[Video] Stepper Motor Dropout

[amishx64]

I am testing the electronics for my new machine and am having quite an issue with my stepper motor and/or driver and/or parallel port. I can't figure out what the issue is.

I have a large nema34 motor powered at 50V 7A by a Centent CN0142 Anti-Resonance Microstep Drive via 14awg wire hooked directly to a parallel port via shielded wire.

Mach 3 is set at 100kHz and axis x is at 20mm/s^2 accel and ~2500mm/s velocity. See attached picture.

The motor runs great up to about 1500mm/s but starts having issues at 1600. The motor is fine after a brief time in that range when it tops out at 3000mm/s. Please see the video:

http://www.youtube.com/watch?v=iuAtGrrvM9I]Strange Stepper Motor Mid-range Dropout - YouTube

[Eurisko]

I think that your 'steps per' in the X axis movement profile is set incorrectly.
Note that the 'steps per' is not steps per revolution of the motor, but the number of steps needed to move the X axis 1 mm.

'steps per' = (#steps per revolution of screw) / (screw pitch in mm)

For example, if you have a 5mm pitch screw, the 'steps per' would be 400.

[amishx64]

I think that your 'steps per' in the X axis movement profile is set incorrectly.
Note that the 'steps per' is not steps per revolution of the motor, but the number of steps needed to move the X axis 1 mm.

'steps per' = (#steps per revolution of screw) / (screw pitch in mm)

For example, if you have a 5mm pitch screw, the 'steps per' would be 400.

It is not connected to any screw drive or linear system as of yet. The 'steps per' does not make a difference in this case. Thanks though.

[WoodSpinner]

It is not connected to any screw drive or linear system as of yet. The 'steps per' does not make a difference in this case. Thanks though.

absolutely steps per matters, you have it set at 2000 steps per/with a max velocity of 2500, so thats 5000000 steps per minute going out, you didnt mention what your micro stepping rate was, but you need to consider how fast you trying to spin that stepper, you most likely over reving it given your current settings.without microstepping thats 200 steps per rotation on most steppers, so divide 5000000, by 200 your trying to get 25000 rpm, get real.

I'll shut up now

John

[amishx64]

absolutely steps per matters, you have it set at 2000 steps per/with a max velocity of 2500, so thats 5000000 steps per minute going out, you didnt mention what your micro stepping rate was, but you need to consider how fast you trying to spin that stepper, you most likely over reving it given your current settings.without microstepping thats 200 steps per rotation on most steppers, so divide 5000000, by 200 your trying to get 25000 rpm, get real.
John

John, I understand your concerns about me trying to run the motor too fast. I don't necessarily think this is the problem. My motor is indeed 200 steps/rev and the controller is doing 10 microsteps.

Remember from the first post that the motor starts failing at 1600. It runs fine at 2500.

The fact that the motor runs fine at speeds 0 - 1600 and 2000 - 3000 but not that 1600 - 2000 middle band. This is what I am concerned with. It makes no sense that the motor can run fine at higher speeds and stall at lower speeds.

I'll shut up now

John

Please don't. If you have corrections, I wish to learn. Thanks

[WoodSpinner]

John, I understand your concerns about me trying to run the motor too fast. I don't necessarily think this is the problem. My motor is indeed 200 steps/rev and the controller is doing 10 microsteps.

Remember from the first post that the motor starts failing at 1600. It runs fine at 2500.

The fact that the motor runs fine at speeds 0 - 1600 and 2000 - 3000 but not that 1600 - 2000 middle band. This is what I am concerned with. It makes no sense that the motor can run fine at higher speeds and stall at lower speeds.



Please don't. If you have corrections, I wish to learn. Thanks

Sounds like what I've heard refered to as mid band resonance, usually the comments suggest using a damper to smooth it out, I've never had that particular problem, hopefully someone else will speak out, there are threads dedicated to this problem here, maybe with a little searching..
John

[amishx64]

Sounds like what I've heard refered to as mid band resonance, usually the comments suggest using a damper to smooth it out, I've never had that particular problem, hopefully someone else will speak out, there are threads dedicated to this problem here, maybe with a little searching..
John

This seems to be exactly the problem I am having. Thank you!

Now to solve it...

[Eurisko]

amishx64,

I'm curious how you are calculating linear speed from rotational speed with no linear reference. Also, unless you're using a tachometer to measure the rpms, you can't be sure that it isn't losing steps at the higher rpms.

With the settings that you're using, you're assuming a linear movement of 1 mm per revolution of the motor. So, linear speed=rotational speed.

2500 rpms won't produce much torque, and the numbers you have are meaningless if there is no load on the motor.

[WoodSpinner]

John,

I'm curious how you are calculating linear speed from rotational speed with no linear reference. Also, unless you're using a tachometer to measure the rpms, you can't be sure that it isn't losing steps at the higher rpms.

With the settings that you're using, you're assuming a linear movement of 1 mm per revolution of the motor. So, linear speed=rotational speed.

2500 rpms won't produce much torque, and the numbers you have are meaningless if there is no load on the motor.

actually, I took his settings which refer to linear motion, and converted it to rotational speed
John

[Eurisko]

actually, I took his settings which refer to linear motion, and converted it to rotational speed
John

Sorry, John.

My question was directed to amishx64, I don't know why I used your name...

[amishx64]

Eurisko,

The numbers are really completely arbitrary. I don't have a system currently using these units. I was simply using the Mach defaults and using them to provide a (fake) velocity range of where the motor would and would not work.

I don't know what rotational speed the motor was moving at. I simply wanted to know why there was a stall / droupout at a certain speed and not speeds above or below the problematic speed range.

I am sorry for any confusion this has caused all of you.

[Mariss Freimanis]

I listened to your video. The drive is having problems reading step pulses at high rates of acceleration. The drive also has problems with step pulses that have a lot of phase jitter such as what Mach3 puts out. Finally, the CN0142 is a 3.5A drive and not a 7A drive.

I know because I'm the guy who designed it in the early '80s.

Mariss