Platform motion as we pull on the tie downs
13 apr 2001
To check how the platform moves when we pull
equally on all 3 tiedowns, tests were done on 02apr01 and 13apr01.
The temperature was about 80 deg F and the positions were:
| date |
az, za position |
tiedown motion |
| 2apr01 |
az:271 za:19.69 |
19"-12"-19" |
| 13apr01 |
az:60 za:19 |
13"-17"-13" |
The platform position was recorded every 30 seconds with the distomats.
The figures
(.ps) (.pdf)
plot the relative change from the lowest most platform position versus
time.
-
The top plot shows the vertical motion for corner 12, 4, and 8.
-
02april a seven inch move in tiedowns caused the platform to move
by 4.1 inches. Corner 4 moved .2 inches more than corners 12 and 8 (5%).
The average motion was -1.70 tiedown inches per platform inch.
-
13april a four inch move in tiedowns caused the platform to move 2.2 inches
(-1.84 tiedown inches per platform inch). The data was noisier but corner
4 appeared to move more that the other two.
-
The center plot shows the rotation about the x,y,z axis (x-west,y-north,
z-down)
-
The bottom figure shows the relative x,y,z translation of the center of
the platform. With a large imbalance (dome at 19za) when you pull down
on the platform, the horizontal motion is in the direction of the imbalance.
The rotation angles are noisy. Part of this could be from the accuracy
of the distomats (about 1 mm or .04 inches) and possibly from oscillations
in the platform. A .1 inch difference would give a rotation of about 10
asecs.
If the vertical difference is caused by variations in spring constants
of the cable system then a model made at night (with higher tension in
the tiedowns) would have a systematic offset for daytime observing.
The test should probably be redone at night when the temperature is stable.
processing: x101/010402/lr02apr.pro,lr13apr.pro
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