Servo motor selection

Hi All,

I've been looking into building a small CNC XY table using one of the
Phase II XY tables, servos and Gecko 340 drives. The reason I'm planning
on using servos is because I may go to a bigger machine in the future
and having the Geckos sounds like it would be a good thing.

The problem I'm having is that I don't know a whole lot about servo
motors and how to size them. I've located a few motors on C&H Sales'
web site and two of them look like they might be promising. The first
is described as:

1550 RPM PITTMAN, #14203D244-R1. Permanent magnet, reversible. Ball
bearing.
Rated 38 VDC. At 38 VDC input the no-load rpm is 3440 with a no-load cur
rent of 0.12 amp. Tested with 24 VDC input the no-load speed is 2190.
No-load current 0.10 amp. With a 30 oz-in load the rpm is 1550 @ 2.2
amps.
The encoder mounted on the rear of the unit is a Hewlett Packard
HEDS-9000
Series with 500 counts per revolution. The encoder output is two phase
quadrature. Outputs are TTL logic compatible. Input power to encoder is
5
VDC nom. @40 mA. Shaft: 1/4" dia. x 7/8" long. Dimensions: 2-3/4" max.
wide
(across encoder) x 2-1/8" dia. (motor body) x 4-3/8" long (including
encoder,
but excluding shaft). Stock #DCME9701

The second is:

2600 RPM GLOBE MOTORS, #537A274. 30.3 VDC permanent magnet reversible
motor.
The motor has ball bearings and has an optical encoder mounted on the
rear.
The no-load speed is 3780 rpm, no-load current is 0.2 amp. With a load
of 60
oz-in, the rpm is 2600 @ 5.6 amps. This is a very powerful cool running
motor. The encoder employs a Hewlett Packard HEDS 9100 read head with a
custom encoder disc. The encoder has a two-channel quadrature output
with
512 counts per revolution. The encoder requires 5 VDC at approx. 40 mA
for
operation. The shaft is 1/4" dia. x 7/8" long. The shaft has a flat
running
full length. The motor has four tapped mounting holes on the shaft end
of
the motor face. The holes are tapped for #6X32 tpi screws. The bolt
centers
are 1-1/16" apart. Electrical connections are made via 3/16" quick
connect
tabs connected to the brush bosses. Dimensions: 2-1/8" dia. x 5" long.
Stock #DCME9950

The criteria I'm basing my picks on is that I think I want somewhat low
rpm motor and normal old quadrature output on the encoder.

Does anyone want to speak up about either of these choices, recommend
a better motor/encoder combo from C&H or recommend some other place to
find used servos? I've been watching ebay for a while and have seen some
servos go by but a lot of them sound like pretty huge motors.

The page with C&H's servo motors is at:

http://www.aaaim.com/cgi-local/shop991/shop.pl/SID=13784101471/page=DCME.htm

Thanks,
Drew

--
Drew Rogge
drew@...