Misc facts


     I 've kept a list of some numbers that i've needed now and again. Here they are, but be forewarned that they may not all be correct...


length 1 side of triangle 216.ft
center triangle to vertex of triangle 124.71 feet 38.012m
center triangle to tiedown cable 192.2 feet 58.583m
center triangle to tiedown block (the cable is not vertical) 190.? feet 57.912m
azimuth arm length
304. feet
Working point pins (includes 2" offset from design drawings that maldo says exists) 1257.76 feet 383.365m
Center triangle to center of tower
700 feet
horizontal distance main cable pins to center of tower (700-124.7)
575.3 feet
Top of towers (from drawings above sea level)
1386.5 feet
angle main cables ( atan(1386.5-1256.1)/575.3))
12.77 deg

length main cable (575.3/cos(12.77))
587.44 feet
radius of curvature (design) 870 feet 265.176m
radius of curvature (measured photometry may01) lynn baker email 17jun2002
869.883 feet
Center curvature to ao9 dimple (jan02) lynn baker email 17jun2002
883.125 feet 269.1765m
radius to rolling surface 420.75 feet 128.245m
Spacing between centers of ZA rolling surfaces (drawing S-24 B and G) 12' 2 1/2" 3.7211m
primary reflector panels 3 by 6 feet with the 6 foot direction east-west.  
center opening. 25 ft by 3 foot panels. +/- 50 feet from center east/west. 7 rows (3*7=21 feet centered at y=0).

geocentric radius of telescope focus:(jpl ephemeris)
6376.5176 km

LIMITS (ch,gr,az)

position limits:

           There is an emergency limit that cuts the power to the drive system. To exit the emergency limit, you must use the limit override key and the pcu to drive the axis out of this limit. These limits are located to guarantee that the equipment does not have a catastrophic failure. In normal operation the emergency limits should never be encountered.

           For each axis there is a prelimit, a vmesoftware limit, and a final limit. At the prelimit the max velocity is decreased to 10% of slew rate (normal max velocity). The vme software  will not command a position beyond the vmesoftware limit (although rate mode will keep driving.) .  At the final limit, the plc will only allow you to drive the axis out of the limit (the power is not cut at the final limit). The prelimit and final limit are both created as an "or" of two inputs:

  1. the plc has  pre and final limit data values set in the plc program.
  2. There are switches positioned as the final limit and prelimit that generate ttl levels that the plc reads. The plc data values are set so that they are reached before the switch limits.
Either set going true will cause the prelimit or final limit to become active. The reason for the two sets of inputs is that the encoder could malfunction and the switch limits would still cause the prelimit/final limit to be reached. 

      The switch limit positions are adjusted by:

  • the emergency limit is the reference
  • the switch final limit is positioned .04 degrees before the emergency limit. This is what is tried for, the actual setting will be a little different
  • the switch pre limit is positioned .04 degrees before the final limit. This is what is tried for, the actual setting will be a little different.
      The plc limits are set so that the plcprelimit is .06 degrees before the plcfinal limit. 
  • 04feb05: the dome pre/final limit switches were changed from a cam switch to limit switches.
 velocity limits:
        When tracking a source (as opposed to slewing to a position) it is a good idea to limit the velocity to .4 deg/sec (az) .04 deg/sec (dome/ch) so that the control loop has a little extra velocity to apply in case it gets behind.

Greg limits high (za deg)
emgLim              :19.7804 (measured 04feb05)
switch finalLim:19.7374 (set 04feb05)
switch PreLim   :19.7019 (set 04feb05)

plcfin    :19.70
plcpre   :19.64

Greg limits low (za deg)
emglimit              : 0.9581 (measured 04feb05)
switch finalLim:  1.0187 (set 04feb05) 
switch PreLim    : 1.05     (set 04feb05)

plcfin    :1.05
plcpre   : 1.11

Greg velocity limits (deg/sec) .0417
Greg acceleration limit (deg/sec^2) .025
Carriage house limits high (za deg) plc/vme
plcfin    :20.00
plcpre   :19.94

Carriage house limits low (za deg) plcpre   :-.18
plcfin    :-.24

Carriage house velocity limit (za deg/sec) .0417
Carriage house acceleration limit (za deg/sec^2) .025
Azimuth limits (high az)
(i'm not 100% sure of these. I think the pre limit is not a switch like the dome,ch).
plcpre: 719.0

Azimuth limits (low za) plcpre:1.0
plcfin: 0.0

azimuth velocity limit (deg/sec) .4167
azimuth acceleratation limit (deg/sec^2) .100

Az,za to  position dome above the cal dipole:
  • az=277
  • za=8

Positions for hurricane stow pins (values  used 22aug12):
  • az: 257.5356
  • gr:8.4769
  • ch:8.8302


tower  offsets indegrees (2.87-T12, 122.87-T4, 242.87-T8) 2.87 degrees
Reflector offset from AO9 (from photometry survey may01) 1.34 in East
0.69 in South

Platform main bearing offset from AO9 (survey aug01) 0.2 in East
2.2 in North

Platform offset from center of reflector
is this from lynn or 1az terms of pointing?
1.14 in West
2.89 in North

The optic axis za (read from the encoders) is uphill from the dome centerline.
8' 5.25"
1.1113 deg

