# Machsupport Forum

## Mach Discussion => Mach4 General Discussion => Topic started by: thespindoctor on July 08, 2018, 10:42:33 AM

Title: angular axis incremental stepping
Post by: thespindoctor on July 08, 2018, 10:42:33 AM
I have an A axis which is working well except when I jog 1 degree repeatedly, I get 1.01 then 2.02 then 3.03
The addition of hundreds is not always consistent.  I expected that a jog of 1 degree would always show a DRO of 1 more degree.
It also happens when I use a Gcode move to 1, 2, and 3 degrees.

Is this a step per unit issue or something else from the plugin etc?

I have a Pokeys57E and a CNC4PC C62 BOB.

Thanks
Title: Re: angular axis incremental stepping
Post by: thespindoctor on July 08, 2018, 12:01:02 PM
I have 20000 steps per revolution with a Gecko 201x drive.

That would be 55.56 steps per degree rounded.  I have entered 55.56 in Mach4 motor settings.

Should I have used 55.555555?

Thanks
Title: Re: angular axis incremental stepping
Post by: joeaverage on July 08, 2018, 02:55:46 PM
Hi,
I would have thought that the servo can move an integer number of steps, it can't do fractional.

I think Mach calculates and stores its position as a real number but the axis motor can only step integer numbers.

May I suggest trying entering 56 as steps per and try your series of moves and then try 55 steps per.
My expectation is that while the axis will move a little more than one degree (Steps Per=55), say 1.02 degree but it would be consistent.

Craig
Title: Re: angular axis incremental stepping
Post by: thespindoctor on July 08, 2018, 04:15:04 PM
I will try it thanks!

I was wondering about the fractional vs integer step number.
Title: Re: angular axis incremental stepping
Post by: joeaverage on July 08, 2018, 04:45:20 PM
Hi,
one other possibility is if you can introduce an additional gear or belt reduction?

If you can and choose a ratio of 1.8:1 then your steps per unit would be 100, ie integer.

Craig
Title: Re: angular axis incremental stepping
Post by: Mauri on July 08, 2018, 04:45:32 PM
thespindoctor,
What micro steps do you have set on your Gecko 201x card 1:1 to 1:10.
This card if moving fast (4000mm/min) has issues, we had them on our router table and them replaced with G203V and all issues went away.
The card sends pulses to the stepper via the Gecko, so the minimum amount of pulses depends on the micro steps you have and the 201x is not suitable for high speeds.
The better Gecko is the G203V with a 10 Micro step it works great on our Mill and Router 4 Axis.
We run the Mill 45:1 ratio and 15:1 ratio on the Router Table A Axis. (speed on the A Axis is 3600mm/min Router)
Regards,
Mauri.
Title: Re: angular axis incremental stepping
Post by: joeaverage on July 08, 2018, 11:18:59 PM
Hi,
if you have Gecko and are using 10 microsteps that suggests you have a mechanical reduction of 10:1 in addition?
If that is so could you change that reduction to 9:1 instead?

200(steps/rev for a two phase stepper) X 10 (10 microsteps per full step) x 9 (mechanical reduction)= 18000

18000 / 360 =50....an integer!

Craig
Title: Re: angular axis incremental stepping
Post by: Mauri on July 09, 2018, 07:27:33 PM
Hi,
As the best resolution you can get down to is 1 pulse it does not matter if the 1 degree movement has decimalized pluses, what does matter does it have at least 1 pulse.
As mentioned before if you CNC is running at the speeds I mentioned that and you have at least 1 Pulse on the movement you have selected then the issues is with the 201x or 210x that you have.

The G901/G902s synthesize 1,2,5 or 10 pulses for every received step pulse. If full-step mode is selected, 10 synthesized pulses are sent to the base 10-microstep drive, it emulates a full-step drive and everything works wonderfully. The problem is the multiplier is not not psychic; it can issue the 10 synthesized pulses only after it has received an input step pulse. This can take 50mS to complete (10 pulses with a spacing of 5mS between each pulse). If the direction is changed during that 50mS, some pulses will be in the correct direction, the remainder will be in the wrong direction. The result is a 'drift' in the accumulated axis position during CNC CV motion. Non-CNC, non-CV applications have a dwell time after each motor move so this is of no consequence.

The G203V completely resolved this issue and can run at all resolutions and speeds as long a you have at least one pulse.

Regards,
Mauri.
Title: Re: angular axis incremental stepping
Post by: thespindoctor on July 09, 2018, 08:00:32 PM
I only am moving slowly through + and - 6.5 degrees
Look like it is fixed now when I discovere a cracked pulley!!
Title: Re: angular axis incremental stepping
Post by: thespindoctor on July 10, 2018, 08:41:59 AM
Thanks Mauri and Craig!
I love Geckos!
Title: Re: angular axis incremental stepping
Post by: thespindoctor on July 11, 2018, 08:31:24 AM
Mauri,

I switched out the 201x for a 203v and it does work better!
Thanks!