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Anyone ready to join the Heavy West Club?

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#1 sdh

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Posted 10 April 2009 - 11:46 PM

I have always read that mounts will autoguide better by setting them heavier on the East side for astophotography. This last week, I did a night of testing and found that the Celestron ASGT mount I have performs significantly better when set heavier on the West side rather than heavier on the East side. When set Heavy East, or balanced, there is significant bumps and jumps in its periodic error, and guiding is poor. When set Heavy West, the jumps and bumps go away and guiding is significantly improved. Heavy West was achieved by moving the weights 1 inch from the balanced position. I am attaching plots which show these results (gathered in PhD and plotted in Matlab). I am wondering if anyone else has had similar results. If not, and if you are interested in experimenting, you might want to try setting your mount Heavy West and see what happens.

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#2 famax

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Posted 11 April 2009 - 01:08 PM

Nice find , but do you know what happen passing the meridian ?

#3 sdh

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Posted 11 April 2009 - 10:33 PM

Well, that is a good question. A couple things, this mount does not track very far past the meridian. Plus, the scope runs into the mount near the meridian (8" Newtonian on an equatorial mount).

I did do tests on the West side of the merdian and got the same poor results using the Heavy East method. But, yes by the time I discovered this improvement, it was about 4:00AM, so only verified the improved performance using the Heavy West setting on Vega in the East. But, I did go back and forth (Heavy East vs. Heavy West) several times to verify that I was not imagining the improvement.

#4 Joe F Gafford

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Posted 11 April 2009 - 10:38 PM

Doug, I do both on my GEM to my 10". Just as long as it is slightly out of balance I find that the tracking is better. I added a nylon washer to the bolt that goes to the Dec tangent arm for that clutching and have very little slop in the RA gear, that going over the meridian, I have very little back slop (I can go 85 minutes over before hitting the pier).
Joe.

#5 sdh

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Posted 11 April 2009 - 11:16 PM

Joe,
Thanks for the reply. So, are you saying that going heavy East or heavy West gives you about the same results, just as long as there is some imbalance? I am starting to think that it could be that my gears are smoother on one side than the other. I get consistent bumpy guiding heavy East even though it makes sense to me that it should work. Thanks again.

#6 Joe F Gafford

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Posted 12 April 2009 - 04:03 AM

Doug,
It is probably is the nature of the gear faces in your system. If is a worm, they are all different, even made with the same machinery! Also the friction effects other than the clutches that may influence how your drive reacts during changes in the guiding sequences.
I recently figured out the high PE problem with my GEM was the manufacture of the new worm and the worm gear was off by 1.5 degrees off of parallel! I then tilted the worm block mounting to compensate and got the PEC range down to less than 40% of what it was and the PEC profile was more sinusoidal than ramp. It was not getting enough gear face in the meshing! This applies to the Dec as well. The DEC has a tendency to oscillate more during autoguiding than the RA in most instances, even with good polar alignment. There is an "aggressiveness" control in most autoguiding programs for this. That's why I added a clutching washer to the Dec tangent arm slot.
The 18" is not a GEM and has no PE problems in RA due to it is a direct drive friction system. But it uses a same kind of tangent arm for the Dec and uses stepper motors for the Dec as well as the RA. It has a different construction on the Dec tangent arm than the 10" does and has not the clutching the 10" has. That stepper motor is a jackhammer compared to the DC Dec motor on the 10".
Joe.

#7 blueman

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Posted 12 April 2009 - 11:55 AM

Hi,
By accident I had my G-11 set heavy West one night. I did not catch this until I had taken a lot of exposures. The guiding was smooth with the heavy West condition and the exposures were very good.
I will not say that it was better, but it did seem to work just fine this way, even past Meridian.
I still use heavy East however, as this is the accepted method. Having the mount work against gravity is thought to be better than having gravity pulling the gear into the teeth. But, I guess if one side of the teeth is smoother than the other, then that side would give the best PE?
Blueman






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