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?

On Wed, Jan 3, 2024 at 12:36 PM, @darkairmouse wrote:

Hi Chip,
Understood.
Despite the not-so-good RA guiding the accuracy of the pointing was very good.?

Yue

So getting good GOTO results I think tells us that the mechanical basics are solid and all you really need to do is fine tune your autoguiding. Leave the mount hardware alone for now and look at the what your autoguiding corrections are doing. Are you autoguiding using a OAL or piggybacked guide scope? If you are looking at images from an SCT and using a piggybacked guide scope what is the working focal length of the SCT and guide scope??

Some years ago I tested autoguiding results using both an OAG and a piggybacked scope on my pre-update classic 2-piece worm block G11 which had the Belleville spring disc mod installed. I had solid results at prime focus of my 10" f/6.3 LX200 SCT both piggybacked and using the OAG with the same QHY 5-II mono camera. Auto guided PE was well under 0.5" RMS - within 0.46" - 0.38" PE RMS, this is about at good as this mount gets. I had the chance to retest after Scott did the tucked in servo motors and spring loaded OPWs and the results were virtually identical on the now all stock new spec drivetrain. The difference is that the reworked mount is now ALWAYS in this range or better if the seeing is good.?

I cannot repeat the exact same setup using the latest L6 firmware because several years ago I switched to ZWO cameras and I am now using the ASIAIR Plus controller in place of the laptop and full suite of ASCOM apps like PHD2. That said the ASIAIR did show a slight autoguiding improvement over the normally slightly lower performing simplified ASIAIR PHD2 autoguiding.?
?
--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather Forecast - South Pasadena, CA?

Hi Chip,
Understood.
Despite the not-so-good RA guiding the accuracy of the pointing was very good.?

Yue

On Wed, Jan 3, 2024 at 05:59 AM, @darkairmouse wrote:

Ok finally got a chance to test my 811G last night, and honestly, not as I expected. Not as bad as 'disappointed' but not as what I 'expected'.
The DEC turned out smooth, no issues at all however the RA..... jumping up and down on PHD2 graph, worse than my eq6-r pro.
I did everything was as usual i.e. I did what I'd do if that's my eq6-r pro and PHD2 didn't report any issue/problem after calibrating but still the RA curve showed ugly and I can see that from the final 20-min sub.
Anyways, now I adjusted the RA adding very little backlash, waiting for next clear night to see if this helps.

Yue

Yue,

The Losmandy GM811 is not an EQ6 and you need to do things a bit differently to find the mount's sweet spot. Every Losmamdy mount is capable of a slightly different different minimum PE value. The most important things to check are related to constraint of the worm between the bearing blocks and the alignment of the gearbox and worm before the Oldham grubs are glued and tightened. After that it is all about spring force to push the worm into the worm wheel and the worm lift bolt adjustments.?
?
--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather Forecast - South Pasadena, CA?

“Nudge mount out of safety limit on slew” which is set in ASCOM driver dialogs, not in Gemini screens.
--
Edward

Ok finally got a chance to test my 811G last night, and honestly, not as I expected. Not as bad as 'disappointed' but not as what I 'expected'.
The DEC turned out smooth, no issues at all however the RA..... jumping up and down on PHD2 graph, worse than my eq6-r pro.
I did everything was as usual i.e. I did what I'd do if that's my eq6-r pro and PHD2 didn't report any issue/problem after calibrating but still the RA curve showed ugly and I can see that from the final 20-min sub.
Anyways, now I adjusted the RA adding very little backlash, waiting for next clear night to see if this helps.

Yue

On Mon, Jan 1, 2024 at 07:29 AM, WayBack wrote:

Michael,

Micro step position does vary but I'm not sure it represents a significant issue; this not accumulating during guiding.? The issue appearing like corrected backlash.? And it cannot accumulate in physical position between motor poles (true steps).

I always felt power consumption and the related issue of producing less torque for the power were my issues.? The benefit of being open loop becomes significant only if the weight and power allow for this.

With torque levels at tracking quite small, as you illustrate here, the variation cannot be large, or it shows up in guiding.? I've never seen anyone ask David Partridge?but the RMP of our motor during tracking must be quite low and the ability of our motor to arrive exactly on count at a moment in time also a variant.? Still there too, all just esoteric when compared to the tracking RMS achieved.? Hence the importance placed on achieving Level 6 functionality.

Doug? ?

I did not write the firmware or design these systems but my understanding of the way these system work is that they are quite different.?The way an open loop stepper drive system works vs the closed loop of the Gemini 2 servo motor drive is quite different.

A stepper motor controller like the OnStep (not the stepper driver IC which can be quite sophisticated) blindly sends the step or microstep pulses calculated and has no idea if the stepper motor has actually completed the full step count or lost steps. This is an inherent problem with an open loop stepper drive system especially a marginally powered system for the load. This means that an open loop stepper drive system cannot ever know the mount axes position with certainty. Encoders on the drive motor itself or the movement axes allows the mount controller to know with reasonable certainty the mount's position. Certainly there are encoder equipped stepper motors but they are not being exploited widely yet.?

So open loop stepper motor drive mounts using a worm screw can basically only successfully step and move the mount or lose steps and physical position but the mount controller's model is not aware and has to assume the mount? position is correct which puts the slew off target requiring the mount be recentered. Depending on the how many steps were lost and the application it may or may not matter.?

The closed loop system with encoders on the DC motor drive shaft as used in the Gemini 2 allow the controller to just run the motors and watch the encoder count slowing, then stopping or assuming the selected movement rate for tracking. Positional data for the mount is generally? known and the mount position can be corrected in the case of an under or over shoot of the desired tic count. The Gemini sends a known amount of current to the motors and watches the resulting movement through the tic counts. If the tic count is not accumulating as predicted vs time more or less current is sent as required to match the desired movement rate.?

