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Dynamic propeller balancing sensor.

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aero(at)rwaltman.com
Guest

Posted: Thu Sep 06, 2012 8:33 am Post subject: Dynamic propeller balancing sensor.

I'm beginning to look into how difficult would it be to make my own 

"poor man's" dynamic prop balancer.



Any recommendation for an of-the-shelf accelerometer to be used as sensor?



Thanks,



Roberto Waltman

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Sep 06, 2012 10:03 am Post subject: Dynamic propeller balancing sensor.

At 11:32 AM 9/6/2012, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Roberto Waltman <aero(at)rwaltman.com>



 I'm beginning to look into how difficult would it be to make my own "poor man's" dynamic prop balancer.



 Any recommendation for an of-the-shelf accelerometer to be used as sensor? 	


   There are a number of variable capacitor accelerometers offered

   on eBay. You'll also need a charge amplifier and a 'charge-stable'

   coax signal cable to run between the accelerometer and

   amplifier.



  http://tinyurl.com/9hhege2



  http://tinyurl.com/9o324vg



  http://tinyurl.com/8nd2y9y



 



   The output of the amplifier may need to be filtered to

   get rid of vibrational noises. I'm thinking a band-pass

   filter centered on the vibration-frequency of some

   handy test rpm would do the job.



   Since your data is only used for comparative measurements,

   calibration is not an issue. You could build your own

   charge amplifier



  http://tinyurl.com/d4t67hd



   If charge amp is built into a single assemlby with

   the accelerometer, you can do away with the fancy

   'low capacitive noise' coax.



   Then read the conditioned signal with an rms reading

   voltmeter. This setup will only give you gross unbalance

   data . . . it won't tell you which blade is heavy.

   But test weights will quickly reveal whether adding

   some small weight made things better (light blade)

   or worse (heavy blade).



 

   Just saw this critter

 

  http://tinyurl.com/8ejraxb



   which seems to be an internally signal conditioned

   device. You could google the device and see

   if there are any user's manuals floating around

   out there.



   I wasn't aware of this product. 



 [img]cid:.0[/img]



   Signal conditioning built in and designed for

   use on machine tools. See:



  http://tinyurl.com/8v3ejxe



   Looks like just what you need. You'll still need

   to filter irrelevant vibrations so that you can

   take a close look at the relevant data.



 

 

   Bob . . .

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aero(at)rwaltman.com
Guest

Posted: Thu Sep 06, 2012 12:14 pm Post subject: Dynamic propeller balancing sensor.

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   Then read the conditioned signal with an rms reading

 voltmeter. This setup will only give you gross unbalance

 data . . . it won't tell you which blade is heavy.

 But test weights will quickly reveal whether adding

 some small weight made things better (light blade)

 or worse (heavy blade).


	


Brilliant! I was planning to go the FFT and Adroid tablet GUI way.

For the one single airplane/propeller that I want to take care of, your 

suggestion is perfect.



 	  Quote: 	
		   Just saw this critter

 http://tinyurl.com/8ejraxb

 which seems to be an internally signal conditioned

 device.

 http://tinyurl.com/8v3ejxe

 Looks like just what you need. You'll still need

 to filter irrelevant vibrations so that you can

 take a close look at the relevant data.


	


Thank you very much for the pointers. (If going with capacitive sensors, 

I almost forgot about the existence of charge amplifiers. Worked with 

Kistler force plates, years ago.)



Roberto Waltman

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Sep 06, 2012 1:59 pm Post subject: Dynamic propeller balancing sensor.

 	  Quote: 	
		  

 Thank you very much for the pointers. (If going with capacitive sensors, I almost forgot about the existence of charge amplifiers. Worked with Kistler force plates, years ago.) 	


    I've used up this month's 'play money' exploring

    some thermocouple readouts off eBay . . . but

    as soon as it's doable, I'll pick up a self-amplified

    accelerometer and get educated. I've got some

    work coming over the hill that might benefit from

    this technology.



    Here's an exemplar band pass filter for 30 Hz, (1800

    propeller RPM).



 [img]cid:.0[/img]



    This is a rough order of magnitude swipe at the task.

    You can fiddle with alternative gains, center frequency and bandwidth at:



  http://tinyurl.com/9xwbwfm



    Good luck!



 

   Bob . . .

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Fri Sep 07, 2012 4:56 am Post subject: Re: Dynamic propeller balancing sensor.

Bob's inputs here are great. 



