Re: [CAD_CAM_EDM_DRO] Axis Stall Problems

HI Wayne,

Half-step should be a little better. Also consider slowing down the
acceleration; plenty of suggested starting INIs on the TurboCNC list.

What size steppers?

Alan KM6VV


Wayne C. Gramlich wrote:

> All:
>
> My Sherline conversion is getting dangerously close to working,
> but I'm running into some problems with axis stalling.
>
> Hardware:
> I am using an old Sherline lathe as my base, with vertical
> milling column and a 13" inch table. Standard Shereline
> CNC mounts are being used. I have 180 oz-in Sanyo-Denki
> bi-polar stepper motors for each axis.
>
> Electronics:
> The electronics I designed myself. Here's a URL that
> has the schematics and everything:
>
> <http://gramlich.net/projects/cnc/motion/rev_d/index.html>
>
> Basically, I use a venerable L298 with heatsink and eight
> 1N5822 (40PIV 3A Schottky Diodes) for each axis.
>
> The power supply is 24VAC transformer, so the top voltage
> is 34V.
>
> The chopper is implemented using a dedicated Microchip
> PIC16F676 microcontroller (one for each axis) running
> at 20MHz where a couple of A/D lines are used to measure
> the current flowing through each L298 H-Bridge. Each
> axis is being sampled at approximately 20KHz. If the
> current is too high, I turn the H-Bridge off and if
> the current is too low, I turn it on.
>
> Software:
> I am running TurboCNC on FreeDOS. It is running on
> 1.1GHz Celeron processor.
>
> The problem:
> Each axis can turn slowly under TurboCNC, but after just
> a little acceleration, the axis stalls. This could be
> some sort of resonance issue, but I think it is more likely
> to be problem with my chopper electronics.
>
> I am currently using ripple drive (only 1 coil at a time)
> in the stepper controller with a maximum current of 1 Amp
> through each coil.
>
> I have many options:
>
> 1) Increase the current to 2 amps.
>
> 2) Switch over to Full Step drive.
>
> 3) Switch over to Half Step drive
>
> 4) Switch over to Micro Step drive.
>
> 5) Find somebody who has a working system and
> plug their controller into my steppers to
> isolate whether it is my electroncis or
> my mill.
>
> Any suggestions on how to track this problem down and
> rectify it would be greatly appreciated.
>
> -Wayne
>