Hy, Bill, Alfred and any interested Losmandy Gemini owners.
I have observed a mathematical error and it's not from KStars / Ekos so you can breath easy Hy. I put my Gemini mini and two motors on a bench test with no computers in sight.
Now this is the setup that was sent back to me with the latest level 6 update, In fact, I believe my Gemini was used in the developing that update, but I was noticing issues while tracking the moon 2 nights ago.
RA tests were all fine with a RA Divisor of 448770 and Dec Divisor of 0
DEC had appeared OK but when I selected Lunar tracking the Dec Divisor was now 23,225,329. This is much slower and with the lightest finger touch on the end of the gear, the motor started to get small shudders and only advance on about one pulse out of three. At the same time the Handbox RA and DEC numbers kept incrementing. It appeared to be normal even though the motor was not advancing reliably.
Ironically, in late June 26 I was critical of Gemini L6 mods as they replaced the absolute lock (or sync) between electrical input and encoder count output with a mod that allowed for uncounted pulses during stall conditions, and there was a complete lack of torque. The July mod has fixed the torque issue but it has not returned the motor to the previous state where it had multiple turns of tolerance (if stalled for some reason) and then return to absolute lock again.
Small steps may be the guide calibration issue. If Hy can please tell me how to increase these steps, I can determine the effect of those larger steps on my calibration.
Thanks
Len

Len, I'm not 100% sure what you're asking, but it you mean "how do you get larger movements in calibration?" the answer is to just increase your pulse duration.

Thanks, yes that was all at the moment and I'll report back tonight.

I'm not on Level 6 so any problems with that update are not causing my issues.

However, I do believe I found the culprit for why my Dec calibration was inconsistent. It looks like there was some slop in the Oldham coupler between the Dec motor and the worm. This doesn't feel like backwash when you wiggle the mount in Dec so I thought I had minimal Dec backlash. I have tightened that up and tonight is supposed to be clear. I will directly compare the built-in guiding against the PHD2 guiding and report back tomorrow.

Thanks Bill, and hope it goes well

Bill:"It looks like there was some slop in the Oldham coupler between the Dec motor and the worm. "

That would easily explain your funny DEC calibration. Good luck for tonight!

Well, that wasn't it. I got even worse results last night.



I just don't see how a pulse in Dec could cause it to move mostly in RA. It just doesn't make sense. As I previously mentioned, my GoTos are fine and plate solving and centering is working.

I will make one more attempt at adjustment and try again tonight. I might put an eyepiece in place of the camera to see if i observe a noticeable backlash when using the hand controller.

Well, that wasn't it. I got even worse results last night.



I just don't see how a pulse in Dec could cause it to move mostly in RA. It just doesn't make sense. As I previously mentioned, my GoTos are fine and plate solving and centering is working.

I will make one more attempt at adjustment and try again tonight. I might put an eyepiece in place of the camera to see if i observe a noticeable backlash when using the hand controller.

You should do the box test or, as the phd guys call it, the cross test. It's basically the same thing.

openphdguiding.org/man/Trouble_shooting.htm

Scroll to "Validating Basic Mount Control - the Star-Cross Test". The software (Ekos and losmandy driver) works flawlessly here. The same software should work flawlessly with your equipment, too.

OK, I posted on the Losmandy forums about my problem. PHD2 reported bad Dec backlash but I could see nothing in the mount when either wiggling the Dec axis or when using an eyepiece a moving back and forth in Dec.

A very knowledgable person said that PHD2s backlash calculation is thrown off by the spring-loaded worms that modern Losmandy mounts use. He said to ignore the warning.

He also said to use a larger pulse length if needed to get a reasonable looking calibration. If I set my pulse to around 1000ms then my calibration looks pretty normal. I think I might be good to go.

Last night I was still only getting maybe 1" RMS with guiding. I need to play some more but I think (hope??) this is due to the poor seeing I get in the lee of the Rocky Mountains. We occasionally get good nights of seeing, but I haven't tried guiding during one yet.

Hola amigos, os escribo desde España y lo hago en español para que con el traductor me podais entender, ya que mi ingles es limitado. Tengo una Losmandy G11 y tubo parecido al tuyo Alfredo, y he estado probando con el guiado de PHD2 porque el de Ekos no me da muy buenos resultados posiblemente por las configuraciones. Las calibraciones las hace bien pero no obtengo guiados por debajo de 1,6RMS, por lo que tus guiados de 0,5 o 0,65 son sorprendentes. Mis tornillos bisinfin son de precision y creo que estan bien ajustados. Me podrias ayudar con los parametros de configuracion completos tanto en Ekos o PHD2, aunque preferiria utilizar Kstars para todo. Por otro lado la velocidad de guiado la tienes en 0,5 ??. Gracias Alfredo por tus aportes y ayuda.

Gracias por abrir este hilo, y lo seguire a diario . Un saludo

Hola Juanjo!

I never use PHD2 so I can't help with these settings. It is important to realize that without proper calibration you won't get good guiding results. I'm glad to hear your calibration is going well. Maybe you can post your calibration plot.

Yesterday evening I had another run with the internal guider. I was very pleased with Ekos' whole performance: Focusing, Calibrating, Guiding, taking subs, everything worked very well. Here are my guiding results and settings:











You're correct, guiding rate is 0,5. I had GPG turned OFF.

Seeing was ca. 1.1" which is outstanding for my place in Frankfurt. Guiding deteriorated a bit to around RMS 0,5-0,6 when the moon came up which is to be expected.