Or you could rotate the whole OCXO on flexible leads through 180* and
let gravity tune your frequency.
The range might be small, but an occasional tweak on the frequency
control might be acceptible.
cheers, Neville Michie
On 03/05/2010, at 6:00 AM, Bob Camp wrote:
Hi
An R-390A (or an not an A) has a lot of examples of how to do anti-
backlash gear trains. Pretty tough to do on a one up fab from
scratch in the basement basis though.
Lots easier to kludge in a low capacitance tuning diode .....
Bob
On May 2, 2010, at 3:54 PM, Bruce Griffiths wrote:
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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