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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Noob focuser questions (Rigel NStep)

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I am about to install a Rigelsys NStep motor on my WO Z61, but I feel that there might be some sort of initial setup required that I'm not finding guidance for. Maybe it will all be obvious once I get it connected, but I'd rather ask first than wind up with it all bolted on and be clueless about how to make it work.
Setting up a new profile to include the Rigelsys driver is simple enough, and I understand the part about racking the focuser all the way in to set the zero point.

But I'm lost from there. The StellarMate focuser group documentation page says "For absolute focusers, you can set the ticks count." But the only entry field shown are two labeled Steps. Now, "the step size is in units of ticks", which is nice to know, but I'm not sure what to do with that information, or how to "set the ticks count".

In the screenshot   where did the 3677 come from? Then comes: "The step size can be changed by specifying its value in the 2nd Steps field." How should I choose a value to enter in that field?

Hopefully the first reply is just "It will be clear once you get started", but if not, any information will be appreciated.
2 years 11 months ago #70313

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The 3677 value on the left is the current position. The 0 on the right is where you manually enter where you want to move when you hit the play button next to it. Doing so will drive the motor in, then it will read 0 on the left.

Elsewhere under mechanics, you can set the initial step size. This is used my the autofocus algorithm. But it is also how far it will focus in/out with the arrow buttons above.

Lastly if you want to set the current position to a custom value without moving the focuser. Use the Sync box in the INDI diver itself.
The following user(s) said Thank You: Ron DeBry, Hank
2 years 11 months ago #70315

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Thanks. I spent some time with the focus simulator, which has some quirks but is actually more helpful than I expected, given what it is trying to simulate.

Still not sure about the 'ticks/steps' business, but maybe it will turn out to be just a matter of the documentation being confusing (which is likely, given that the statement about what the 2nd Steps field represents is just incorrect).

Does the zero-point need to be established separately for every profile that uses the focuser (for example, separate profiles for with/without a focal reducer, or for PHD2 vs internal guiding)?
2 years 11 months ago #70332

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In my experience, just consider the zero point to be the default software starting position when you run EKOS. I'm not sure about this but this may not be true if the motor has encoders.
Starting from zero can be a bit annoying at times, Say your focuser is already near the focus point. If it starts at 0, it will have no valid inward travel steps available.
In that situation, I use the Sync box under the focus driver's Main Control Tab to give it some arbitrary higher value.

I would recommend you rack he focuser all the way in. Sync it to zero. Focus the telescope on the sky and note the position.
Save that position as a preset in the INDI driver. Now the next time you start from zero and fully racked in, you can call upon the preset to get a roughly accurate focus to begin with.
The following user(s) said Thank You: Hank
2 years 11 months ago #70334

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Still working on getting the hang of autofocusing. The principles are certainly simple enough, yet I'm not surprised that I'm having trouble getting things dialed in, because that's how everything is in astrophotography :)
The INDI driver for the Rigelsys NStep does not have a field for backlash, so for now I am concentrating on using the Linear mechanism. I have 0 set as fully racked in, and I find focus at around 51000 steps - about 24mm, but is there a reason I should know exactly the correspondence between physical distance and motor steps?

Once I set the mechanism, the tolerance (5%) and number of exposures to average, as far as I can tell main parameter that will govern success is Initial Step Size - am I correct in that conclusion? I've done a bit of experimenting, and it appears that somewhere between 20 to 40 is where a move starts to consistently produce a change in FWHM values, so I set it there.

The other night was the first time I left it alone to perform a temperature-based refocus (set to >1.5 degrees)

 

The arrow shows when the focus routine ran. From an imaging standpoint, I clearly would have been better off to not have refocused. But I'm not sure what to tweak. Smaller Initial Step Size and larger Multiple? Any other tips?
2 years 10 months ago #71044
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A couple more questions, in case anyone ever wanders by this thread:

I did find that you can enter a backlash value on the temperature compensation tab - does that have any impact on regular operation?.

I have so far left the stepping settings to the default, which is full. Would I expect any performance difference by choosing half or wave, or would it just use a different mechanism to go to the same position that the algorithm has determined anyway?
2 years 10 months ago #71099

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Hi Ron,

Half stepping will double the number of steps, so if you are using wave and have focus at 51k steps, this would now be 102k steps if racked in then moved to focus position.
Half stepping has less torque but finer granularity.

For your focus run, I am not an EKOS user but 134 frames seems quite excessive.

I advise playing around with the initial step counts in Ekos, if you find 20 to 40 causes a change then start with 100 or 200.

From your graph it looks like you were chasing seeing turbulence. About what intensity was the chosen star to focus on? I believe Ekos help says mag 3 or 4 star but that is so dependent on aperture, exposure length, camera sensitivity. Given any specific exposure duration, try manually picking a star that has about 50% to 75% full well when close to focus at a given exposure length and for sure not saturated or too dim.

Gene
2 years 10 months ago #71113

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Hi Gene,

Thanks for the reply. Sorry - I did not include enough context with my screenshot. It is from Siril and shows the ave FWHM value for each frame in a registered stack. I used the Ekos Linear algorithm to focus prior to frame #1. After sub #107 had been taken, the NStep's temperature probe triggered a re-focus. I should look to see if there's an Ekos log for this. Anyway, inspection of the subs' FWHM values after the re-focus suggest that focus was worse after the re-focus than before, though it could have been that seeing deteriorated coincidentally at the same time.

(as I understand it, the Ekos focus routine detects stars (SEP) and averages them, rather than performing focus based on a single pre-chosen star)
2 years 10 months ago #71118

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It's raining, so I played around with just the focus motor.

Setting to Half-step mode doubled the rotational speed and apparently halved the number of steps to the same physical position, instead of doubling the number.

My normal focus preset is 51000, which is at ~24mm out according to the scale engraved into the focuser. I racked in to 0, clicked on Half-step mode and told it to go to 51000. Instead of going only halfway out (what I would expect if 24mm travel would be 102000 half-steps), the NStep blew right past 24mm and kept going.

From a mechanical perspective it makes sense that the higher-torque mode (full) would move more slowly, but I'm not sure how to translate that to also explain how half-step mode should have smaller steps & higher precision.

Wave mode apparently did nothing at all, as far as I could tell.
2 years 10 months ago #71125

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Hi Ron,

You are correct, setting to half step should move only half the distance for a given count.

What does it mean "wave mode did nothing at all' ?

As far as distance moved, wave and full should be identical, it is just how the phases of the motor are energized that changes.

If interested in how the motor is controlled, see the charts on phases energized based on wave/full and half (in the chart, nstep full = two phase on stepping).
Simple steppers

I just did the half/full and wave on my unit with nstep and it worked as expected with half step = half distance for same count.

What is your phase wiring set to, default is '0'

Which version of nStep do you have (a picture is worth a thousand words :-)

Gene
2 years 10 months ago #71126

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Sorry for the delayed response - waiting on clear weather for testing. I think I have, through sheer brute-force (Monte Carlo?) arrived at focus parameters that work consistently.

To answer your questions:
Yes, phase is 0
I'm not sure what version of NStep, the outer cover only says USB NStep, but it is a very recent vintage
And when I tried setting the Mode to Wave, the motor did not appear to respond to any commands to move

Thanks for your time!
2 years 10 months ago #71294

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