Re: [CAD_CAM_EDM_DRO] Re: small servo motors keep stalling

feck123 wrote:

>yes after looking at the motors it says 5:9 ratio gear motor...is that good or
>bad ? the 1/2-20 is bad too, buti gotta try to work with it for now...i know of
>lots of people that have no problems with this setup using stepper
>motors..is the servo setup a lot less tolerant of low pecision
>machine/screw setups?..i do not know specs on the drivers and power
>supply..i bought the whole setup from place called jra co.....website
>jraco.com...the csp-1 system...it is a nice setup and should be ok --if i can
>ever figure out how to mount my motors correctly ! :) --- thanks for the
>help ! Mike
>
>

Well, so it appears that the motor has a 1.8:1 reduction. The problem
is that the
gears presumably have backlash. Where is the encoder? Right on the
motor shaft?
Then, the backlash is between the encoder and the leadscrew, which is
not good
for accurate positioning.

Without some info on the motors, most especially the Kt or torque
constant, it is
very hard to know what to do. But, it is pretty clear that the
available torque is
way too low. My Bridgeport design delivers 1000 Lbs of linear force to the
table. This is not enough for very rapid acceleration, but is enough for my
uses. it sounds like, after the gears and the high-friction screw, you
have just a few
pounds of force left. I can't imagine this outfit can get their system
to work
on anything. They claim 200 Lbs linear force, but that is probably assuming
a ballscrew, with 90% efficiency. Your screw is probably 20% efficient, and
it gets worse as more load is applied. I am assuming you have their
SERVOMO-3 and the PWMAMP3. Note that to get full rated torque on
the SERVOMO-3, you need 8 amps. but, the PWMAMP3 only supplies 3 Amps!
So, you are only getting 3/8 of the rated torque, instead of 175 Oz-In,
you are
getting 65.5 Oz-In. That would be unsuitable for even a ballscrew machine.
Note, also, that they say PWMAMP-3 can be used with ballscrew-equipped
machines. If you have a larger capacity amp, then maybe things aren't as
bad as this. The CSP-1 sales doc doesn't mention which amps are included
with that package. You certainly spent a LOT of money for what looks like
a pretty marginal system, at best, and without seeing it first.

The SERVOMO-3 is rated at 1043 RPM, which works out to 52 IPM.
So, putting in a belt reduction ratio would severely limit the top speed.
I think you need to get more amps to the motor, or exchange for ballscrews.

Jon