Hello Guest it is November 29, 2021, 07:04:24 PM

Author Topic: Really need help  (Read 29947 times)

0 Members and 1 Guest are viewing this topic.

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Really need help
« Reply #10 on: August 12, 2009, 05:50:20 PM »
Dont know too much about them but looks like it will do the job.
Hood

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Really need help
« Reply #11 on: August 12, 2009, 06:39:25 PM »
What voltage are you running for the steppers?
Re: Really need help
« Reply #12 on: August 12, 2009, 08:16:55 PM »
The motors are 3.5 volt so I assume the drive is outputting something close to 3.5VDC?  I didn't build that part of the lathe.  I do have a scope coming... so I can measure the voltage then.

I can say, the motors have PLENTY of torque... I don't think I can stall them by holding the hand-wheels on hte lead screws.

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Really need help
« Reply #13 on: August 13, 2009, 02:32:43 AM »
Stepper motors should run on 3 to 25 times their rated voltage. I have had trouble with lost steps below about 10x voltages.  Stepper problems do not manifest at a steady state. That is when they are the most powerful. It is at speed where the power drops off sharply that the problems occur.

You mentioned a parallel port monitor. That sounds like a bad idea. If the program is, or if it uses a TSR type of utility, it may be polling the port occasionally. That would be enough to disrupt the pulse stream. Also, remove any printer drivers, and run the port without interrupts.

If you look back a couple of months in the postings, or do a search, I posted info on an add-on parallel port that works with Mach. I have found it to be faster and a little more robust that the built in port on older machines. It is dirt cheap and would answer the question as to whether your existing port is the problem.

You will see a lot of posts showing calculations for max stepper speed based on the pulse rate Mach is running at. Remember to consider that the pule rate is the total and must service all of the drives. While it is unlikely all of the motors would run at full speed simultaneously, it is unwise to set a speed based on all pulse frequency being available for each motor. This is probably why your motors work fine individually and loose steps when both are running.

Make sure any wire shields are grounded on one end only, preferably at the control box.

Lastly, use the driver test program to see how fast your computer can generate the pulse stream, but do not assume you can run Mach that fast. Back off at least one speed setting slower than what the driver test determines.



« Last Edit: August 13, 2009, 02:39:19 AM by simpson36 »

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Really need help
« Reply #14 on: August 13, 2009, 04:03:31 AM »
You will see a lot of posts showing calculations for max stepper speed based on the pulse rate Mach is running at. Remember to consider that the pule rate is the total and must service all of the drives. While it is unlikely all of the motors would run at full speed simultaneously, it is unwise to set a speed based on all pulse frequency being available for each motor. This is probably why your motors work fine individually and loose steps when both are running.

Mach can output the kernel pulserate on all axis simultaneously.
Hood

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Really need help
« Reply #15 on: August 13, 2009, 04:17:07 AM »
Hood,

That may be true in theory, but in practice, I can reproduce an error every time if I max out the stepper speed on more than one motor.

With the exact same motor settings, increasing the pulse rate makes the problem go away. This is true for XY with two steppers or also with one stepper and one servo (I am in the process of changing over).

My conclusion is that Mach is unable to provide the full pulse rate to all axis simultaneously and needs some headroom for whatever else it is doing at the same time.

Your results may be different.  

I don't know what the breakpoint is, but if someone wanted to do a bunch of testing, maybe some guideline could be formulated, for example not to exceed 90% of maximum theoretical speed, or something like that.

Another area where theory and practice collide is in the driver test vs actual program execution. My observation is that there is a correlation between CPU load and kernel speed when Mach is running. I can state with confidence that a successful driver test at a given speed is no guarantee that Mach can actually perform reliably at that speed, as theory may suggest.

« Last Edit: August 13, 2009, 04:33:58 AM by simpson36 »
Re: Really need help
« Reply #16 on: August 13, 2009, 04:36:50 AM »
Simpson 36...

