astrogene1000_stuff post=70123 wrote: Hi Mohamed,

True backlash in opposite direction can vary but more than likely comes from drawtube tilting than gear train backlash, which is more repeatable -if- the gears are fixed to the shaft and do not ride on the shaft they are mounted to. Coming from drawtube tilt also implies amount may change depending on how far the drawtube is extended.

Here is a video I did of a stepper motor head used, gears only in the head. Repeatability is good considering any slip that may have occurred of the dial indicator on the moment arm and the 5 pound weight hanging from the 2 inch moment arm :-)

Stepper motor head video from 2012
 

Hi Gene,

Thank you for the video, but I couldn't grasp how it was related to the focuser backlash. From what I can tell your stepper motor worked well :)

 

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DerPit post=70210 wrote: One thing you can try:
Most (all?) focusers have an option to reverse the direction.  So do an auto-focus run with the linear algorithm (that works around a possible backlash) in the normal direction, and write down the value (also look at the curve to verify it is a reliable one).  Then activate the 'reverse' option in the focuser driver, and repeat the AF run.  This time, because of the reversal, it will always end moving outward, and you get the focus 'coming from the other side'.  The difference between the two values you get that way would be your backlash.


Hi Peter,

Thank you for your suggestion, but when I tried it, I got variable readings. Please find the below table...

 

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RDBeck post=69544 wrote: I'm out under the stars and got my issue sorted out. My mount was pointing a fair bit off, apparently enough to foil stellarsolver.

I did a cold start on my Losmandy/Gemini and issues seem to be resolved now.
 


Hi Richard,

I faced the same issue and looks like my scope was off as well. I was able to fix it by increasing the search radius from 15 to 30. I wanted to share this so as anyone in the future may find this helpful tweak...

 
 

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Mohamed replied to the topic 'Re:Precise backlash measurement' in the forum. 7 days ago

astrogene1000_stuff post=70105 wrote: If the focus routine always moves to final position in the same direction then oversizing the backlash steps when reversing basically makes it a do not care because the backlash cancel's out.

Think about it this way, currently at 500 with actual backlash = 25
Move back 200 physically moves it to 325 (175 = 200 - 25 backlash), counter though shows 300
Move forward 200 (physically moves 175 = 200 -25 backlash) up to 500 physical and counter shows 500



Hi Gene,

The problem is as Ihoujin mentioned if you are approaching the final focus point from one direction as in linear it won't matter, but the problem is that (1) IN and OUT backlashes could not be equal, and (2) This confuses the algorithm as at the final position, the algorithm is not equally going IN and OUT, and that is the cause of the shift of backlash that causes the problem.

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Mohamed replied to the topic 'Re:Precise backlash measurement' in the forum. 7 days ago

Ihoujin post=70080 wrote: It's pretty straightforward. Setup an artificial star at a workable distance for your optics. I have the Hubble 5-star Artificial Star with 5 star sizes to choose from. Use the smallest one you can. Set exposure and gain and ensure Auto Select star can pick out the artificial star.
Initial steps should be set high enough to make a noticeable change. Then run an autofocus routine. Observe the graphs. Once it reverses directions note if the reverse HFR values are above of below the earlier HFR at the same step position.
If you are above, you have uncorrected backlash. Below, the backlash is overcompensated for.
You can do this with real stars, but atmospheric seeing will reduce the accuracy. Using average of 2 or more frames helps.


Thank you Ihoujin, will give this a try in the cloudy week...

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Mohamed replied to the topic 'Re:Precise backlash measurement' in the forum. 1 week ago

Ihoujin wrote: I used an artificial star averaging 2 frames. Then adjusted the backlash value until the points focusing in matched well with the points focusing out.


Thanks Ihoujin for the tip. Can you please advise more details on the steps?

