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[on:]

I am interested in setting up a system to control the dome over a telescope.  The dome, about 12 feet diameter at the base, covers a Meade 16" telescope.  The telescope can be automated with a laptop computer to point to locations in the sky, but then the dome needs to be rotated manually (left/right switch - turns on electric motor) to position the opening slot for a clear view.

My 1st pass at designing this goes as follows:

* Light sensor attached to the telescope detects the position of the dome by sensing:
    * no return light when shining into space through the slot
    * colors to indicate direction
* The sensor sends a signal to xBee transmitter
* xBee receiver gets the analog signal
* Arduino sets relays corresponding to left/right switch

The advise I'm looking for is about alternative sensors to detect the position of the dome.   When the system starts, we need a means of indicating the shortest way to turn the dome to position the opening in the direction of the telescope.

I was thinking that perhaps there might be large bar codes or color codes to indicate that the dome should turn left or right.  The distance from the telescope to the inner dome wall is about 6-8 feet.

Remember that low light is preferred for viewing, so a small laser would be best as the light source.

Please see the image below to see how it might hook up.
Image will be in second post, I guess.

Thanks for any advice,
Chris.

[Reply #1 on:]

[Reply #2 on:]

Interesting project. You might want to consider ultra-sonic transeiver as your sensor for doom slit opening detection. Here is some data on one example:

http://www.maxbotix.com/uploads/MaxBotixNewProducts.pdf

offer at:

http://www.sparkfun.com/commerce/product_info.php?products_id=8501

Good luck
Lefty

[Reply #3 on:]

How about another tack.

Rather than detect the dome with a sensor on the scope. Why not take the azamouth of the scope from your telescope positioning system or digital setting circles and compare that to the position of the dome slit determined by measuring the number of turns from the dome turning motor using an opto slit detector.

In that way you know where both things are and it is a simple matter to let one follow the other. Then there are no sensors to go wrong.

[Reply #4 on:]

RetroLefty,
I was thinking about an ultrasonic sensor but I also was wondering how it might detect the shortest route to the opening.  I think it could be used to stop the motor when the dome opening was detected, but how might an ultrasonic detect where the opening is when the dome and telescope are off axis.  Multiple sensors pointing in different directions?

Grumpy_Mike,
I get the idea of detecting the scope's azimuth settings, but I don't understand your concept of "measuring the number of turns from the dome turning motor using an opto slit detector".  I'm including another diagram to show (kind of) how the motor is positioned to turn the dome.  The gears of the motor turn in a continuous track (something like sprockets on movie film) to rotate the dome.

I've thought of creating a continuous tape with positioning codes on the dome but a simple turn left/turn right seems so simple.  IOW, the dome should simply move to where ever the scope is pointing.

Another thought is to always start the session with the dome opening in the correct position, then detect a left or right motion of the scope and go from there.  For future "remoting" of all the astronomy functions, I'd like the dome to first find the proper position.

Thanks for your advice,
Chris.

[Reply #5 on:]

but I don't understand your concept of "measuring the number of turns from the dome turning motor using an opto slit detector".

If you look at the dome turning motor as it rotates it moves the dome a bit. It might take say 20 rotations of the motor to move the dome one degree. So you count the number of turns the motor is making, you can do this in many ways. One way is to use a white spot of paint on the motor shaft and a reflective optical switch. Another way is to put a small stick on the shaft and have it break a beam every revolution, say in an optical slot.
In any event if your arduino knows how many turns the motor has to make it just powers on the motor until it counts it has made them.