You will probably need two reduction stages to get a 10:1 belt drive
reduction.
There are some fairly cheap servo motor gear boxes out there now being
made in China.
That may be the cheaper/easier way to go.
FWIW, 1 KW servo motors x 2 is probably an overkill unless you want to
go really fast or if your gantry is
heavy steel.
Dave
On 10/3/2018 9:41 AM, Leonardo Marsaglia wrote:
Sorry for the lack of detail, I wrote the message too fast this morning
when I just got up.
I'm planning to use 1 kw servos on each side with a max RPM of 3000. The
idea is to gear down from the motor to the pinion 10 to 1 using the timing
belts. The pinion I'm planning to use is a MOD 2 with 20 teeth. That would
give a theoretical linear max speed of 37 meters/minute.
I was thinking about making a custom component for offsetting the index
pulse on the encoders but I don't know if this approach will be reliable
enough.
El mié., 3 oct. 2018 a las 10:17, Todd Zuercher (<to...@pgrahamdunn.com>)
escribió:
I haven't really looked at the documentation for Master lately, but the
means for setting up a multiple joint axis (like a gantry) was documented
reasonably well last time I checked.
My personal experience with rack and pinion driven wood routers is that
for stepper-motor drive you are going to want between 2.5-5
revolutions/inch of travel. With a leaning towards the lower end of that
scale. With a 2.5 rev/inch ratio and half stepping the machine should be
capable of 600ipm rapids and about 0.001" resolution. If you are going to
run servo motors I would suggest a ratio probably double what you'd want
for a step-motor, but that will depend on the max rpm of your servo and
what you want your max feeds to be.
The 10:1 ratio you mention doesn't tell us much without the pinion size,
is that motor revs to pinion revs, or motor revs per unit length?
Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street
Dalton, Ohio 44618
Phone: (330)828-2105ext. 2031
-----Original Message-----
From: Leonardo Marsaglia <ldmarsag...@gmail.com>
Sent: Wednesday, October 03, 2018 6:01 AM
To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net>
Subject: [Emc-users] Yet another topic about gantry homing
Hello to all!
I'm building a CNC router for wood machining for a friend of mine and the
best way I found to drive the Y joint for this particular design, given the
size of the machine, is the following:
One rack and pinion on each side of the longitudinal axis of the machine
and each pinion conected to a servo motor using two steps of reduction with
synchronous belts to achieve a 10 to 1 ratio.
I've found several topics on the forum talking about the homing of an axis
arranged like this. I guess to have screw regulated home switches for each
Y joint is almost a must (in case you don't use linear scales). But I was
wondering if it's possible to use ,in conjunction with that, the index
pulse of an encoder coupled to directly to the pinion.
My idea is to offset the index pulse on each encoder via HAL to make both
sides of the Y joint trip the index pulse together and stay squared during
homing. Is this a good practice?
About how to drive both Y joints as one axis: I've read that there's a way
of simply adding two Y joints for the Y axis in the 2.8 master branch but I
don't know if there's documentation available already.
But I was thinking about slaving one of the motors (using them as pulse
and direction at the beginning to make things easier) and use the encoder
on the pinion only for following error and homing. I don't like the open
loop approach a lot, but I don't know if it's that easy to use them as
servos in position mode without having too much trouble.
Any thoughts?
Thank you as always!
Leonardo
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