Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: biggermens on July 16, 2018, 01:02:41 AM

Title: Knocking X axes, whats going on ??
Post by: biggermens on July 16, 2018, 01:02:41 AM
Hello again everyone

I would like to Thank everyone for helping me out with this headache i mead project

machine was working fine, now all of a sudden the X axis knocks

you are moving the X axis and y axis at the same time, no problem until you change Y direction and knock
you can start, stop Y in the same direction and no problem, the second you change it direction X axis knocks
you can play with Z axis and every thing is fine, only with Y axis

What can be wrong ?? I am using 2 parallel ports one has the 4 motor and the other has everything else,
and them Stepper drives with the elephant on it

Thanks again   
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 16, 2018, 01:21:42 AM
Also I just notice my elephant drives are set for 1000 pulses per revolution, should that be around 2000 ??
I am also running at 33,000 HZ
Title: Re: Knocking X axes, whats going on ??
Post by: joeaverage on July 16, 2018, 07:54:57 AM
Hi,

Quote
Also I just notice my elephant drives are set for 1000 pulses per revolution, should that be around 2000 ??
This refers to micro stepping. A two phase (normal) stepper motor requires 200 full steps to turn one revolution, that's 1.8 degress
per step.

Stepping a motor backwards and forward with full steps is pretty harsh and you end up getting resonances at moderate speeds, all
in all not too good. Just about all stepper drivers offer microstepping to overcome this. It will break each full step into a number of smaller
steps and its a lot smoother.

Sounds like your Elephant drives have 5 micro steps, so each full step is broken into five smaller ones so it will take 5 X 200= 1000 pulses to get your stepper
to rotate once.

The most common microstepp regimes are 2,4,8,16,32...... and less commonly 5 or 10. These ratios result in pulses per rev of:
400, 800, 1600, 3200...... and 1000, 2000.

Its nice to think that your stepper has a lot more resolution. Say you have set it up for 3200 pulses/rev or 0.115 degrees per step. Unfortunately it doesn't
work like that although there are plenty of people who believe it does. There is a very good reason that this is the case...but I can't be bothered trotting it out
unless you really want to know. Its reasonable to expect 1/2 (400 steps) and maybe 1/4 (800 steps)and maybe even 1/5 (1000 steps)microstepping to genuinely
increase resolution but not more.

For this reason most CNCers opt for a microstepping regime of 1/5 or 1/10 or 1/8 or 1/16. With these ratios you get useful and genuine increase in resolution
with much improved smoothness. You can make it even smoother by having 1/32 or 1/64 microstepping but you don't get any better resolution and you run into
pulse speed limitations for little gain.

Quote
I am also running at 33,000 HZ
This is the kernel speed of Machs parallel port. It means the fastest pulse stream your parallel port can produce is 33kHz.

Lets say your Elephant drives are set up for 1000 pulse/rev. Mach could possibly drive them at 33,000 pulse a second or 33 revs per second
or 1980 rpm. Plenty quick for a stepper, in fact most steppers lose a lot of torque by 500 rpm and very few will run reliably above 1000 rpm.

If you set up your drives for 1/32 microstepping or 6400 pules/rev then Mach could drive  your stepper to 33000 /6400 = 5.15 revs/sec or
309 rpm. You can see that by increasing the microstepping you run the risk of not being able to drive your steppers fast enough.

Just as a matter of interest an ESS, which of course doesn't have to rely on the PC's CPU to generate pulse streams can pulse up to 4Mhz,
that's 121 times faster than your parallel port. The ESS is quick, in fact, one of the quickest modestly priced motion controllers. Galill is even
quicker at 22MHz!!!! of course it is several thousand dollars too.

Craig
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 16, 2018, 10:11:58 AM
That is awesome Craig Thanks
but what do you think that kock is when i change direction ??
I even unplugged the Y motor and it still knock when you change y direction
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 16, 2018, 12:25:08 PM
I changed the drives to 3200 @ 10000 pulses for fun ( i know its wrong ) and when switching Y directions the knock got much much worse 
Title: Re: Knocking X axes, whats going on ??
Post by: joeaverage on July 16, 2018, 12:49:15 PM
Hi,
I suspect that there is a momentary hesitation in Machs pulse stream,

Try slowing Mach from 33kHz to 25kHz and try again. Note that you'll have to restart Mach for the change to take effect..

Craig
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 16, 2018, 05:00:44 PM
I have tried everything from 25000Hz to 65000Hz I do restart Mach every time and i also do a driver test ever time too and no changes
But Mach 4 works fine
Title: Re: Knocking X axes, whats going on ??
Post by: garyhlucas on July 16, 2018, 06:12:10 PM
Bad motor coupling?
Title: Re: Knocking X axes, whats going on ??
Post by: joeaverage on July 16, 2018, 07:07:03 PM
Hi,

Quote
But Mach 4 works fine
??? Are we talking Mach4 and the Darwin parallel port or Mach3 an the parallel
port?

Craig
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 16, 2018, 10:44:29 PM
Quote
But Mach 4 works fine
??? Are we talking Mach4 and the Darwin parallel port or Mach3 an the parallel
port?

Both I been playing around with Mach 4 all evening and kind of got it working pretty good, that knock i get in mach 3 is not there, I am not sure whats up with mach 3
I am using the darwin parallel port plug in, i think i will order a ESS tonight
Title: Re: Knocking X axes, whats going on ??
Post by: RICH on July 17, 2018, 07:24:38 AM
I would suggest you have a look at the pulse stream with an o'scope. You may find that there is ringing on the generated pulse stream. Usually it would be constant but it can be random. You need to get rid of it at the source and can be difficult to remove.
 The ringing will just carry through to other electronic devices if you don't eliminate it.

RICH
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 17, 2018, 08:22:44 AM
Hey Rich

I know there is the possibility of noise being produced unfortunately i don't have a scope to test it with
but why would it do it with Mach 3 and not with Mach 4 ???

Thanks
Title: Re: Knocking X axes, whats going on ??
Post by: RICH on July 17, 2018, 06:11:16 PM
Quote
why would it do it with Mach 3 and not with Mach 4

Have no answer to that question. It would be interesting to see the signal output from both since it's the same computer and
and physical pp port.

RICH
Title: Re: Knocking X axes, whats going on ??
Post by: biggermens on July 18, 2018, 06:08:13 AM
Quote
Have no answer to that question. It would be interesting to see the signal output from both since it's the same computer and
and physical pp port.

Yes you are right it would be interesting to see
I just orders a ESS board and going through a pile of extra parts i found a American made 48V power supply, and 4 gecko drives.
That should solve lots of my problems if not all of them :)

Thanks