G-11 vs EXOS-2 #G11 #EXOS2 #TECHNICAL


Jeremy Parker
 

Hi Jerry, All,

I might be interested in doing this firmware update, but I'm not sure if it would benefit my RA guiding. I sometimes I run off of a battery setup, so power consumption is somewhat of a concern, too. I would be very interested to know if Jennifer or others can attribute any improved guiding performance with the 1300mA current. I have the O-Vision worm in RA, with a loose mesh and east-bias, and it's been performing pretty well. However, on the DEC, I have the OPWB with a spring-loaded setup (my own modification, not Losmandy's), and I do think I could benefit from having more torque in this case. I believe my moment of inertia is greater in DEC than in RA, so I think the added torque might help in DEC guiding, and would let me use more spring force in the OPWB mesh.

So my question for Jerry is: Could you release a version of the G11 firmware that only increases the current for the DEC motor to 1300mA, while leaving RA motor at 900mA? (Seeing how it would be a change for DEC, and DEC doesn't move constantly like RA, it should have less of an impact on power consumption during normal tracking/guiding.)

Thanks,
Jeremy
--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jerry Hubbell - Explore Scientific VP Engineering
 

On Mon, Jun 17, 2019 at 11:53 AM, Jeremy Parker wrote:
So my question for Jerry is: Could you release a version of the G11 firmware that only increases the current for the DEC motor to 1300mA, while leaving RA motor at 900mA?
Hi Jeremy,

Currently, the motor current settings apply to both axes in the firmware, it would take some changes to apply the change to each motor separately.  Let me look at it and I could probably create a version for you to test out. I am not sure how useful it would be for general use, so I probably wouldn't post it. The reason I introduced the increased motor current wasn't because the 900 mA did not provide enough torque, it absolutely does, I released it because it seemed to help smooth out the tracking a bit. At our observatory using the Telescope Drive Master, our unguided tracking was typically 0.6-0.7 arc-seconds RMS (we do have a slight amount of lash) but when I increased the current to 1300 mA the unguided tracking reduced to 0.3 - 0.4 arc-seconds RMS. The nice thing about this measurement is that it is independent of and doesn't include any star scintillation error.

I will take a look at it.
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jeremy Parker
 

Hi Jerry,

OK thanks for taking a look at this. I did the 1300mA update last night and figured I would just try it. There is a noticeable increase in torque. Previously, when I would push my spring-loaded DEC OPWB mesh in tighter by hand, it would cause the motor to lose steps and make an audible 'knocking' sound. With the 1300mA current now, it doesn't lose any steps as I push in. So in the colder temps, I could probably leave my mesh spring setting alone and not loosen it as I previously had to. And perhaps this increased torque will allow better control of DEC as the wind pushes my scope around, for example.

With RA, I couldn't test my guiding due to the clouds (and the weather is not looking good for the next week), but I did notice the sound of the RA motor is now louder when tracking. That ~2 second periodic, modulated sound seems more pronounced. On my O-Vision worm, the shaft of the worm actually sticks out the end of the block, so I can feel the rotation of the worm itself. I do notice the rotation of the worm corresponds to the sound, if that makes any sense. There's a 'stop-start' moment in every 2 second cycle of the sound, and so it seems I can feel this in the worm. I wonder if there's anything you can do to smooth that out, and if it would lead to better tracking? It's so quick that it might not be visible in guiding data or perhaps convoluted with star scintillation/seeing conditions.

The power consumption on my inline power meter showed an increase as expected, but not dramatically so. Maybe it was an extra watt or two when slewing. In any case, I'll certainly report back on what improvements I notice with the 1300mA setting, and if making a DEC-only 1300mA version of the firmware would be worthwhile.

Regards,
Jeremy

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jerry Hubbell - Explore Scientific VP Engineering
 


Hi Jeremy,

I found the opposite with our G11 in the MSRO, the motor became smoother with the increased motor current, here is a plot using PECPrep of the tracking error as measured by the Telescope Drive Master on our G11. As you can see, the error is only 0.38 arc-sec RMS. This was an improvement for our mount over the previous motor current (900 mA) which had a measured TE of 0.6-0.7 arc-sec RMS. I would be interested in seeing any guide logs you may have with the 900 mA and also any you take in the future with the 1300 mA current. This cycle you are talking about has been reported by an iEXOS 100 customer in Germany also, I am waiting on some more data from him also.


--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jeremy Parker
 

Hi Jerry,

Well I do hope my results match yours, and I'll be interested to try this out. It looks like your sample interval on the TDM-captured data was 0.17 seconds, so presumably you'd be able see any unusual behavior on the order of ~2 seconds, which is about the rate of the motor noise. I'm not sure if the 'smoothing' impacts the calculated RMS numbers, but if you were to turn it off and focus just on the short-period energy, around 2 seconds, would you see any spikes? Would they be different between 900mA and 1300mA current settings?

