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post #181 of 280 Old 01-09-2011, 11:15 AM
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You do not want to connect the actuating arm directly to the blade.
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post #182 of 280 Old 01-09-2011, 11:28 AM
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Originally Posted by Mike_WI View Post

Interesting stuff.
Any interest in having a SE WI meet to demo your room?

Mike


I agree, I would love to see/hear this sucker in action....

I'm just up in grafton and would love to make the drive to check it out....

I personally like this picture with the BLOSE radio right next to the TRW....

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post #183 of 280 Old 01-09-2011, 12:21 PM
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Originally Posted by Warpdrv View Post

I agree, I would love to see/hear this sucker in action....

Count me in too!!
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post #184 of 280 Old 01-09-2011, 03:47 PM
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Quote:
Originally Posted by Warpdrv View Post


I personally like this picture with the BLOSE radio right next to the TRW....


What I want to know is if the fence is to keep a toddler or a small pet out of the fan blades? And are those bags of lead shot or bread mix for the custom base dampening.
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post #185 of 280 Old 01-09-2011, 05:11 PM
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My guess is toddler and rice.
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post #186 of 280 Old 01-09-2011, 05:13 PM
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I have 4 children and that pic is scary.
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post #187 of 280 Old 01-09-2011, 09:53 PM
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Quote:
Originally Posted by haanjamin View Post

That Sonic boom generator looks interesting... looks a little easier to construct than the rotary woofer. Someone want to doublecheck some calculations I made and tell me if my thinking is off?

100 ft^3/min = 1.667 ft^3/sec = 2880 in^3/sec
Using 10 Hz, the rotary woofer would displace 2880/10 = 288 in^3 during each cycle. This is about the same displacement as a 21" Mal-X.
If you half the frequency, the displacement doubles and thats why the rotary woofer is flat all the way down?

According to my thinking, a 100 cfm fan would have the same output at 10 hz as a 21" MalX, twice as much at 5Hz, and half as much at 20Hz. This is with the MalX at full excursion at each of those frequencies.

Someone let me know if my thinking is wrong. If it isn't, I may try to make a small scale model with the stock EP4000 fan that should have some measurable output.

I have also done a lot of thinking on this as well. A sin wave has two sides to it, so cut that in half, then multiply it by 2/pi because it is a sin wave in stead of a square wave, giving you about 92 cubic inches in stead. So you would really need closer to 300 cfm, but I know of 120mm computer fans that can get close that, not very quietly though.
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post #188 of 280 Old 01-10-2011, 06:56 AM
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Quote:
Originally Posted by Nardokor View Post
I have also done a lot of thinking on this as well. A sin wave has two sides to it, so cut that in half, then multiply it by 2/pi because it is a sin wave in stead of a square wave, giving you about 92 cubic inches in stead. So you would really need closer to 300 cfm, but I know of 120mm computer fans that can get close that, not very quietly though.
This fan looks pretty good compared to other similar fans: 49.2 db for 525 cfm and only $87.

http://search.digikey.com/scripts/Dk...&name=CR144-ND
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post #189 of 280 Old 01-10-2011, 07:00 AM
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Quote:
Originally Posted by LBDiver View Post
What I want to know is if the fence is to keep a toddler or a small pet out of the fan blades? And are those bags of lead shot or bread mix for the custom base dampening.
lmao, so true.


Is that the $14K rotrary sub? Maybe some money spent on a better kitchen might make the house match what is spent on audio?

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post #190 of 280 Old 01-10-2011, 07:02 AM
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I think haanjamin's calcs are more correct. Again, assuming full excursion at all frequencies, which doesn't happen with a driver. The SPL is related to the velocity of the air and is limited by voltage/watts at higher frequencies and excursion at lower frequencies. I could have made that all up though.

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 #191 of 280 Old 01-10-2011, 08:00 AM
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Oh, and for the linkage on the blade side, I would use something like this in the lower part of the pic:

The arm is clamped directly on the blade shaft that rotates. Then you use something like the linkage shown or just a hole in the arm with a clevis. I would not use a ball and socket since you will then need that slip yoke. This device shown is used for actuating one half of a 60-80" wingspan plane flying up to 130mph or so. Each wing half could weigh a couple of pounds. It is WAY overkill for the little, slow rotary fan sub. On the driver side of the link, just bolt the linkages down (immobile) to the inside of a bearing. The outside of the bearing is attached to the driver.

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 #192 of 280 Old 01-10-2011, 12:01 PM
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Quote:
Originally Posted by haanjamin View Post

This fan looks pretty good compared to other similar fans: 49.2 db for 525 cfm and only $87.

http://search.digikey.com/scripts/Dk...&name=CR144-ND

By my guesses, that should get you close to 105 db all the way down. 60 meters cubed per second gets 132 db, .25 meters cubes per second should get you 105, in theory.
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post #193 of 280 Old 01-10-2011, 12:01 PM
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Good find, Andreas. That linkage is probably one of the more difficult components to build, so good to see there's some off-the-shelf parts available.

