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Author Topic: Astoeq tracking pause every seconds.  (Read 40855 times)

robotmonster

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Re: Astoeq tracking pause every seconds.
« Reply #45 on: September 25, 2017, 17:51:44 »

Many thanks to everyone in this thread for super useful info! Sharing my (newbie) success story below.

Pulled Orion SVP mount (EQ-5 equivalent) from collecting dust, re-greased it, fine-tuned it, and bought the cheapest NEMA17 motors I could find on ebay - 4.2V / 1.2A, "reversed-shaft" to use for the mount. These "reversed shaft" motors despite being super cheap (~ $12), turned out as an DIY advantage for me at the end, because I could use standard "off the shelf" pololu motor bracket, which would cover more usable area against the mount when placed in reverse to the motor's shaft. Got brackets attached to 6mm aluminum plates via tapped M5 holes, and aluminum plates to the mount via tapped M6 hole.

Got the 8825 driver current output calibrated measuring 0.6V = 1.2A, and while everything was running fine in high speed / slew mode, I got the clock ticking effect (micro-stepping half way, and then jumping to a full step) while tracking. Tried fast decay mode, by shorting 2 neighboring pins per earlier post, and while it made things much much smoother on expense of the extra noise, it did NOT fix the skipping effect entirely in my case. Remains of a jerky skipping effect could still be seen when looked super-closely. I attached a thin long straw to the motor's shaft with some blue tuck and obsessively looked at the far end of the straw while tracking. Next, connected 8 diodes per motor, as described in the linked blog post, and things got way better if not perfect! Not sure if I can still see a little (barely noticeable) thug per step when looking at the straw's end, but perhaps it is also the looping / grinding sound of the motor per step that makes me see what is not there. Movement does appear extremely smooth now in comparison, but I did notice that even with diodes, lowering current (below 0.6V = 1.2A) makes this subtle remaining thug a little more noticeable, but at 0.6V or cranked at 0.7V it is almost if not completely gone (only the slightest hint of a thug near the end of the step). Anyone with similar experience?

As I am using full current to drive motors, they are very loud while micro-stepping and sound like an old school fax modem or noisy/broken sound card. Perhaps due to cheap motor quality or is this to be expected with any motor?

Had cloudy weather since, so keeping fingers crossed it will work smooth while tracking / guiding in real use. Considering that I was opting for cheapest and shortest route to motorize the mount, I am pretty happy where I got to, so again, thanks everyone for contributing and of course Tom for making this project available / taking care of everything else.

Lastly, perhaps it would not be a bad idea to factor these issues on the motor recommendation page. When I first looked it was in lines of "the lower the better" in terms of voltage, which is not entirely true without having 8 big diodes in place, per this thread. That said, I did need a PCB fabricated to mount RJ11 to Motor connectors near the motors, so including 8 vertically placed diodes in the final design will not be a biggie. =)
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TCWORLD

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Re: Astoeq tracking pause every seconds.
« Reply #46 on: October 14, 2017, 10:40:40 »

@robotmonster,

Thanks for your feedback, I've updated the information page accordingly. When I originally wrote that tutorial I wasn't aware of the problem.
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Tom Carpenter (AstroEQ)

Jonesdee

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Re: Astoeq tracking pause every seconds.
« Reply #47 on: October 28, 2017, 00:21:06 »

Hi Robotmonster, your experience is very similar to mine regarding experimetation with solutions to thye microstepping issue.  I tried the 'shorted pin decay solution with minor success, then found that the diode array fix works very well indeed. Due to poor eyesight, my main interest is imaging and have found that 15+ minute exposures without trailing can be easily achieved by quiding the mount with PHD2.

I have contemplated attempting to use the diodes in a dew heater, as they certainly get quite warm, however the long connections required would probably cause more issues  :).  Have you mounted yours on a heatsink?

At the moment I am contemplating building another AstroEQ controller to be housed in an eclosure with controllers for focus, filter wheel and dew heater, so I have scouredthe web for newer Stepper drivers that may have resolved the problem, however it seems that the diode network may still be the best solution.

Dave
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TCWORLD

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Re: Astoeq tracking pause every seconds.
« Reply #48 on: October 28, 2017, 10:18:03 »

Hi Dave,

You might want to consider the TMC2100 drivers for your DIY. They are pin compatible with the DRV8825s and I've added support for them in the latest beta firmware. I can confirm what others have reported that they are very smooth - a lot more so than the DRV8825 drivers. Down side is that the only go up to 1/16th microstepping, so would probably need to go with a 0.9 degree stepper to compensate and keep the same resolution.

They don't seem to have the same issues that the DRV8825 has, so the diode trick isn't needed.
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Tom Carpenter (AstroEQ)

Jonesdee

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Re: Astoeq tracking pause every seconds.
« Reply #49 on: October 28, 2017, 15:25:42 »

Hi Tom
Hi Tom

Thanks for that - I will try a pair in my upcoming new controller build - I hadn't realised that they are pin-compatible with the 8825.

OMC Stepperonline have some 0.9* NEMA 14 units at 10v 0.4A which could be good. Slightly bigger than my NEMA 11s, but should fit OK with the existing belts.

I suspect that with good guiding, 1/16 stepping would probably be fine anyway.

Cheers

Dave
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rvaneynd

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Re: Astoeq tracking pause every seconds.
« Reply #50 on: November 28, 2017, 18:38:49 »

Dave,

I just installed the OMC NEMA 14 0.9 Steppers at 10v 0.4A and they work great with my EQ5.
I use them at 1/32 stepping.

Raoul
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David

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Re: Astoeq tracking pause every seconds.
« Reply #52 on: November 29, 2017, 14:48:51 »

Useful spreadsheet I believe ... To be tested!
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jslight

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Re: Astoeq tracking pause every seconds.
« Reply #53 on: September 02, 2018, 20:44:20 »

The diode modification works well to smooth the ticking when using low current, low voltage steppers and DRV8825 drivers.

I used two bridge rectifiers (four diodes inside) per motor instead of eight diodes; just tie the DC legs (+ & -) together, then wire the AC legs (~) in series with only one side of each phase.  The rectifiers got hot as expected, but nowhere near dangerous levels, just make sure they are rated for the phase current of your steppers.
« Last Edit: September 02, 2018, 20:48:59 by jslight »
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