Re: Orthoganol balancing - twinwheel grinders
- From: "Stu Fields" <eh@xxxxxxxxxx>
- Date: Fri, 31 Jul 2009 14:20:37 -0700
<pentagrid@xxxxxxxxx> wrote in message
news:fjj6759t3s0137jbatcq9fta7d9lcqusub@xxxxxxxxxx
On Fri, 31 Jul 2009 20:35:43 +0200, Robert Roland
<fake@xxxxxxxxx> wrote:
On Fri, 31 Jul 2009 15:05:13 +0100, pentagrid@xxxxxxxxx wrote:
the job can be done with an oscilloscope and an
old 2" computer loudspeaker
That's brilliant, Jim.
How about adding some sort of synchronization signal? Paint a white
dot on the cup and use a photo transistor connected to the scope's
other channel to get a reference to make it much easier to figure out
where to add weight.
I have played with that sort of system but it gets complicated.
For the comparatively small balance improvement needed for a twin
wheel grinder the stark simplicity of the speaker plus 'scope is
all that is needed.
Is a grinder fast enough to use self-balancing similar to what they do
in CD-ROM drives? I think it's simply some sort of drum with loose
steel balls inside.
I'm pretty sure that would work but I've never tried it.I think
the system is a bit like my cup but with the edge of the cup rim
turned in to retain a partly filled complement of balls. Wen run
up to speed the balls space themselves out into a pattern that
cancels the unbalance.
Jim
Another method is available and is normally referred to as the "No Phase
Method" where like the scope and speaker coil method you don't have any
reference marks. Larry Meidell who is a rather famous helicopter vibration
expert wrote an article for the Experimental Helo magazine whereby three
locations were used at 120 degree angle separations were used for trial
weight positions and then a graphical solution was made using the initial
vibration level reading and the three additional readings using trial
weights. The result shows at what angle and how much weight is needed.
Several books have been published showing this method. I've have
successfully used it on my tail rotor and one of the magazine readers
balanced his tail rotor using just a dial indicator in lieu of an
accelerometer and the "No Phase" method. An article describing that
experiment also ended up in the Experimental Helo Magazine. If anyone is
interested, let me know and I can check with the author and see if he is
willing to release the article to all. Send me an e-mail at the address
below.
Stuart Fields
Experimental Helo Magazine.
eh@xxxxxxxxxx
.
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