[NSRCA-discussion] Servo Signals

[John Pavlick]

Actually the VERY early R/C systems were truly digital as far as the controls went. The escapements drove the surface either neutral or full left, etc. Galloping Ghost just had more "bits". :)
 
The fact is that we want the control surfaces to move in an analog fashion. Regardless of how the servo determines and maintains it's position. We live in an analog world.
 
John Pavlick

--- On Tue, 6/23/09, James Oddino <joddino at socal.rr.com> wrote:


From: James Oddino <joddino at socal.rr.com>
Subject: Re: [NSRCA-discussion] Servo Signals
To: "General pattern discussion" <nsrca-discussion at lists.nsrca.org>
Date: Tuesday, June 23, 2009, 4:51 PM


They are called digital because they use digital techniques.  The transistors are either on of off.  As far as I know Jerry Pullen was the first to build them and this was his explanation.  Doug Spreng who worked with Jerry at JPL was the first to produce and sell a system with them (Digicon).  Many improvements were made through the years and eventually JR made what they called a Super Servo that contained a microprocessor.  This led to the modern day "Digital' servos that also contain microprocessors.  At that point all the previous digital servos began being called analog.  The truth is they are all analog and the basic concept has never changed.  The input is a pulse that varies in width from 1 to 2 milliseconds and the output position is proportional (analogous) to the pulse width.  A true digital servo would be sent a binary coded input (ones and zeros) like a PCM transmitter sends to the receiver.


Hope this helps, Jim








On Jun 23, 2009, at 5:03 AM, Vicente Vince Bortone wrote:




Jim,
 
I don't know anything about electronics.  I am sure that the following question if very simple for you:  Why the digital servos are called digital?
 
Thanks,
 
Vicente "Vince" Bortone
 

----- Original Message -----
From: "James Oddino" <joddino at socal.rr.com>
To: "General pattern discussion" <nsrca-discussion at lists.nsrca.org>
Sent: Tuesday, June 23, 2009 12:12:23 AM GMT -06:00 US/Canada Central
Subject: Re: [NSRCA-discussion] Servo Signals

What do they say in the Capital 1 commercials, not literally?  Transmitters communicate with receivers digitally in PCM mode and analog in PPM mode.  Receivers communicate with servos analogy (?) with PWM.  The servos are analog.


Jim O





On Jun 20, 2009, at 7:23 PM, Bob Richards wrote:






--- On Sat, 6/20/09, Richard Lewis <humptybump at sbcglobal.net> wrote:





And....Interestingly enough.....It does not matter what kind of fancy whopping digital super latest and greatest TX/RX system you have, the signals to the servos are still firmly rooted in good old 1970's technology....:)  And...Your super whopper digital brushless whatever servo still has an analog pot for position feedback....:)
 
I for one am eager to see a leap in servo technology.....Bidirectional serial comms to the servos with the servo being able to feed back torque, amps, position, rate, etc.....and encoder/resolver position feedback in the servos to really catch up with the world we live in......
 
Amen to that. We have digital servos and digital receivers, yet they talk to each other via an analog method and use analog feedback.
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