Adding plate-solving into the ScopeDog drive opens new opportunities.
One that is proving very popular is a ‘Lite’ mode. Now if ScopeDog on powering fails to find a Nexus DSC connected, it will reboot into Lite mode, (direct boot to Lite is also possible). Lite mode employs three operating principles …
- Stepper motor step counts are used to build a virtual encoder model for both axes.
- The virtual encoder is syncronised to real sky by the plate-solver.
- ScopeDog generates a wifi feed for Apps like SkySafari, providing a real time display of scope position, plus control via on screen move, goto and align functions.
The plate-solve syncronisation can be manually triggered from the ScopeDog sandbox, or SkySafari. It s also automatically triggered as part of a goto operation.
Physically the hardwire is the same as for standard ScopeDog, albeit without a Nexus DSC, but with a usb GPS dongle plugged into the third ScopeDog control box usb port.
At this stage, the virtual encoder model is a simple one purely based on motor steps and takes no account of any mount tilt. Hence in general the virtual encoder will not be very accurate as you move the scope away from a syncronisation point. However a ‘sync’ will quickly remove any error, and indeed produce a position fix more accurate than any conventional axis mounted encoder system.
I am starting to code a ‘learning’ feature by which ScopeDog Lite uses the plate-solves at the start of an observing session to add mount tilt and possibly cone error to the virtual encoder model. This is stretching my maths skills and may take a while! If you are interested in the maths look here.