Flying Electron wrote: > [snip] > Does that mean for most servo based machines, EMC sampling the encoders > at 1khz is good? Yes. > I think I remember reading the parallel port can get > accessed at 10khz, At least, but it depends on what you mean by "access". (see below) > so does that imply the PCI 5i20 is overkill if I just > want to read 3 encoders for 3 axis and the parallel port based mesa card > is more then enough? > The parallel port mesa card can run 3 axes, and have 30 I/Os left over. You can't sample the parallel port mesa card at 10 kHz. There's too much data to move around. Also, at higher rates, like 2-5 kHz, you'll be using most of your CPU time waiting for parallel port data. If you think you might want to use a servo rate higher than 1 kHz, the PCI cards are a good idea - they just give a bit more margin on the timing. They also give you an additional 24 I/Os, which can come in handy for things like handwheels and whatever. > Just an off the cuff idea, but would it be possible with a proper hal > driver to have a microcontroller count encoder pulses and then have emc > query the microcontroller across a serial port in realtime using a > custom hal driver? with a baud rate of 115200 maybe it's possible to do > 1000 samples a second? > That's a long question :) The short answer is no, though it's somewhat feasible to do some of what you ask, it doesn't seem like it would be practical to me. Remember, 115200 baud is 1152 bytes. That gives you 1.152 (one point one five two) bytes per servo period at 1000 Hz, which is clearly not enough for even one axis. > So with a hypothetical setup of a mesa card, a brushless dc servo drive, > and a 1000 CPR encoder, the mesa card's only job would be to read the > encoder and report back to EMC and EMC would send the pwm signals out > parallel port pins to the servo drive? > The mesa card has encoder inputs, stepgen and PWM outputs, and possibly "whatever else" anyone comes up with.
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