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Backlash on Celestron SLT 130


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Hi all, I have the Celestron SLT130 with Starsense Align which I'm having great difficulty setting up correctly. I have been battling away on nights so I can to get it 'autonomous' if you will, though viewing great objects has been really great with manual input viewing the typical objects, such as the Moon, Jupiter and it's moons and Saturn and it's rings. I would like to be able to use the Starsense Align facility though to align and view some further objects, this is proving a little more tricky. I've made good progress , however, my latest issue is that once the scope is aligned, then second alignment is complete, when I slew to a named target, it is not in the eye piece. I'm wondering if it is because there is alot of backlash in the azm movement. I have done a backlash compensation today but yet to try it out tonight, however, my concern is that when I slew manually at a motor rate of 5 or 6, the backlash is 'more or less' gone, however, when at a faster rate, it is quite severe and I can't get rid of it. When the Starsense Align is aligning, it uses motor speed 9.
Does anyone have any wise words here? I'm guessing the backlash can be an issue when auto aligning?

Kind regards,

Neil.

Edited by Cornelius Varley
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Hi Neil

"when I slew manually at a motor rate of 5 or 6, the backlash is 'more or less' gone, however, when at a faster rate, it is quite severe and I can't get rid of it. "

In what way are you seeing Backlash in this situation ?

Michael

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Hi Michael, 

 

Thanks for your reply.

If my scope is focused on an object, in this instance a chimney top, at speed of 5 or 6 going from left to right and right to left, the scope will slew almost instantly, albeit with a small jerk.....there is negligible delay. However, when I up the motor speed and slew left and right of the chimney, there is a very noticeable delay before the scope starts to move, in the order of 3 or 4 seconds. 

I found instructions somewhere online (many have been Celestrons) on how to compensate for it and it says to use a motor speed you would normally use, 4, 5 or 6.This is what I've done.  No further details in that instruction regarding speeds over that.

 

Kind regards and thankyou.

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Tried it last night following the backlash compensation, annoyingly I found the scope would still has a massive delay in slewing left to right and right to left, even at slower speeds. At the risk of sounding like a spoilt brat, I am almost ready to give up this hobby! When I find the enthusiasm I think I need to open up the mount and look at the motors.

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What you are describing does not sound like a backlash issue to me. If you speed up or slow down the mount in theory total backlash should remain constant. A few seconds delay at high speed is unlikely to be backlash also. Providing the motors react instantly, it sounds more like something is slipping in the drive train. Can you move the scope when the mount is stationary? Assuming the clutches do not slip it sounds like a gear wheel slipping or something similar.

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You do need to set the backlash of these mounts for consistent gotos. It takes about 10 minutes to do during the daytime.

The gears in the mount from factory have quite a bit of play in them.

I am not sure what you mean by second alignment (or are you meaning aligning to the second star?) Using staralign you just align the 3 stars and you are ready to view.

 

Here is how I have done it for years.

Set up mount and when ready to star aligning look for the 3 stars you want. I usually face south when doing alignment.

The first start is to the west, second star to the east as far away as possible then the third higher up on the east side. 

Something like this:  /___ (right, left, up)

 

Then other thing you mention is slewing with the mount, it does not have double encoders so if you do all goto slews it will stay good for 3-4 hours.

If you manually slew then do a goto it will likely lose its precise alignment. The object should be close by though. 

 

For best goto, approach your alignment stars from below so your final approach is up to the object then right to center it. 

Being consistent with your object approach will also help with goto function. 

 

Great little mounts once you start figuring out their quirks :)

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