OnStep with Sky Safari #backlash #maxesp3


Burton
 

Hi, so I have had a few nights under my belt with my finished goto dobsonian, which uses belt drives and planetary gearboxes. I have been using a 4-star alignment with a 200x magnification, and have done my best to follow the directions for tuning backlash. The problem, which I don't know if it is fixable or how it works, but when I goto an object, it shows up somewhere in the 8x finderscope, but I always have to recenter it and then sync the scope. This is when using the OnStep app or SkySafari. 

I was wondering if SkySafari is able to use the backlash settings and the 4-star alignment that I did in the OnStep app?

Also, how do I tell if backlash is functioning or how to adjust it?

The best way I've found to get accurate results is to use SkySafari to goto a bright nearby star to my target and sync there and then goto the target. This seems to work in order to get the object in the view of the eyepiece even at 200x


Burton
 

Also, I would like to know if OnStep saves backlash settings after being powered off?


Mike Ahner
 

On Mon, May 31, 2021 at 01:46 AM, Burton wrote:
Also, how do I tell if backlash is functioning or how to adjust it?
Hi Burton,

Here is the Wiki for Backlash adjustment.

It's possible to do the same thing in daylight by using a faraway object, e.g. transmitter tower or water tower, etc.
-Mike


Mike Ahner
 

On Mon, May 31, 2021 at 01:56 AM, Burton wrote:
Also, I would like to know if OnStep saves backlash settings after being powered off?
Yes, it does.


Mike Ahner
 

On Mon, May 31, 2021 at 01:46 AM, Burton wrote:
The problem, which I don't know if it is fixable or how it works, but when I goto an object, it shows up somewhere in the 8x finderscope, but I always have to recenter it and then sync the scope.
I didn't realize your telescope is the Zhumell Dob conversion. It looks good, good work.

However, I wonder if you backlash issue is mainly with the Altitude axis? That's a very long belt reaching down to the base of the telescope and I would think you would always have backlash due to stretching, even with tensioner pulley. Is it possible to mount the stepper motor higher up, perhaps where the tensioner pulley resides? Then you'd have a very short belt and I think your backlash would be drastically reduced. You might have to mount the stepper outside the base because of tube clearance issues, but that be made to look nice.

Another way I've seen the Altitude axis handled is to glue a belt around that axis, "inside-out", that is glue the flat back to the axis with the teeth outside. Then the stepper motor pulley is mounted very near the axis so that when the tube is placed in the cradle, the teeth of the reversed belt mesh with the teeth in the pulley. I don't know how the performance compares, but the advantage is ease of assembly/disassembly.

Let us know how it goes, I'm curious about your findings.

P.S. You can tell if backlash is working by how long it takes for the object to move in the eyepiece after pressing a direction button. What OnStep is doing is running the motor at highspeed for the value set in the backlash adjustment, the dropping back to guide rate. So if the star doesn't respond instantly, not enough time for backlash, if the star jumps, then you have too much time for backlash.

-Mike


Khalid Baheyeldin
 

On Mon, May 31, 2021 at 02:46 AM, Burton wrote:
I was wondering if SkySafari is able to use the backlash settings and the 4-star alignment that I did in the OnStep app?
Sky Safari, and the Android OnStep app, don't use the backlash setting nor the n-star alignment internally.
They are stored within OnStep, and OnStep uses them for its own purpose.

In other words, those values are totally transparent for OnStep clients.

Also, how do I tell if backlash is functioning or how to adjust it?
In daylight, point the scope to something far away.

Use the E button to center the object, then reverse the direction using the W button.
See how responsive they are? Does the view 'jump', or 'lag'?
If it does then you have too much compensation, or too little.

Then set the values to zero. If you have backlash, you will certainly see lag when you reverse the direction.


Burton
 

Hi Mike, 
Yes, the main issue with backlash seems to be on the altitude axis. I probably will move it to a closer location at some point, but I have 3 different opportunities for campouts to dark sky sites in the next weeks, so I wouldn't have the time to redesign until after that, I think.

My backlash settings are RA: 340 and Dec: 2100.

In daylight, point the scope to something far away.

Use the E button to center the object, then reverse the direction using the W button.
See how responsive they are? Does the view 'jump', or 'lag'?
If it does then you have too much compensation, or too little.

Then set the values to zero. If you have backlash, you will certainly see lag when you reverse the direction.

Khalid, thanks for the tip. I also just made a basic hand controller to eliminate any lag from the app in my backlash calibration. When I slew the telescope, it lags behind, moving very slowly for a couple seconds and then goes at the set speed. This is most apparent when I am using VFast slew speed, and most apparent on the altitude axis, which has significantly higher backlash settings. 
So I'm just not quite sure what you mean by lag, because with backlash not at zero, it seems to lag even more. I'll keep trying things and report back if I find any more info. 

The inaccuracy of the GOTOs after a 200magnification 4-star alignment doesn't seem to be in any axis in particular, so I think that means that it isn't related to how the backlash is tuned? I don't know what kind of accuracy to expect in those regards. Typically, it is always in the view of the finderscope at least. Is there any way I can increase this accuracy?

Also, the main concern I have with the backlash is that it doesn't immediately hold the object in view when tracking until it picks up the tension. Is this directly effected by the backlash settings?