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post #194 of 280 Old 01-10-2011, 12:08 PM
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You can buy "giant scale" clevises off the shelf combined with making those arms. I can (and have) make 5 arms in less than two hours with just a drill press, metal band saw and a tap. They won't be pretty, but who cares? Make one, and use it as a template for the holes in all the rest of them so you have the same deflection in each of the blades.

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 #195 of 280 Old 01-10-2011, 12:25 PM
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Please don't forget to check the throw needed at the VC when factoring in your control arms ratios, and the blade pitching needed.

The exact stall point will very with the blade size/profile, and fan speed, but you should count on at least 90deg from -45 to +45deg.
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post #196 of 280 Old 01-10-2011, 02:44 PM
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Quote:
Originally Posted by SteveCallas View Post

Rotating the blades is easy - even when they turn 90 degrees and offer up significant resistance. What I am worried about is that the voice coil has to shift the blades from 0 degrees to the desired angle, not the fan motor.

Poor analogy, but stick your arm outside your car window while driving fast and keep your hand out flat to act like a wing cutting through the air. Now twist your wrist so that your flat hand is now perpendicular to the air movement. The load on your arm changes, but it's ok, your deltoids and pectorals can take it, they are strong. That's like the fan motor - no sweat. The voice coil/magnet in this is your forearm muscles that twist your wrist, and they aren't nearly as strong. Yet they will have to precisely control the exact angle of the blades (your flat hand) while overcoming that resistance. Not easy for a voice coil or for your forearm. Am I missing something?

From personal experience I can tell you that it doesn't take much force to pitch the blades.

First, here's a link to a page on my website very briefly detailing my diy rotary sub attempt. EDIT - I'm not allowed to post a link. Maybe later. It was never completed but the pictures are kind of cool.

Me and another guy challenged each other to build one with an absolute max budget of 4% of the cost of the retail version ($560). The other guy bailed almost immediately but I continued. The budget restraint was the first mistake.

The second mistake was using an rc helicopter swashplate and accessories, but that was the only way we could come in under budget. Once I had it mocked up with everything in place except the driver, I was able to pitch the blades (not shown in the pics) by hand and it took surprisingly little force on my part.

At that point, after playing with it for a couple of hours, I noticed that the rc heli parts had already started to wear out. That was the main reason I abandoned the project. It would be easy enough to finish and have a fully functional model but I don't want to destroy the driver for a subwoofer that requires regular maintenance. (I also don't have anywhere to actually use the thing so there's not much point.)

Anyway, the point is that the concept is pretty simple but rc heli parts are not the way to go, and I'm not a machinist so I quit. In the unlikely event that I try again one day I'll have a good long chat with soho54 first, that guy really knows what he's talking about. I just wish I had talked to him before I ever started...

At least I got a cool looking paper weight out of this exercise and it only cost me a couple hundred bucks.
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post #197 of 280 Old 01-10-2011, 02:53 PM
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I hope this isn't against the rules, but since the post above is useless without the link and I can't post a link, here's a picture of the link. Don't try to click it or copy and paste it, it's just a picture, sorry for the inconvenience.

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post #198 of 280 Old 01-10-2011, 03:42 PM
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Originally Posted by diy speaker guy View Post

I hope this isn't against the rules, but since the post above is useless without the link and I can't post a link, here's a picture of the link. Don't try to click it or copy and paste it, it's just a picture, sorry for the inconvenience.




Here's the link to click:

http://www.sites.google.com/site/ama...the-rotary-sub
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post #199 of 280 Old 01-10-2011, 04:26 PM
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Originally Posted by soho54 View Post

Please don't forget to check the throw needed at the VC when factoring in your control arms ratios, and the blade pitching needed.

The exact stall point will very with the blade size/profile, and fan speed, but you should count on at least 90deg from -45 to +45deg.

Do tell what you figured. Originally I thought they may have been using a longer lever (figuring the driver would need the mechanical advantage) but after seeing the pictures it seems they are using a very short lever. They also have the control arms closer to center I assume to reduce there RPM and self-noise. The other thing is at the connecting plate between the driver VC and rods they have no means to pivot as the circumference changes at the hub due to the levers. Which leads me to believe they opted for a shorter throw but higher force driver.

Also, did you figure out how they are retaining the blade arms in the hub. It's clear that the arms have a wider shoulder at the outer edge of the hub. But can't tell from the small pictures of the internals whether they are using a nut or e-clip to retain them, and maybe some thrust bearings in addition to sleeve bearings?
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post #200 of 280 Old 01-10-2011, 05:37 PM
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Quote:
Originally Posted by Andreas View Post

I would not use a ball and socket since you will then need that slip yoke

I'm fairly certain you will need the slip shaft no matter what.

Quote:


Me and another guy challenged each other to build one with an absolute max budget of 4% of the cost of the retail version ($560). The other guy bailed almost immediately but I continued. The budget restraint was the first mistake.

I saw your thread a couple days ago and was wondering about the swash plate. I have no budget restriction on this, but I'm quite confident I can do it for right around $1000, maybe less. Once I saw this thread and learned the blades don't pitch in and out, but rather, they twist, it all became much more achievable.

