esb post=69469 wrote:

El Corazon post=69468 wrote: Simple worm gears, yes. Globoid worm gears with variable gear ratios are a different story. But perhaps I am too much of a perfectionist here.


 

Now you've got me curious.  I have no idea what those are and assumed a simple worm gear would work in this case.  It sounds like I've got some reading to do.

Wow... those are really cool.  I'm with you.  Nothing less will do now that I know/understand what they are.  I did find this on thingiverse, though I have no idea how good / applicable it is here:

www.thingiverse.com/thing:2776688

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El Corazon post=69468 wrote: Simple worm gears, yes. Globoid worm gears with variable gear ratios are a different story. But perhaps I am too much of a perfectionist here.

 

Now you've got me curious.  I have no idea what those are and assumed a simple worm gear would work in this case.  It sounds like I've got some reading to do.

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I haven't looked yet, but I bet there are decent gear/worm gear generators available for OpenSCAD that could be imported into your Blender project.  I've done that for regular gears in other projects.

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Thanks for the link.  It looks like I was on the right track with this eBay listing I found ;)

www.ebay.com/itm/DC-5V-Micro-10mm-Precis..._CLK%7Cclp%3A2334524

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Very nice!  What stepper did you use?  I ended up using a larger stepper (NEMA-17) with a belt/loop under tension.  I really like the smaller stepper and worm gear arrangement you used.  And for this purpose, a larger gear ratio seems better since it enables finer control and decreases the required torque to move the focuser.

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Everything has been working well over a few nights of imaging with one exception. I had an (apparently) unrelated issue where I had Kstars crash on me a couple of times. Once that happens while the focuser is not at zero, I have to manually move focus back to the zero position before starting indi / Ekos again. If I don't, the focuser is at the previous focus position (say 78) but the driver now thinks its at zero and there's no way to move past the zero point. Does anybody know of any way around this? I'm not sure there is a good solution. The best I can see would be to always save the focus position and assume it hasn't moved (while also moving to zero on a clean shutdown). Support for going below zero would also help manually get out of this situation if there was then a "set as zero" option to go with it.

I was hoping the stepper driver hardware might have support for stall detection so we could use something like 3d printers use for senseless homing, but it doesn't look like it does. I suppose another option would be an actual end stop / zero switch, but that would be a good bit of extra work / hardware.

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Eric Brown created a new topic ' Scheduler question' in the forum. 2 years ago

Is it possible to have the scheduler configured to interrupt a sequence when a higher priority sequence becomes runnable? For example, if my primary target isn't visible until a certain time / elevation, I typically want to image something else before then, but as soon as possible I want to start on the primary target. If I set the primary sequence to a priority of 20 and the filler sequence as a priority of 10, the scheduler shows that it will run the filler sequence to completion before starting the higher priority sequence. I have to decrease the number of images to get the primary job to start as soon as it meets the criteria to start (at least I have to do this according to the sequence info in the list for start times).

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Eric Brown created a new topic ' Polar Alignment question' in the forum. 2 years ago

Is there any way to control the slew speed used by the polar alignment process between images? It seems to want to use the "Find" speed for me which is set to quite slow in my mount. Regular gotos use the max speed, and it seems like the PA process should use the same. This seems to be new behavior, though its possible a firmware update to my mount has changed the default Find speed.

And is it possible to control what the mount does after the PA is finished? It seems to want to try to park the scope when done. But typically I'll want to run the process multiple times as I get the alignment dialed in. Ideally it would return to the starting position.

On a related note, is there any predictable way to automatically slew the mount to what it thinks is due north with the RA axis straight up? That's the position that I want to start my polar alignments from as there are obstructions that prevent it from working if I start too far from that.

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Its not needed, but it might provide some additional resolution, though it remains to be seen whether the mechanics of the RedCat or my seeing conditions lend themselves to improvement.

