Tonight's Dumb Idea...

[JOddino]

Everything has a resonant frequency including a block of aluminum. You never
want a critical component to go into resonance.  You want to keep the
resonant frequency of all the critical components high and keep them from
being excited by the engine vibration.  The idea of engine soft mounting is
to build a low pass filter that attenuates the higher frequencies so they
don't excite the resonanat frequency of the servos, etc.  If there is no
isolation, there is no attenuation and you stand a better chance of shaking
your servo apart.
That's about all I remember from my course in vibration umpty years ago.
Notice I didn't say umpteen.
Jim

----- Original Message ----- 
From: "Bob Pastorello" <rcaerobob at cox.net>
To: <discussion at nsrca.org>
Sent: Tuesday, February 17, 2004 5:11 PM
Subject: Re: Tonight's Dumb Idea...


> Actually, Jim, the vibration frequency of a typical YS or large 2 stroke
is
> QUITE a bit lower.  Simply, the 049 piston/counterweight is slapping
around
> at 22000 or more...the pattern motor somewhere around 8K.  That's an order
> of magnitude less.
>     Where the concern may be is the IMPULSE strength...the "thump" of that
> counterweight.  Kinda like an oil rig pump....HUGE counterweight, and the
> earth shakes with every thump....smaller pumps, pumping same rate but with
> different MASS counterweight - way less thump.
>
> Then there's the actual impact....If the servo, attached to the motor
mass,
> is moving at exactly the same rate and intensity as the motor itself, I'd
> challenge that the RELATIVE force transmitted to the servo is LESS than
that
> of a servo constrained someplace in the airframe.  My theory is that the
> constraining force, distance, and rigiditiy of mounting actually modifies
> the resonance or thump that hits the servo.  AND - it's connected full
time
> via the pushrod to the motor that is thumping along at it's natural rate.
>
> So we'll try it, and see what happens!!
>
> Bob Pastorello, Oklahoma
> NSRCA 199, AMA 46373
> rcaerobob at cox.net
> www.rcaerobats.net
>
>
> ----- Original Message ----- 
> From: "jim ivey" <jivey61 at msn.com>
> To: <discussion at nsrca.org>
> Sent: Tuesday, February 17, 2004 6:59 PM
> Subject: Re: Tonight's Dumb Idea...
>
>
> > Ok enough. Have you ever held a .049 in you hand,between your fingers
> while
> > it was running.Multiply this vibration by 280 times and that is what the
> > servo feels that is mounted on the mount of a YS 140.
> > I'm dodging now.
> >
> > Jim Ivey
> >
> >
> >
> > jivey61 at msn.com
>
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