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Im using ASI120MM mini with ASI183MM Pro, and ASI120MC with ASI533MC Pro with no issues

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Mohamed created a new topic ' Precise backlash measurement' in the forum. 1 week ago

Hello,

Is there is a precise way to measure the backlash for a focuser? Online and youtube methods depend either on visual observation of the start of movement or Digital Caliper. I tried both but every time I get zero backlash results!!!


Thank you

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Hello,

yesterday I was slewing from parking to M 81 (west of the meridian at the time), solver failed, and when I solved it online I found myself EAST of meridian in the exact mirror-like spot... Any idea what went wrong?

Expected
 



Actual
 

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Another suggestion is to use the same picture for solving using Astrometry nova.astrometry.net/upload

You may want to double-check the failed solving if caused by the not expected sky zone.

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That's odd Richard. The solver should be working anyway!!! I have a scenario that can cause the solver to fail, which is miss-aligned scope. If your scope is not properly polarly aligned, and you slew to a target, the solver may not be able to work as it only searches within a predefined distance from the target coordinates. It happened to me when I was totally off.

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Hi Richard

Can you share one of the images that failed solving?

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Hi Richard,

I found that you are using the latest version of KStars 3.5.2, BUT your solver is trying to remotely connect and authenticate to somewhere else. Keep in mind that the default option of remote is disabled, and I have been using the new StellerSolver with success

The following is from your log...

