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Re: Optimising gear ratio : alt ratio correction calculation

 

Raphael,

The "stop" might be with only 0.1+ degrees left. It would then just go to the second move and you'd not notice the stop. That is extremely good for the purpose for which it was designed - visual astronomy. Keep in mind - on the vast majority of 'hand made' scopes, there's enough variability in the dimensions and mounting of the drive surfaces on either the ALT or the AZ (ground board or bearings) that it isn't going to be one value.?

If your alignment is accurate and especially if you are using TPAS to correct for mount errors then it should track extremely well since it is closed loop (based on the user centering the object at the start).

If you want to take the time since you are dialed in so well the only way to do so is indeed to do the drift test you did over a longer period of time. Alternatively you can do the drift method for shorter period but just tweak the ratio (on the axis you're testing for - do one at a time!) by a count of say 5. Then repeat the test and see what that gives you. You can then ratio the results on 2 tests to get it (better) corrected.?

The other thing is there could well be?issues like friction and slippage and other mechanical things that the system is not designed to account for. Even torque induced bending might well be enough to move the object.?

My suspicion is you might be asking too much from such a large scope.?

g.

?


------ Original Message ------
From "Raphael Guinamard via groups.io" <rguinamard@...>
Date 4/27/2025 11:33:22 AM
Subject Re: [ServoCAT] Optimising gear ratio : alt ratio correction calculation

Dear Gary,
I did it already one and corrected ratio. But there is still a remaining of correction of ratio needed.?
I mean yesterday night, the scope was pointing accurately because I had just calculated the IE of TPAS (with other persistant terms already computed from previous test)so I had a computed TPAS leading to RMS of 6'. OK
Then I centered a star and after 35 min it was 20' offcenter (0.33¡ã). Frankly this is OK for visual follow up but still not accurate enough to follow ISS that move 200 times quicker than sideral.
?
But I?can't I achieve anymore the "Simple Track Improvements Test" because :
In the "Simple Track Improvements Test" it is said :? ?
"Push the GOTO ¨C it will start to move ¨C now watch carefully the GUIDE value for this axis (left for AZ, right for
ALT). The scope will move a distance and then come to a stop. It will will then quickly pick up and start moving
again. You need to get the GUIDE value when it first stops"
The problem is since I'm already close to perfect ratio I can't notice any stop even if I put 170¡ã instead of 100¡ã in the procedure.
Maybe this is because my scope is massive, so I need to put? a 5 seconds deceleration => could this make it more difficult to notice the "stop" if it occurs during the deceleration ? I don't know... but I can't notice any stop.
?
So this is why I wanted then to use? the "track improvment" method described in the Sercocat quick V3 file since this one is unsensitive to deceleration.
But then I have the calculation issue I indicated in my first message
I hope this clarify my original question
Regards
Rapha?l
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