Astronomy/Sidereal time questions

[Varun]

Hello everyone.

I'm finishing up my diploma in Computer Engineering Technology, and it is time to start thinking of final projects. Basically we have to build something that incorporates a microcontroller and we can do pretty much anything we want. I have decided to build an equatorial telescope mount for my reflector telescope, and have it do star tracking as well as a "go to" feature from a database of likely just the Messier objects.

I have a few questions that I really need to find some clear answers on before I can decide on what type of stepper motors etc that I will need to buy.

Should I do a PWM motor for a constant speed for tracking or would a stepper motor work? How many degrees per second (or fractions of degrees) does the mount have to move to track stars? This is likely the most important question so I can get to work on finding a drive system for my mount.

Also, can anyone point me to some good websites explaining sidreal time? Google has not turned up anything that does a really good job of explaining this to me. I was thinking of just having a real time clock chip on my PCB that I could set to my local sidreal time and just have a simple way to program it if I needed to change sites. I was thinking of just having one of the big dipper stars as HOME and I could set the scope to that star and just press a button to set up my sidreal time. Would this work?

Any input is appreciated!

 

[Varun]

bump

 

[Calin]

To track stars, your equatorial telescope would need to do one full turn every 24 hours. I think you can use a stepper motor but it should take very small steps (a pixel wide steps if you use a digital camera). Use a very precise gear system (and with great amplification).
An equatorial mount will need just one rotation to track stars, if your axis of rotation is aimed at the Polar Star (or Southern Cross, depending of the Earth hemisphere you are in). If you want to track a star for prolonged periods of time, you will need another motor to rotate the axis of the telescope (rotate the telescope around its own axis). The amount of rotation needed is maximal (full turn per 24 hours) when looking at the North Star, and minimal (0) when looking at the equator.

Hope this helps

 

[Calin]

And it's sideral time

 

[Armitage]

Originally posted by: Calin
And it's sideral time

Actually, it's sidereal

Back to the OP...
I would suggest a stepper moter/worm drive combination for R.A., and a lead screw assembly for Dec. You can find various components on eBay.

That said, building a mount of any quality will be a big undertaking and involve more machining & mechanical work then computer engineering. You might consider picking up a cheap Meade or Celestron GoTo scope that can interface directly to your PC, then write some custom software to make it do cool stuff. One cool project would be to hook up a CCD - some amateurs are using webcams - pm me for links. Then using the image on the webcam, develop an auto-alignment function, or satellite tracker.

 

[Varun]

I have thought seriously about purchasing the mount and just doing the interface with my own PCB and circuits. I do know some people with a lot of knowledge in machining though, and was considering building my own mount. The problem with buying a GoTo scope is that it is quite expensive to purchase (remember I'm a student) and I have had no luck finding a seperate mount with motors built in - though I am checking ebay from time to time.

Thanks for the tips guys

 

[Varun]

I should also mention that I do have an equatorial mount already, and I could just add a motor drive to it.

 

[Armitage]

You might check out the Meade Factory Outlet: http://stores.ebay.com/Meade-Factory-Outlet_W0QQsspagenameZL2QQtZkm
GoTo scopes for around $130 - $150
Don't know if that's in your budget or not, but the parts for a mount will cost you a few bucks as well.
Do you have a telescope already?

 

[Varun]

Yes I have an equatorial reflector already. The mount is not motor driven but I am pretty sure I can add drives if I can't find a suitable mount. Thanks for the link I'll check it out right away.