Thanks for your information. This is all sort of new to me. I will look more closely at the applied voltage to the motors.
The Parallel port monitor is not TSR. It is not running when Mack3 is. I used it to set/clear data bits to see what effect they had.
I will find your post. and look into all matters you have outlined above.

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Really need help
« Reply #17 on: August 13, 2009, 04:52:30 AM »
Something I forgot to mention is to leave the task manager running on top of Mach to observe the CPU load. If the CPU pegs, you loose steps.

I just chased down a new problem where my X axis stepper (640 oz-in) was loosing .020 after every flat out run (135 in/min 10 accel). If I drop it back to 90 and 8.5 (where it is normally set), it stops loosing steps. I am switching to servos and decided to have a foot race between the stepper and servo while I had one one each axis. Needless to say, the servo won. I don't know where in that range the stepper started loosing steps and since the stepper is out of there in about a week, there is no incentive to dig into it. I have to measure each time to find if the stepper has been a bad boy as there is only an audible clue if it skips quite a few steps at a time. Onesy - twosy misses are acoustically invisible.

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Really need help
« Reply #18 on: August 13, 2009, 06:01:06 AM »
Hood,

That may be true in theory, but in practice, I can reproduce an error every time if I max out the stepper speed on more than one motor.

With the exact same motor settings, increasing the pulse rate makes the problem go away. This is true for XY with two steppers or also with one stepper and one servo (I am in the process of changing over).

My conclusion is that Mach is unable to provide the full pulse rate to all axis simultaneously and needs some headroom for whatever else it is doing at the same time.

Your results may be different. 

 Certainly had no issues on the lathe when I was maxing it out on the PP at 45KHz, because it was a new build I was monitoring the following error in the drives software and no problems there. Possibly this would point to computer rather than Mach but no intentions of starting arguments so suffice to say mine conformed to the theory.


Another area where theory and practice collide is in the driver test vs actual program execution. My observation is that there is a correlation between CPU load and kernel speed when Mach is running. I can state with confidence that a successful driver test at a given speed is no guarantee that Mach can actually perform reliably at that speed, as theory may suggest.



To my mind the driver test is there to weed out the really bad computers that have no chance of running Mach in their present state rather than saying it will definitely run Mach.

Hood

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Really need help
« Reply #19 on: August 13, 2009, 10:05:48 AM »
Hood,

Arguments are emotional and useless. Debates are factual and beneficial. Methinks we are both fact guys. You are far more experienced than I on these topics and I certainly would not question your observations. What it means to me is that both behaviors occur, and that becomes the fact that begs explanation.

You mention following error on a lathe at 45k. Three significant differences in my scenario (and I perhaps that of the OP) steppers, three axis moving simultaneously, high speed. Which actually brings up an interesting point; In the past, I had all steppers and therefor had no point of reference outside that realm. However, with my current odd combination of steppers and a servo on the same machine, only the stepper, which was maxed out speed wise in the motor tuning, lost position. The servo was spot on, although it was nowhere near maxed.

I make the assumption that Mach sends only pulses and no positional information, therefor it must have sent all of the pulses to the servo in order for it to maintain its positioning. One interpretation of this would be that these curious errors are confined to steppers. I have observed the lost steps with three different models of stepper motors on two different computers. All were being driven by Gecko203V, so perhaps that might be a suspect.

An interesting twist on this topic is that the Smooth Stepper in invariably described as having a 'high quality' pulse train. The logical implication being that Mach and the PP do not produce same. Although I do not recall ever reading any hard evidence to that effect, experienced an knowledgeable people use the SS, so I have to assign credibility to the concept. Taken together, all of the above evidence might seem to siggest that the Gecko 203V is particularly sensitive to a 'dirty' pulse stream, yet the OP is using differnet hardware, which defeats that theory. It takes time to learn which sources are reliable and which are not. The lesson in all of this is that in a situation where an unresolved problem is manefest, all possible known causes deserve mention.