Ronald Schreiber
Ronald Schreiber created a new topic ' Guiding Alt-Az mount with indi_synscan_telescope does not work' in the forum. 12 months ago

I observe a very strange behavior when trying guiding (internal guider and PHD2) my SkyWatcher “Star Discovery AZ SynScan WiFi GoTo” mount. After wasting many nights I did some experiments at daytime with the CCD simulator. My setup for this test was:

  • Mount: “Star Discovery AZ SynScan WiFi GoTo” (Alt-Az mount with a WiFi dongle)
  • SynScan Pro app (latest version) on Android phone, in same WiFi network as the WiFi dongle of the mount
  • Linux laptop with KStars/EKOS and INDI (latest versions), in same WiFi network as SynScan Pro app and mount
  • INDI server runs on laptop, drivers are: indi_simulator_ccd (to simulate guiding camera) and indi_synscan_telescope (to control mount)
SynScan app and mount work fine together. I do alignment with the SynScan app before connecting the INDI mount driver. When connected to EKOS I can control the mount without problems:
  • “Find telescope” in KStars sky map shows same position as the SynScan Pro app
  • “GOTO” in KStars sky map moves mount as expected to new positions (position in SynScan app also gets updated)
  • Tracking works as expected
  • When taking photos with the CCD simulator I get pictures of a simulated sky
  • When tracking is enabled the simulated stars hold position on the photos
  • When tracking is disabled the simulated stars move on the photos (as expected)
  • When moving mount with SynScan app in North, South, East and West the simulated stars move as expected
  • When moving mount with the “Motion Control” tab of the indi_synscan_telescope driver the simulated stars move as expected
Everything fine so far. But when I try guiding the trouble begins. I slewed the mount to a good guiding star in the East at about 30° altitude. During calibration the guider makes movements in RA and DEC. The calibration diagram (and the photos of the simulated stars) show:
  • RA forward pulses move star.
  • RA reverse pulses move star in same direction as forward pulses. Step size is larger and growing.
  • RA and DEC movements are not orthogonal.
I tried guiding with PHD2 and the internal guider, both show the same strange behavior. The symptoms match to the ones I saw at night with a real camera and real sky, so I think it is not caused by the CCD simulator.

The driver has a tab which allows to send guiding pulses in North, South, East and West directions. I tried a number of such guiding pulses in each direction and watched the effect on the photos:
  • Pulsing to North moves the simulated guiding star in one direction
  • Pulsing to South moves the star in the same direction like a pulse to North
  • Pulsing to East moves the star to a direction which is not orthogonal to the North/South movements
  • Pulsing to West moves in opposite direction as the East movement
It is clear that guiding can not work when North/South movements are not reversible. When this does not work with simulated sky it will also not work with real sky. I am sure this is an issue in the indi_synscan_telescope driver or in the SynScan app.

I also tried the indi_synscanlegacy_telescope driver. This driver has no tab to send guiding pulses and is not supported in PHD2. But the internal guider seems to support this driver (does it use the normal motion control for guiding?). With the legacy driver the internal guider works nicely: it has a perfect orthogonal calibration diagram and makes a stable guiding. Of course, on a real sky I will see the imperfections of my mount.

The SynScan App user’s manual (inter-static.skywatcher.com/downloads/sy...nual_en_20201008.pdf) states that a 3rd party software (INDI driver) has to connect to TCP port 11882. But the command set description (inter-static.skywatcher.com/downloads/sy...and_set_20210824.pdf) specifies port 11881. Both INDI driver work on port 11882 only. The command set description is about a complete different protocol than the one used by the INDI driver. I could not find a description of the protocol used by the INDI driver. Can it be that Sky-Watcher uses now a new protocol and does not bug fix the old one anymore?

Is there an INDI driver which uses the new communication protocol?
Is there something I need to setup in the indi_synscan_telescope driver to make it work?

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