Here's my two-cents:



GovernmentLiquidations.com frequently has complete Chadwick Helmuth vibrex and strobex units for cheap. A business in a box! These are very professional units that are still used (for helicopters mainly...but hey, they still use propellers). Alternatively, pick up stuff from Ebay. 



Failing this, if you still want to roll your own, at least grab some C-H Strobex manuals to see how they do this, online: http://www.scribd.com/doc/40565507/Strobex-Manual  . 

BTW: I knew and worked with Jim Helmuth personally when I worked on Endoscopic Strobo-Laryngoscopy for vocal cord vibration analysis. He was a brilliant, gentle and greatly admired man (Chadwick was the biz man, Jim Helmuth the engineer.) We all watched helplessly as he smoked himself to death far too young because he couldn't break his cigarette addiction. Damned shame.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 07, 2012 7:15 am Post subject: Dynamic propeller balancing sensor.

Failing this, if you still want to roll your own, at least grab some 

C-H Strobex manuals to see how they do this, online: 

http://www.scribd.com/doc/40565507/Strobex-Manual  .

  Looks like a valuable addition to the archives.

  Do you have a membership to download this?

BTW: I knew and worked with Jim Helmuth personally when I worked on 

Endoscopic Strobo-Laryngoscopy for vocal cord vibration analysis. He 

was a brilliant, gentle and greatly admired man (Chadwick was the biz 

man, Jim Helmuth the engineer.) We all watched helplessly as he 

smoked himself to death far too young because he couldn't break his 

cigarette addiction. Damned shame.



   The guy had an impressive resume. He's referenced

   a lot in the arena of lightning-in-a-jar.





   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Fri Sep 07, 2012 10:37 am Post subject: Re: Dynamic propeller balancing sensor.

Sorry Bob, 



But the whole PDF appears to be there. The download is $9. An enterprising person could image grab it all some rainy Sunday.



C-H's manual called "Smooth Propeller" and the Vibrex 2000 manuals are good too. I can't believe the military doesn't have free downloads on all this stuff.



Maybe some AeroElectric lister can find them.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 07, 2012 2:03 pm Post subject: Dynamic propeller balancing sensor.

At 01:37 PM 9/7/2012, you wrote:

 	  Quote: 	
		  



Sorry Bob,



But the whole PDF appears to be there. The download is $9. An 

enterprising person could image grab it all some rainy Sunday.


	


   No problem. Next time I have enough wishes in

   the que, I'll pay the one-day feed and go grab

   some stuff. But if I get flush (got a couple

   of $jobs$ on the back burner) I'll get a year

   subscription. Scribd is a fantastic resource.



   Bob . . .

aero(at)rwaltman.com
Guest

Posted: Fri Sep 07, 2012 6:04 pm Post subject: Dynamic propeller balancing sensor.

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		     ...it won't tell you which blade is heavy.

   But test weights will quickly reveal whether adding

   some small weight made things better (light blade)

   or worse (heavy blade).


	


Not being a mechanical engineer, that's all I could think.

Fortunately, other peoples are. [Mech engineers, physicists, 

etc.]



See slides 36 to 42 in this presentation:

sem.org/PDF/Suri_Rotor%20Balancing.pdf



Roberto Waltman

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 07, 2012 7:18 pm Post subject: Dynamic propeller balancing sensor.

 	  Quote: 	
		  Not being a mechanical engineer, that's all I could think.

Fortunately, other peoples are. [Mech engineers, physicists, etc.]



See slides 36 to 42 in this presentation:

sem.org/PDF/Suri_Rotor%20Balancing.pdf


	


   Cool! That's a flashback to and engineering graphics

   course I took way back when . . . The dudes that

   figured out that process had some pretty twisted

   grey matter. One of those cases where a protractor,

   compass and ruler can be used to yield some interesting

   results.  There's a process using similar tools whereby

   you can use star sightings to draw circles representing

   lines of possible position (each star sighting has

   an infinite number of possible positions which inscribes

   a circle on the surface of the earth). Plot LOP from

   three stars and the intersection of three circles

   is pretty close to where you're at. Love it . . .



   Hmmm . . . I wonder if this would adapt to a

   two bladed system? Anybody out there with sufficient

   twist in the cognitive neurons?

   Bob . . .

millner(at)me.com
Guest

Posted: Fri Sep 07, 2012 7:24 pm Post subject: Dynamic propeller balancing sensor.

>> This setup will only give you gross unbalance data . . . it won't 

tell you which blade is heavy.  But test weights will quickly reveal 

whether adding some small weight made things better (light blade) or 

worse (heavy blade).



