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Author Topic: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots  (Read 8548 times)

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Hi Everyone.

I'm new to this forum, but pleased to annouce that I now have stepper motor movement, at least on the bench. Mach3 seems to be working exactly as hoped. I had a devil of a time getting the old Camtronics driver boards to communicate with my new C10 Breakout board. But all is working now, and I have a question about tuning and stepper "jitters."

When I installed the evaluation version of Mach3, and studied the tutorial videos, I then went to load some Gcode samples that come with the Mach3 files. These seem like a good starting point. One code is called something like "Ball" and it causes the x axis motor to run at full speed, then very slowly deccelerate until stopped, then very slowly accelerate until full speed.

When the motor hits a certain low speed, both deccelerating and accelerating, it "jitters" like it can't handle this speed. No matter what I do in the Motor Tuning window, it always does this jittery movement.

So, is this the whole point of this sample of Gcode? To help us locate the problematic area of the system? Is there a way to correct this? My drivers do not do X 10 microstepping, like the Gecko's can. And there's no mid-band resonance circuitry to compensate for this rough motion.

The good news is, that I've set my acceleration and velocity to values that seem to operate smoothly in jogging and fast-jogging. I can't be sure if my motors will ever encounter a speed that will cause them to jitter while machining something. It seems logical that they will encounter this speed, since it's greater than zero, and less than full rpm.

Any thoughts on how to deal with this using the tuning in Mach3, or other methods?

Thanks, Tom.
« Last Edit: October 16, 2012, 10:53:03 AM by rrmerlin60 »

Offline mr.c

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Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #1 on: October 16, 2012, 09:08:54 PM »
If you are running the motors just sitting on the bench top, this is normal behaviour for a stepper motor. The jitters will most likely go away when the motors are mounted solidly.
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #2 on: October 17, 2012, 09:33:24 AM »
Mr C;

Thanks. I'm not sure if this is a solid mounting issue, or pushing-against-a-mass issue, but this is something that sort of makes sense.

It'll be a while before these motors are mounted and ready for real action, but I appreciate the feedback. I'm trying to run through as much of the learning curve as I can now, while I wait for the vertical mill to show up.

Tom.
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #3 on: November 29, 2012, 11:33:43 AM »
I am curious how you made out on this.  I am currently converting a Bridgeport to CNC.  This is my first time doing a project like this.  I am bench testing my steppers and it seams I am having similar problems.  I have consulted with someone I know that has converted a Bridgeport, and he said he had issues when he did not have the motors mounted, but didn’t after he had the motors mounted to his machine.  This didn’t make any sense to me.  Logic would dictate that if there were problems when bench testing, you would have the same problem when mounted on the machine. However, Mr. C seems to be concurring what my friend told me.  Possibly this is a time when logic doesn’t apply.  (Don’t tell my wife I said that.) 

Have you got your motors mounted to your machine, if so how are things working for you now?
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #4 on: November 29, 2012, 11:41:06 AM »
Hi jvereecken;

Thanks for asking. I'm afraid that it will be a long time (months or years) before I have a mill to mount the motors on. It's just not in the cards for right now, although I did really want to iron out the motor/driver hardware for now, and learn the Mach3 software. That part seems to be going well.

Once I finally got the C10 breakout board to communicate with the bipolar drivers, things improved tremendously, although the "jitters" at low speed still exist, no matter how I tune the accel/velocity in Mach3. So I'm just going accept that for now until I buy some heavy iron.

Sorry I couldn't update this further. Perhaps you could keep us informed of your efforts and success. It does seem odd that the steppers would jitter on the bench, but run smoothly when strapped to a machine, but if it works I won't question it too much. We'll see......

Cheers, Tom.
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #5 on: November 29, 2012, 11:52:56 AM »
I will try to remember to update you after I get the motors mounted.  I should be doing this in the next week or so for the x and y axi.  I have all the mounts and hardware for the x and Y axis complete.  I still need to fabricate my quil drive.   Feel free to contact me if I forget.
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #6 on: November 29, 2012, 12:26:19 PM »
Stepper motors will behave very differently when there is zero rotational mass on their shafts, the mass of the hubs and belts will likely smooth out the jitters you are seeing "on the bench".
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #7 on: March 08, 2013, 11:50:41 AM »
I am currently trying to tune the step motors on my machine.  The problem I'm having is the motors on all 3 axis have negative rotation, however, positive rotation is intermittent on all 3 axis.  A pulse is going to each of the motors during the positive rotation movement, but does not continue to run the motor.  If this only happened on a single motor, I would think the problem was mechanical.

Your help would be most appreciated.
Re: Question about Mach3 Stepper Motor Tuning. Still a few Rough Spots
« Reply #8 on: March 08, 2013, 01:26:51 PM »
McFlyman;

Hmmm, tough one, but then again, I'm no stepper guru.

Are you using a passive or active breakout board? I had a problem with a passive board because the pulses put out by the parallel port were whimpy 3 volt pulses, so I bought an amplified board which completely solved the problem. My symptoms were sort of like yours, but maybe not exactly.

I'll keep thinking, but that's about it for the moment. The only other (im)probable error is all 3 motors hooked up improperly. The phases fighter each other, or something.

Let us know if you solve it and what it took to fix it.

Tom.
« Last Edit: March 08, 2013, 01:33:07 PM by rrmerlin60 »