Welcome to Ga-Lun-La-Ti Observatory! I'm glad you found your way to my strange part of the universe. Click the links above or on the left to see more of the site.

Control System

The observatory will be controlled with a home made drive and control system.  My main goals are to control it remotely and, by necessity, cheaply.  I'm a software and systems engineer by profession so you might think it would be super high tech but I tend to take a decidedly cheap and good enough approach to my hobbies so expect to see motors from the junk yard and pieced together hardware driven from a PC.



I have done some work lately on my control system so I have a pretty good idea what I will be using.  The diagram to the right shows the component relationships.

Remote
I thought about building my own client and server to handle this but honestly I think that remote desktop that comes with advanced versions of Windows works just great.  I have used it extensively at work and I have done several Messier marathons this way with my scope and laptop out in the cold and my wife and I RDPed into it from the warmth and comfort of our living room.  Since the windows version I am currently running doesn;t have RDP and I am too cheap to buy it unless I really need it, I decided to try VNC.  Right now I am running TightVNC and it seems to be running just fine.  I'll know more once I get everything automated.

Scope Control Software
TheSky - I know there are others out there but I have used it for years and I like it.  It does pretty much everything I want and I already own it.

Control Bridge Software
I am writing a custom data bridge in Java to pull the scope position from TheSky and use that and encoder feedback on the dome position to drive DC motors to position the dome.  I have the control bridge almost finished already and have been running it slaved to TheSky for weeks and it hasn't glitched yet.  I put speech into it on a whim but I have decided it is a pretty good feature.  It tells you verbally when it is slewing the dome or when dome slewing is complete and anytime it moves the dome for any reason or if there is an error with any part of the system.  That means that you don't have to look to see if anything is wrong because it will tell you out loud in english.  The coolest part is when the scope is tracking an object, the bridge will say "Dome repositioned to 123 Degrees" or whatever degree it moved the dome to every so often so you know it is doing it's thing.  I thought it might be a pain to listen to but I have had it running for days while watching TV and it doesn't bother me at all.

It's still a little rough but to see a video of the bridge in operation click
HERE for WMV Version  (NOTE: This takes a few minutes to load so please be patient...)   

            The bridge has several functions:

                    A) Get the scope azimuth from TheSky
                    B) Read the dome encoder position to see where the dome is
                    C) Use A and B to drive DC motors to reposition the dome
                    D) Communicate with the encoder through a serial port
                    E) Communicate with the drive through the parallel port
                    F) Inform the user verbally of the dome position
                    G) Inform the user if anything errors

Motor Control
I decided to make the hardware more modular so I designed a passive backplane system with daughterboards.  While poking around digikey, jameco, EBay and other places looking for decent prices on relays, I came across a complete circuit board kit that came with the board and all components cheaper than I could buy just the relays.  My design would be much more flexible but this approach is much cheaper so I'm planning to us it.  

Dome Position Encoder
I am planning to use a simple 5V quad encoder talking to a parallax basic stamp that will be hooked to my PC and talkling to the control bridge software through a serial port.  It will be polled IO but that should be sufficient for this application.  The stamp will also monitor a home position prox sensor that will either be set at 360 degrees or 180 degrees that will act as a home position marker for the dome.  I also intend to use that position to improve the position scale factors automatically every time the dome transitions past it.  In other words, I expect that my dome position sensor will not be exactly accurate to start with so I intend to use the home prox to have the encoder teach itself what the correct scale factor is as it runs.

UPDATE: I have the stamp working fine but it looks like it may be too slow so I am writing the PIC assembler version and will be using a PIC microcontroller instead.  

Motors
After some research I have decide to use simple 12V DC car windshield wipers to drive the dome.  From what I can tell  by poking around forums, the dome takes about 15 foot pounds to drive.  Wiper motors typically give 12-15 foot pounds in high speed and up to 18 foot pounds in low speed mode.  I intend to use two motors set 120 degrees apart to hopefully eliminate most of the tangential drive warping issue and to allow me to run on a single motor if one motor smokes.  Obviously, these won't run forever but I can buy them for $15 each and I'd rather change a $15 motor every few months than spend hundreds to put one in that runs forever.  I have used wiper motors for light automation and animatronic work before and they always worked well.  Contrary to what most folks believe, wiper motors do not run back and forth.  They actually go round and round and mechanical linkages translate that into back and forth motion to clean your windows.  They usually run in high and low speeds and forward and backwards and are design to live in pretty nasty environments and run in all temps.

UPDATE:  I just got my 2 wiper motors in and they look nice.  They are smaller than I expected but they seem super strong.  No way to know if they are going to work but try it and I am getting very close to that.

Drive Gear and Track
I have looked at a bunch of alternatives but right now I am planning to buy track and two gears from the nice folks at Exploradome.   There are other options but so far I haven't found anything as good for much less cost. 

UPDATE: After a few crazy ideas I decided to buy double row 10B chain and gears.  The chain will cost about $60 and I got the gears off EBay for $8.  I will use one row of the chain to attach to the inside of the dome and the other row to drive the gear in.  I already have a 10 foot piece of chain and two gears so I should be hooking that up to test soon.  If it works well I will buy the remainder of the chain I need to complete the 360 degree drive.

More details to follow...