Z axis stepper motors speed limitation ?

Hi,
I have purchased a SINTRON kit. ( Don't do that. Plexi is too thin.)
I am calibrating the Z axis. According to Josef Prusa's calculator (thank you for that) 4000 steps/mm is a good starting point.
Not so. If i reduce to below 3500 steps/mm, the motors run flawlessly. Above that, they seem to get stuck (don't turn) and hum, as if the coils operate against each other.
I use Marlin/ramps 1.4.
I have tried to turn up power, but no effect.
At 3500 steps/mm i get 9.48 mm per 10 steps, so I seek 4061 steps/mm.

Ideas ?

You confuse steps/mm and steps/ second.
Leave the steps/mm at 4000, but change the speed setting from 5 to 3 ( in Marlin )

#define DEFAULT_AXIS_STEPS_PER_UNIT   {160.0,160.0, 8000.0, 140.6} // for drv8825 // extruders with MK8 gear and a4988
#define DEFAULT_MAX_FEEDRATE          {450, 450, 3, 25}    // (mm/sec)

Happy printing
Olaf, another Sintron user

Try to turn down the acceleration rate, this might help

Quote
o_lampe
You confuse steps/mm and steps/ second.
Leave the steps/mm at 4000, but change the speed setting from 5 to 3 ( in Marlin )

#define DEFAULT_AXIS_STEPS_PER_UNIT   {160.0,160.0, 8000.0, 140.6} // for drv8825 // extruders with MK8 gear and a4988
#define DEFAULT_MAX_FEEDRATE          {450, 450, 3, 25}    // (mm/sec)

Happy printing
Olaf, another Sintron user

That did it. Much better. I now have 10.15 mm@ 10 steps with 4061 steps/unit
Another thing: Olaf Lampe, I expect you to be norwegian (i'm danish). :-)

Quote

Another thing: Olaf Lampe, I expect you to be norwegian (i'm danish). :-)

I´m german, but my parents named me after King Olaf from Norway My brother "Klaus" was named after Prinz Klaus from The Netherlands, so we are a royal family
-Olaf

Edited 1 time(s). Last edit at 08/06/2015 01:25AM by o_lampe.