Scobie - 
Here is my guess...and this is just a guess.

The servos require a certain amount of voltage to work.  Moving the servo
puts a load on the battery and causes the voltage to drop a little bit.
Once the load is taken off of the battery, the voltage will jump up a little
bit.  

So, if you're at the limits of what it takes to move the servo:
The servo starts to move then pulls down the battery too low for the servo
to move.  

Once the servo is no longer putting a load on the battery the pack starts to
go up in voltage.  

The threshold for the servo voltage is met and the servo starts to move
again.  

This could also be a function of the voltage the RX needs to work as well.
If the RX is powering on and off because of the servo load you'll experience
the same problem.

Most receivers require less voltage to work than servos do...at least in my
experience.  It's always a good idea to stop flying when you have these
issues :-)

Jared




-----Original Message-----
From: Scobie Puchtler [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, January 26, 2005 6:07 PM
To: RCSE
Subject: [RCSE] servo-receiver behavior question

Ok,
so,
when an onboard battery pack winds down to nearly exhausted, and the servos
start to get erratic, meaning they start moving to do the requested motion,
but only get part way there, then quit, then jump the rest of the way,
perhaps in two or three of these steps for a full deflection, what exactly
is going on?
 
Is this the servo simply demanding more power than the battery can provide?
Why isn't the servo simply slowing way way down, as opposed to jerking in
steps to its destination?
 
Does the receiver have any role in creating this erratic motion?  Is the
receiver somehow "cutting in and out" or is this familiar behavior just a
symptom of how the power demands cycle between the servos and the battery?
 
Thanks for insight from anyone with more mastery of electronic interactions
than I have (which is an awful lot like just saying anyone) 
 
Lift,
Scobie in Seattle.

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