[TheForge] Off-topic: Anyone have experience with dynamic balancing, vibration sensing & vib-synched stroboscopes, and/or critical disk and/or rotor speeds?

[wmullett at bright.net]

Bruce, 

You don't say how large this is and if you can take it apart or not.  I know nothing about dynamic balancing but could you use any of the following:

Forty years ago I was into slot car racing - not the home variety.  We used to take brand new motors, cut the windings out and re-wind them with a different wire.  When done, we would balance the armature using epoxy.  Not in place but we placed the armature straddle across two razor blades so that there was no friction.  

I would think similar principles could be applied to larger items.

Walt 

---- Original message ----
>Date: Tue, 14 Jul 2009 22:21:05 -0400
>From: theforge-bounces at mailman.qth.net (on behalf of Bruce Freeman <freemab222 at gmail.com>)
>Subject: [TheForge] Off-topic: Anyone have experience with dynamic balancing, vibration 	sensing & vib-synched stroboscopes, and/or critical disk and/or rotor speeds?  
>To: Blacksmithing List Sponsored by ABANA <theforge at mailman.qth.net>
>
>I'm working on a mechanism that involves a high-speed rotor, and I'm
>to the point where I really need to dynamically balance the thing.
>I've run it at about 1740 RPM and maybe as high as twice that.  (I
>haven't measured the pulleys.)  I get more vibration than I want, but
>it's not flying apart or anything scary.  (I'm aiming for an arbitrary
>10kRPM.)
>
>So, I've spent the day reading up on dynamic balancing and have
>learned a fair amount, but nothing I can put to immediate use.  I have
>learned that above the (first) critical speed (i.e., the speed
>equivalent to the fundamental vibration frequency of the rotor), the
>vibrational behavior changes and it is possible to automatically
>balance the device.  There are patented mechanisms that utilize this
>phenomenon.  However, I have no idea whether I have yet approached the
>critical speed for this rotor, and trying to calculate that speed
>(which is possible, in principle) would be rather difficult due to the
>odd construction of the rotor.  Furthermore, I'm not at all sure I
>want to take it up to the critical speed without first dynamically
>balancing it.
>
>The best alternative I've come across so far is to utilize some sort
>of sensor that will register vibrational period and amplitude and,
>preferably, trigger a stroboscope so that one can visualize where the
>excess weight is on the rotor.  Unfortunately, I'm quite unclear about
>what sort of sensor this requires.  I actually have a stroboscope, and
>can easily "stop" the motion of the rotor with it, but it is triggered
>by time, not by an external sensor, and correlating the flash to the
>vibration is beyond my abilities for the nonce.
>
>Furthermore, I read that in dynamic balancing, it may be necessary to
>have a support structure with "soft" bearings.
>
>As anyone knowledgeable in the field can tell, I'm in over my head
>here.  I would appreciate any pointers, assistance, words of wisdom,
>URL's or whatever that you can provide.
>
>-- 
>Bruce
>NJ
>
>The total lack of evidence is the surest sign that the conspiracy is working.
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