Platform tilt model for 2017

• az,za points used for the model (.ps) (.pdf)
• these are the az,za locations of the data.
• The platform translations vs azimuth (.ps) (.pdf)
• All of the data is plotted vs azimuth.
  
• black points are translations in x direction (+ is west)
• red points are translations in y direction (+ is north)
• The platform will translate horizontally when the dome moves in za.
• when pointing at a tower and the corner goes down, the tension in that main cable increases
• This increases the horizontal force toward the tower.
  
• platform rotations vs azimuth (.ps) (.pdf)
• black points are rotations about X (west)
• red points are rotations about Y (north)
• platform translations by az and za with fits for each za range  (.pdf)
• data is separated into 1 degree strips 1 to 20 deg
• Each frame is  x,y translations vs az for the data in the 1 degree strip
• Black is  x translations (west)
• red is y translations (east)
• the green lines are the locations of the towers.
  
• The blue lines are the fits to the data:
• y=offset  + amp1*sin(az-ph1) + amp2*sin(2az-ph2)
  
• Page 1 za 1 to 5 degrees
• page 2: za 5 to 9 degrees
• Page 3: za 9 to 13 degrees
• Page 4: za 13 to 17 degrees
• Page 5: az 17 to 20 degrees
• for most za's the 1az fits do a pretty good job of fitting the data.
• platform rotations by az and za with fits for each za range (.pdf)
• each frame is a 1 degree za range. 1 to 20 degrees
• black is rotations about x (west)
• red is rotations about y (north)
• The green lines are the locations of the towers
• the blue lines are  fits to the data.
• y=offset  + amp1*sin(az-ph1) + amp2*sin(2az-ph2)
• The azimuth arm balances around za=8 degrees, so the amplitude of the 1az term is small.
  

• stability of the laser ranger data (.ps) (.pdf)
• the top frame plots the x,y translations for za=8-9 degrees vs day of year
• the bottom frame plots the x,y rotations for za=8-9 deg vs day of year
• at 8 degrees, the platform is close to balanced.
• there is a small drift from dayno 0 to 100 in the translations, and a little in the rotations.
• i wonder if this could be temperature related (colder in the winter).
  
• But there are no rapid jumps so the distomats were probably working ok..
  
• plotting the fit parameters vs az for 1 deg za steps (.ps) (.pdf)
• The fit was: tilt RotAng= offset + amp1*sin(az - phase1) + amp2*sin(2az -phase2)
  
• black: rotations about x (west)
  
• red: rotations about y (north)
• the top frame is the offset
• it does not change with za.
• This could be a residual tilt, or a calibration problem with the distomat measurements.
  
• 2nd frame: the 1az amplitude.
• The rotations about x(west) and y(north) have the same za dependence.
• The max amplitude goes from -.15 to +.2 deg (we get the negative from the phase flipping).
  
• it goes to 0 around za=8 where the azimuth arm is balanced.
• This is  the platform tilt, the elevation rail shimming should compensate for this.
  
• 3rd frame: the 1az phase.
• the phase is the azimuth of the rotation axis (where the amplitude should go to zero since there is no torque about the rotation axis). At 8 deg za, there is a phase jump by 180  because the tilt is going negative to positive (and the amplitude is always positive.
• 4th frame: the 2az amplitude
• this is constant vs za.
• it is the same for x and y.
• 5th frame: the 2az phase
• it is constant with za.
  

2017 Summary

• This model can now be used to compute the pointing error when we lose tension in a tiedown (if you have a distomat reading).
• It is valid for pre maria. I need to check post maria to see if things changed.
• I still need to write the routines that input the model and compute the pointing error.