Re: [Emc-users] stepgen step rate

[Gene Heskett]

On Tuesday 05 January 2021 10:47:16 andy pugh wrote:

> On Tue, 5 Jan 2021 at 15:40, Thomas J Powderly  
wrote:
> > Thats a max step/sec of 1 for that particular sequence of 2
> > steps.
> >
> > That sequence can happen at anytime in a cnc path.
>
> Not so. A stepper will only ever reverse at zero speed, when the step
> rate is zero. So you don't need to make allowances for setup.

This might be so, but zero speed is very fleeting for the reversal at the 
bottom of a g33.1. Even if being sequenced by hal tricks like I am. And 
a step loss  at the bottom turnaround could cause the sloppy oversized 
threads I am getting when I have to peck exec with a descending turn 
around due to lack of torque to drive the tap of that size in one stroke 
so I write a peck loop.

I'd have no trouble expanding that spindle stopped window, its a setp in 
my hal code, so how long a dead time between encoder pulses do I need in 
order to guarantee no loss of Z steps in that condition?

Thanks Andy.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] stepgen step rate

[andy pugh]

On Tue, 5 Jan 2021 at 16:24, Thomas J Powderly  wrote:

> but , a special case ignores/allows for when the velocity is zero.

I don't think that it is a special case, just that because the
reversals always happen at very low step rates you don't need to
factor in the setup time when calculating maximum step rate.

Also look at the "reset" function, which allows for steps shorter than
a full base period, and for a step every base period.


-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] stepgen step rate

[Thomas J Powderly]

Thx Andy

I will look for what the code says it does when there's a zero speed 
reversal.


So I take it is true that the 4 values _are_ up rounded to the base 
period length.


but , a special case ignores/allows for when the velocity is zero.

I didnt see that yet.

TomP

On 1/5/21 10:47 PM, andy pugh wrote:

On Tue, 5 Jan 2021 at 15:40, Thomas J Powderly  wrote:


Thats a max step/sec of 1 for that particular sequence of 2 steps.

That sequence can happen at anytime in a cnc path.

Not so. A stepper will only ever reverse at zero speed, when the step
rate is zero. So you don't need to make allowances for setup.




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Re: [Emc-users] stepgen step rate

[andy pugh]

On Tue, 5 Jan 2021 at 15:40, Thomas J Powderly  wrote:

> Thats a max step/sec of 1 for that particular sequence of 2 steps.
>
> That sequence can happen at anytime in a cnc path.

Not so. A stepper will only ever reverse at zero speed, when the step
rate is zero. So you don't need to make allowances for setup.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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[Emc-users] stepgen step rate

[Thomas J Powderly]

Hello

I am studying the stepgen.c code.

I see that the 4 parameters

  steplen stepspace dirhold and dirsetup

are rounded up ( ulceil() )

to the next larger interger value of the BASE period.


That means for my Gecko 540, the 1uS Steplen 2uSstepspace 200nSdirhold 
and 200uS dirsetup


all become 25uS for the typical 25uS Base thread period.


But the DirSetup and DirHold must co-exist in a single StepSpace when 
the direction reverses between 2 step pulses.



I think that makes the stepspace become 50uS ( to accomodate the dirhold 
plus dirsetup )


and the steplen and stepspace now total 75uS.


Thats a max step/sec of 1 for that particular sequence of 2 steps.

That sequence can happen at anytime in a cnc path.

Som I must allow for these 'random' ocurrances,

and this lowers the max steprate to 1 ( 1 sec / .75 )..


The commonly mentioned 2 steps per second rate appears to be only 
for unchanging direction


and 1 steps per second for useful paths.

( 2 for drag racing  vs 1 for gymkhana )


Coreections invited, I am still studying.


Thx TomP



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