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> G-11 Gurley Mounting

SitechExe has the capability to use a high resolution encoder in a way that is unique to the Sitech Servo control system.   This approach is called "Tick Management", and uses the servo motor encoder in conjunction with the mount encoder to increase the effective resolution of the mount encoder.  Details of this capability are in the OPERATIONS manual for the Sitech system.
"Gurley" is the brand name for the high resolution encoder that is used.  It provides 320,000 ticks per revolution (read in quadrature).
The encoder mounting I used was to duplicate the polar alignment scope "body" with a machined plug, and use the same threaded ring as for the polar alignment scope to hold it in place.  The plug has a precision machined hole for the gurley's shaft, and an adjustable bracket that uses the stock Losmandy encoder attachment holes supports the body of the Gurley encoder.
The picture below shows a closeup of the mounting for the encoder.   The silver plug inserted into the RA axis has a brass screw with a knurled knob to secure the encoder shaft into the plug.    The bracket uses thumbscrews that are in oversize holes with washers to allow adjusting the encoder body position along the RA axis, and radially since you do not want to have any loads on the Gurley encoder input shaft.   Note the thinner section of the bracket to allow small flexing if the system needs it, but does not allow any rotation of the encoder body. 
The next picture (below) shows details of the plug for mounting the encoder:


The real question is whether this Tick Management capability works.  So, I included a plot showing the measured performance without the Tick Management routine turned on (the blue curve), and the performance with Tick Management active (the red line).  It works quite well!!!!!  Without Tick Management on, the Periodic error of the stock Losmandy "precision worm" is measured as 17.94 arcseconds, peak to peak.  With Tick Management turned on, it is reduced to 1.41 arcseonds, peak to peak (which was close to the seeing on the evening the measurements were taken):