Go-to facility with GPUSB?

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Ross Wilkinson
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Joined: Tue Dec 12, 2006 4:51 am
Location: Bolton, England

Go-to facility with GPUSB?

Post by Ross Wilkinson » Tue Dec 12, 2006 10:26 am

Last week I saw a demonstration by David Ratledge at the Bolton Astronomical Society of the GuideDog software operating on an old (DC motor-driven) EQ-5 type mount fitted with your GPUSB interface adaptor.
:idea: I was particularly interested in this, since I use an EQ-5 myself, but I've been wondering if the system could be extended to provide a primitive "go-to" capability to help locate faint objects? I currently use the manual "star-hopping" technique, where the the telescope is first pointed at a known nearby star, and then iteratively slewed toward the target, but I wonder if this process could be automated under computer control, where the "deltas" in RA and dec could be calculated, and then the telescope driven straight to the object? It would certainly help on occasions like last night, when my attempts to locate comet Garradd were hampered by intermittent cloud cover (I did find it in the end :-))
I already use the Cartes du Ciel program, which I believe includes an ASCOM control interface: could this be used in the manner suggested? If not, perhaps the additional capability could be added in a software plug-in? I think that many other EQ-5 owners may be interested in this possibility too. :?:

Bolton, England

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Post by dpanderson » Wed Dec 13, 2006 1:40 pm


A true GoTo mount has some form of positional feedback so that it knows where it is pointing, or at least exactly how far it moved. This is usually done with shaft encoders. It can also be done with just stepper motors as long as nothing happens that causes it to not step when the motor thought it had stepped.

With DC motors and no shaft encoders, there really is no way to know exactly how far the scope has moved, thus making your incremental goto idea hard to implement. Of course, you do have a rough idea of how far the scope will nudge for each second the motor is turned on, but this is only approximate, and the rate can change with temperature, battery voltage, age, etc. However, even an approximate move may be good enough to do what you want it to do.

In general, I try to focus Shoestring with hardware products and let the software guys come up with creative ways to use them. You might want to run your idea by the CdC developers.
Doug Anderson
Shoestring Astronomy

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