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Starting out with a Pegasus motor focuser


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I've never had a motor focuser before and I have just fitted a Pegasus universal motor focuser to my Esprit (controlled from a Powerbox).

When I attached it, the focus tube was at mid position (which seemed sensible) and of course it's now 'locked' to the focus motor.

In NINA, the position is showing as zero and entering a positive number moves the focuser inwards (which I think is to a more distant focus), but NINA doesn't accept negative mumbers, so how would I move the focuser in the opposite direction?

Is there a 'motor focuser 101' I need to read somewhere? I've never thought of focus as being a 'number' before. It's always just been turning the knob clockwise or anti clockwise!  

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What you should do is move the tube all the way in all but a couple of MM then put zero in the steps box and Sync, then move all the way out and see how many steps it moves, in my case with the same motor it 19,000 then I set a max limit of say 18,500 this way it won’t go all the way in or out and crash the tube…

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As Stuart has said.

OK so the motor focus systems use a start (zero position), I usually recommend this is a few mm from fully inwward as well.

Next is to measure the distance out the max position is and work out how many steps that equates to. Again leave it shy of a few mm so you have a small safety factor each end.

In the software you then set zero at the inward setting and the number of steps to max setting.

If you find a nice focus say mid-way is handy there are usually presets that can be saved to make that a goto focus point. But the position is not remembered on power off so always park the focuser at a set position (inward home for example).

HTH

Steve

 

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12 minutes ago, Stuart1971 said:

What you should do is move the tube all the way in all but a couple of MM then put zero in the steps box and Sync, then move all the way out and see how many steps it moves, in my case with the same motor it 19,000 then I set a max limit of say 18,500 this way it won’t go all the way in or out and crash the tube…

err.. ok. I can't use the focus knobs with the motor attached so I shall have to take the damn thing off and re-fit it with the tube wound in, right?

One issue I have is that entering a positive number in NINA moves the focus tube inwards. Shouldn't it be outwards? Otherwise, setting it to zero with the tube all the way in will mean NINA can't move it (as it doesn't seem to like negative numbers!).

COnfused

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6 minutes ago, StuartT said:

err.. ok. I can't use the focus knobs with the motor attached so I shall have to take the damn thing off and re-fit it with the tube wound in, right?

One issue I have is that entering a positive number in NINA moves the focus tube inwards. Shouldn't it be outwards? Otherwise, setting it to zero with the tube all the way in will mean NINA can't move it (as it doesn't seem to like negative numbers!).

COnfused

First of all, you only need to loosen the grub screw on the shaft collar to move manually…

Secondly with the Pegasus motors you need to reverse the in and out setting in NINA, I have to do this on mine too….

Then move it all the way in except for a few MM, then sync on zero, this should then show its at zero steps, the move out all the way except for a few MM, and note the steps, and set a max position slightly lower than this number…

Edited by Stuart1971
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8 minutes ago, Stuart1971 said:

First of all, you only need to loosen the grub screw on the shaft collar to move manually…

Secondly with the Pegasus motors you need to reverse the in and out setting in NINA, I have to do this on mine too….

Then move it all the way in except for a few MM, then sync on zero, this should then show its at zero steps, the move out all the way except for a few MM, and note the steps, and set a max position slightly lower than this number…

thanks so much! super useful!

Ok, so I have loosed the grub screws and wound the focuser all the way in, then a little way out (as I wanted one of the grub screws to be on the flat part of the shaft - that seems important!)

And I opened the Pegasus app and reversed the motor direction.

Now... I have set the focuser position in NINA to zero. Is that what you mean by syncing it?

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Just now, StuartT said:

thanks so much! super useful!

Ok, so I have loosed the grub screws and wound the focuser all the way in, then a little way out (as I wanted one of the grub screws to be on the flat part of the shaft - that seems important!)

And I opened the Pegasus app and reversed the motor direction.

Now... I have set the focuser position in NINA to zero. Is that what you mean by syncing it?

Yes, with it all the way in set to zero…now when you tell it to move to say 1000 it should move out to that point, so the next step is to set the max position, so it does not crash the tube…as if you have a rack and pinion focuser it can cause some damage, not an issue really on normal crayfords…

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16 minutes ago, Stuart1971 said:

Yes, with it all the way in set to zero…now when you tell it to move to say 1000 it should move out to that point, so the next step is to set the max position, so it does not crash the tube…as if you have a rack and pinion focuser it can cause some damage, not an issue really on normal crayfords…

ok, I'm not really sure how far out the max extent of the tube is, so I shall have to bit by bit add 1000 to the number in NINA until I get to the end.. Hope I don't overdo it. A bit trial and error!

so when I reach that max number, do I enter it in NINA somewhere?

Edited by StuartT
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If you loosen the grub screw temporarily you can measure the travel of the focuser between zero & max - let's say that was 250mm

Now reset the focuser to your zero start point & re-tighten grub screw. Now move say 1000 steps - we can say that was 10mm as an example. So max position would be 25,000 (25 lots of 1000 would move 250mm).

Steve

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1 hour ago, StuartT said:

ok, I'm not really sure how far out the max extent of the tube is, so I shall have to bit by bit add 1000 to the number in NINA until I get to the end.. Hope I don't overdo it. A bit trial and error!

so when I reach that max number, do I enter it in NINA somewhere?

Yes, the should be a max position somewhere to enter this number, and then it will not go over that…so you have max and minimum set..

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11 minutes ago, Stuart1971 said:

Just as a matter of interest, what initial step size did you use in NINA..?

