Re: Re: Stepper resonance - not a problem

> If thats the case, it probly wouldn't work in full step mode either.

You might be right .. theory and the real world are rarely in sync.

> I had thought about doing this, my controller has the capability to adjust
> the current sense reference voltage from 50 - 100%, with a resistor change
> it could do 60/100. But are the motors ratings limited by the temprature
> rise - or core saturation?

Good question, although neither may be important. Torque is roughly
proportional to core characteristics, so increasing the current to maintain
a constant torque implies that if the core hasn't saturated with both
windings engaged ( at some particular torque level ), it shouldn't
saturate at the same torque level with only one winding engaged.

Just to be on the safe side, since my motors are quire big enough for my
machine, I mentally derated them just a bit. Instead of running them
at 5 amps per winding in full step mode, I run them in half-step at 4 amps
with both windings on, 5.6 amps with one winding on.

Again, though, this should not be necessary for either temperature reasons
( assuming a reduced current "stop" feature ) or for core saturation reasons.

> My controller does a power saver function where the current is reduced
> automaticaly if it has nor recieved a step pulse in 1 second - it resumes
> full power imediatly when a step pulse arrives.

As does mine, for the reason stated just above.

> This is the second time If seen 1/4 stepping mentioned - could you explain
> how this works? Do you have to be able to set different current levels
> simultaniously when two coils are energized?

Exactly, in the proportion mentioned - sin(a) cos(b). The relationship
is actually the same for all modes, full, half, quarter, eighth, etc.
Increasing the number of intermediate steps does mean increasing the number
of discrete current levels. This usually ( but not necessarily ) means
a microprocessor to assist things. It IS possible with discrete logic,
but ... <G>

Alan

--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta