Newbie questions... be gentle...

I've already found the IC I'm going to use. its from TI and I have a free sample of it on the way. it costs $14 each just for the IC and these are good enough to run the biggest Nema 52's. just so I can upgrade later if I needed to...

I'm looking at using a 7a nema 34's ST8918D6708

de.nanotec.com/schrittmotor_st8918.html

also I heard that there was some problem with usb as far as the way Linuxcnc uses "realtime" but I could have misunderstood...

No misunderstanding, for Linuxcnc usb is not a current solution.

For more I/O's you could look at Mesa 5I20 / 5i25.

Rick G

Yea I was checking out what Mesa has to offer. I think the 5I25 would suit my needs perfectly. As far as the manual controls, sensors, e-stop, etc I should be able to run those through USB if I'm not mistaken.

Don't get me wrong I totally understand why USB won't work with the Stepper motors but it would be nice if we could just go through USB for everything. Plus now days we have USB 3.0 on the newer computers like my retina Macbook, I think with 3.0 the latency wouldn't be too bad.

What are your thoughts?

Thanks Rick

Hi

Plus now days we have USB 3.0 on the newer computers like my retina Macbook, I think with 3.0 the latency wouldn't be too bad.

If you search USB on the forum you will find chapter and verse on it and why it is not suitable for software step generation stepper control.
USB does not work with windoze and Mach either, it is just that they use external smooth-stepper boards to generate the pulses

You must not confuse port speed with latency, the throughput of a USB 3 port is miles faster than a parallel port but it still suffers from the same problems regards latency.

regards

As far as the manual controls, sensors, e-stop, etc I should be able to run those through USB if I'm not mistaken.

Yep.

Might look at Simple remote pendant
and Hidcomp
hidcomp.sourceforge.net/

Just to get an idea of what can be done.

Rick G

As to your desire to use USB - don't.

It is not a question of hoe LinuxCNC handles USB ports it is the way your PC handles them and it can be (quite literally) pretty dangerous or at the least expensive. In layman's terms USB ports are not as responsive as the parallel port which means that your mills or lathe cannot be controlled as fast as is necessary because there is significant lag in when an output can change state, so it is quite possible that a command to raise the spindle will be received too late, causing the tool to crash into the material, wrecking your workpiece or worse.