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Fwd: RE: [ATM] Active damping
Ken Hunter <atm_ken_hunter@yahoo.com> wrote:Date: Sun, 14 Aug 2005 10:24:45 -0700 (PDT)
From: Ken Hunter <atm_ken_hunter@yahoo.com>
Subject: RE: [ATM] Active damping
To: Richard Schwartz <richas@earthlink.net>
CC: 'Don Clement' <clement.focuser@verizon.net>
Thr resistance to vibration depends on the length and DIAMETER of the truss tube. You can shorten the length (not viable) or increase the diameter of the tubes to reduce the vibrations.
To go active damping, you'd have to put at least 2 sensors on EACH truss tube 90* apart. Each sensor would need an instrumentation grade amplifier, an A/D converter and a multiplexing scheme to input the data into the computer. The computer program would be fairly simple (X 12 or 16 depending on the number of truss tubes), the filters are software driven in the computer which you realize cannot be the same one using Mel's software for driving the scope as it will definitely need a version of a higher operating system than DOS. You will also need a demultiplexer, an amplifier and actuator for each sensor. I can easily see this costing into the HUNDREDS of THOUSANDS of dollars unless you might know a friend of a cousin who's son works with the son of a friend who owns a surplus store... as Jeremy (almost) said.
I still think it's better to design the problem out than to design a fix in.
Can it be done? YES!
Should it be done? NO!
Ken Hunter
Richard Schwartz <richas@earthlink.net> wrote:
Lightweight and stiffness lead to rapid damping. However, these two
attributes sort of fight each other, as we can't make truss tubes out of
soda straws. Light weight, when properly done, is NOT a cause for all that
other paraphernalia.
Adaptive filters are implemented as computer algorithms. If you have the
complexity of a vibration sensor, amplifier, and actuator, you might as well
throw in the adaptive filter; it adds zero mass.
With the adaptive filter and active damping, it may be possible to get
really sloppy about our mounts, and still have a viable scope. There may be
a further saving in total weight.
Energy? You already have a motorcycle battery to power the drive don't you?
Don't go traditional on us, Ken! John Hindle is DEAD here.
. . . Richard
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Ken Hunter
Sent: Saturday, August 13, 2005 6:56 PM
To: Don Clement; atm@atmlist.net
Subject: Re: [ATM] Active damping
OK... Lets analyze this again for at least the tenth time...
We build a lightweight telescope to reduce weight and the size of the load
we have to carry!
To compensate for the problems caused by the lightening of the members, we
insert adaptive detectors, filters, computers and actuators... not to
mention the power supplies, wasted energy etc...
Why not just build a REAL telescope instead? Remember the KISS principle?
Ken Hunter
Don Clement wrote:
> You could also run a loose piece of rope from one end to the other inside
each truss tube > to absorb the vibrational energy. Just like HAM RADIO
operators have been doing in
> their big aluminum tubed beam antennas for generations now.
One of the major advantages of active dampening over passive dampening (like
the rope) is that is doesn't take several or even one complete cycle to
correct unwanted vibration. If the system is modeled correctly, or with
adaptive filters, only a portion of a cycle is needed for corrective action
to be applied. With active dampening, the system is damped almost before
vibration can occur.
Don Clement
Running Springs, California
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