Problem(s) Encountered:

Beginning of the night had problems pointing and accurately finding targets. In order to determine position, pointed to a bright star and uploaded the image to nova.astrometry.net to determine the center of the field coordinates. We then reset the telescope coordinates to reflect these coordinates.

The telescope then lost pointing within an hour and this procedure had to be repeated once more. After this point, the telescope pointed without incident for the remaining 8 hours of the night.

At the end of the night when the telescope was pointed to the zenith the tip tilt sensors read: E/W -003 N/S -014, although pointing previous to this had left targets centered in the field of view.

Solutions:

The pointing issue may not be fully unexpected as I re-zeroed coordinates after the work on the failed coupler in the dec drive system.

The E-W oscillation is likely the same as has been seen on occasion last month.  It’s worth noting that moving to the west appeared to correct this issue so a potential workaround may be to move east of an offending target, then return, approaching from the east, to see if that corrects the issue.  I am also going to slightly adjust RA preload this afternoon (reduce gear lash) to see if that changes anything.

For more on the E-W oscillation, see below:

RE: Oscillations:

Treffers recalled this issue from the early days of the new TCS.  He remedied the situation by implementing a “notch filter” in the PLC.  He went into the code this morning and verified that those notch filter parameters are still in place (they are).  He commented that this problem is not easy to diagnose or resolve as it is dependent on telescope position, balance and preload.  He and I will run some further tests on Monday to see if we can isolate any potential trouble spots.

In the meantime, it might be worth pondering an upgrade of the HA motor to an Omron, equivalent to the one we now use for dec motion.  It’s a much more robust system that plays nicely with the existing PLC.  Treffers has one “on shelf” and since we already ran the 220V for the other Omron, swapping over would be simplified compared to when we did the declination system.