Typically with dynamic balancing, though, one isn't just adding weights 

to one blade or the other, but rather just the right amount of weight at 

just the right circumferential point on the hub... Typically, NOT at the 

blade attachment location.



Perhaps your technique will give you sufficient resolution for that, I 

haven't investigated... but your heavy/light blade reference concerns me 

in that regard.



Paul

aero(at)rwaltman.com
Guest

Posted: Fri Sep 07, 2012 7:55 pm Post subject: Dynamic propeller balancing sensor.

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		     Hmmm . . . I wonder if this would adapt to a

   two bladed system? Anybody out there with sufficient

   twist in the cognitive neurons?


	


It is not a three-blade system. It is a rotating mass, of 

any geometry, measured/balanced by placing sample weights 

120 degrees apart. I assume you need at least three to make 

the intersection of the three circles unique.



Roberto Waltman

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 07, 2012 9:14 pm Post subject: Dynamic propeller balancing sensor.

At 10:54 PM 9/7/2012, you wrote:

 	  Quote: 	
		  



Robert L. Nuckolls, III wrote:

>   Hmmm . . . I wonder if this would adapt to a

>   two bladed system? Anybody out there with sufficient

>   twist in the cognitive neurons?



It is not a three-blade system. It is a rotating mass, of any 

geometry, measured/balanced by placing sample weights 120 degrees 

apart. I assume you need at least three to make the intersection of 

the three circles unique.


	


    aHHH . . . but of course. Guess it would be

    pretty hard to make this work on a two bladed propeller

    unless you could put the weights on the hub.



    I suspect the professional chasers of propeller

    shake use a methodology not unlike the old Bear

    alignment systems that used a strobe to mark wheel

    position when the heavy (or light) spot was straight

    up or straight down. I remember my mechanic putting

    a chalk mark on the tire and using the 'scope to

    clock the chalk mark. The 'scope only located the

    weight, he put his hand on the fender to judge when

    he was getting close to the right weight . . . if

    he overshot, the 'scope would report a swap of

    the heavy/light sides.



    Kinda crude by today's techniques but it sure

    worked better than the static bubble balance

    method.

   Bob . . .

dave.saylor.aircrafters(a
Guest

Posted: Fri Sep 07, 2012 9:38 pm Post subject: Dynamic propeller balancing sensor.

We balance props on a regular basis using an ancient Chadwick.  It

usually takes about an hour.



The Chadwick system uses an accelerometer and a strobe.  A black box

calculates when the acceleration reaches it peak and flashes the

strobe at that point.  The box also indicates a quantity for the

vibration, in units of "inches per second", or IPS.



There's also a mag pickup system but that's more for helicopter main rotors.



Since the peak occurs when the heaviest part of the weighted disc is

adjacent to the accelerometer, you know where to add weight (opposite

the accelerometer, with the target positioned as it appeared in the

flash).



The user fine tunes the flash rate by watching for shift in the target

position while pushing a tuning button, and simultaneously adjusting

for RPM.  It takes a little practice but once you know what to watch

for it's pretty easy.



Chadwick used to have an FAA-approved pamphlet called "The Smooth

Propeller" that talked about how and where to add weights.  It's

pretty much trial and error until you get a handle on how much weight

has a resulting effect.



Dave Saylor

831-750-0284 CL

On Fri, Sep 7, 2012 at 10:12 PM, Robert L. Nuckolls, III

<nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 10:54 PM 9/7/2012, you wrote:

>

> 

> <aero(at)rwaltman.com>

>

> Robert L. Nuckolls, III wrote:

>>

>>   Hmmm . . . I wonder if this would adapt to a

>>   two bladed system? Anybody out there with sufficient

>>   twist in the cognitive neurons?

> It is not a three-blade system. It is a rotating mass, of any geometry,

> measured/balanced by placing sample weights 120 degrees apart. I assume you

> need at least three to make the intersection of the three circles unique.

    aHHH . . . but of course. Guess it would be

    pretty hard to make this work on a two bladed propeller

    unless you could put the weights on the hub.



    I suspect the professional chasers of propeller

    shake use a methodology not unlike the old Bear

    alignment systems that used a strobe to mark wheel

    position when the heavy (or light) spot was straight

    up or straight down. I remember my mechanic putting

    a chalk mark on the tire and using the 'scope to

    clock the chalk mark. The 'scope only located the

    weight, he put his hand on the fender to judge when

    he was getting close to the right weight . . . if

    he overshot, the 'scope would report a swap of

    the heavy/light sides.



