Jasem Mutlaq writes about his experiences
as the control mechanism for a telescope at an observatory in Kuwait:
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 and 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 and 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.
Here is a video showing the telescope and KStars. I used my digital camera so I apologize if it's not clear enough.