Re: [ATM] Active damping

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> competition I had an interesting conversation about
> active damping to reduce vibration.  I don't know much
> about this.  It seemed to involve adding a mass that
> would vibrate near the same fundamental frequency as
> the rest of the scope to soak up the excess vibes.
> Some electronic or mechanical black box controls it, I
> imagine.  I know something similar is done on big
> buildings in quake zones.  Can anyone point to an
> ATM-friendly source on this?

You disapate energy passively or actively.  Energy comes from wind and from 
human touch.

Passive dampening includes Sorbethane pads, designing for higher instrinsic 
dampening frequencies, disapation schemes such as metal chains, pre-tuning 
or pre-stressing vibrating members, and the like.

Active dampening consists of a feedback loop that's responsive to the energy 
dumped into the telescope system.  You'll need a sensor that accurately 
measures absorbed energy, a control loop, and a moment of inertia (in 
otherwords, mass) to work on.  Most amateur sized scopes have characteristic 
frequency in the range of 3-12 Hertz.  See The Design and Construction of 
Large Optical Telescopes by Baly for a great deal more on this.

Mel Bartels

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