The main reason I am planning on getting rid of my EQ6 is because I do want to get rid of the tiny ripples that cannot be guided out, 1" oscillations that happen sub second, some of which is an artefact of seeing but other parts are purely imperfections within the mount.
I think this is where the Linear will be better, having something like a four stage reducer it not only gets rid of backlash but should vastly smooth out all those little inconsistencies that cannot be guided out. The 30" PE that my EQ6 has is fine, that is not even noticeable, its those small bits in between
Just for info, have attached a piccy of my AZEQ5 before and after tweaking the belt tension. The linear has much larger/stonger belts, and probably has a more precise belt tensioning system, but it pays to understand what can happen, even with belts
Andrew
ie Some problems can be removed at the expense of possibly introducing new ones.
That black graph looks heaps better with much less ripple.
Interestingly it seems the error is mostly negative arcsec, ranging from -20 to +2 as if the motor is turning too slow. If you could speed that up slightly it would also improve the graph.
Anyway its a big improvement, I wonder if many other users know that trick.
You are slightly misinterpreting the graph.
I have normalised my plots and then taken a snapshot from a section of the plot that highlighted the before and after effects.
The underlying tracking rate is actually pretty good.
I think this is where the Linear will be better, having something like a four stage reducer it not only gets rid of backlash but should vastly smooth out all those little inconsistencies that cannot be guided out. The 30" PE that my EQ6 has is fine, that is not even noticeable, its those small bits in between
I'm not sure if the multi-stage reduction will have much of an impact there, maybe an engineer can chime in?
I've been thinking about trying to build my own mount (as a project, not a commercial endeavour), and having considered building a friction drive or belt driven system, I suspect that multi-stage reduction is simply there to keep the physical dimensions small.
You need a really large reduction ratio to move something in small enough increments that it's suitable for tracking with a stepper motor.
Worm gears are great being a "simple" single-stage mass reduction step, but when using a friction or belt system, you need another way of creating very large reduction ratio.
To give you an idea, the EQ6 has a ~700x reduction ratio so it can move in steps of around 0.14" (from memory). Of course, if you tried to have a 700x reduction ratio with one pulley, you'd have a 7m pulley on one side and a 1cm one on the other (or a 70cm, 1mm for that matter, but you get the idea).
However if you use a multi-stage approach, you can greatly reduce the physical size by making a pulley version of a compound gear. Maybe it has some impact on high frequency noise as well, but I'm not sure about that (but then again, I know jack about mechanical engineering as well, so I'm keen to hear about it if someone knows more on this).
I'm actually a bit cynical on timing belts because they must introduce some relatively high frequency noise into the system, so I'm still expecting some small-scale, high-frequency fluctuations, however I'm not expecting them to be significant enough to cause me issues imaging at 1.1"/px.
Quote:
Originally Posted by AndrewJ
Just for info, have attached a piccy of my AZEQ5 before and after tweaking the belt tension. The linear has much larger/stonger belts, and probably has a more precise belt tensioning system, but it pays to understand what can happen, even with belts
Andrew
ie Some problems can be removed at the expense of possibly introducing new ones.
Thanks for posting that, interesting graph! Excuse my ignorance, but can you please confirm the scales on each axis?
Edit: Soooooon
Last edited by codemonkey; 20-01-2016 at 06:22 PM.
Gday Lee
For the upper graph, the left axis is in "axis" arcsecs.
This was just a grab of unguided, PEC off data, to see what the raw tracking was like. The large ripple due to the belt teeth shows very clearly, superimposed on the much larger worm error.
The lower graph is an FFT analysis ( similar to what PEMPro would do )
The left axis is scaled such that the maximum fundamental detected in the data becomes 1.
In my case, the worm ( ie fundamental 1 ) is plotted as 1.0, as it has by far the larges amplitude.
The no 36 fundamental is showing up as approx 0.11, and that indicates the PE caused by the belts meshing is approx 11% the magnitude of the primary PE of the worm, and hence is noticeable.
I've been thinking about trying to build my own mount (as a project, not a commercial endeavour), and having considered building a friction drive or belt driven system, I suspect that multi-stage reduction is simply there to keep the physical dimensions small.
I have looked into friction drives like the Mesu and they look really interesting... Buggered if I know how they actually work though
Anyway, I know the EQ6 can do what I need it to do when it's playing nice, it's the constant fiddling I find myself doing with it to try and get it to play nice that's my issue with them.
