RE: [CAD_CAM_EDM_DRO] Geckodrive

Unless I'm missing something in your post (you said "step motor").

A stepper motor by its very nature is stallable via load, inertia, and
resonance. Unless you're suppressing mid range instability caused by parametric
oscillations then you're always in danger of stalling regardless of loading.
These suppression or damping features are usually found on high end
micro-stepper drivers.
You can fix this some what by having a stepper with extra torque than needed but
that's a wasteful and expensive route and all you've really done is changed the
rotor inertia.

Once a stepper stalls it enters a very chaotic state and at this point the
pulses from the incremental encoder are all invalid. You always have to re-index
after a stall to remove the chaotic error. Still the end effect is; you're part
is screwed.

At any rate an incremental encoder is not going to give you advance warning of a
stall in order to avoid it. You might try putting a tachometer on it and
programming a DSP to sense the instability but that's not a cheap route either.

This technique might be useful on a servo motor using current and tach/encoder
feedback. This is also something you find on some high end servo drivers.