I'll make a recording of the noise as well, in case it's useful. It's the same kind of noise I used to hear at 900mA, just noticeably louder....

Regards,
Jeremy

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jerry Hubbell - Explore Scientific VP Engineering
 
Edited

On Tue, Jun 18, 2019 at 06:27 PM, Jeremy Parker wrote:
Well I do hope my results match yours
Hi Jeremy,

I think the actual oscillation is more like 1.3 seconds, at least that is what Gunter in Germany reported.
How has this impacted your images?  Do you have any examples to share?
 
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jeremy Parker
 

Hi Jerry,

Yes, that could be more like 1.3 seconds, I was just guesstimating on my memory of it. I made a little 'propeller' jig to stick on the end of the worm shaft, in order to quickly visualize what I was feeling by hand. So I took a movie which shows a 'lurching' of the worm rotation during tracking, and it does correspond to this periodic sound. I placed it in the User Contributions folder in the files section.

To answer your question, I'm not sure how it's impacted my images, as I haven't had a chance to try the 1300mA firmware. I only made the update last night, and unfortunately the weather is not looking good in the next week. I would guess it's been occurring this whole time with 900mA as well, but perhaps just to a lesser degree?

Just to get back to what I was asking, would you happen to see this also in the TDM-acquired data if you were to look at short periods in the FFT, like 1.3 seconds, and without any smoothing applied? It may be possible that the moment of inertia in RA would effectively filter this out mechanically, but in theory wouldn't it be better if this lurching behavior was eliminated? Possibly even better PE could be realized?

I'll be happy to share data when I have it, as I'm just trying to be helpful to the group here and pointing any possible improvements that we all might be able to benefit from.

Regards,
Jeremy

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jeremy Parker
 

Hello Jerry, All,

I was just out with the mount tonight at 1300mA motor current to gather some guiding data, especially unguided error with PHD2's Guiding Assistant. The bottom line is that I couldn't sample quick enough with PHD2 to ascertain the magnitude of the ~1.3s oscillation in the RA movement. The Nyquist criterion would require that I sample at 0.65s or quicker to actually be able to measure an oscillation with a 1.3s fundamental, let alone the harmonics of that waveform. I was only able to sample at about 1/second. Probably your Telescope Drive Master data would be the only thing fast enough to allow the FFT analysis on the RA error. I still went ahead with Guiding Assistant, Calibration and some actual guiding.

The conditions weren't very good, between the wind, clouds and poor seeing, and so I lost the guide star a few times and saw the star SNR drift around. I set up PHD2 with a 0.2s guide exposure, which seemed to give the quickest correction/guide rate. In other words, although the camera might have been only taking 0.2s exposures, the calculation and communications wouldn't move any quicker than about once per second. Quicker than 0.2 seconds didn't buy me anything and started to compromise the star quality on even the bright star I had selected. I had the scope pointing near the meridian and equator, so that I could also do a calibration and guide all in the same area. For guided error, I stayed under 1" RMS total, which was to be expected based on conditions, and I think the quietest regions gave me around 0.8" RMS. Compared to my best guiding, this wasn't very good, but I think the conditions were to blame here.

I will say the DEC performance seemed pretty good at this 1300mA setting, where the wind would push in one direction and the guiding seemed to correct in the other direction fairly effectively. I think this might be an improvement, but it might be tough to quantify.

I've attached my guide log for anyone who's interested in looking at it, as I was unable to upload to the user contributions folder on Groups.io. The 'Upload Files' button seems to be grayed out for me. Has anyone else noticed this?

My feeling is that this 1.3 second lurch/oscillation when tracking is small compared to poor seeing, wind, etc. like tonight's conditions. When I eventually do get some better conditions, maybe I could better see it in some 'undersampled' way in PHD2 data or more importantly, maybe it might show up in my actual image. I'll keep an eye out but will stick with the 1300mA firmware in the meantime, as it seems to be helping my DEC performance.

Thanks,
Jeremy 

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jerry Hubbell - Explore Scientific VP Engineering
 

On Mon, Jun 24, 2019 at 12:35 AM, Jeremy Parker wrote:
When I eventually do get some better conditions, maybe I could better see it in some 'undersampled' way in PHD2 data or more importantly, maybe it might show up in my actual image.
Hi Jeremy,

Thanks for the data. As I have said in previous messages, this tiny 1.3 second oscillation does not impact any imaging that I have seen. Unless we have a customer trying to use their PMC-Eight mount on a mountain where the typical seeing is 1 arc-sec FWHM or less, and the pixel scale of their imaging camera is < 0.5 arc-seconds/pixel, you will not see the oscillation in my opinion when not autoguiding. I don't think anyone would notice it while guiding so in my opinion, it is not a problem that customers should worry about. As far as my results with the Telescope Drive Master (TDM), I think I shared my corrected PE when the TDM is active. The typical TE is about 0.35 arc-seconds RMS and the sample values appear to be random.

Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jerry Hubbell - Explore Scientific VP Engineering
 

On Mon, Jun 24, 2019 at 03:11 PM, Jerry Hubbell - Explore Scientific VP Engineering wrote:
Hi Jeremy,

Thanks for the data. As I have said in previous messages, this tiny 1.3 second oscillation does not impact any imaging that I have seen. Unless we have a customer trying to use their PMC-Eight mount on a mountain where the typical seeing is 1 arc-sec FWHM or less, and the pixel scale of their imaging camera is < 0.5 arc-seconds/pixel, you will not see the oscillation in my opinion when not autoguiding. I don't think anyone would notice it while guiding so in my opinion, it is not a problem that customers should worry about. As far as my results with the Telescope Drive Master (TDM), I think I shared my corrected PE when the TDM is active. The typical TE is about 0.35 arc-seconds RMS and the sample values appear to be random.
Here is the PECPrep chart of your data. The measured residual PE is 0.57 arc-seconds RMS which is very good for standard auto-guiding performance.


 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Jeremy Parker
 

Hi Jerry,

Thanks for the message. I'm not overly worried about it at the moment, but I do hope to get to better seeing conditions. I can only dream of imaging on a desert mountaintop, but I would want to take my PMC-Eight with me. :) More realistically, I may be at a smaller image scale in the future (currently at 1.13"/pixel), especially if I go for a longer focal length scope to get the galaxies (and planets) and things that are currently small in my relatively wide-field refractor. In my best of best guiding stretches while still at 900mA, I've been in the 0.2" RMS range on RA, so if I can get there again with the 1300mA firmware, then this won't realistically be a concern until I go to an SCT or something in >2000mm range of focal length.

Yes I did see your data, but it looked like maybe smoothing was turned on and that any energy in the 1.3 second period and shorter wasn't visible. Hypothetically if you were to quantify it and subtract it, I wonder how much you would beat your 0.35" RMS record by. In the spirit of continuous improvement, shouldn't this be something that could be addressed in a future firmware update, for example? If the RA worm could and should turn smoothly, isn't that preferable? As a fellow engineer, I hate to see performance 'left on the table', so to speak.

Thanks for your efforts,
Jeremy 

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jeremy Parker
 

Thanks for the analysis Jerry, I think I saw about the same when I used PHD Log Viewer to review the data. I'll be happy to share my future guiding data, especially under better conditions and if I approach my 0.2" RMS 'record'. And just for your enjoyment, and to assure you that I do more than look at PHD graphs :) , here's my last image of M51 where I had about 3 hours in a fairly dark sky...

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Wes Mcdonald
 

Jeremy

I'm glad to see your mention of the undersampled nature according to Nyquist.  Something you might consider is go ahead and design an undersampled scenario that in fact would yield your waveform, just at the incorrect frequency.  Sampling at 1 hz indeed undersampled any wave form with frequency higher than .5 hz.  Your 1.3 sec guy has a frequency of .77 hz or so.  What happens is waveforms which are undersampled are folded back into the digital spectrum, first from the top then from the bottom and back and forth.  So when you sample the .77 hz wave at 1 hz the waveform is translated (aliased) to a frequency of .77-.55= .22 hz.  It is in your data it is just not represented in the spectrum at the correct place.  Note that if your trouble was at 1 hz it would aliase back to zero and you would not see it at all in the digital domain or show up as a DC constant ( which in life it never would as you could never sync the sample rate and the sampled waveform with exactitude).  But for your guy you will see it and you can analyze it and its amplitude.   

If this is new to you, you can play around in Excell and see what happens to undersampled waveforms.

