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Offline Zaae

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Stepper motor setup questions
« on: April 24, 2008, 03:42:00 PM »
Hello again :)

I'm working with a set of KL23H276-30-8B steppers from Keling technology.

The machine moves pretty quickly on rapids and on geometry codes, but when it's run on small, detailed work, it slows to a crawl. I've never operated any other machines, but from what I've read, the last project I ran should take around 15 mins on this machine, but it took over 30. I'm cutting very shallow, so faster isn't a problem.

Presuming I already have the steps/mm set correctly, aside from velocity and acceleration, what other settings should I tweak? I am using CV mode @ 180units. 45* override and CV feedrate @ +1.0000.

I realize there are physical limitations on the motors and such, but if I have simple geometry, say a circle, the machine flies. If I'm working a cut where the toolpath is made up of a bunch of connected points, it's slow city again.

One last example: If I cut a true circle that mach 3 runs a geometry command, that goes fast. If I draw an oval the same size and mach 3 reads it as a bunch of locations to move to, it's slow.

Hope I'm making sense, I'm kind of new to this software.

Is there a way to overcome this?

Thanks!
 

Offline jimpinder

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Re: Stepper motor setup questions
« Reply #1 on: April 24, 2008, 04:00:47 PM »
Mach 3 needs to calculate each move before it can start to run the steppers. If you are using a G2 or G3 code, this is one calculation. If, instead, your circle, or arc is compounded from many small straight lines, this is many small calculations for Mach to do. Mach is also, at the same time generating the drive pulses to drive the motors in a strict time sequence so that your many straight lines appear as a curve. It also, at the same time, calculates acceleration and deceleration times on CV to smooth the lines as well.

This is a well known problem and is the subject of quite a few posts.

There is a new board coming out, called Smooth Stepper to run from your USB output. This board has an on board pulse generator, which relieves Mach3 of a lot of calculation. It might be the answer to your problems.

In the meantime, try and use code which has as few lines as possible.

It gets even worse if you try Absolute Stop mode.


Not me driving the engine - I'm better looking.

Offline Zaae

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Re: Stepper motor setup questions
« Reply #2 on: April 24, 2008, 04:08:38 PM »
So, aside from simply not using so much code that does not contain actual geometry, does any other post-processor do a better job of 'compressing' the code, or using the geometry whenever possible?

For instance, I had a piece I cut recently that had rounded corners on it, and it came into mach 3 with the corners in a different color, and the code was geometry, yet other curves in the same model were treated as many straight lines.

I appreciate your help :)

Offline jimpinder

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Re: Stepper motor setup questions
« Reply #3 on: April 24, 2008, 06:57:53 PM »
I have honestly no idea. I am an engineer and my applications are of a structured nature, that do not look like a sea on a choppy day.

Yes, the problem must be, for a CAM program, if it is tracing a complex curved surface, it only has a straight line it can draw. It cannot, by definition draw a parabola - they do not exist in GCode. It must, therefore draw a straight line, until that line strays out of pre-defined limits, then move the line and set off again. Again, by definition, the motors must stop at the end of the line, and start at the beginning of a new one.

You could try speeding up your computer - and putting additional RAM memory in is one of the best ways to do that. Also cut out all the programs, or processes that are running in the background. If your computer is dedicated, then you need the minimum number of processes running to support Windows.

As I say - I have heard that Smooth stepper also helps in this - perhaps someone else could comment.
Not me driving the engine - I'm better looking.

Offline Zaae

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Re: Stepper motor setup questions
« Reply #4 on: April 24, 2008, 08:42:18 PM »
Oh yes, I can understand what you mean. I have cut parts that were square here, round there with no problems, smooth as butter. It's just that I'm trying to do some artsy fartsy type of stuff, and I always expect more :)

I guess what I was thinking of was some program or something that could identify an arc in a gcode file and replace that code with an arc function. This may or may not exist, and if it does, it most likely costs more than my truck.

