Tics determination #tickmanagement


Matthew Nelson
 

I have a telescope where I haven't been able to get a precise tic determination on 
its alt axis.  The scope only has an 8192 tic mount encoder, so using that doesn't
yield a very accurate determination on the motor tics, and there isn't any way to
physically measure angles.  

Is there any way to pull gain errors on tics/rev from a pointxp model?  I don't see
any terms that are appropriate, and the sky is after all the best reference.

Thanks,
  Matt


Dan Gray
 

Hi Matt, yes there is.
Once you make your model, call up the PointXP screen and click on the View/Advanced Features, click on "start optimization".
This uses successive approximation (at least I think so). When finished, you'll get a number in the Theta box which you can multiply your current ticks per revolution by.

But I fear that your low resolution scope encoders will interfere unless you're in the ignore mode when you make the model.
Do you have some slippage on the altitude axis?  If so, balance very, very carefully, this will help slippage.  Make sure the acceleration is low, so there's no added slippage because of the acceleration of mass.
This is Bruce Howard's model with just the cone and hub terms turned on (it's a really good mount with renishaw encoders).  Notice the 17 arc seconds.  Notice most is in the altitude.
image.png


Here's after the optimization of the ticks per revolution, 7.1 arc seconds :
image.png



Notice the Phi (azimuth or right ascension) is nearly 1.0, so no help there.
Notice the Theta (altitude or declination) is 1.000408.  In this case, lets say your current motor ticks per rev was 13,000,000.
You would try 13,005,304 ticks per rev.

Another note, if you have slippage, or other non-repeatable error, and this might not help that much.

Hope this helps.
Dan



On Thu, Nov 3, 2022 at 6:36 AM Matthew Nelson <mjcanelson@...> wrote:
I have a telescope where I haven't been able to get a precise tic determination on 
its alt axis.  The scope only has an 8192 tic mount encoder, so using that doesn't
yield a very accurate determination on the motor tics, and there isn't any way to
physically measure angles.  

Is there any way to pull gain errors on tics/rev from a pointxp model?  I don't see
any terms that are appropriate, and the sky is after all the best reference.

Thanks,
  Matt