Balancing a fan

I think I saw that Russian technique described somewhere along the line.
The technique may be incomprehensible to some PhD's because a coherent, linear-thinking approach may fail to derive theory supporting it. It may be a technique that uses bits of disjoint theory and perhaps some assumptions that aren't generally supportable, but works most of the time and/or perhaps all of the time in most real-world cases -- one of which may be tail rotors.
I led an R&D team that developed a self-balancing washing machine some years ago. Interesting problem because of severe cost constraints of the whitegoods market and ill-defined boundary conditions. Example: consumer washers are never bolted to concrete, and some set on the flimsy floor of a doublewide. The structure was comprised of stamped sheetmetal and some plastic, certainly not cast iron like machine tools or tire balancing machines. There were a shitload of resonances, and many of them weren't very predictable. In addition, this washer went much faster than traditional washers in the spin cycle, because it could self-balance. That reduced energy necessary for drying. Barely-damp clothes peeled off the drum with pronouced dimples in them.
The team used a technique using oversensing and SVD (singular value decomposition) sometimes used in aerospace guidance & control systems. It worked! At least a dozen patents were spawned.
Then politics and corporate infighting rendered the project stillborne.
Reply to
Don Foreman
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I 'spect that if the cage were in balance statically, it wouldn't exhibit any pathology in application.
Yes? No?
(...)
*Then* get tossed out on your can.
--Winston
Reply to
Winston
This is analogous to resonance in an electrical RLC circuit, wherein "critical speed" is resonant frequency. The response to excitation of such a circuit will be in phase well below resonance, lag by 90 deg at resonance, and lag by 180 deg well above resonance. All phase angles between 0 and 180 will occur somewhere between way below resonance and way above resonance. The speed (frequency) bandwidth of this region of uncertain phase angle depends upon the "Q", or sharpness of the resonance.
Reply to
Don Foreman
Reminds me of a company I used to work for. There's a reason I dropped the huge salary job and now farm for a living.
Karl
Reply to
Karl Townsend
How'd you know my ulterior motive to go shopping with the boss?
2000 small rifle and 1000 small pistol primers. ordered .223 rifle lead from Midwest and 9MM from Berry. Got the brass covered. But i do have a new problem. I can't seem to keep the lead and primers in the brass. And the neighbors keep asking about the noise.
karl
Reply to
Karl Townsend
On Fri, 14 May 2010 22:16:49 -0700, Winston wrote the following:
How the hell do you answer that question with a y/n? Sheesh!
Wrong, sorry. It can and does in reality. I found that when I worked at the body/frame repair shop with a Hunter balancing machine for auto/truck tires. You can balance to static perfection and still have a very noticeable OOB condition due to dynamic imbalances, which rip the spinning object out of a smooth axial path and beat the bearings to an early death.
But there's still less evil in your world as a result of your actions. Painful justification, wot?
-- Men never do evil so completely and cheerfully as when they do it from religious conviction. - Blaise Pascal
Reply to
Larry Jaques
Weird how that works. One time I was installing a new electronic device in everyone's cubical. This area was pretty high security in a bureaucracy and the women administrators were gathered together discussing if I had clearance to be there. I held up 8 fingers and stated this is 7and then the inverse. The head one turns to the rest and said he's clear.
If anything made sense something was fishy.
There must be a good book on this subject, somewhere. One that explains why people throw ball bearings into open gears, pull petty power trips, create computer viruses, establish frivolous red tape, give false directions, ect.
SW
Reply to
Sunworshipper
On Sat, 15 May 2010 04:59:52 -0500, "Karl Townsend" wrote the following:
An apple a day keeps the infighting politicians away? When the corporation bought the company I was working for, I bailed and started my own company rather than face, um, let's call them The Dilbertian Uncertainties. Like you, I'm very glad I did. Low pay, hard work, and total satisfaction. What's a guy not to like?
-- Work and struggle and never accept an evil that you can change. -- Andre Gide
Reply to
Larry Jaques
I'm working on early retirement to subsistence farming and ignoring the imploding world myself...
