Encoder Count Rate

I am considering the Mesa 5I25 for a setup and would like to control both stepper and servo motors. It looks like I can attached a 7I77 and 7I76 with the correct firmware and this should do the job. Can anyone confirm that this is the case and it should be pretty straight forward?

I was also wondering how fast can the Mesa cards count encoder pulses. Will the cards ever be the limiting factor or will it generally be the computer that limits my ability to count encoder pulses? Thanks for any help.

The cards will be the limiting factor, (but not very limiting). The 7i77 can count encoder pules to 2MHZ (or more if without filtering), and the 7i76 can step at up to 8 MHz. Both faster than is usually needed.

Thanks for the info. The encoder documentation says that, "The limit is in the range of 10KHz to 50KHz, depending on the computer speed and other factors." Wouldn't that make the computer the limiting factor?

squan09 wrote:

Thanks for the info. The encoder documentation says that, "The limit is in the range of 10KHz to 50KHz, depending on the computer speed and other factors." Wouldn't that make the computer the limiting factor?

This is for SOFTWARE encoder counters, not hardware. You must be looking at docs for the software encoder counter HAL component.

When you are using a hardware encoder counter, the computer's speed is irreverent. The hardware counts the encoder pulses, keeps record of the position and reports it every servo thread period.

That makes sense. I did not realize that the 7I77 is counting and reporting position. I need to set up an sample configuration and take a closer look, but I assume that means encoder.N.phase are not used and encoder.N.position or counts reads the position count from the card. Does that sound about right?

You don't use the hal encoder component at all. The hardware driver (hal component) will have a position feedback that is connected directly to the axis.N.position-fb.

Thanks for the hostmot link. This is the first time I am working with a Mesa board, but I think I am starting to get this. If the 5i25 is counting the encoder is it possible to set up a 5i25 and 7i76 with steppers and encoders. I saw that the 7i76 has encoder input for a spindle, but is it possible to close the loop with stepper and encoders using these boards?

Yes, you could by either adding another card that can read encoders (such as a 7i85), or maybe by connecting the encoders directly to the other 5i25 port, but that would be limited to a TTL connection (no differential input) and I'm not sure what firmware is available for what number encoders.

If you wan steppers with encoder feedback you might be better off skipping the 7i76 and using a 7i85S and a smart serial card for extra IO.