I would suggest though, bearing in mind that I've not used the Avalon yet, if you happen to have an EQ6/AZ-EQ6 that's playing nice consistently, reports in the field (i.e from Sara) suggest that your tracking is unlikely to be significantly improved, so it may not be worth the significant upgrade cost. Might not be. I'll find out shortly whether it's worth it to me :-)
I think satisfaction with EQ6/AZ-EQ6 varies from person to person. It largely depends what telescope sits in top of it and also how descending a user is in terms of quality data. In case of narrowband imaging, in particular with 3nm filters, I feel that tracking errors will show more readily as opposed to RGB imaging. Same as you Lee, I have found that although my mount can deliver outstanding data, many subs are substandard.
I have faith, based on evidence/data available on the net, that Linear FR will consistently track more smoothly than Synta mounts. And with auto guiding, PE does not need to be small, as long as it is smooth.
I still have a HEQ5 that has a relatively small PE, but it also has sudden ripples so it is not optimal for the type of photography I do. This graph shows 50 minutes of unguided tracking: http://www.iceinspace.com.au/forum/a...e.php?a=170518
I suspect that several guys on IIS (me for sure!) are quite curious about this mount's usability for AP
Gday Lee
For the upper graph, the left axis is in "axis" arcsecs.
This was just a grab of unguided, PEC off data, to see what the raw tracking was like. The large ripple due to the belt teeth shows very clearly, superimposed on the much larger worm error.
The lower graph is an FFT analysis ( similar to what PEMPro would do )
The left axis is scaled such that the maximum fundamental detected in the data becomes 1.
In my case, the worm ( ie fundamental 1 ) is plotted as 1.0, as it has by far the larges amplitude.
The no 36 fundamental is showing up as approx 0.11, and that indicates the PE caused by the belts meshing is approx 11% the magnitude of the primary PE of the worm, and hence is noticeable.
Andrew
Aha, ok, thanks for clarifying Andrew. Just looking at that graph it looks like while the change might have improved #36, #4 seems to have gotten worse.
Quote:
Originally Posted by Atmos
I have looked into friction drives like the Mesu and they look really interesting... Buggered if I know how they actually work though
Basically just a big metal disc pressed up against a small metal shaft. As the small shaft rotates, it rotates the big disc by friction. There's no gears, or lubrication, just metal on metal, so there's no slack in the system, no possibility for backlash.
Quote:
Originally Posted by Slawomir
I think satisfaction with EQ6/AZ-EQ6 varies from person to person. It largely depends what telescope sits in top of it and also how descending a user is in terms of quality data. In case of narrowband imaging, in particular with 3nm filters, I feel that tracking errors will show more readily as opposed to RGB imaging. Same as you Lee, I have found that although my mount can deliver outstanding data, many subs are substandard.
I have faith, based on evidence/data available on the net, that Linear FR will consistently track more smoothly than Synta mounts. And with auto guiding, PE does not need to be small, as long as it is smooth.
I still have a HEQ5 that has a relatively small PE, but it also has sudden ripples so it is not optimal for the type of photography I do. This graph shows 50 minutes of unguided tracking: http://www.iceinspace.com.au/forum/a...e.php?a=170518
I suspect that several guys on IIS (me for sure!) are quite curious about this mount's usability for AP
That graph actually looks pretty good to me for an HEQ5. Not that I've ever looked into those, but I expected them at least to have a greater amplitude than the NEQ6 but that doesn't look to be the case.
Just looking at that graph it looks like while the change might have improved #36, #4 seems to have gotten worse.
Correct, but the overall result is much smoother over time ( esp by removing the high freq 36 ripple ), and hence is easier to guide.
Im not 100% sure where the no 4 fundamental really comes from
as the worm has a 36 to 12 tooth belt reduction
and the stepper has an inbuilt 2:1 gearbox.
I assume that by increasing the belt tension, it has changed the loading inside the gearbox, and this results in the changes seen.
That said, interpreting some FFT data is not as simple as saying, fundamental 4 is large, hence it is something that repats 4 times per rev of the worm.
With the new mount due to arrive on Monday, the weather gods are up to their old tricks. (red means cloudy, basically, if you're not familiar with clearoutside.com).
No matter anyway, I've only just gotten the retailer who sold me my imaging laptop a mere three months ago to agree to have a look at it after the battery decided to go kaput, so there's not a lot I can do with the mount right now anyway.