Reply to
Pete C.
Get a couple of load cells and a digital storage scope, trigger from a signal once per revolution. Perhaps a vibration sensor at each pillow block would do the same thing? This probably isn't practical unless you already have the DSO.
RogerN
Reply to
RogerN
Given the geometry you mention, it sounds like a two plane balancing job similar to that used on the auto crankshafts or in the case of the Helicycle turbine engine the compressor and turbine wheels. (63,000 rpm) I watched several of those things being balanced and it does seem to require simultaneous balancing of both ends. It would seem that the Squirrel cage might require a two plane static balance by both balancing in the plane perpindicular to the rotation axis as well as the plane containing the rotation axis. That might be a first step in taking care of the rotational balance as well as the "rocking couple". I've seen a helicopter rotor carefully statically balanced span wise that needed no more span wise attention when run with the dynamic balancer.
I certainly agree that balancing a spinning mass can often involve requiring the balancer to have the proper DNA and family history.
Reply to
Stu Fields
Hi,
I have not seen this on this thread.
Fan blades can be balanced in terms of weight, even dynamically balanced in terms of weight, but one needs to check that the blades match in angle. One could imagine a fan with one blade and one counterweight arm. The areodynmaics of the blade would add odd torques to the system.
That said, if the dynamic balancing is done in air, it might be good enough. I do know someone who used a dynamic tire balancer on his ceiling fan.
Thanks Roger
----------------------------------------------------------------- Stu Fields wrote:
Reply to
Roger Haar
Roger: You are dead right. On the Helicopter, the first move is to track the blades. aerodynamically. Out of track blades on the helo will cause a 1/rev vertical vibration that can confuse a balancing operation if the operator isn't paying attention. On our ship we put two different color grease pencil marks on each blade. When the rotor is spun to full speed, my wife takes a pole with the center cardboard tube from a paper towel roll attached to the top of the pole and carefully brings the paper towel roll in until it just ticks the blade ends. We get two different color tick marks of one blade is higher than the other. We adjust until we get just one color combined from the two. This doesn't guarantee good aerodynamic tracking at cruise speed on the helo since aerodyanic differences of the two blades can cause a "climbing" blade. Helps to have a fearless wife...
Reply to
Stu Fields
I do something sort of similar on my R/C helicopters. I use 2 different color tape strips near the tip of each blade, hover the helicopter and look at it from the side, you can see if one color of tape is flying higher than the other. When the blades are out of track it causes a lot of vibration.
RogerN
Reply to
RogerN
With our bigger ships, a tracking tip light was invented where you install a red LED on one blade tip and a white LED on the other. The LEDs are pointed at the pilot. The first time I tried these, I was nervous about them coming off in flight and creating a hellatious vibration. While running up I noticed a red streak and a white streak and thought "This is Great". Then at flight rpm the lights disappeared. No vibration so they must have both left at the same time. Slowed back down and there the lights were again. Great design. Centrifugal force pulled the little battery away from the LED. Tremendous idea though. It eliminated the need for a passenger operating a strobe light to check track during cruising flite. One design used centrifugal force to turn the LEDs on...
Reply to
Stu Fields
You're right. It is just a habit I've picked up reading Baumeister and Marks Mechanical Engineering Handbook where they refer to the definition of centrifugal force on page 3-25. Ir does remain a useful concept.
Reply to
Stu Fields
Got a big electric motor? Can you borrow a VFD off something for an hour? It might be REALLY instructive to spin the thing up on electric power and see if the vibration shows up, or not. If you can't detect any vibration under electric power as you vary the RPM across the troublesome range, then I think that proves it is NOT an out-of-balance condition. That leaves speed pulsation from the IC engine as the cause of the problem. Some kind of coupling that softens the pulsations would be the fix. When the engine puts out these pulses, it slams the gear train from one side of the teeth to the other, and this is REALLY hard on all the parts. I still think that is what is going on in this case.
Jon
Reply to
Jon Elson

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