Alt-BEAM Archive

Message #01766



To: beam beam@corp.sgi.com
From: "Sathe Dilip" sathe_dilip@bah.com
Date: Thu, 25 Mar 1999 18:41:18 -0500
Subject: [alt-beam] Re: small parts....




Bruce Robinson wrote:
>
SNIP
> gears being metal. Typically these are gearing down from 60 Hz (3600
> RPM) to 1 or 2 revolutions per hour, or about 200,000 to one! Most of
SNIP

Excellent description of the gear boxes (deleted). However this ratio
may need correction. For an AC motor, the synchronous speed can be
calculated by the equation:

(120 x f)/P

Where f is the frequency of supply and P is the number of poles. So for
a motor with 2 poles operating with a 60 Hz supply, 3600 RPM is
correct. However, usually the motors used in these timers have many
more poles(may be 20 ?) so they run quite slow. Depending on the number
of poles on the motor, the gear train may have a ratio of 20,000 (more
or less).

Dilip

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