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[engreric]

Hi everyone, I'm trying to troubleshoot and diagnose some issues with oblong stars. Forgive me if I'm not providing all necessary info to help track down my problem but I'm trying my best and I still have a lot to learn.

My setup is a G11 with direct drive 1.8deg steppers, 360:1 worm gear on RA and DEC and 32ustepping DRV8825s, diy mega2568 astroeq. This should be 0.563 asec/step

I'm noticing quite oblong stars with any length of exposure with my EAA setup, 2sec etc..
Askar 140mm APO f/7 with a Lodestar X2C and 0.5x Reducer
FOV Calc: Focal Ratio: 3.5 Resolution: 3.45"x3.54" per pixel Field of View: 0.72d x 0.72d

I switched to a fast 100ms exposure and no focal reducer with my ASI178MM and I took a video of it to help me diagnose:
https://www.youtube.com/watch?v=II5HO-2NPuw
The video was taken pointed at M42 with an Askar 140mm APO f/7
The FOV calulator is telling me this: Resolution: 0.51"x0.51" per pixel Field of View: 0.43d x 0.29d
I can also see this movement visually when I'm at higher magnification on jupiter.

The movement does coincide with the frequency of the RA axis noise while stepping.

So I guess, do I even have an issue or is this just what I should expect with 0.563 asec/step of the RA stepper motor?
Would it be worth it to try 0.9deg steppers or do I need to move up to timing belts and 4:1 gear reduction before the worm gear (hopefully not)?
Could this be more of an issue with backlash, skipping steps, or something else...

Thanks in advance for reading this and helping me understand...

[engreric]

I'm still trying to figure this out and I have some new thoughts...

Camera+Telescope in the video
0.51" asec/pixel

https://www.youtube.com/watch?v=II5HO-2NPuw
I tried zooming in on the video and I counted about 15 pixels per "jump"
15 pixels * 0.51" = 7.65 asec!!!

32 ustep, 1.8deg stepper, 360t worm
.563" asec/step

So, I don't think its a lack of stepper motor resolution...
The "jump" is periodic and it looks like between the "jumps" its tracking well...
I don't think it's missing steps as I would expect the stars to slowly drift across screen...

It "jumps" then goes right back to its original position so I'm wondering if it's a backlash issue, or an issue with the 32ustep driving of the stepper motor?

[TCWORLD]

Sounds like it might be either a balancing or binding issue, or possibly the motors not having enough torque.

What is most likely happening is the micro-stepping doesn't have enough power to move the mount for a few micro-steps. Then once it moves close to the next half step, it jumps into position. That would cause jumps of up to 9 arc-seconds. Essentially as if the micro-stepping were not being done.

I'd start with a quick double check the mount is free-moving on the worm (not too tight) and that the scope it is well balanced. After that make sure that the stepper drivers have the current limit properly adjusted as under or over current can cause micro-stepping issues.