Thanks - I use sharpcap's electronic polar alignment, but like having a back-up polar scope just in case. Too bad the G11G's polar scope doesn't have the graduated circle option.?

On Sun, Jan 7, 2024 at 07:10 AM, John Natale wrote:

I am considering getting the illuminated polar scope that is an option for the G11G. Does anyone know what the reticle looks like? I am hoping it is just a simple 360 degree circle, so I can use the "Polar Scope Align Pro" app, and just put Polaris in the spot where the app tells me to during alignment. I have seen reticles with the big dipper, Cassiopeia etc and am wondering what this one looks like.

Also, if I get this polar scope, are there installation instructions, or does it come installed already? I'm wondering if there is some sort of calibrartion/adjustment I will need to do (similar to my EQ6 mount's polar scope). It seems like it would need to be installed precisely in the right spot and at the right angle for it to work.

?Hi John
? I have a G11G with all the options including the polar scope. It is disappointing compared to my EQ6-R's polar scope which I love. There is no graduated circle. Just star patterns where you have to insert the stars, there are no accurate circles to center the star in, just a gap between some lines. I do not use it anymore. I have the Ipolar camera and the PoleMaster cameras.

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When I bought my G11G I bought the 2 cases for the 2 parts of the G11 if you get the RA extension. It was cheaply made plastic. I returned it when I went to NEAF. It is not on their website anymore, rightly so. The case for the heavy duty tripod is a good case though, it is an SKB. I am still looking for mount case options myself. I have bought cases from this company, and I plan on having them make me some more.

Hi John,
? ?Considering all the responses and that I am late to the party; I think you have a lot of useful information. Actually, I may be able to learn something too.

What is the best option for a carrying case for the G11G? Is there one commercially available, and if so, can someone post a link to it? I have heard that the RA axis needs to be disassembled from the alt section for storage, and the two parts put in different cases. Is that correct? Does that work well, or is there another storage method that you recommend (i.e., buying a pelican case with foam and storing the whole thing as one unit)???

I am considering getting the illuminated polar scope that is an option for the G11G. Does anyone know what the reticle looks like? I am hoping it is just a simple 360 degree circle, so I can use the "Polar Scope Align Pro" app, and just put Polaris in the spot where the app tells me to during alignment. I have seen reticles with the big dipper, Cassiopeia etc and am wondering what this one looks like.

Also, if I get this polar scope, are there installation instructions, or does it come installed already? I'm wondering if there is some sort of calibrartion/adjustment I will need to do (similar to my EQ6 mount's polar scope). It seems like it would need to be installed precisely in the right spot and at the right angle for it to work.

Thanks everyone- I really appreciate the info.

Thanks again Ken-? the screen shot really helps. From the picture it looks like I will need to use a baud rate of 9600 with the G11G. My Skywatcher EQ6 mount/EQMOD uses a baud rate of 115200. Hopefully in Sharpcap I can just input all the data for the G11G, and in the future when I choose that mount its settings will automatically come up. That way I won't have to reprogram sharpcap every time I change a mount.

I have been trying to find out the sub-second dynamics of my G11S with OnStep for which a guide error log is sampling too slow.? The only way I could think of was to create star trails using the hand controller and analyze them.? Speed variations result in variations of light intensity.? This can easily be inverted and integrated to retrieve the deviations from the nominal trajectory.? Its power spectrum then tells the oscillations of which some may be attributed to the stepper motor.?

For a focal length of 755 mm (ES127CF+FF) and a pixel size of 3.8 mu (ASI2600) at nominal RA tracking speed (relative to the sky) the stars move at 14.6 pixels/s so we can analyze up to about 7 Hz.? I took some star trails at various speeds, rotated them vertically in Gimp then imported them in Scilab for analysis.? I used an order 10 polynomial trend removal to account for incident angle, dust motes and other low frequent disturbances, and the median for background removal.? The DEC position is done by a weighted average of pixel values.? This is pretty crude in some ways, but I don't think it is complete nonsense.

The RA 1x relative speed is shown below.? The 700x100 pixel image on the left is the star trail (DEC is horizontal, RA vertical).? The center column has the DEC (X) and RA (Y) errors relative to the nominal trajectory.? The RA plot also shows the 10-th order polynomial trend-removed version.? Their power spectra are to the right.? DEC shows errors tapering down at 1 Hz, RA tapers down at 0.5 Hz.? Since RA is moving at 2x tracking speed, maybe this translates to errors up to 0.25 Hz at tracking speed, if it is due to the stepper motor.? Take it FWIW.

About the number of microsteps, at 64 microsteps my Nema17 micro-steps at 107 Hz.? I don't know if it makes a lot of difference with 32 microsteps at 53 Hz or 16 microsteps at 27 Hz.? The mechanical telescope system limits the bandwidth quite a bit, so any errors above 8 Hz or so get smoothed out quite a bit.?