Quote:
Originally Posted by LBDiver View Post

Also, did you figure out how they are retaining the blade arms in the hub. It's clear that the arms have a wider shoulder at the outer edge of the hub. But can't tell from the small pictures of the internals whether they are using a nut or e-clip to retain them, and maybe some thrust bearings in addition to sleeve bearings?

I think I may use graphite bushings for this part. I want the twisting to be very controlled, and just a little bit of friction won't necessarily be a bad thing.


Going back a few posts, about the motor possibly needing feedback to keep the RPM constant when the blades pitch, I don't know if you really have to worry about this. If I go with a 0.5hp, 3 phase motor and drive, and Thigpen was using 0.3hp, there may be enough additional torque that the motor doesn't slow down.
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post #201 of 280 Old 01-10-2011, 06:18 PM
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Slap a nice big flywheel on there and I wouldn't worry too much .

Being an electrical engineer, the hardest part for me is to visualize how to handle the bearings. Any Mech E's want to take up the call?

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post #202 of 280 Old 01-10-2011, 07:57 PM
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Quote:
Originally Posted by SteveCallas View Post

...I'm quite confident I can do it for right around $1000, maybe less.

If you own a machine shop (or at least have a good friend that owns one) I'd imagine you could do it for quite a bit less than $1000, basically just the cost of the driver and motor and a few pounds of scrap aluminum. OTOH if you are paying someone an hourly wage to make the parts it might end up costing several times that much. The simple shaft I commissioned cost me $60 IIRC, and it's basically just a metal rod.

Anyway, good luck. I'm out of the game but I really want to see someone get a maintenance free diy rotary sub to a fully functional level.
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post #203 of 280 Old 01-10-2011, 08:22 PM
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Steve, you do realize that the installation requirements are the same as IB (large back volume), right?

Noah
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post #204 of 280 Old 01-10-2011, 09:14 PM
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I would say they are even more limiting than IB.

First, you have to have room for the hushbox, which is what it really is. Then you have to have the rear space climate controlled, or deal with(pay for) the extra heat in the summer/draft in the winter. People worry about an IB manifold in the attic, but it has nothing on this.
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post #205 of 280 Old 01-10-2011, 09:22 PM
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Good point.

Noah
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post #206 of 280 Old 01-10-2011, 09:49 PM
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Quote:
Originally Posted by SteveCallas View Post

I'm fairly certain you will need the slip shaft no matter what.

You can work around it. You could u se more stable control arm gear to float the flange off the shaft, or you could use a linear rotary bearing.

rwaaudio posted some pictures from Eminent were the covers are off the hub, and the control arms and flange are attached pointing up towards the camera.
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post #207 of 280 Old 01-10-2011, 10:28 PM
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Quote:
Originally Posted by soho View Post

You could u se more stable control arm gear to float the flange off the shaft, or you could use a linear rotary bearing

Ok, I just realized an error in my logic. The shaft doesn't have to transfer rotational force directly to the flange. The shaft will rotate the blade housing - the blade arms are connected to the blade housing - the flange bolts are connected to the blade arms - the flange bolts are connected to the flange. So the shaft can indirectly cause the flange to rotate.

That makes it even easier. Instead of this project getting harder and harder, it's getting easier and easier.
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post #208 of 280 Old 01-10-2011, 10:50 PM
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Quote:
Originally Posted by SteveCallas View Post

Ok, I just realized an error in my logic. The shaft doesn't have to transfer rotational force directly to the flange. The shaft will rotate the blade housing - the blade arms are connected to the blade housing - the flange bolts are connected to the blade arms - the flange bolts are connected to the flange. So the shaft can indirectly cause the flange to rotate.

That makes it even easier. Instead of this project getting harder and harder, it's getting easier and easier.

That might give a little too much chance for vibrations though. Well at least if I'm picturing it the same way as you were explaining it.
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post #209 of 280 Old 01-10-2011, 11:44 PM
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I haven't thought much about it and have only been following this thread from a distance. Not sure exactly what you guys have in mind so far. But sketch the current concept (napkin is fine with a couple of dimensions) and I'll take a look at any specific bearing or mechanisms problems.

I have pretty extensive machine design experience.

But my first thought when looking at the trw is... why couple the linear air source to the mechanism that differentially directs it?You're just asking for complexity. The sonic boom thing looks like a decent first attempt in decoupling them.

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post #210 of 280 Old 01-11-2011, 07:08 PM
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I keep thinking of different and better ways to handle the joint at the blade arm. Here's the latest, a ball joint linkage:



Screw the bolts from the flange into the shank of this ball joint linkage, have a perpendicular rod extend from the blade arm, then tap the threaded end of this ball joint linkage into the rod.

I think I have also come up with a small improvement over the original design when it comes to the fan blade housing and blade arms. Instead of twisting the blade arms so close to the center of the housing near the shaft like they do - which makes your cutouts very cramped and close together - make them further out from the center. This allows you to use two small bushings for the blade arm, providing more support than one long one, it gives you way more room to play with, and it should allow a smoother transition of movement from the flange bolt to the blade arm, as it won't try to pivot with two bushings instead of one.
LL
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