Subject: Re: steppermotor as encoder -> presto, moterized pot.
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
Organization: The Armory
X-Newsreader: trn 4.0-test69 (20 September 1998)
From: email@example.com (Richard Steven Walz)
Date: 09 Oct 2002 04:20:52 GMT
In article ,
Tony (remove \"_\" from email address) wrote:
>For all the desirable attributes of Selsyns, then don't really address the issue
>here- the OP wanted to use the knob as both input and output. You can simulate a
>Selsyn waveform to drive one as an out device, OR you can sense the waveform and
>use it as an input device, but to do both you need to do something similar to
>what I suggested for the stepper solution (and even if you can still get
>Selsyns, old floppy drive motors are still lots easier to get).
That's true, selsyns are one way, I recalled after I reviewed my notes.
It may be possible to sense feedback on each coil and arbitrate it into
rotation data, however.
>On 08 Oct 2002 02:16:34 GMT, firstname.lastname@example.org (Richard Steven Walz)
>>In article <email@example.com>,
>>Tony (remove \"_\" from email address) wrote:
>>>On 06 Oct 2002 22:43:52 GMT, firstname.lastname@example.org (Richard Steven Walz)
>>>>Okay, problem. When you turn a stepper VERY slowly, nothing comes out of
>>>>it. You STILL need either a motorized pot or encoder or some sort on the
>>>>stepper shaft. Now a geared stepper would probably work!
>>>Yes, this is the real issue, but it can be overcome.
>>>A disk drive stepper is ideal, its normal detent torque should be
>>>any holding current, and the position can be measured (even if the shaft is
>>>turned infinitely slowly) by a differential inductance measurement, instead of
>>>BEMF. Perhaps if the stepper coils are PWM current controlled, a tiny bit of
>>>excitation will be enough to sense inductance. One of the AVR's timers could
>>>drive the PWM, and also a CMOS switch to synchronously detect the inductance
>>Why not just use some three-phase selsyns??