I am interested in stepper motor related errors, which is why I did this.? Based on the above (if it can be believed), the highest frequency peak at tracking speed is below 0.25 Hz, and the magnitude looks minor compared to the rest.? Just my 2 cents.

Enter in the hardware tab and the Gemini.Net should be available in the roll down selection per below. The Properties button allows you to set what interface you are using to the Gemini.Net setting and I use the Ethernet setting. If you are using the ethernet connection then SharpCap does not have to be on the same PC that the Gemini.Net driver is on.

For Stellarium and others you may want to see if it supports ASCOM's Alpaca server so that you can also run the Stellarium on another system to the Gemini.Net driver. Alpaca is a newish server/client model for ASCOM that does not require .Net (i.e. install Alpaca Server on the PC with the Gemini.Net driver and as long as the Stellarium has the Alpaca client then it can communicate to the Server syste with Gemini.Net - see

Ken

Thanks Ken. This is very helpful!

Question... in the sharpcap settings page, any idea which tabs I would need to enter info into? Maybe the hardware tab? I can look at each tab if/when I get the mount; just curious. Also, I think the mount needs to be connected to the PC for it to show up in sharpcap, correct?

John,

I use the ASCOM Gemini Telecope.Net driver - (Under the Ascom section)
??????? Video here -

SharpCap just needs the ASCOM Gemini Telescope.net installed and you can set it up in the Settings area -
Stellarium - /g/Gemini-II/topic/trying_to_control_gemini_2/82816694?p=

Good luck,
Ken

Hi all,
I just joined the group. I am considering buying the G11G mount, to be controlled by my PC via a USB cable (I don't use asi air). I use Sharpcap and Stellarium.? Can someone please indicate the correct PC control software I would need to download (Gemini II)? And are there instructions on how to use this software for mount control?? Is it compatible with Sharpcap and Stellarium, and how well do they work together- any issues??

If there are any introductory tutorial videos on PC control of the G11G, using sharpcap and stellarium, can you send a link, or let me know where I can find one??

Thanks!

On Sun, Dec 31, 2023 at 04:52 PM, Michael A. Covington wrote:

On 2023-12-31 18:06, Brendan wrote:

You can increase torque by using a larger to smaller belt hub, which
is the same as any large to small gear ratio.
--
Brendan

Yes, but it remains the case that torque is not the same across the
entire microstep cycle, leading to slight speeding up and slowing down.?
We're not talking about lacking the torque to move the load.

Michael A. Covington, Ph.D.
Consultant, Covington Innovations, Athens, Georgia, USA

Micheal,

There is a fair amount of starting friction that has to be overcome on top of the normal load forces. When the mount is moving steady state the standing friction is lower overall. When you look at the available.torque for a micro stepped motor it is easy to see why it is desirable to start a static load using full steps or at least much lower micro step values to get the drivetrain moving. I expect that the static load never actually goes away completely with stepper motors drivetrains because their motion is not actually continuous like a servomotor driven by a small DC motor.?

The reason Losmandy can use such small DC servomotors is the high reduction in the Losmandy drivetrain. So stepper motors need to be run with lower microstep values and still need significant reduction to work smoothly. For the G11 I think 5:1 is the minimum for a stepper motor drive. The standard gearbox for the Gemini servomotors is 25:1 but this would yield a very slow slew for a stepper motor driven G11 with most of the OnStep controller boards because they don't have fast enough clocks to generate the required step pulses.?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather Forecast - South Pasadena, CA?

On Sun, Dec 31, 2023 at 12:26 PM, Michael A. Covington wrote:

Microstepped stepper motors do not have equal torque at all microsteps.?

And Michael's description becomes likely one of a motor that lost position during micro-steps while synchronizing position as the motor passes the next pole position (full torque).? Requiring either a larger stepper motor or mechanical transmission reduction (belts or gears).? ?Allowing more torque, more resolution, or a mixture of torque and resolution.

It should have a rough PHD2 graph with moments of hope.? ?It's very interesting Michael could see the issue visually.?

Thanks Michael and Chip,
Doug

This is from an old Hackaday article about microstepping stepper motors. It is old but the rules and torque losses are immutable laws of the universe and explain the problem using very high microstep values. You can easily validate this information using a stepper tester. If we had an imaginary 0.9 degree (400 step)? 100 oz/in NEMA 17 stepper even at only 32 microsteps the stepper could at best only provide 5 oz/in of torque. At 256 microsteps less than 1 oz/in torque. As you can see this is not very reliable. A high torque standard NEMA 17 size frame normally delivers 59 oz/in torque. Obviously some mechanical reduction is in order as well as some mode switching and stepper speed ramping.? ?


--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather Forecast - South Pasadena, CA?