, but then maybe the skinny blades won't move enough air.

OK, you're right

Noah
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post #212 of 227 Old 12-23-2011, 03:49 AM - Thread Starter
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Quote:
Originally Posted by noah katz View Post

Actually, why do you need a driver; couldn't the controller be modified to send the audio signal?

It looks like the blades are of sufficient diameter as is.

As for rpm, a slower motor could be used, but then maybe the skinny blades won't move enough air.

OK, you're right

RC servos are not as fast as a driver. A pretty fast servo will do 60 degrees in .05s in one direction. Maybe you can get faster, but I haven't see strong ones even that fast. Still, the servo needs to go 120 degrees in one direction, then reverse 120 degrees for a total of .2s which is only 5hz (1/.2=5).

...and yes, a skinnier blade will not create as much lift/air movement as a fatter, stubbier (lower aspect ratio) blade. The high RPMs are better for the motor and for aerodynamics, but terrible for noise. I would not want that thing running in my house!

That said, someone could probably get it to work with different blades and and some modification....but no one has!

Current HT: HTPC-->Epson 5010 projector-->135" screen, BFM TLAHs x7 & THT
Build log: DIY rotary sub for contemporary HT in 100 year old house?
Andreas' Slow Rotary Sub build
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post #213 of 227 Old 12-23-2011, 09:37 AM
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Propeller design is sort of a black art. Activity factor, aspect ratio, etc.
Curious, does anyone know how an airfoil cross section would work with this as opposed to flat blades? I would think there would be efficiencies to be had with the right symmetrical airfoil.
Flat plate l/d is very predictable, but also not so efficient.

An airfoil could theoretically be employed that has less drag (and therefor less noise) and higher lift when alpha changes - implying greater output per energy expended. Also, an airfoil could be employed to get either more output, or less required motor force from the driver. (speaker coil) A fatter airfoil near the base, and less towards the tip would maximize and even out the the velocity cone across the disc.

Lot's of low rent stuff stacked up into a medium rent pile.
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post #214 of 227 Old 12-23-2011, 11:19 AM - Thread Starter
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I used to design, manufacture and sell RC sailplanes, so I know a lot about airfoil and wing design. I do not know as much about propellers though! The rotary has some similarities to the pitcheron planes I've designed that twist their wings to roll and pitch.

I was planning on using a "real" airfoil. It will perform better than a plate airfoil. I'm not sure it matters much which one for a symmetrical wing that is powered. I may do a bit of design work for the airfoil, but may just "wing" it. Ha ha

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post #215 of 227 Old 12-23-2011, 02:02 PM
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Well, again, digging into the hele parts bin may yield some useful airfoiled rotor blades. I have no idea if they would be appropriate for your project though.
I am digging this thread, and can't wait to see some results.

Lot's of low rent stuff stacked up into a medium rent pile.
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post #216 of 227 Old 12-23-2011, 02:32 PM - Thread Starter
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My blade spars are 9mm in diameter. I don't think heli blades are that thick, and more area on the blade will be beneficial at slower RPMs.

The one thing I don't have a 100% answer for yet is how to get the shaft through the driver's magnet without pulling it to one side of the vent hole. This will cause the coil to go with the shaft and crunch it on the magnet. I have a couple of ideas, but haven't been 100% successful yet.

I could also get a stainless steel shaft, but it would cost $80. Decisions, decisions....

Current HT: HTPC-->Epson 5010 projector-->135" screen, BFM TLAHs x7 & THT
Build log: DIY rotary sub for contemporary HT in 100 year old house?
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post #217 of 227 Old 12-23-2011, 09:48 PM
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Quote:
Originally Posted by AndreasMergner View Post

My blade spars are 9mm in diameter. I don't think heli blades are that thick, and more area on the blade will be beneficial at slower RPMs.

The one thing I don't have a 100% answer for yet is how to get the shaft through the driver's magnet without pulling it to one side of the vent hole. This will cause the coil to go with the shaft and crunch it on the magnet. I have a couple of ideas, but haven't been 100% successful yet.

I could also get a stainless steel shaft, but it would cost $80. Decisions, decisions....

Use a centering bushing, and remove it after the magnet is attached to the motor frame.

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post #218 of 227 Old 12-24-2011, 05:41 PM - Thread Starter
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I am doing that...but you also have to get it off the shaft so it needs to be cut in half. Also, I have not found any off the shelf bushings in the right size. I am using an aluminum tube for the linkage that is not quite as big as the vent hole....it is a bit tricky to implement, but it might be possible.

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post #219 of 227 Old 12-24-2011, 06:53 PM
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Quote:
Originally Posted by AndreasMergner View Post

I am doing that...but you also have to get it off the shaft so it needs to be cut in half. Also, I have not found any off the shelf bushings in the right size. I am using an aluminum tube for the linkage that is not quite as big as the vent hole....it is a bit tricky to implement, but it might be possible.

Lotsa lube and just give it a good hard shove. Works for Ron Jeremy.

Matt

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post #220 of 227 Old 12-25-2011, 06:35 PM - Thread Starter
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I knew it was just a matter of time with all the talk of "shafts". Ha ha

Current HT: HTPC-->Epson 5010 projector-->135" screen, BFM TLAHs x7 & THT
Build log: DIY rotary sub for contemporary HT in 100 year old house?
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post #221 of 227 Old 12-26-2011, 06:03 PM
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Quote:
Originally Posted by AndreasMergner View Post

I am doing that...but you also have to get it off the shaft so it needs to be cut in half. Also, I have not found any off the shelf bushings in the right size. I am using an aluminum tube for the linkage that is not quite as big as the vent hole....it is a bit tricky to implement, but it might be possible.

What is the O.D. of the shaft, and the I.D. of the vent hole?

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post #222 of 227 Old 12-19-2012, 06:06 AM
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post #223 of 227 Old 12-21-2012, 06:07 PM - Thread Starter
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That's a neat contraption he built there! It looks a little weak, but what do I know? Well, obviously the cardboard blades need to go. wink.gif

I posted this in my HT thread, so figured I'd copy it here as well.
Quote:
blackoper: I think it is a somewhat simple idea, but as with a lot of stuff the devil is in the details. My design mounts the fan, linkage and driver on a shaft supported on both ends with angular bearings. The shaft goes through the vent in the driver. Then I plan to use a 3 phase motor and speed control to turn it. One issue I am having is that if you leave the driver whole, you have a large cone (mine was 15") in the way of your airflow. The Thigpen is only 17" in diameter, so that doesn't leave you with much! If you cut out the cone, then the coil is only supported by one spider and the bushing of the linkage. You have to mount the driver in nearly perfect alignment otherwise the coil will rub on the magnet. There is very little clearance. In addition, the driver has this rather strong magnet that wants to pull it to the shaft which will basically crush the coil instantly. There are ways to mount everything in a order that would work, I think.

Also note that going "beefy" and with metal blades you will need a strong driver and you will need to calculate the max frequency it will do based on the additional mass you are adding to the "cone". I need to get to ~25 hz because I am using a folded horn above that.

I don't know if any pictures are left on either thread, but I can edit the links to them if you ask. (They are a pain to fix.) The new version of AVS broke all my pic links.

Current HT: HTPC-->Epson 5010 projector-->135" screen, BFM TLAHs x7 & THT
Build log: DIY rotary sub for contemporary HT in 100 year old house?
Andreas' Slow Rotary Sub build
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post #224 of 227 Old 12-22-2012, 09:18 AM
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Looks like he used some LEGO pieces... smile.gif
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post #225 of 227 Old 12-23-2012, 11:04 AM
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speaking of crazy things built with lego biggrin.gif

http://www.youtube.com/watch?v=4xxDuqpyjOU
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post #226 of 227 Old 02-22-2013, 04:01 AM
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post #227 of 227 Old 02-22-2013, 05:32 AM - Thread Starter
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Never seen that, but it is cool. Not sure why he is low passing at ridiculous freqs since he probably isn't getting much above 20 hz or so. Full movement of the fastest RC servos takes about .06 s so a cycle would be .12s which is not even 10 hz.

Still, cool demo.

Current HT: HTPC-->Epson 5010 projector-->135" screen, BFM TLAHs x7 & THT
Build log: DIY rotary sub for contemporary HT in 100 year old house?
Andreas' Slow Rotary Sub build
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