Stepper Motor Speed does not match MaxVel

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25 Sep 2025 19:04 #335424 by richcolvin
Stepper Motor Speed does not match MaxVel was created by richcolvin
I am finding that
  1. the stepper motors for the two spindles work as expected, however
  2. the stepper motors for the axes (B, U, V, X, &, & Z) run at a VERY slow speed. 
The latency test on my Raspberry Pi 5 gave:
  • Servo Thread
    • Max Interval = 1,013,089nS
    • Max Jitter = 13,089nS
  • Base Thread
    • Max Interval = 46,407nS
    • Max Jitter = 24,074nS
I ran the Step Timing Calculator to set the BASE_PERIOD based on using StepperOnline DM542T drivers.
  • Step Length = 2.5µS
  • Step Space = 2.5µS
  • Direction Setup = 5µS
  • Direction Hold = 5µS
The recommended BASE_PERIOD = 26.57µS.

When I run LinuxCNC based on this configuration, the value for the parameter, hm2_yi92.0.stepgen.02.maxvel = 1.

Regardless, the stepper motor does NOT run at 1 rev / sec.


Attached are the HAL, INI, and include files for
  • Spindle0 (Spindle1 is the same)
  • Axis X (axes Y, Z, B, U, & V are the same)
The X Axis is set as Joint 0, Channel 02.


Help would be GREATLY appreciated!

Thank you and kind regards,
Rich
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25 Sep 2025 19:30 - 25 Sep 2025 21:53 #335425 by PCW
The velocity units for linear axis are in inches per second, not revolutions per second
If the linear velocity is not correct, its likely the the step scale does not match the hardware
(hardware meaning the ball screw pitch, step drive microstep ratio, any intermediate gear/belt reductions etc.)
 
The velocity units for rotary axis are in degrees per second.

Note that latency will have no real affect on scaling unless its
so bad that you get stalling (which would be obvious)
Last edit: 25 Sep 2025 21:53 by PCW.

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