The za of the dome center of mass is downhill from the dome centerline:
.793 deg

dome Optic axis za is above the dome center of mass za by
1.904 deg

Dome balances chCounterWeight. (use 1.904 to go optic axis to center of mass) (pre maria, zach=0deg) (more info)

za dome  (optic axis)
za dome (CenterOfMass)
computed using torques


Total platform weight (does this include tiedown pretension?) 1760 kips
Gregorian weight (excluding trolleys) from maldo 01aug01. this is from felipe lifting the dome. 
Trolleys weigh 18kips??? (more info)
152 kips
Ch1 weight (guess)
22sep17 line feed falls. pieces on ground weighed 3244lbs.
35 kips
Ch 1 counterweight (approx) (guess was 44)
26oct17 counted bars. got 47kips (assuming 190 lbs/large bar)
27oct17 added 1.4 kips to compensate for missing line feed
maximum allowable 54kips (does this include the frame?)
48.4 kips

Distance to ch1 counter weight (approx) 145 feet
Lead at apex of triangle (30jan02) 5365 lbs T12
6913 lbs T4
1010 lbs T8

line feed weight (from merle lalonde memo)
about 3000 lbs


Radius of feed (435 feet) 1in=39.5 asecs
Radius of rolling surface (420.75 feet) 1in=40.8 asecs
1 deg za motion at feed 1 deg=7.59 ft
1 deg za motion at rolling surface 1 deg=7.34 ft
slew speed za .04 deg/sec
slew speed azimuth (at the encoder) .4 deg/sec
az slew speed on the sky vs za
za    :  2    ,      4,       6,       8     10,    12,    14,   16, 18, 20
slew: .014, .028, .042, .056, .069, .083, .097, .11,.12,.14   deg/dsec
za<6 gr faster
za>6 az faster

azEncoder. 4096 counts/turn, 64 teeth, 2.5 inches diameter

Platform corner motion when ch moves in za
.0756 Inches

TURRET/horn (also see motions and angles)

radius horn phase center: 70.48"+18.75"*sin(8.11)= 73.125 inches
scribe mark on rotary floor at radius:
70.611 inches

great circle sky motion for 1 degree turret motion
Same as moving the azimuth by -45 asecs in az..
-45 asecs
Inches motion at the horn for 1 turret degrees 1.276 inches
great circle motion on sky for 1 inch horn motion  uphill..
same as moving the dome uphill by 35.26"
Note: the odd number of mirrors moves you in the opposite direction.. but this is on the sky.
az, za motions use only 2 reflectors so they are the same direction as the horn motion.
-35.26 asecs

Increasing turret encoder value will move a horn at focus toward the stairwell (+y domeCenline)  
turret weighed 14jan04 (with floor, no 6oto8 rcvr)  9200 lbs
9450 with cbh

focal point to edge of tertiary
60 deg


tiedown cable: wire rope, diameter
1.5 inches

main cables (101)
18.9 lb/ft
page 2-1 drawing &mike davis' note
backstay cables 102-104
3 1/4",
22.18 lb/ft

aux mains 301
3 1/4",22.18?
not sure of the w/ft
aux backstays 302-304
3 5/8",
27.60 lb/ft


Targets on primary at ne corner of ajusting stud.


  • aux main connection points:Let l be the line from triangle center to vertex:124.71feet. The dist perpendicular to l to the aux main connection point: 30ft:joe vellozi memo 15feb97. using sin(30)=30/auxdist gives auxdist from vertex of 60' along the triangle beam from the vertex.
  • old cable car limits (before upgrade): wrap1:355-326.5, wrap2:(147.5-175.5)
  • Panel points (from jnmt.. note .5 is panel point 1-0). The za position is that of the panel point. The 3rd column is the za of the dome when the dome straddle it (this is the 1.1113 offset of optic axis from dome center).
  • panel pnt
    zaWhen center of gr straddles it
    panel point
    za when center of Gr straddles it
    0. 21.117760 22.2291 4.5 10.27130  11.3826
    0.5 20.2512 21.3625 5.0 8.78690  9.8982
    1.0 19.3303 20.4416 5.5 7.31360 8.4249
    1.5 18.2515 19.3628 6.0 5.84520 6.9565
    2.0 17.1793 18.2906 6.5 4.38050 5.4918
    2.5 15.8654 16.9767 7.0 2.91880 4.0301
    3.0 14.5600 15.6713 7.5 1.45890 2.5702
    3.5 13.1574 14.2687 8.0  0. 1.1113
    4.0 11.7628 12.8741


  • platform vertical motion (original design specs from joe vellozi): 24 kips/inch (tiedowns not connected),8kips/inch tiedowns connected.
  • Measured platform motion from pulling on tiedowns:
  • pulling vertically all td 1.74 tdIn/pltfmIn (before 28apr00)
    1.66 tdIn/pltfmIn (28apr00)
    rocking platform
    (avg hght stays fixed)
    1.25 tdIn/pltfmIn(before 28apr00)
    1.31 tdIn/pltfmIn(28apr00)
  • 1 deg F temp change moves platform .205 inches. changes tension by 4.8 kips.

  • Frequencies of platform:

        To compute the vertical freq of platform:
    f=-kx, solve:ma=-kx-->-w^2cos(wt)+kx=0 with w=sqrt(k/m).
    Using m=1760 kips/32.2 and k=24kips/inch gives .365 hz (m might be wrong)
    VerFreqCmp: .365 hz
    VerFreqMeas: 6dec98 during hurricane georges 
    using the load cell tensions
    .35 hz
    Rocking Frq along az arm(dome up,down):during georges
    pitch tilt sensor (az arm at stow position) (more info)
    .633 hz
    Rocking Frq along az arm (dom up,down): during georges
    tiedown load cells (after undoing sampling alias)
    .65 hz
    rocking freq along az arm during hurricane maria
    tilt pitch sensor (more info)
    .641 hz