Bob Camp wrote:
Hi
A coupe of issues with mechanical servo tuning:
1) It wears out the tuning capacitor pretty fast. They are designed for a
limited number of adjustments. They loosen up with a lot of tuning and this
degrades their stability.
2) It would be much easier to tear apart the mechanical tune OCXO and put in a
tuning diode than to rig a thermally isolated high resolution servo stepper
3) Mechanical tune arrangements normally have backlash. That's not an issue as
long as the servo only goes one way. It becomes a real pain to correct for each
time you reverse direction.
One solution to which is to add (in addition to the servo motor) a
torque motor to preload the gear train so that the same flank of each
gear tooth is in contact for both directions of rotation. Zero backlash
drive reduction systems are also available at some considerable cost.
4) Making a mechanical setup with a minimum step below 1 ppt is going to be
more than just a simple stepper. A gear chain based system will be pretty
exciting to work up. Backlash in the gears will add to what ever you have in
the tune it's self.
5) The tuning on the OCXO may not be monotonic. That's especially true if you
do indeed run the trimmer at a higher resolution than a normal human could
adjust it. Tuning reversals tend to drive servo loops a bit crazy.
None of that says that it can't be done. All it says is that it will be hard to
do well.
What kind of accuracy are you trying to obtain?
Bob
Bruce
On May 2, 2010, at 3:18 PM, [email protected] wrote:
That is a really cool picture.
Can I be like you when I grow up?
I've figured out which of these silvered modules
in this Schomandl sig gen is the oscillator (the one that
got warm). I have to figure out if it is voltage adjustable
in some way.
Does anyone use mechanical adjustment with a servo,
gear train and microcontroller?
I did hear all of those good advisers telling me to
buy the Thunderbolt. But I already have these pieces
so...
--
Chris
w0ep
Niels Lueddecke wrote:
You see? Don't do it, don't even think about starting.
Go buy a trimble thunderbolt, it will save you LOTS of time!
http://www.dulli.org/pics/20100502%20-%20Clock.jpg
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