[Kstars-devel] Ujari Observatory Control System

[Jasem Mutlaq]

Hello all,

I've been working on Kuwait Science Club 0.5m telescope for the past few 
months and what an interesting project it is! It is one of these projects 
where you have to dwell deep in many disciplines to get things right.

The observatory houses a Swiss-made equatorial fork telescope with two OTA 
each 0.5m in diameter. It was used to do pretty interesting research up until 
a few years ago when new cities were build close by and now light pollution 
degraded its abilities drastically.

Since its commision, it's always been in manual control where the observer 
uses a keypad to move around in the sky. This is obviously a tedious process 
but for the few bright objects in the sky. Furthermore, the Swiss company who 
delivered the system with a computer never really got it to work, or so I'm 
told since the computer was thrown away long time ago.

What was particularly irritating is the complete lack of documentation. No one 
knew anything about the telescope save for the diameter of the mirrors and 
its commission date, it seems that everything else got lost somehow. So this 
is when I had to 'reverse engineer' the system starting from the keypad up to 
the servo motors..etc. I had to install new 12 bit absolute encoders for the 
RA & DEC axis, and design a PCB to act as a 'digital' keypad using 
optocouplers primary.

Then by using NI 6905 Digital I/O card, which is well supported under Linux, I 
controlled the new board, and received the encoder data. Then all I had to do 
was to write the INDI driver to achieve a closed-loop control.

Suffice to say, the hardware took the most time, mostly because I had no docs 
and I had to find how the electronics work out on a deep level. It was all 
new to me. Also, since this is a really heavy telescope (I was told 9 tons, 
but I really doubt it), safety is quite important.

There are minimum allowable altitude safety guards in the driver, auto & 
emergency park in case something goes wrong, and a watchdog that shuts the 
telescope even if the whole operating system crashes. But would you bet your 
life on software alone?

There are also two hardware limits switches for each axis that shuts the 
telescope down if it goes too far, and if all that fails, I installed an 
emergency stop button connected directly to mains. If THAT fails, then you 
probably deserve to die anyway.

The last tricky part of the whole deal was pointing performance. Since we're 
dealing with a really old mechanical system, the pointing accuracy is limited 
by numerous factors including index and collimation errors, fork flexture, 
and a lot more. We had to use TPoint to build a pointing model for the 
telescope to bring the pointing accuracy down. This is still in progress, but 
the overall control system is done.

I posted a video in youtube showing the telescope & KStars. I used my digital 
camera so I apologize if it's not clear enough.

http://www.youtube.com/watch?v=YiJqIAkyCz0

Regards,
Jasem