Pot-less servos

Thu Mar 27 10:26:32 AKST 2003

Dean,
That's why steppers are  not the best fit in this application.  However, 
optical encoders could be a better solution than pots.  Aren't these 
available in small enough size?
--Lance

"Dean Pappas" <d.pappas at kodeos.com>
Sent by: discussion-request at nsrca.org
03/27/2003 11:40 AM
Please respond to discussion

        To:     <discussion at nsrca.org>
        cc: 
        Subject:        RE: Pot-less servos

Mike,
A stepper motor is a kissing cousin to the present generation brushless 
motors. Several sets of windings are popwered in rotating sequence, kinda 
like a 3-phase AC motor. If the sequence is reversed, it rotates the other 
way. Each run through the sequence corresponds to an angle. 100-position 
per rev steppers are common, but we would likely use a coarser one and 
gears. The motor can hold position one of two ways: steppers "cog" by 
design, so when powered down, there is a certain amount of breakout torque 
required to turn the output shaft. If you power the winding(s) that 
correspond to the present position, then you get great holding torque, but 
at currents similar to a DC motor at stall. If a critical torque figure, 
that is related to the desired motor speed, is never exceeded, then 
control is open loop: you count steps, both left and right forever. You 
need a home position (usually optical like John said) to make the position 
information absolute, rather than relative. For the kind of reliability we 
need, one home position, near neutral will not do! You end up needing a 
position feedback element, anyway.
Dean

-----Original Message-----
From: Michael Ramsey [mailto:michaelr at flying-models.com]
Sent: Thursday, March 27, 2003 9:32 AM
To: discussion at nsrca.org
Subject: Re: Pot-less servos

It's just a motor right? But a step motor moves in increments of measure. 
Is
that technology "pot-less". I've only heard about them, but have wondered
how they might work for R/C use.

Michael...

----- Original Message -----
From: "Dean Pappas" <d.pappas at kodeos.com>
To: <discussion at nsrca.org>
Sent: Wednesday, March 26, 2003 5:05 PM
Subject: RE: Pot-less servos

What about stepper motors?

-----Original Message-----
From: Michael Ramsey [mailto:michaelr at flying-models.com]
Sent: Wednesday, March 26, 2003 5:03 PM
To: discussion at nsrca.org
Subject: Re: Pot-less servos

Does anyone know anything about "step" motors?

Michael...

----- Original Message -----
From: "Bill Glaze" <billglaze at triad.rr.com>
To: <discussion at nsrca.org>
Sent: Wednesday, March 26, 2003 5:40 PM
Subject: Re: Pot-less servos

> Remember the Bonner Mailbox?  Didn't have a potentiomenter; didn't need
one!
> Bill Glaze
>
> Dean Pappas wrote:
>
> > Hi John,
> > Pot-less servos are our history! The old KPS-9 had a variable cap, and
F&M sold a servo back in the same time period with a variable L-R
multivibrator, called the Magnevac. But you remember that, don't you!
> > Back as a fresh-out I wedged an optical unit into the variable cap
housing of a KPS-9.
> > I have no idea where it is, but I don't think I tossed it.
> > Dean
> >
> > -----Original Message-----
> > From: John Ferrell [mailto:johnferrell at earthlink.net]
> > Sent: Tuesday, March 25, 2003 6:19 PM
> > To: discussion at nsrca.org
> > Subject: Re: New Futaba wc?
> >
> > Pot-less servos may be nearer than you think. Clarostat has rotary 
hall
> > effect devices available now.
> >
> > John Ferrell
> > 6241 Phillippi Rd
> > Julian NC 27283
> > Phone: (336)685-9606
> > Dixie Competition Products
> > NSRCA 479 AMA 4190  W8CCW
> > "My Competition is Not My Enemy"
> >
> > ----- Original Message -----
> > From: "Koenig, Tom" <Tom.Koenig at actewagl.com.au>
> > To: <discussion at nsrca.org>
> > Sent: Tuesday, March 25, 2003 5:52 PM
> > Subject: RE: New Futaba wc?
> >
> > >
> > > Thanks Dean...now I'll be disappointed for a while. Maybe they will 
do
it
> > > when they introduce their 'potless' servo's.<G> I too have been
waiting
> > for
> > > these! I guess I'll keep dreaming.
> > >
> > > -----Original Message-----
> > > From: Dean Pappas [mailto:d.pappas at kodeos.com]
> > >
> >
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