[time-nuts] GPSDO time constant

[Lux, James P]

> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Magnus Danielson
> Sent: Thursday, January 08, 2009 11:19 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPSDO time constant
>
> Poul-Henning Kamp skrev:
> > In message <4965E869.4090205 at rubidium.dyndns.org>, Magnus
> Danielson writes:
> >
> >> Ericsson created a rack system in which the bottom of the rack was
> >> actually forming a closed container with the floor.
> >
> > We had that at one place I worked, except it was two small
> "dogs" you
> > attached front and back a standard 19" rack.
>
> I never seen it myself, so you have more correct info. I go
> back from something told to me way back in time, so details
> got a bit fuzzy.
>
> > Trouble was that you had to wash the floor first, or the dust would
> > blow all over the place.
>
> You also have some rather high requirements on the floor
> quality, it needs to be fairly flat as well.
>
When I worked in the special effects business, we used to use these all the time to move heavy stuff around. It actually doesn't require a "real flat" floor (1 cm grooves aren't a big issue).  Think about them as small hovercraft. It also doesn't take much air pressure to lift things (large area * small pressure).  For instance, folks build small hovercraft using electric leaf blowers as the pressurization fan to support a disk some 1.2m in diameter which will easily support a couple people.

The lift pads we used were about 30cm in diameter. 1 psi (7kPa) lifts about 50kg. Moving around 1 ton things with 4 pads wasn't unusual.

The rougher the floor, the more airflow you need.