[2021-03-26T21:22:38.399 CDT INFO ][     org.kde.kstars.ekos.align] - "Image received."
[2021-03-26T21:22:38.462 CDT INFO ][     org.kde.kstars.ekos.align] - "Automatically downsampling the image by 2"
[2021-03-26T21:22:38.481 CDT INFO ][     org.kde.kstars.ekos.align] - "Evaluating Installed RAM for inParallel Option.  Total Size of Index files: 2.44583 GB, Installed RAM: 15.5053 GB, Free RAM: 12.0155 GB"
[2021-03-26T21:22:38.482 CDT INFO ][     org.kde.kstars.ekos.align] - "There should be enough RAM to load the indexes in parallel."
[2021-03-26T21:22:38.482 CDT INFO ][     org.kde.kstars.ekos.align] - "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++"
[2021-03-26T21:22:38.482 CDT INFO ][     org.kde.kstars.ekos.align] - "Starting Internal StellarSolver Sextractor with the 4-SmallScaleSolving profile . . ."
[2021-03-26T21:22:38.557 CDT INFO ][     org.kde.kstars.ekos.align] - "Stars Found before Filtering: 182"
[2021-03-26T21:22:38.558 CDT INFO ][     org.kde.kstars.ekos.align] - "Removing the stars with a/b ratios greater than 1.5"
[2021-03-26T21:22:38.558 CDT INFO ][     org.kde.kstars.ekos.align] - "Keeping just the 50 brightest stars"
[2021-03-26T21:22:38.559 CDT INFO ][     org.kde.kstars.ekos.align] - "Stars Found after Filtering: 50"
[2021-03-26T21:22:38.559 CDT INFO ][     org.kde.kstars.ekos.align] - "+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++"
[2021-03-26T21:22:38.559 CDT INFO ][     org.kde.kstars.ekos.align] - "Configuring Online Solver"
[2021-03-26T21:22:38.560 CDT INFO ][     org.kde.kstars.ekos.align] - "Authenticating. . ."
[2021-03-26T21:22:38.560 CDT DEBG ][   org.kde.kstars.ekos.capture] - setAlignStatus:  4
[2021-03-26T21:22:38.666 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[DEBUG] ReadScopeStatus: TrackState is <2> "
[2021-03-26T21:22:38.666 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[SCOPE] CMD <:GR#> "
[2021-03-26T21:22:38.667 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[SCOPE] RES <07:40:32> "
[2021-03-26T21:22:38.667 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[SCOPE] VAL [7.67556] "
[2021-03-26T21:22:38.667 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[SCOPE] CMD <:GD#> "
[2021-03-26T21:22:38.669 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[SCOPE] RES <-02:02:50> "
[2021-03-26T21:22:38.670 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[SCOPE] VAL [-2.04722] "
[2021-03-26T21:22:38.670 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[DEBUG] CMD: <:Gm#> "
[2021-03-26T21:22:38.671 CDT DEBG ][           org.kde.kstars.indi] - Losmandy Gemini : "[DEBUG] RES: <E>, lst 8.317997, ha 0.642442, pierSide 1 "
[2021-03-26T21:22:38.931 CDT INFO ][     org.kde.kstars.ekos.align] - "Reply Received"
[2021-03-26T21:22:38.934 CDT INFO ][     org.kde.kstars.ekos.align] - "{\"message\":\"authenticated user: \",\"session\":\"gzzlsuj5d8vnv855260yzqumuy6tz0yb\",\"status\":\"success\"}"
[2021-03-26T21:22:38.937 CDT INFO ][     org.kde.kstars.ekos.align] - "Authentication to astrometry.net is successful. Session: gzzlsuj5d8vnv855260yzqumuy6tz0yb"
[2021-03-26T21:22:38.940 CDT INFO ][     org.kde.kstars.ekos.align] - "Uploading file..."
[2021-03-26T21:22:39.106 CDT INFO ][     org.kde.kstars.ekos.align] - "Reply Received"
[2021-03-26T21:22:39.109 CDT INFO ][     org.kde.kstars.ekos.align] - "{\"hash\":\"41acc6883c7f7ddaf80027a861523d6816f6be8e\",\"status\":\"success\",\"subid\":4348365}"
[2021-03-26T21:22:39.112 CDT INFO ][     org.kde.kstars.ekos.align] - "Upload complete. Waiting for astrometry.net solver to complete..."
[2021-03-26T21:22:39.114 CDT INFO ][     org.kde.kstars.ekos.align] - "Waiting for Processing to complete..."
[2021-03-26T21:22:41.225 CDT INFO ][     org.kde.kstars.ekos.align] - "Reply Received"
[2021-03-26T21:22:41.227 CDT INFO ][     org.kde.kstars.ekos.align] - "{\"images\":[],\"job_calibrations\":[],\"jobs\":[],\"processing_finished\":\"None\",\"processing_started\":\"2021-03-27 02:22:40.496105\",\"user\":2633,\"user_images\":[]}"
[2021-03-26T21:22:43.225 CDT INFO ][     org.kde.kstars.ekos.align] - "Reply Received"
[2021-03-26T21:22:43.227 CDT INFO ][     org.kde.kstars.ekos.align] - "{\"images\":[10383427],\"job_calibrations\":[],\"jobs\":[null],\"processing_finished\":\"2021-03-27 02:22:41.691268\",\"processing_started\":\"2021-03-27 02:22:40.496105\",\"user\":2633,\"user_images\":[4489266]}"
[2021-03-26T21:22:43.229 CDT INFO ][     org.kde.kstars.ekos.align] - "Waiting for the Job to Start..."
[2021-03-26T21:22:51.231 CDT INFO ][     org.kde.kstars.ekos.align] - "Reply Received"
[2021-03-26T21:22:51.234 CDT INFO ][     org.kde.kstars.ekos.align] - "{\"images\":[10383427],\"job_calibrations\":[],\"jobs\":[null],\"processing_finished\":\"2021-03-27 02:22:41.691268\",\"processing_started\":\"2021-03-27 02:22:40.496105\",\"user\":2633,\"user_images\":[4489266]}"
[2021-03-26T21:22:51.348 CDT INFO ][     org.kde.kstars.ekos.align] - "Online Solver aborted."
[2021-03-26T21:22:51.350 CDT INFO ][     org.kde.kstars.ekos.align] - "Solver Failed."
[2021-03-26T21:22:51.369 CDT INFO ][     org.kde.kstars.ekos.align] - "Solver aborted after 12.81 seconds."

So I believe that astrometry.net is not responding with correct plate solving for whatever reason (parameters could be one of them).

Do you want to try the built-in StellerSolver instead?

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