SW SA GTI good news story.

[Walter ZAMBOTTI]

I have had the GTI since pre order days (So a while).

For over a year I have been trying to use PHD2 to improve the guiding without much success.

I went to great lengths to understand how PHD2 and the GTI interact which each other including modifying PHD2 code to add specific functionality for the GTI.

While none of these changes significantly improved the guiding they did educate me as what was going on.

In my instance they revealed the primary guiding issue with the GTI is the DEC axis which appears to suffer from a combination of stiction and slack at the same time.

The slack I addressed mechanically by adjusting the DEC worm gear spacing and the stiction I addressed via higher aggression with the INDI guide speed rate and the PHD2 DEC algorithm aggressiveness.

I found and suspect but cannot confirm that over tightening the RA slack adjustment caused problems on the DEC axis. I now have a small amount of slack on the RA.

I started with a train wreck with an average RMS of aprox 2.67 an have finally ended up with an average RMS of < 1.0 RMS. Quite often the RMS will be less than 0.8 RMS for several minutes.  Spike are now infrequent and when they occur less severe.

My guiding assistant setup now produces excellent results with an orthog error of only 0.5.

My images have gone from streaks to round but fuzzy stars at best to pinpoint sharp and I am now throwing away very few (2 minute) subs.  (I'm operating at 900mm focal length)

The mount is still sensitive to wind gusts so I have had to mechanically shield the mount from wind.

Since I'm am using a client server setup I have learnt that network speed and through put is important and I am running high speed protocols with other minimal traffic.  I have not tested physical Ethernet cabling.

I also run the PHD2 guiding assistant on the actual target rather than another object near the equator.

Some setup info:

SW SA GTI

SW F8 114mm / 900mm FL newt with Canon DSLR

50mm/190mm FL guide scope with QHY5III715C guide camera

Total weight 5KG

Kstars/Ekos/Indi

Kstars / PHD2 Linux client Wifi 

Indi Linux Server Wifi

RA Guide rate 50% 

DEC Guide rate 100%

X guide algorithm = Predictive PEC, Control gain = 0.800
Prediction gain = 0.500
Minimum move = 0.250
Y guide algorithm = Hysteresis, Hysteresis = 0.330, Aggression = 1.500, Minimum move = 0.250
Backlash comp = disabled, pulse = 40 ms
Max RA duration = 2500, Max DEC duration = 2500, DEC guide mode = Auto