Re: [CAD_CAM_EDM_DRO] PIC-Servo

hello,


I am currently using the pic-servo product on a 6x9x8 inch travel, cnc
mill. I am using a severly modified version of the cnc mill software that
kerr had on his web site, to run the machine. This software drives the 4
axis machine via a serial port, and loads the command buffer that is on each
axis. I can also use emc to control the machine via the step and direction
interface, but I loose the 400imp rapids I get with the rs232 command
interface, and the ability to control the spindle speed:(

At this point I use 4 pic-servo chipsets to control x-y-z and the spindle
motor. I cant tell you how nice it is to have direct control over the
spindle speed from within the part program. I call this 4 axis because it
gives the ability to accomplish semi rigid tapping wich, I am working on
now. I have a 2.5hp treadmill motor running the spindle at speeds from
1-7000 rpm. I dont know how they come to a rating of 2.5hp beacuse this
thing is a whimpy 2.5. Without the ability to command the spindle position,
even semi rigid tapping would never be a posibility, much less rigid
tapping. I have preloaded ballscrews on all 3 axis, and air counter balance
system on the z axis. Each axis develops approx. 100 lbs of linear force
with direct drive servos.


I like the pic-servo products, but they have some short comings that I
have not, as yet, found a way around via software. One is the delay between
moves. If you are not in constant contour mode, each move has about a .25
second pause before the next move is excecuted. Second, when you are in
constant contour mode, the delay is gone, but you are left in an exact stop
mode. Being in exact stop mode is not a bad thing unles you program a move
that requires more than a 90 degree change of direction. The machine is
making all moves without deccelerating, so it feels like a thud. On a small
machine you dont notice it much, but I think a bridgeport x-axis would be
much more noticable. All rapid moves accelerate and deccelerate, but feed
moves can be programed in constant contour mode or not. I notice a big
difrence in the way the machine moves when the machine is controled by emc.
So far I dont see much difrence in the finished parts, but the machine seems
to move much more smoothly.


I would trash this system If I could find a way to run emc with direct
command control of servos, and do it on a hobby budget. I think some folks
are very close to comming up with just such a system, but until then Ill
keep making chips fly with pic-servos.


I like to tackle the chalenges, so this is the system for me. If you are
looking for somthing that just works, then look for another solution.


just my opinion on the matter.

andrew-kn6za



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