Last updated: 9 July 2001

Saving Backlash Percentages

Subject:	setting percentages and calibrating motors
Sent:	Thursday, July 5, 2001 16:06:27
From:	sherrodc@ipa.net (Clay Sherrod)

I have gotten a lot of mail lately from ETX and LX 90 users who are
attempting to change their percentage settings on either or both
altitude and azimuth with versions v2.1 or v2.2 AutoStar.  I highly
recommend this option for users with delayed response when pushing
either arrow keys, particularly at very slow slew rates.

However, many users have reported that they do not know HOW to enter the
percentages OR that once entered properly the telescope appears to have
NO CHANGE in their response.  Indeed, this WILL be the case it seems
unless the following steps are taken exactly as described:

Changing to higher percentage allows the AutoStar and telescope to
bypass the delay time and essentially "jump starts" the drive system to
compensate for the computed time of backlash; if the telescope is too
jumpy after adjusting the percentages upward, the user can merely
re-enter a lower number and press "enter."

As an example of changing a percentage (both axes are factory pre-set
upon upload to either of these versions anew to 01%, the lowest possible
correction, or virtually no correction whatsoever for backlash delay)
the following example is given:

Let's say that the RA (or azimuth) axis has a long delay when changing
directions with the "4" slew speed selected.  To REDUCE that delay time,
we can INCREASE the "AZ PERCENT" on AutoStar to, say, 17% to start with.
I recommend experimenting with such a percent and then increasing or
decreasing to fit your personal preference...too high a percentage and
the response is noticeably jerky when responding!

The following steps are taken to enter this percent:

1)  Turn on scope and initialize as normal all the way past "Daylight
Savings Time;"
2)  Mode to "SETUP"
3)  Scroll to:  SETUP / TELESCOPE / AZ PERCENT...press "Enter";
4)  The default "01%" should appear with a flashing cursor;
5)  Using your number keys, type in "17";
6)  Press enter to lock into AutoStar default mode;
7)  Press "Mode" to escape from AZ PERCENT;
8)  Scroll down one step to ALT PERCENT
9)  Press "Enter" to change this percentage if necessary, following the
same steps described above.

One of the most common problems with new percentages being entered but
NOT being recognized by AutoStar is that the user does NOT press "Enter"
after the desired setting is keyed in.  The only way ANY user change can
be locked into Autostar (such as this, or site....for example) is to
press "enter" after each new or selected listing.


Here is the trick and this one surprised me....caught me totally
unaware.  Many experienced users were complaining that frequently their
"minor" adjustments with percentages did not seem to "take" or influence
the backlash problem when numbers were changed.  Since my percentages on
my personal telescope are set very low, I had not really thought much
about it until recently when I experimented with actual delayed response
times compared to values entered.

Sure enough, when changing below about 50% increasing in increments of
3%, 5" and even 7% all the way up to a total change of about 40%, not
much difference was noted in the actual TIMES of response at all.  This
was true in THREE (3) AutoStars tested on FOUR telescopes, including TWO
LX 90's.  There is a noticeable change in the "kick" of the gear train
(as monitored by the motor noise when the slew button is pushed), but
the actual change in motion itself seems almost unaffected.

HOWEVER, after each percentage change entered as just described, IF you
go back to:
SETUP / TELESCOPE / and scroll down to "CALIBRATE MOTORS" and "Enter"
(the motors will engage and move the telescope) the difference is
immediate and very pronounced.

Thus, a new tip when attempting to improve the overall performance and
eliminate backlash of your telescope by changing the percentages:

1)  Change the percentages and experiment with them;
2)  You do NOT need to change both axes if only ONE of them has backlash delays;
3)  Always press "Enter" after your new percentages are keyed in;
4)  Go back and CALIBRATE your motors after each new percentage change!

You will be very pleased with the immediate difference that you will see
from not using the "Calibrate" function of the Autostar which assists in
the recognition of the motor characteristics by AutoStar.

Clear skies and enless nights...
P. Clay Sherrod
Arkansas Sky Observatory

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