Computing power definitely isn't the problem. I won't bother with details, but it's not.

I did manage to get it to go a little faster by ramping up the acceleration numbers for the axis, but at the time I had CV set at 45* which was making the table shake when it would get to a corner. I haven't tried it with the "stop CV on angles >" set at 0 yet with this new found speed, but I'm going to try it out yet tonight. I did notice that while carving in wood, my bits left a less than desirable finish with higher speed + CV stopping now and then.

Thanks for your thoughts on the subject :)

Offline stirling

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Re: Stepper motor setup questions
« Reply #5 on: April 25, 2008, 05:47:59 AM »
Jim is absolutely right that this comes up time and again. However the reason for the problem is often down to a misunderstanding of which angle is being referred to in "Stop CV on angles >". In the UG it describes it as being the angle BETWEEN the paths - sadly this is plain wrong.

The whole idea of being able to "Stop CV on angles >" is to stop CV blending "sharp corners" whilst still allowing it to blend "gentle corners". If it was the angle BETWEEN the paths then this would mean you would blend sharp corners but "exact stop" shallow ones - which is clearly completely the wrong way round.

The angle in question actually refers to the change in heading. So if you want to maintain the sharpness of corners where the angle BETWEEN them IS LESS THAN 45 degrees then you set "Stop CV on angles >" to 135 degrees. For example - you're heading east then change direction to north west - the angle BETWEEN your paths is 45 degrees but your change in heading is 135 degrees - make sense?

Try this:

First go to the settings screen and turn both CV Distance and CV Feedrate options off. (They just confuse the issue)
Then go to the general config menu screen and set "CV Distance tolerance" to its max of 180 and "Stop CV on angles >" to 180 also.

This tells Mach to use CV all the time. Result - smooth as a baby's bum.

Offline Zaae

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Re: Stepper motor setup questions
« Reply #6 on: April 25, 2008, 11:31:52 AM »
Hmm, I hadn't thought of that Stirling. I'll give that a try tonight. So, does un-checking "Stop CV on angles >" cause CV to be enabled all the time then?

Offline stirling

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Re: Stepper motor setup questions
« Reply #7 on: April 25, 2008, 12:02:30 PM »
So, does un-checking "Stop CV on angles >" cause CV to be enabled all the time then?
Indeed it does - unless of course you affect it by your CV Distance setting. For example setting CV Distance to 0 would effectively turn off CV. The trick is to decide firstly what angle you want to turn CV off at (if any) and then for those that are less than this how tight do you want the blend to be via CV Distance. Personally I don't bother with CV Feedrate - more trouble than it's worth IMHO.

Offline Sam

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Re: Stepper motor setup questions
« Reply #8 on: April 25, 2008, 12:10:02 PM »
The answer could be as simple as redrawing your shapes. If your importing an image of a design, and having some software automatically create the g-code, or trace the shapes automatically for you, this is where problems can arise. The number of line segments are often waaaaay out of the ballpark, and when you do manage to get the segments to a reasonable number with the different program settings, the quality usually suffers to an undesirable amount. Through much wasted time, effort, and headaches, I have came to the conclusion thats its just much simpler to draw over the shapes myself, that way I control all the arc's and lines. I have seen some drawing go from several thousand lines of code, to a hundred or so. It makes a HUGH difference. The setting in your post processor, as you mentioned, can also help. I know some have a minimum line length setting.
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."

Offline Zaae

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Re: Stepper motor setup questions
« Reply #9 on: April 25, 2008, 12:13:57 PM »
Okay, thanks for the tips. I have to drive a couple hundred miles today, but when I get back I'll try out your instructions.

One more thing... The "Auto tool zero" button still says it's not yet implemented. I was dreaming of having an alligator clip on the bit, and a small 1mm thick metal object I could use to set Z to -1.0000 when they make contact. Is there anything like that around? I haven't had much time to check out macros or brains yet.
« Last Edit: April 25, 2008, 12:15:55 PM by Zaaephod »