--- In mach1mach2cnc@..., "carlcnc" <carlcnc@y...> wrote:
Thanks for the replies and advice,
see any flaws in my scheme below?
condensed version,
3:1 reduction from motor to screws,
screws are 2.54 turn per inch
needed motor rpm for 300ipm 2286
mount 800 cpr[3200pulse] encoder on screw so
pulses per inch travel =8128
Mounting the encoder at screw end means less than 8 ft cable to
drive,
thanks again
Carl
Might want to check your math again. It takes 2.54 revs at the shaft
to move your screw 1 inch. It takes 3 times that because of the gear
reduction back at the motor so that adds up to 7.62 revs to go 1
inch. It takes 3200 pulses to turn the motor 1 rev so you have 3200
X 7.62 = 24,384 pulses to move one inch. Each step moves the
load .000041 inch. Now if you want to move 5 inches per second (300
IPM) you will have to supply 121,920 pulses in one second (pps) from
the PC....not possible in MACH2 (45,000 pps max).
I thought you said the pitch was 1 mm? There are 25.4mm per inch.
The numbers you gave were for a 10mm pitch screw . If it is 1mm
multiply all of the above numbers by 10!
You will have to investigate a step multiplier for the 320 or live
with much slower speeds. Max speed even at 45,000 pps is a little
over 110 IPM and that is with a 10mm pitch screw.
I don't remember the upper limit of the steps for the Gecko. With a
10:1 multiplier you can get the numbers back into the world of
reality if the Gecko will digest the rapid encoder counts and
incoming steps. Technically you could do your 300 IPM with room to
spare.
The killer in this is the 800 count encoders. 200 count would lower
the numbers to 800 * 7.62 = 6096 pulses per inch. Provided the pitch
is 10mm (2.54 turns/inch) you can get your 300 IPM rapids.
Its easy to loose sight of the fact that even though the motor might
be rated at 3500RPM (58.33 rev/sec) which is plenty fast to get the
speeds you want, every incoming pulse to the Gecko moves the motor
1/4 encoder counts. Since every rev requires 3200 pulses, to get
58.33 rev/sec, you would need 186656 pulses per secound to spin it at
3500 rpm. Working backwards if you can only supply 45,000 pps from
the parallel port, then your max rpm is about 14 rps or 843 RPM.
Divide that by your gear reduction (3:1) and you are down to 281 RPM
at the shaft. Divide that by the 2.54 turns per inch and you have
110 IPM.
YOu can work the math several ways. The numbers come out the same.