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Thanks for the advice everybody. Full Field mode worked *great* last night! It was bang on and worked the first time. Linear worked just the way that I would expect it to. I even tried polynomial mode and it picked the same focus point as Linear, though it didn't seem like it took enough data points to come to that conclusion. I'll have to play around with it more before I put my trust in it.

Woot! I'm really happy with how things are working. I'll still probably switch to the 5:1 stepper at some point, but I'm not in a hurry.

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The focused worked much better last night. I now get the expected V / curve during auto focus. I could repeatably move focus away from the focus point and back to the same step number and things were in sharp focus. I still need to tune the parameters for the auto focus algorithm itself. It was never able get it to automatically choose the focus point (though I was able to choose it myself based on the data from the auto focus process). I’m using the linear focus algorithm. Once it finishes the first pass, it then appears to try to take multiple readings at the same steps right around the focus point. However my seeing must be varying enough that it couldn’t get consistent enough readings without moving the focuser and would eventually error out. I adjusted the tolerance % without success, though I’m not sure that’s the right parameter. I didn’t spend a lot of time as I wanted to get started imaging, so I just chose the best focus point and moved on.

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kross wrote:

esb wrote: And a problem like this wouldn't be complete without a facepalm. I just noticed with the stepper attached to my RedCat, if I ran it from 0 (fully retracted) to nearly max (500) and then back to 0, it kept missing the zero point by a few degrees (it was always short). It turns out the grub/set screw for the pulley attached to the stepper is loose. Double-d'oh! That means I have at least 10+ steps of backlash. I'm guessing it will work much better with a tight pulley.


Consider yourself getting off easy! When I did the Rowan belt mod for my Orion Atlas mount, one of the set screws on a pully deep inside the mount wasn't tight enough. Took me a month to figure out why I was getting such bad backlash in Dec movements! So I had to tear the mount apart to tighten that screw. I put blue Loc-Tite on those screws, just because I was mad at them!


Its especially ironic because the grub screw is one of the first things I advise others to check for many different kinds of 3d printer issues. I need to take my own advice.

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With my existing stepper, backlash now seems to be around 1 step. I can see clear consistent movement for even a single step and when changing directions at most that first step doesn't show full movement. I can see that with large moves in one direction followed by single step moves in the other. When does darkness get here? I really can't way to try it out again.

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And a problem like this wouldn't be complete without a facepalm. I just noticed with the stepper attached to my RedCat, if I ran it from 0 (fully retracted) to nearly max (500) and then back to 0, it kept missing the zero point by a few degrees (it was always short). It turns out the grub/set screw for the pulley attached to the stepper is loose. Double-d'oh! That means I have at least 10+ steps of backlash. I'm guessing it will work much better with a tight pulley.

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kross wrote:

El Corazon wrote: My 2 cents on this is that upon microstepping down to 1/32 and using only one step for each move, the motor does not have enough torque to reliably move that one microstep.


When using the Waveshare INDI driver that I wrote, a single step in the INDI control panel will equate to 32 microsteps at the motor. I always end on a full step boundary. I use microsteps for smoothness and quietness, not for increased resolution. If it were to stop on less than a full step, then the motor would need to have power applied to it constantly to hold that position, thus using more power and causing the motor to get warm (or very hot if you haven't tuned the current limit). But with my approach, that allows me to turn off power to the motor when not actively moving for focus.

So I'm not sure if that is esb's problem of it not always moving the same amount with a single step. Does that also happen if you disconnect the belt, just letting the motor run free? If it works fine when the motor is running free, but misses a step when connected to the belt, then it is most likely a lack of torque. You can try slowing down the motor with the delay settings, since stepper motors lose torque when running faster. You can also try using less microstepping via the DIP switches. You will need to modify the source code to match the micrstepping setting of the DIP switches. Eventually I'll make that a configurable option in the INDI control panel.


Ha... our messages crossed. I think the timing is indeed my problem. With the geared stepper, the inconsistent (even reversed) movement happens under zero load. I think I'm just pulsing the motor too quickly.

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