Zhumell Z8 Dobsonian accuracy troubleshooting/showcase #backlash #maxesp3 #dob


Alright, so I've had a night out under the stars with my telescope! I had to increase stepper current to 1000 and decrease microsteps to 32 as I was running into stalling problems due to high RPMs on the stepper motors. I don't know if that was overkill, but I am pretty sure that solved the issue. 

Here's my build so far:
I used Nema 17 motors with 100:1 gearboxes, then going from a 40 tooth gear to a 320 tooth gear for an 8:1 ratio. I had to make belt tensioners in order to get things tight enough. I just bought a 5 meter length of GT2 belt from amazon, and used a 3D printed belt clamp on the altitude axis, and I sanded 2 inch sections and Gorilla Glued the belt together for the azimuth axis. So far after a week of being under tension, all seems good! 

So far, I've been having issues with figuring out backlash, which using the method layed out on the wiki, I am using 960 for the altitude, and 300 for the azimuth. Do these sound like they could be in the right range? After doing a 3 star alignment, here is the view that I get with my aligned laser when slewing to a star for reference. It is probably more than a moon's width away from the target star. Is this a good level of accuracy? 

Besides that, I just really don't understand how the backlash feature works.. Because even when I align it with the star, because of the backlash it doesn't track the star until it has moved around significantly in the eyepiece, usually leaving the view. 

I'll also link my config file and Excel spreadsheet.


Alright, so I've done some more reading on here, and found some threads talking about using over 200x magnification and making sure the base is leveled. I had previously been using 80x magnification, so I will try those two things independently and then together to see what works. If someone could confirm that would help or any other tips, I'd really appreciate it!

Mike Ahner

hi Burton, I wrote some thoughts on this in your post about backlash adjustment.
Re: OnStep with Sky Safari (groups.io)