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May 20 2104 

setting up sky tracking turntable at CTIO with Newport rotation stage. 

Rotation stage is Newport RVS80PP. 1:180 worm gear so one rev of shaft is 2 degrees of turntable motion.

micro stepper drive determines how many pulses needed to turn shaft by one rotation. For N steps per shaft rotation, we get 2 degrees/N per step. 

Sky rotates at 15 degrees per hour. So we need to rotate shaft at 15/2 = 7.5 times per hour= 0.002083333 Hz=f_shaft

So if controller is set to send out N micro steps per revolution, we need a drive frequency given by 


where f_shaft is number given above. So f_drive=N*f_shaft. So if N=1000, f_drive=2.08333 Hz. That gives us steps that are 2/1000 degrees each=7.2 arc sec.

Pixels are 6.5 microns in size, focal length is around 70 mm so we have theta=6.5/70E3 radians per pixel so 19 arc sec per pixel.  

Microstepping controller manual: manual, PDF file

Rotation stage manual: Newport_stage_manual.pdf

So to drive the rotator at sidereal rate would require about 106 Hz drive frequency, as a TTL square wave.

More precisely, at dec of -6 deg the sky moves at 15cos(dec) arcsec/sec = 14.92 arcsec/sec. So sidereal rate at geo would be 14.92/0.1406 = 106.10 Hz. 

Twice sidereal is 212.2 Hz. FOV is 14.8 degrees. It takes 24 hours/360 deg * 14.8 deg~ 1 hour to move by one FOV. 

DB-15 connector on turntable is male pins. 

1: phase 1+

9: phase 1-

2: phase 2+

10: phase 2-

stepper wants rms of 0.71 A so full amplitude of drive current is 1A, into 1.7 Ohms. 

Microstepper drive unit wants switches 1,2 and 3 all on to get this current limit. 

24 Volt supply should be OK. Stripe is (+) on AC adapter. 

Wired up DC adapter and function generator. Worked best with microstepper controller switch 1 set to increase motor current one notch above the minimum. Seems to do a fine job of driving the turntable. 

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