On Wed, 25 Nov 2009 22:38:22 -0500, Bob Engelhardt
wrote:

wrote:
On Nov 26, 1:07 am, Bob Engelhardt wrote:
...Could I use this orthogonal balancing on a gas engine? ...

I can not think of any reason why it would not work.

I guess what I was wondering about, without having my finger on it
specifically, is whether the inherent vibration of a gas engine would
drown out the impeller's imbalance. As far as being able to see it on
the 'scope.

But it has just occurred to me that I can do the orthogonal balancing of
the impeller off the gas engine, on an electric motor. Turning on a
motor would be a lot easier than pull starting the engine, for all those
trials. And I could do it inside. I'd probably have to use a 3 phase
motor & VFD to run at a speed that wouldn't overload the motor.

Now, as to the procedure, is this right:
1. add some weight, w, to the "1" spot & measure the amplitude of the
vibration
2. try the same weight at "3" & measure
3. put the weight at the location of lesser amplitude
4. put on an additional weight of w/2 & measure
5. move the w/2 weight to the other side & measure
6. put the w/2 weight at the location of lesser amplitude
repeat 4 - 6 with w/4, w/8, etc

If at any weight the 1 & 3 amplitudes are the same, skip that weight &
go on to the next size.

Repeat for the "2" & "4" spots.

You didn't say, but it seems to me that it's possible that "w" is going
to be significantly too small. I.e., all the weights will be on the
same side, desperately trying to get big enough to balance. In
anticipation of this, if "w" & "w/2" are both on the same side, start
over with 2w.

Also, the weights don't have to accumulate, they can be partially
eliminated. E.g., if you have w at 1 & w/2 at 3, that's a net of w/2 at
1. Or, generally: if w/(n+1) is opposite w/n, then remove w/n & put
w/(n+1) in its place. I don't see a real advantage to this, but maybe
there is. And it's dependent upon accurately making weights 1/2 the
previous size. OK, it's not a good practical idea.

Thanks,
Bob


Motor drive is the way to go - there would be too much
vibration from th gas engine. Belt drive is often more convenient
than direct drive.

You've got the balancing sequence dead right and it's
important to stick to it It's only too easy to chase your own
tail if you cut corners or if the balance weight placements are
not correctly 90 deg apart

Good luck

Jim