Wes




--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired


Jeremy Parker
 

Hi Wes,
That’s a good point about the implications of undersampling. Since there is no anti-aliasing filter on the data, we should indeed see the difference frequencies folding back into the spectrum as you describe. I’m sampling at 1.1Hz, and I suspect the lurching part of the waveform has quite a bit higher harmonic content than the 1.3Hz fundamental, so I’ll take a look for those products in my FFT. Thanks for pointing that out.
Regards,
Jeremy 


On Jun 24, 2019, at 5:37 PM, Wes Mcdonald <wesmcd6@...> wrote:

Jeremy

I'm glad to see your mention of the undersampled nature according to Nyquist.  Something you might consider is go ahead and design an undersampled scenario that in fact would yield your waveform, just at the incorrect frequency.  Sampling at 1 hz indeed undersampled any wave form with frequency higher than .5 hz.  Your 1.3 sec guy has a frequency of .77 hz or so.  What happens is waveforms which are undersampled are folded back into the digital spectrum, first from the top then from the bottom and back and forth.  So when you sample the .77 hz wave at 1 hz the waveform is translated (aliased) to a frequency of .77-.55= .22 hz.  It is in your data it is just not represented in the spectrum at the correct place.  Note that if your trouble was at 1 hz it would aliase back to zero and you would not see it at all in the digital domain or show up as a DC constant ( which in life it never would as you could never sync the sample rate and the sampled waveform with exactitude).  But for your guy you will see it and you can analyze it and its amplitude.   

If this is new to you, you can play around in Excell and see what happens to undersampled waveforms.

Wes




--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired

--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Wes Mcdonald
 

Jeremy

Yes probably.  If theyrch is sort an impulse. But the mount mass makes the whole guiding system a low pass filter.. just because I deliver an impulse to the mount doesn't mean it will respond....and if it doesn't then the impulse.will disappear in the guiding data..?sorryfor typos to.manu long island iced teas

Wes


--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired


Jeremy Parker
 

Agreed, and I suspect there is some mechanical low-pass filtering as well. This might be the only time you'd want more moment of inertia. A long island ice tea sounds good right about now!

Jeremy

On Mon, Jun 24, 2019 at 7:06 PM Wes Mcdonald <wesmcd6@...> wrote:
Jeremy

Yes probably.  If theyrch is sort an impulse. But the mount mass makes the whole guiding system a low pass filter.. just because I deliver an impulse to the mount doesn't mean it will respond....and if it doesn't then the impulse.will disappear in the guiding data..?sorryfor typos to.manu long island iced teas

Wes


--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired


--
Jeremy Parker - North/West of Boston, MA
Scope:
StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2, SGP, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks


Jerry Hubbell - Explore Scientific VP Engineering
 

On Mon, Jun 24, 2019 at 04:44 PM, Jeremy Parker wrote:
In the spirit of continuous improvement, shouldn't this be something that could be addressed in a future firmware update, for example?
Hi Jeremy,

I wish it was as simple as a firmware fix, I would have already fixed it probably. The issue is that the stepper motor driver chip (TI DRV8834) is the source of the jitter. When I discovered it I worked with a TI engineer to try and resolve it by changing the configuration of the hardware (via the decay mode, see http://www.ti.com/lit/ds/symlink/drv8834.pdf ) but it turns out that it didn't make any difference. The only noticeable improvement came about when increasing the motor current. So as far as leaving performance on the table, that is not the case here.

Fortunately, the issue is more of a "cosmetic" issue in that it really does not impact the performance of the mount as far as the end result is concerned as there are other factors that have a much larger affect. 
 
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


 

I've watched this thread with interest - and even looked up Nyquist, Wes! :-)
 
From what I've seen with my EXOS2 mount, this fast jitter would, indeed, be lost in the noise of other effects.  The mount itself can already give me round stars at 621mm FL, for long stretches, at well under 1" RMS, using the original firmware, when set up with care, and conditions permitting.  Fine for any reasonable DSO work I should be giving a portable mount.  
 
The other side of this coin is power consumption.  While I'm running on house power, 900mA vs 1300mA doesn't matter.  But soon, I'll be ready to venture out of the back yard and into darker skies (and cold winter nights...) on battery - and then it might matter.  So I think I should be happy with 900mA...  
 
- Bob
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2-IMX224C
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Wes Mcdonald
 

Bob

The currents bring discussed are for a G11 mount.  The exos2 runs along on about 500ma....most due to the PMC8.  When slewing is about the only time my ammeter shows more.  I can run an evening on about 10 amp hours.  

Wes


--
Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired


Jerry Hubbell - Explore Scientific VP Engineering
 

On Tue, Jun 25, 2019 at 11:22 AM, Wes Mcdonald wrote:
The currents bring discussed are for a G11 mount.  The exos2 runs along on about 500ma....most due to the PMC8.  When slewing is about the only time my ammeter shows more.  I can run an evening on about 10 amp hours.  
 
Wes
Yes,  our testing has shown that the EXOS 2 while tracking draws about 450 mA and around 600 mA when slewing, so an average of 500 mA over the session is reasonable. The motor current limit is set to 600 mA in the firmware and is close to the maximum rated current of 650 mA for the motor. I would not have a problem increasing the motor current slightly above that limit to 700 mA if that would make a change in this small jitter, but again, it would probably not be noticeable in your images.
 
--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home


Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
Mounts
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!