Wiring 2xPK296A2A-SG18 + 2xPK299-F4.5A
 

Hey All, hope to grab some minutes from more experienced people.

I happened to have this mix: 2x PK296A2A-SG18 + 2x PK299-F4.5A. 299s are going to X. 296s with 1:18 going to the Y and Z. I plan to connect 299s unipolar 50V and not sure about 296s. Unipolar?
I have 400W transformer with 36 and 22 AC outputs. so having 30V and 50V DC possible.
My old but rather nice Pacific Scientific 5410 drivers are able to give 18-75V and 5A or 3.5A (DIP switch). And (DIP switched too) choice of 1/5, 1/25 or 1/125 step sizes.
Also 5A or 3.5A better to set for my F4.5A?

If possible, I would suggest that you use the same motors and the X and the Y axes so ramping values could be the same or very similar. Ted Hall, from Shopbot advised to use the same gear ratios and pinion sizes on the X and Y axis. Shopbot software is not the same as Mach 3, but even the "heavy iron" machines usually use the same gear ratios on their X and Y axes.

You'll need to contact Pacific Scientific for recomendations about the voltages that they would suggest for your application. I've never used their drivers, but I have used their motors. The motors worked fine for their intended application.

Ooops.. Thank you Mike, I will sleep worse tonight :).
Anyway - how about to have driver current 0.5A more than motor rating? is it still Ok?

better more than less. If your really worried, see if you have a current limit setting on the driver to reduce the available output.

Oriental Motor rates the PK299-F4.5A motor at 620 oz*in when wired unipolar and drawing 4.5A. (Of course, that rating largely depends on the stepper driver that you use. How the driver supplies electricity is just as important as how much electricity it provides. Different stepper drivers produce current (Amps) differently. The Geckodrive stepper drivers that are used by many on this forum have an excellent reputation.

The more current the driver produces, the hotter the motor and the driver will run when the motor is heavily loaded. The current limit switches or current limit resistors allow you to select the maximum amount of current that the motor is allowed to draw from the stepper driver. Just because the resistor or dip switches are set to allow 4.5A to flow does not mean that the motor will draw 4.5A. The motor will only draw as much current as it needs to handle the load. If the load requires more current than the resistor or dip switch settings allow, the drive will limit the amount of available current. By limiting the amount of current, the possibility of overheating either the drive or the motor is reduced.

Remember that most motors have a duty rating and a heat sink requirement when they are run under heavy load. Except when I ran 3-D work, my motors were most often on standby, waiting for me to load material. 3-D was different. The motors ran non-stop for long periods of time which allowed them to heat up. Many motors can be run up to 80-degrees C before exceeding the manufacturer's rating. Depending on which method your stepper drivers use, your motors may run hotter or cooler than identical motors driven by other stepper drivers.

If possible, ask Pacific Scientific for their recommendation for voltage and current for your Oriental Motor stepper motors. Even with their recommendation, if I were you, I would still use an infared thermometer to verify that the motors are running at a safe temperature.

Part of the "fun" of building your own machine is getting totally familiar with its characteristics. Stepper motors and stepper drivers often require some "acquaintance time" before they do what they are expected to do.

Remember that you can use a belt-drive with the PK299 motors to increase their torque. You could also use a belt-drive with the PK296A2A-SG18 motors to increase their torque, but the 18:1 gear ratio already greatly limits the top speed. Increasing the gear ratio would limit the speed even more.

Mike (Metalhead) sells an excellent belt-drive assembly.

Sorry for long silence. Now back home, did not have proper internet for a while.
It was in my mind - to pull away gearboxes and make my own for all motors. But when I unmounted SG18 I decided to try with them first - motor's shaft diameter looks too small. 10mm OD and 8mm if measure at teeth roots.
I think I better watch temperature as you suggest, Mike. drivers some 20 y.o. and probably nobody from manufacturer remember them.