    Kinda crude by today's techniques but it sure

    worked better than the static bubble balance

    method.

   Bob . . .

aero(at)rwaltman.com
Guest

Posted: Sat Sep 08, 2012 4:46 am Post subject: Dynamic propeller balancing sensor.

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		    unless you could put the weights on the hub.


	


That's were they normally go. Small washers...

The blades are expected to be already statically balanced. 

That is, same weight, but not necessarily same weight 

distribution. That's why dynamic balancing is needed.



 	  Quote: 	
		    I suspect the professional chasers of propeller

  shake use a methodology not unlike the old Bear

  alignment systems that used a strobe to mark wheel

  position when the heavy (or light) spot was straight

  up or straight down.


	


Modern system do not use a strobe light. An accelerometer 

and an optical sensor are mounted near the prop, and a 

reflecting tape is mounted on the prop itself, but not as a 

reference for a strobe. A computer reads data from both and 

provides vibration amplitude and phase information as a 

guide to be used placing weights.



Products:

http://www.rpxtech.com/rpxweb/Dynavibe.asp

http://www.smartavionics.com/pb3/pb3.html

http://dssmicro.com/products/prod_mb_main.htm

http://dssmicro.com/products.htm



A field report (Vibrex):

http://www.dvatp.com/aviation/maintenance/dynamic_balancing/



Roberto Waltman

klehman(at)albedo.net
Guest

Posted: Sat Sep 08, 2012 5:19 am Post subject: Dynamic propeller balancing sensor.

I have a commercial unit that uses the ADXL103 acceleration sensor. I've 

also experimented with that chip (actually one channel of an ADXL203) to 

do a little monitoring of propeller and bearing condition.



The overall concept is to bounce an infra red signal off reflective tape 

on one prop blade to get rpm and the phase of the imbalance. Add a 

weight and repeat the run. Compute a suggested change in phase and 

magnitude which can be done in software or with a paper vector diagram. 

ie. suggest a relative change in the size of the weight and how many 

degrees of prop rotation to move it forward or aft.



FWIW on the few props that I've tested, I've yet to find a significant 

improvement on Warp Drive props or on two blade metal props that were 

already in obvious good condition. And I've greatly increased my opinion 

of how sufficient static prop balancing can be. Graybeards can static 

balance to within a few spray puffs of paint on the tips. That would be 

with the prop on a horizontal mandrel and the mandrel resting on knife 

edges.



It is easy to chase insignificant apparent imbalances that are different 

at varying engine rpms but it was certainly educational.



Ken



On 06/09/2012 12:32 PM, Roberto Waltman wrote:

 	  Quote: 	
		   

 <aero(at)rwaltman.com>



 I'm beginning to look into how difficult would it be to make my own

 "poor man's" dynamic prop balancer.



 Any recommendation for an of-the-shelf accelerometer to be used as sensor?



 Thanks,



 Roberto Waltman

millner(at)me.com
Guest

Posted: Sun Sep 09, 2012 9:38 am Post subject: Dynamic propeller balancing sensor.

>> Modern system do not use a strobe light. An accelerometer and an 

optical sensor are mounted near the prop, and a reflecting tape is 

mounted on the prop itself, but not as a reference for a strobe. A 

computer reads data from both and provides vibration amplitude and phase 

information as a guide to be used placing weights.



The new Insight G3 engine monitor is to eventually include a real-time 

vibration monitor.  Whether it will be capable enough to suggest 

location and size of balance weights, I do not know.  It wasn't 

functional on version 0 IIRC.



Paul



 	  Quote: 	
		   Products:

 http://www.rpxtech.com/rpxweb/Dynavibe.asp

 http://www.smartavionics.com/pb3/pb3.html

 http://dssmicro.com/products/prod_mb_main.htm

 http://dssmicro.com/products.htm



 A field report (Vibrex):

 http://www.dvatp.com/aviation/maintenance/dynamic_balancing/

aero(at)rwaltman.com
Guest

Posted: Mon Sep 10, 2012 8:46 am Post subject: Dynamic propeller balancing sensor.

Dave Saylor wrote:

 	  Quote: 	
		   Chadwick used to have an FAA-approved pamphlet called "The Smooth

 Propeller" that talked about how and where to add weights.


	


Found a copy here:

http://www.expaircraft.com/PDFgallery.htm



Roberto Waltman.

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