Randy, assuming that you're using the steppers and board from Easy-Cnc then they have advised a few people not to set the vref above 1.6V . You are correct that the manual for the board says to set the vref to 2x the required current, but I don't think this is safe with the supplied steppers.

FYI I have all my vref's set to 1.6V, and all axes tuned to Accel=20 and Velocity=40.
The only mod I have made to the PP is to upgrade the y-axis stepper, all other components are the ones I received with my PhlatPremium kit.

Hope this helps.
Si.

 

Randy, my steppers get warm but never hot. I'm not sure of the exact temperature, but they don't get warm until they've been on for around 15mins. My heatsinks on my driver board are always cooler than the motors. I'll try and get some temp readings for you tomorrow when i've been cutting for a while.

Regarding the vref settings for the supplied motors, have a look at this post on RCG which contains the response that tvcasualty got from Easy-CNC when he asked a similar question : http://www.rcgroups.com/forums/showpost ... count=1684

Si.

 

I've posted this before on RC Groups, but it should be mentioned again here....

These motors should not run hot! If they do, you are risking shorting the windings as I did. I burned up 3 stepper motors following the instructions to set the pots to mid position (2.4V).

The 90oz inch steppers from easy-cnc do not have enough power to run the Y axis at much more than 14 inches per minute. I replaced my steppers with higher current NEMA 23 steppers which can handle the 2.4 to 5 volt range without getting hot and they will give you the higher rates you are seeking.

Faster rates is not always a good thing. It puts more stress on the gantry and to get good clean cuts in higher density foam or multiple sheets, it is often necessary to drop the feed rate anyway.

Rule of thumb... If the stepper is running hot, the windings are very likely going to short out!

The windings should read about 11 ohms with an ohmeter. If the windings short, you will find one or more reading anywhere from 1 to 8 ohms in which case, you will need to replace the stepper.

The 1.2 volts that easy-cnc recommends works very well for those steppers and they run cool as intended, but forget about driving the Y axis fast. After the threads are well broken in, you might be able to tune the steppers for better performance.

 

rjarois,

If you haven't figure it out yet, you are using the equation wrong. The motor label says set Vref to 1.2V. That what you set on the driver board. What you are tring to do is double Vref and then say that's really Vref.

The equation for Vref is Vref=2xCurrent. Bascially setting the Vref on the board to a value of 1.2V, is really setting the current to 0.6A.

So that's what you want to set, 1.2V not 2.4V.

-Kwok

 

I would really double check to make sure the IC is not bad before I grabbed a new stepper motor.

This is exactly what happens when IC's go bad.

Hook another (good) known stepper motor to the terminals and jog see what you get.

Incase you havent done this.

Eric

 

rj, think of it like velocity (speed) of a race car. The faster you go, the more likely you loose control due to aerodynamics or road slip. Accelerate to fast and you have the same issues. They are completely seperate but work together.
As to your question, your max velocity will never be obtained if your acceleration is too high (Top fuel drag racer on ice). Set your acceleration low and then increase your max velocity until you get missed steps. You need to test the entire axis travel at this velocity settings to make sure you don't have any 'bumps' in your leadscrew/linearways. Once you have your max velocity set, increase your acceleration until it looses steps. (reduce max settings +/-80% to obtain consistant results)

 

So its the motor. good deal.

Eric

 

Use the black as the '+' for A and the green as the '-' for A. Use the red as the '+' for B and the blue as the '-' for B. If the motor runs the wrong way you can change it in Mach3.

Yoram

 

rjarois, I didn't know, either about how to wire the stepper. So google and found some extra info, quoted below. Seems it doesn't matter what is - or +. And it's kind of like our brushless motors; just reverse any coil if it turns the wrong way:
http://reviews.ebay.com/Stepper-Motor-T ... 0001227707

"To reverse the direction of a stepper motor just reverse the two main phase wires of one phase pair. Reversing both pairs has no effect."

-Kwok