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<DIV><SPAN class=499452719-27032003><FONT face=Arial color=#0000ff
size=2>Optical encoders of useful resolution (4096 pos/rev) are horribly
expensive and too large.</FONT></SPAN></DIV>
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<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> s.vannostrand@kodak.com
[mailto:s.vannostrand@kodak.com]<BR><B>Sent:</B> Thursday, March 27, 2003 2:27
PM<BR><B>To:</B> discussion@nsrca.org<BR><B>Subject:</B> RE: Pot-less
servos<BR><BR></FONT></DIV><BR><FONT face=sans-serif size=2>Dean,</FONT>
<BR><FONT face=sans-serif size=2>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?</FONT>
<BR><FONT face=sans-serif size=2>--Lance</FONT> <BR><BR><BR><BR>
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<TD><FONT face=sans-serif size=1><B>"Dean Pappas"
<d.pappas@kodeos.com></B></FONT> <BR><FONT face=sans-serif
size=1>Sent by: discussion-request@nsrca.org</FONT>
<P><FONT face=sans-serif size=1>03/27/2003 11:40 AM</FONT> <BR><FONT
face=sans-serif size=1>Please respond to discussion</FONT> <BR></P>
<TD><FONT face=Arial size=1> </FONT><BR><FONT
face=sans-serif size=1> To:
<discussion@nsrca.org></FONT> <BR><FONT
face=sans-serif size=1> cc:
</FONT> <BR><FONT face=sans-serif size=1>
Subject: RE: Pot-less
servos</FONT></TR></TBODY></TABLE><BR><BR><BR><FONT face="Courier New"
size=2>Mike,<BR>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 rela! tive.
For the kind of reliability we need, one home position, near neutral will not
do! You end up needing a position feedback element,
anyway.<BR>Dean<BR><BR>-----Original Message-----<BR>From: Michael Ramsey
[mailto:michaelr@flying-models.com]<BR>Sent: Thursday, March 27, 2003 9:32
AM<BR>To: discussion@nsrca.org<BR>Subject: Re: Pot-less servos<BR><BR><BR>It's
just a motor right? But a step motor moves in increments of measure.
Is<BR>that technology "pot-less". I've only heard about them, but have
wondered<BR>how they might work for R/C
use.<BR><BR>Michael...<BR><BR><BR>----- Original Message -----<BR>From: "Dean
Pappas" <d.pappas@kodeos.com><BR>To:
<discussion@nsrca.org><BR>Sent: Wednesday, March 26, 2003 5:05
PM<BR>Subject: RE: Pot-less servos<BR><BR><BR>What about stepper
motors?<BR><BR>-----Original Message-----<BR>From: Michael Ramsey
[mailto:michaelr@flying-models.com]<BR>Sent: Wednesday, March 26, 2003 5:03
PM<BR>To: discussion@nsrca.org<BR>Subject: Re: Pot-less servos<BR><BR><BR>Does
anyone know anything about "step" motors?<BR><BR>Michael...<BR><BR><BR>-----
Original Message -----<BR>From: "Bill Glaze"
<billglaze@triad.rr.com><BR>To: <discussion@nsrca.org><BR>Sent:
Wednesday, March 26, 2003 5:40 PM<BR>Subject: Re: Pot-less
servos<BR><BR><BR>> Remember the Bonner Mailbox? Didn't have a
potentiomenter; didn't need<BR>one!<BR>> Bill Glaze<BR>><BR>> Dean
Pappas wrote:<BR>><BR>> > Hi John,<BR>> > Pot-less servos are
our history! The old KPS-9 had a variable cap, and<BR>F&M sold a servo
back in the same time period with a variable L-R<BR>multivibrator, called the
Magnevac. But you remember that, don't you!<BR>> > Back as a fresh-out I
wedged an optical unit into the variable cap<BR>housing of a KPS-9.<BR>>
> I have no idea where it is, but I don't think I tossed it.<BR>> >
Dean<BR>> ><BR>> > -----Original Message-----<BR>> > From:
John Ferrell [mailto:johnferrell@earthlink.net]<BR>> > Sent: Tuesday,
March 25, 2003 6:19 PM<BR>> > To: discussion@nsrca.org<BR>> >
Subject: Re: New Futaba wc?<BR>> ><BR>> > Pot-less servos may be
nearer than you think. Clarostat has rotary hall<BR>> > effect devices
available now.<BR>> ><BR>> > John Ferrell<BR>> > 6241
Phillippi Rd<BR>> > Julian NC 27283<BR>> > Phone:
(336)685-9606<BR>> > Dixie Competition Products<BR>> > NSRCA 479
AMA 4190 W8CCW<BR>> > "My Competition is Not My Enemy"<BR>>
><BR>> > ----- Original Message -----<BR>> > From: "Koenig,
Tom" <Tom.Koenig@actewagl.com.au><BR>> > To:
<discussion@nsrca.org><BR>> > Sent: Tuesday, March 25, 2003 5:52
PM<BR>> > Subject: RE: New Futaba wc?<BR>> ><BR>> >
><BR>> > > Thanks Dean...now I'll be disappointed for a while.
Maybe they will do<BR>it<BR>> > > when they introduce their 'potless'
servo's.<G> I too have been<BR>waiting<BR>> > for<BR>> >
> these! I guess I'll keep dreaming.<BR>> > ><BR>> > >
-----Original Message-----<BR>> > > From: Dean Pappas
[mailto:d.pappas@kodeos.com]<BR>> > ><BR>> ><BR>> >
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