Re: Stepper Acceleration in RWTS

[Sheldon Simms <wsspammy@gmail.com>]

On Tuesday, December 28, 2010 2:08:26 PM UTC-5, Michael J. Mahon wrote:
> 
> Therefore, for any given L and R, there is a minimum pulse width that
> ensures developing maximum torque.  Woz may have determined the minimum
> pulse width based on this.

Ok that's helpful, but I don't see any of this specified on any motor datasheets.
Would one just determine this empirically?

Assuming that a later motors have higher enough torque/faster enough response,
then wouldn't the motor turn to an energized phase and bounce around it for
a bit until it settles, only to have to start from zero angular velocity again
when the next phase is energized? If that's the case, then the whole idea of
"accelerating" the motor is kind of silly even though the code may successfully
seek to the correct track.

> The state of two phases energized corresponds to a "phantom" pole
> between the two actual poles.  Thus A-AB-B-BC-C is a higher-torque
> way of getting from A to C.  The "real" poles are geometrically
> determined, and the stepper angles they represent are more stable
> than the "virtual" poles, which are based on current and field
> balance between the two actual pole windings.  Therefore, it is
> reasonable to base the track positions on real poles only, so
> any stepping sequence must begin and end with single windings
> energized.
> ...
> As a practical matter, energizing two windings requires twice the
> current and generates twice the heat, so you don't want to hold the
> windings on for an extended period.

Right. I wasn't suggesting putting tracks on a "virtual pole" (although I'm
pretty sure that was actually done for various reasons) but just wondering
about the one-two-one-two pattern for seeking in the light of the fact that
most datasheets I've looked at assume a two-two-two-two pattern  for
stepping.

Thanks for the reply.