Date: Wed, 23 Jun 1999 03:49:54 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990622 ( MJD 51353 )
                          TUESDAY JUNE 22, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
    Observering team:   Stephanie Snedden       (APO)
                        Dan Long                (APO)
                        Matt Newcomb            (CMU)
   We were going to give the pointing model another try tonight.
Unfortunately clouds prevented us from getting a pointing model.
   We did however increase the axes speeds and test various rates and
accelerations.  Thanks to Brian Laubscher for spotting me at the telescope,
and apologies to Steph for only realizing why the telescope moved so slowly
this afternoon, while I was writing the log ( I missed the exponential
notation, so was off by a factor of 10 in acceleration this afternoon ).
It now ramps up to max velocity in about 10 deg rather than 50.  The
telescope now has the following axis parameters in the TCC
            Az     El      Rot
! Maximum |velocity| (deg*/sec)
Vel         1.25    1.25    2.0
! Mmaximum |acceleration| (deg*/sec^2)
Accel       0.1     0.1     0.1
! Maximum |jerk| (deg*/sec^3) (ignored for uncomputed offsets).
Jerk        0.4     0.4     0.2
And in the mcp ( result of print_max )
AXIS 0: MAX ACC limit 4.000000 deg/sec/sec current max 0.100250
AXIS 1: MAX ACC limit 4.000000 deg/sec/sec current max 0.252527
AXIS 2: MAX ACC limit 6.000000 deg/sec/sec current max 0.100189
AXIS 0: MAX VEL limit 2.250000 deg/sec current max 2.000063
AXIS 1: MAX VEL limit 1.750000 deg/sec current max -1.500136
AXIS 2: MAX VEL limit 2.250000 deg/sec current max 2.000009value = 61 = 0x3d = '
   Question, do I read this as the limit for acceleration as 4 deg/sec/sec
or .1deg/sec/sec?
   Some curious behavior was seen in the testing.  For example, the azimuth
would trip due to a current limit ( voltage out > 12000 ) for velocities
greater than or equal to 1.45 deg/sec, but only going in the negative
direction.  If one moved in the positive direction, motor currents (
voltage out on the mcp display ) would stay around 3500 even at velocities
of 2.0 deg/sec.
   Even more curious was that the max motor current did not occur during
max acceleration.  The current would slowly climb once steady state was
reached.  The faster the velocity, the quicker the climb.  At 1.35 deg/sec
the vel out was -5700 with occasional excursions over -6500.  At 1.45
deg/sec the level kept increasing even at a constant velocity ( reached
within about 10 deg of start of slew ) so that at around 30 deg into the
slew the amplifier would trip.  At 1.55 deg/sec the amplifier would trip
only 18 deg into the slew.  This happened at several azimuth locations
anywhere between 150 and 0 deg.  Note that the windscreen was doing a nice
job of staying out of the telescope's way until the amplifier went out of
closed loop, so I don't think contact with the windscreen can be the cause
of the high currents.
   To recap motor currents for various velocities moves were between 150
and 50 degrees typically, though a few tests went to 180 and 0.
        Max     Current         Current
        Vel     Pos dir         Neg dir
        1.25    3500 +/-300     -5500 +/-500
        1.35    3500 +/-300     -5700 +/-500
        1.45    3500 +/-300     -6500 for ~20 deg then climbed to
                                        -12000 in another  10 deg
        1.55    3500 +/-500     -7000 for ~12 deg then climbed to
                                        -12000 in another 5 deg
        2.0     3500 +/-500      Didn't even try it.
  Sadly I couldn't run the tpm during this.  It complained of a version
mismatch "looking for version 3, found version 4" or some similar message.
   There was a high occurance of azimuth hum when sitting still ( maybe 75%
of the time after an axis init ).  This happened even before we started
changing axis params.
   Another interesting find is concerning the 15 deg stop.  At the higher
velocities now permitted the altitude, it won't even try to move out of the
way.  A little experimenting revealed a pattern.  Apparently there is a
_range_ of altitude in which the stop will activate or retract, rather than
a value above which it will activate.  If the altitude moves quickly enough
through this range it doesn't retract.  Subsequent moves below this range
won't get it to move either.  The magic range for retracting is somewhere
close to 18 deg.  If it fails to retract when moving down below 18, and I
try moving around in the few degrees below that before the windscreen
actually hits the stop, the stop doesn't try and retract.  This seems to be
a bug.  I would expect any time the telescope is commanded to move in
elevation below a certain value, it should retract the stop if it isn't
already retracted ( assuming the azimuth is in stow ).  If I moved the
telescope above 18 deg, then back down, the stop would retract if the
starting and stopping points of the slew were such that the elevation was
moving relatively slowly as it passed the 18 deg mark.
   Another observation.  As with the brakes, there are two "puffs" heard
with each retraction of the 15 deg stop.  I don't really understand why
there are two, but perhaps if the telescope has moved far enough between
the first and second, that it no longer recognizes it needs to continue and
issue the second "puff", which may be the critical move for the piston ( I
only would hear one "puff" whenever it failed to retract ).  I only ever
hear one "puff" to extend it, which may explain why I've never seen it fail
to deploy.
                                  Dan