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GM8 Guiding near meridian

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Saturday night I started imaging, guiding with PHD2 (the guide log image has been uploaded).? For the first hour, guiding was perfect.? I then had some severe jumps, but it settled down.? Then, as it approached the meridian, I had sever swings and overshoots.? I changed exposure, aggressiveness and min motion without success.


I'm thinking my GM8 backlash is bad.? Any other suggestions?

Regards,

Charlie
 

Hi Charlie,

First, I am glad you said that your guiding up to the meridian was excellent.? That says all of your hardware and software and electronics are working perfectly. ?

As for the problem itself, I think your counterweight or dovetail balance may have not been exactly on the mark.

When you are pointing at the meridian, the scope is on its maximum lateral extent and the counterweight is at the other end.? If there is a weight imbalance between them, the RA motor and clutch must exert the highest force at that position.? When you are at CWD, there is essentially no force on the RA axis or DEC axis, as these forces are taken up by the mechanics of the bearings. ?

Secondly, check your cabling, etc for any snags...those are common issues in the dark, as the scope is moving things can snag up. ?

Third, check your clutch holding ability.? If you bump your scope does the RA or DEC axis move?? If so I'd be wary of the small 3 inch OD 1.25 inch ID clutch disks of the GM8. ? I have made far better holding clutch disks; if interested contact me.

All the best,
Michael





On Mon, Sep 25, 2017 at 2:27 PM, cbradshaw1@... [Losmandy_users] <Losmandy_users@...> wrote:
?

Saturday night I started imaging, guiding with PHD2 (the guide log image has been uploaded).? For the first hour, guiding was perfect.? I then had some severe jumps, but it settled down.? Then, as it approached the meridian, I had sever swings and overshoots.? I changed exposure, aggressiveness and min motion without success.


I'm thinking my GM8 backlash is bad.? Any other suggestions?

Regards,

Charlie





--
Michael Herman
mobile: 408 421-1239
email: mherman346@...
[email protected]
 

I did check for cable snags, which was my first thought, but everything seemed OK.? Balance seemed good, but I could have had some sliding in the dovetail.? I had to rebalance after I placed a 2" extender to obtain focus.

Thanks,

Charlie
 

Maybe related?

I find that once PHD2 loses its tracking, it doesn't even try to retrack.

I even had the weird situation that it was tracking and seemed fine, then just stopped tracking. It did that several times after I told it to track.? ( I have the "star mass" item turned off...no idea why that even matters. )?

In that last case I cleared the existing calibration, and told it to recalibrate.? That seemed to work... so watch your PHD2 screen for at least one full sub after you turn it on.? Once it loses autoguiding, you can get all kinds of star track zigzags.

Best,
Michael?

On Sep 25, 2017 16:05, "cbradshaw1@... [Losmandy_users]" <Losmandy_users@...> wrote:
?

I did check for cable snags, which was my first thought, but everything seemed OK.? Balance seemed good, but I could have had some sliding in the dovetail.? I had to rebalance after I placed a 2" extender to obtain focus.

Thanks,

Charlie

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