The guys on the NINA Discord channel were super helpful. There was a bit of fiddling, re-trying, fiddling and each time I uploaded my graph and they told me what numbers to change. I literally had no idea what any of it meant, or what my graph was supposed to look like 🤣 but I just did what I was told.

I think the initial step size was 40. Ended up at 120.

I don't think we managed to get it 100% right. They were concerned about the flat part of the curve remaining - apparently they think this is slipping (which I think is the grub screws not being tight enough...). Not sure how much that matters... the autofocus does at least work more or less ok

 

Slipping.png

Edited by StuartT
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6 minutes ago, StuartT said:

The guys on the NINA Discord channel were super helpful. There was a bit of fiddling, re-trying, fiddling and each time I uploaded my graph and they told me what numbers to change. I literally had no idea what any of it meant, or what my graph was supposed to look like 🤣 but I just did what I was told.

I think the initial step size was 40. Ended up at 120.

I don't think we managed to get it 100% right. They were concerned about the flat part of the curve remaining - apparently they think this is slipping (which I think is the grub screws not being tight enough...). Not sure how much that matters... the autofocus does at least work more or less ok

 

Slipping.png

That is not slipping, it is backlash in the focuser and the motor this is normal and you need to work out how many steps of backlash to set on the software, then that flat spot will go…

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Looking at the graph  it’s about 120 steps of backlash so try that in the backlash setting and run it again, and you will get an even better V curve, if you still have a slight flat spot at the start, then increase the 120 to about 140 and try again till you remove it completely….

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Ok, so the NINA guy (Iseborn) progressively got me to increase the backlash until we reached 800, so I am not sure it's that. But I really don't understand any of this stuff (or really what backlash is, to be honest) so I may have misunderstood.

Here are the settings we ended up at.

 

NINA focuser settings.JPG

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11 minutes ago, StuartT said:

Ok, so the NINA guy (Iseborn) progressively got me to increase the backlash until we reached 800, so I am not sure it's that. But I really don't understand any of this stuff (or really what backlash is, to be honest) so I may have misunderstood.

Here are the settings we ended up at.

 

NINA focuser settings.JPG

Backlash is the slack in the focuser, and motor, so the amount it has to move to engage the teeth on the focuser when changing direction, 800 is far too much, as you see on the graph curve, the flat spot is there because  it was taking up the slack and not actually moving the focus tube until the second movement…and the flat spot is approx 120 to 130 steps so that should be your figure to use, if you have it on 800 and are still getting a flat spot then something is seriously wrong…or you need to change it from out to in on the settings, but you can’t use both…

Edited by Stuart1971
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2 hours ago, Stuart1971 said:

Backlash is the slack in the focuser, and motor, so the amount it has to move to engage the teeth on the focuser when changing direction, 800 is far too much, as you see on the graph curve, the flat spot is there because  it was taking up the slack and not actually moving the focus tube until the second movement…and the flat spot is approx 120 to 130 steps so that should be your figure to use, if you have it on 800 and are still getting a flat spot then something is seriously wrong…or you need to change it from out to in on the settings, but you can’t use both…

oh dear... And I was pleased with myself for connecting the thing up! I am not all that good with tools and stuff.

Maybe this is why the NINA guy said it was slippage and not backlash then?

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When using software for diy focusers it's quite common for the  in/out direction to be reversed so there is normally an option to flip it back.  So you may be putting the adjustment in the wrong box. Does the NINA setting allow you to put both an IN & OUT backlash value?

For clarity what was the max setting you ended up with, and was this focus point anywhere fully in or out?

 

 

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1 hour ago, StevieDvd said:

When using software for diy focusers it's quite common for the  in/out direction to be reversed so there is normally an option to flip it back.  So you may be putting the adjustment in the wrong box. Does the NINA setting allow you to put both an IN & OUT backlash value?

For clarity what was the max setting you ended up with, and was this focus point anywhere fully in or out?

yes, in fact the direction in Pegasus motors s reversed, so I already corrected that setting. So now, positive means the focuser moving out of the tube. The max setting was 38,000 (fully out). But I still can't see where to enter that limit in NINA

I have a clear night again (yay!) so I have set the backlash down to 140 and this is the focus curve I get now. I'm guessing focus is around 24600, but I doubt I can get it any better than that with this curve

??

image.thumb.png.f922d85066ecf628b0ef13123d950790.png

Edited by StuartT
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6 hours ago, StuartT said:

oh dear... And I was pleased with myself for connecting the thing up! I am not all that good with tools and stuff.

Maybe this is why the NINA guy said it was slippage and not backlash then?

It’s deffo backlash, and that setting of 120 is not enough as you have the first two moves of the Autofocus routine as flat spots, so that means there is about 240 steps of backlash….because the focus did not move at all in the first two steps…

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1 minute ago, StuartT said:

So I'm on the NINA forum again tonight, and he said just set backlash to 1000 for a test. Here's what I got.

I've no idea what this means, but I assume you do?

Image

 

As you can see the first two moves are flat, this means that the focus did not change at all, the draw tube did not move so these moves were taking up any backlash, as it wasn’t until the third move that the curve dropped, so I am a bit confused by this really….🤔🤔

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2 minutes ago, Stuart1971 said:

As you can see the first two moves are flat, this means that the focus did not change at all, the draw tube did not move so these moves were taking up any backlash, as it wasn’t until the third move that the curve dropped, so I am a bit confused by this really….🤔🤔

so I assume the white points on the graph are actual measurements of focus (star width?). So if those are actual measurements, surely I can just read off the x-axis number of the lowest one and enter it into the focuser? Then it should be in focus, right? I assume 50 or so either side won't make a lot of odds

 

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