With the rewritten PIC code and revised and tuned L6 primary controller firmware the Gemini 2 L6 firmware now has a resolution of 0.14 arcseconds. This is getting into the pretty good range IME and is 4x better resolution of the direct stepper drive G11 mount. But if you added a 4:1 reductio with a pulley you would have very similar theoretical resolution though it would still only be a guess being open loop. Adding encoders on the stepper to close the loop and correct any missed microsteps and now you have something.? ?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather Forecast - South Pasadena, CA?

Yep, safety limits will also do that, and I didn’t think of that option either so, double doh! Lol

You have a couple of options to take the mount off the safety limits. You can use the hand controller to manually nudge the mount away from the limit (with the diamond buttons, in the right direction away from the limit). Or you can enable an option that I don’t remember off the top of my head where it is, so a park command will nudge the mount away from the limit before issuing the command itself. I believe that option is in the gemini.net driver but may also be available on the HC. Once that option is enabled NINA should be able to park the mount, even if it’s at the safety limits.

Doh! Thanks, Jonathan. I didn't even look at the HC this morning. I just went out and checked and the mount had reached a safety limit.

Anyone,

I'm guessing here but once that limit is reached, does it completely lock out control via software until reset by the HC (i.e. is this why I couldn't park from NINA)?

Thanks,
Joel

Hi Joel,

I may not be of much help but there are a couple of things you can check. If you have your hand controller connected try issuing a park command from it. Make sure it’s not reporting a motor stall and that tracking is not set to terrestrial. If you don’t have the hand controller then use the .net ascom driver. If you haven’t rechecked your gear mesh in a few months I’m guessing the cold temperatures may be binding them. Cold temps tend to tighten the mesh, which makes them bind and then stall.?

You can safely turn the mount off and push it to CWD to start over. Just remember to use Cold Start and that you will loose any models you may have built. Speaking of which, I’d make sure the option of “sync performs additional alignment” is also turned off. Just to make sure the model is not being corrupted with too many points.

Also, make sure NINA is not changing the tracking speed. I’ve had instances where it just stops the mount but mostly after TPPA or platesolving. I don’t recall having that happen during an imaging session but it’s worth checking.

Finally, definitely upload your logs. I’m sure others can take a look and find other issues but it all goes over my head so I can’t help you with those

That’s all I can think of at the moment. Good luck

jonathan

Twice over the past week, my G11g has just stopped - not powered off, stopped. Once was during setup while I was trying to slew to a target before my session and last night about four hours into my session. My resolution for the earlier session was a full reboot which fixed the issue and it ran all night. By the time it stopped last night, I was two hours into sleep. ;)

I did not turn the mount off between the previous session (two days ago) and last night's session.

I'm having no *physical* cabling issues (i.e. entanglements causing disconnects) and the mount is still powered up. This morning it just will not respond to commands - I cannot get it to park. I hope it's not because it's about 22 F.

All other commands issued to NINA work fine - I just warmed (heh - at 22 F not much warming I can do) the camera and turned off all the equipment (except the mount which will not respond).?

I'm not sure where to begin looking for issues so I'm asking for a starting point before I turn the mount off to reset it - some logs somewhere... ???

I *know* that's not a lot of information but I'm just not even sure what to ask.

Thanks,
Joel

Even using 0.9.degree (400 step) stepper motors and the maximum possible micro steps a direct drive stepper Losmandy G11 has relatively low resolution. Once you use a.more realistic number of micro steps closer to the guidelines for reliable micro stepping somewhere between 16-32 or maybe 64 obviously resolution goes out the door. Testing steppers online for 3D printers and verified by my own testing has shown that the most reliable microstepping rate range fall between 16-32 and beyond this rate the loss of steps due to tremendously reduced torque as the microstep count goes up becomes noticeable. At least if becomes a serious issue on 3D printers anyway.?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather Forecast - South Pasadena, CA?

I was curious about the CQ350 but went with the EQ8-R Pro. My EQ6-R pro is now my portable mount.?

开云体育

That's what I meant.? The mount was an iOptron GEM45 and it has a 1.5" peak-to-peak oscillation in RA with a period of, if memory serves me right, something like 0.7 second.? (Since a 1.5" p-p sinusoid is only 0.5" RMS, and because the period was too fast for PHD2, it looked like maybe 0.5" of roughness and I still got good guiding.)? The motor may have been underpowered; iOptron sent me a new circuit board with different voltage regulator chips that noticeably ameliorated the problem.

Hi Mike,?

Can you explain what you mean by a "period of a full set of microsteps?" I can see that meaning the period of time it takes the motor to complete a microstepped full step. But in my example the motor is moving?3.23 full teeth a second and clearly not losing a second. Thus you must be speaking of a larger sample size.

Analog Devices' Trimanic division's has extensive efforts to deal with the situation you describe. It would be interesting to see if it shows up in the driver's diagnostic output.

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

Michael,

Micro step position does vary but I'm not sure it represents a significant issue; this not accumulating during guiding.? The issue appearing like corrected backlash.? And it cannot accumulate in physical position between motor poles (true steps).

I always felt power consumption and the related issue of producing less torque for the power were my issues.? The benefit of being open loop becomes significant only if the weight and power allow for this.

With torque levels at tracking quite small, as you illustrate here, the variation cannot be large, or it shows up in guiding.? I've never seen anyone ask David Partridge?but the RMP of our motor during tracking must be quite low and the ability of our motor to arrive exactly on count at a moment in time also a variant.? Still there too, all just esoteric when compared to the tracking RMS achieved.? Hence the importance placed on achieving Level 6 functionality.

Doug? ?