Hi,
Also I just notice my elephant drives are set for 1000 pulses per revolution, should that be around 2000 ??
This refers to micro stepping. A two phase (normal) stepper motor requires 200 full steps to turn one revolution, that's 1.8 degress
per step.
Stepping a motor backwards and forward with full steps is pretty harsh and you end up getting resonances at moderate speeds, all
in all not too good. Just about all stepper drivers offer microstepping to overcome this. It will break each full step into a number of smaller
steps and its a lot smoother.
Sounds like your Elephant drives have 5 micro steps, so each full step is broken into five smaller ones so it will take 5 X 200= 1000 pulses to get your stepper
to rotate once.
The most common microstepp regimes are 2,4,8,16,32...... and less commonly 5 or 10. These ratios result in pulses per rev of:
400, 800, 1600, 3200...... and 1000, 2000.
Its nice to think that your stepper has a lot more resolution. Say you have set it up for 3200 pulses/rev or 0.115 degrees per step. Unfortunately it doesn't
work like that although there are plenty of people who believe it does. There is a very good reason that this is the case...but I can't be bothered trotting it out
unless you really want to know. Its reasonable to expect 1/2 (400 steps) and maybe 1/4 (800 steps)and maybe even 1/5 (1000 steps)microstepping to genuinely
increase resolution but not more.
For this reason most CNCers opt for a microstepping regime of 1/5 or 1/10 or 1/8 or 1/16. With these ratios you get useful and genuine increase in resolution
with much improved smoothness. You can make it even smoother by having 1/32 or 1/64 microstepping but you don't get any better resolution and you run into
pulse speed limitations for little gain.
I am also running at 33,000 HZ
This is the kernel speed of Machs parallel port. It means the fastest pulse stream your parallel port can produce is 33kHz.
Lets say your Elephant drives are set up for 1000 pulse/rev. Mach could possibly drive them at 33,000 pulse a second or 33 revs per second
or 1980 rpm. Plenty quick for a stepper, in fact most steppers lose a lot of torque by 500 rpm and very few will run reliably above 1000 rpm.
If you set up your drives for 1/32 microstepping or 6400 pules/rev then Mach could drive your stepper to 33000 /6400 = 5.15 revs/sec or
309 rpm. You can see that by increasing the microstepping you run the risk of not being able to drive your steppers fast enough.
Just as a matter of interest an ESS, which of course doesn't have to rely on the PC's CPU to generate pulse streams can pulse up to 4Mhz,
that's 121 times faster than your parallel port. The ESS is quick, in fact, one of the quickest modestly priced motion controllers. Galill is even
quicker at 22MHz!!!! of course it is several thousand dollars too.
Craig
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