Help please !!! Servo configuration with stepconf.

I checked 7i77 and they offer 48 isolated i/o which is more then sufficient for me.

But their 7i76 board again confused me that it can support step/dir for servo motors and stepper motor as well. While my drive supplier says that it can be run by step/dir cards by connecting pulseinv +- to pulses and signinv +- to Directions. which I tried but motor seems to crackle and stalls during trial jog. it surely spins but at very slow speed no matter which setting I tried.

If you have step and direction inputs you could use that but it is better to have a closed loop for servos. Did you tune your drive? Many modern drives have a self tune function once your connected up and centered on your travel you should run the drive self tune if it has one.

John

unfortunately it doesn't have self tuning.

ok ! I should go to order mesa cards now. It's really professional to have closed loop system.

Is there any major difference between 5i20 and 5i25 ? any advantage and disadvantage between both ?

Does it have a setup procedure in the manual? You will have to tune the drives to use them.

I have 2 5i25 setups one stepper and one servo. The installation is quite neat with one round cable between the PC and the daughter card. I also have one 5i20 servo setup. For me unless I needed some feature on the 5i20 any new conversions would use the 5i25. You need to study each then make up your mind.

John

ishman wrote:

My drive model is SA3L04C
www.bonmet.com/productshow_eng.asp?id=1506

Actually, contrary to what other have said, it seems that that drive _will_ work with step/dir signals.

As an aside, that looks like a really good driver for LinuxCNC use, and the mains-voltage input is a huge advantage compared to many. The price (£245) is competitive too.

I would guess that to calculate the steps/rev you need to choose the encoder resolution of your motor, though the "electronic gearing" of the drive might change that.

If the motor encoders are high resolution then you will probably need to use the "elecronic gearing" as a standard parport will struggle to output pulses fast enough to give you adequate motor speed.

So, in Stepconf you can probably pretend that it is a 1000 steps-per-rev stepper motor, then see how far off your physical scaling is, and adjust it. (by which I mean program a 1" of 25mm move, measure how big it really is, and then adjust the steps-per-rev to suit.

Having said that, step-dir mode with the position control inside the drive is not the preferred way to control machines under linuxCNC. We prefer to use analogue voltage control and move the PID loop inside the control PC where it is easy to watch what is happening and tune the PID.

If you are using that style of drive and the sorts of motors that suit it, I suspect that you have quite a large and serious machine, and in that case you will probably find yourself running out of IO lines on just a parport, and the 7i77 mentioned earlier will be a good upgrade.