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INDI Library v1.8.9 Released (01 Mar 2021)

INDI monthly update. In addition to driver improvements, major code refactoring is in progress by @pawel-soja to modernize and improve INDI aging code.

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Focus Module revisited

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Currently EKOS arrives at best focus by moving the sensor "in" and "out" with decreasing amplitude, thus arriving at minimum HFR value.

My home built focuser is belt driven, thus backlash in the system becomes an issue: this could be avoided:

First HFR is mapped in one direction (e.g.: "in" movements only) from outside to inside of best focus position. Once the V curve is established the focuser would rewind to its start position, and incrementally, using only "in" commands arrive at HFR minimum. Backlash avoided, that should eliminate most failed autofocus procedures.

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Michael
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1 year 9 months ago #40789

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Replied by wvreeven on topic Focus Module revisited

Michael, I don’t understand. Belt driven systems are known for their low backlash or even complete absence of it. My home built focuser is belt driven and has 0 backlash. Wouldn’t it be possible to eliminate the backlash completely?


Wouter
Wouter van Reeven

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1 year 9 months ago #40814

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I have the same problem as Michael with my Optec PDMS focuser. It is belt driven, but has nevertheless a backslash of 50-80 ticks.
TSA-120 + FSQ-85 + GSO 150/750 | Avalon Linear + M-zero | Moravian G2-8300 + ASI 1600mm pro | KStars/INDI on Raspberry Pi 4 with Raspbian 10
1 year 9 months ago #40819

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Replied by DerPit on topic Focus Module revisited

My Pegasus DMFC fortunately has an internal driver setting to specify backlash.
But I do agree that it would be valuable to have a focus mode in EKOS that can take care of backlash by itself, for those that cannot set it in the driver.
A simple solution would be to have the focusser approach dialed-in values always from the same side, with a definable overshoot. I.e., to go from 10000 to 9950, it first goes down to 9800, and then up again to 9950.
Should of course be optional, so people with driver-internal backlash compensation can switch it off.
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1 year 9 months ago #40828

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Replied by knro on topic Focus Module revisited

Patches are welcome! An option can be added to mimic this behavior. Anyone needs help in setting up their development environment?
Jasem Mutlaq
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1 year 9 months ago #40837

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Replied by DerPit on topic Focus Module revisited

knro wrote: Patches are welcome! An option can be added to mimic this behavior. Anyone needs help in setting up their development environment?


That part is not the real problem. It's more understanding C++ and the layout of the code. KStars/EKOS is a complex beast and not the best starting point to learn I'm afraid :(

(Just wanted to have a look at what is needed to add also the Hour Angle to the "Mount & Alignment" overview, instead of issuing a wish. But even that looked to me like Olympus Mons to an ant :ohmy: )
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1 year 9 months ago #40880

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Replied by Megiddo on topic Focus Module revisited

Unless your belt is tight... I don't see how there wouldn't be backlash. I have mine loose enough to get off so I can do large adjustment. I just put a 'bar' on one side of the belt to take out some slack, but slide the bar out and I have slack enough to get it off the gears.
1 year 9 months ago #41270

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Replied by Lead_weight on topic Focus Module revisited

Most focuser motors have a gearbox, this is where the backlash comes in. It’s not typically from the belt.
-Andrew
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1 year 8 months ago #41355

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Replied by MikeCEM60 on topic Focus Module revisited

Well, that is probably true for the pro units, but if you have a 3D printer, and too much time on your hands?



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Last edit: 1 year 8 months ago by MikeCEM60.
1 year 8 months ago #41376
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Replied by james_lan on topic Focus Module revisited

Off topic: That's a cool idea for design. I can't do it on mine, but I'm assuming that's a rotator as well?

On Topic: I also use a 3D printed focuser, and I have similar issues with backlash, though usually it's pretty good about it. I'll put it on my list of things to look at doing. But I've been quite involved with a local makerspace lately, and that doesn't show signs of letting up.
1 year 6 months ago #43976

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Replied by Megiddo on topic Focus Module revisited

I'm also doing the same. Mine is the Deepskydad AF1. So far, it's been working great. The focuser module hasn't worked very well lately, once the module creates the "donut" it gets lost and reverts back to the original position. So I've been using my bahtinov mask. But to the subject of backlash, the bar in the photo below seems to do the job. I'd like to have some sort of pulley setup with a spring, but this works.

1 year 6 months ago #43983

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Replied by hy on topic Focus Module revisited

I'd happily volunteer to code a unidirectional focuser, if I get one or volunteer testers!
If you're interested, respond on this thread or message me.
I've been thinking the same thing for a while.
I warn you, though, that I believe backlash is only part of the problem.
I believe the HFR calculations (and, of course, seeing) are noisy and contribute to the lack of good v-curves.
Hy
Orion Atlas Pro, William Optics ZS105, Moonlight V2 focuser
ZWO ASI1600, OAG & Filterwheel, Astronomik Filters, QHY 5L-IIm guidecam.
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Ekos Projects: Terrain Backgrounds, Polar Alignment, Analyze, Linear Focuser, SEP MultiStar & GPG Guiding, FITS autostretch.
1 year 6 months ago #44008

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