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Re: Please help confirm my theory


Feb 23 5:59 AM

 


----------------------------

#41882 Feb 23 5:59 AM

Hi all,



I think I know what's going on and how to fix it, but I'd like some

confirmation...



I had my G-11 out this weekend and experienced a bit of trouble.

Small slews (say within Leo or within Virgo) were fine. But if I

performed a meridian flip, or slewed from western Leo to Eastern Virgo

the scope would end up pointing well away from my target. I would

regain pointing accuracy by doing a sych on a bright star and then go

on about my business. Ideas?



When I set up I got polar aligned with the PAS, balanced the gear,

tightened the clutches and alt-az knobs, and built a model with four

stars (one west, three east of the meridian). Initially, I slewed and

found objects within a 30' AFOV (good enough for me that night).

However, later on that same night, after adding a few more stars to

the model, I started having trouble with slews.



----------------------------

#41884 Feb 23 9:05 AM

If your scope is an sct you might be getting mirror flop. If the

errors occur after a flip, I'd suspect this, especially if after 2 or

three short movements things settle down. What scope are you using?









--- In Losmandy_users@yahoogroups.com, "macdonjh" macdonjh@...>

wrote: >

> Hi all,

>

> I think I know what's going on and how to fix it, but I'd like some

> confirmation...

>

> I had my G-11 out this weekend and experienced a bit of trouble.

> Small slews (say within Leo or within Virgo) were fine. But if I

> performed a meridian flip, or slewed from western Leo to Eastern

Virgo > the scope would end up pointing well away from my target. I would

> regain pointing accuracy by doing a sych on a bright star and then

go > on about my business. Ideas?

>

> When I set up I got polar aligned with the PAS, balanced the gear,

> tightened the clutches and alt-az knobs, and built a model with

four > stars (one west, three east of the meridian). Initially, I slewed

and > found objects within a 30' AFOV (good enough for me that night).

> However, later on that same night, after adding a few more stars to

> the model, I started having trouble with slews.

>



----------------------------

#41885 Feb 23 12:45 PM

Jeeze that would have to be pretty severe mirror flop. I would

double check to make sure that the time is correct on your paddle and

also your location as accurate as you can make it. Paddle times can

get out of whack due to daylight savings and that will introduce a

big error. A failing paddle battery can contribute to time issues

that affect pointing accuracy.



You also want to have your clutches tight for gemini. If you have

them loose you might get the motors turning without the rest of the

mount moving with them until you've overcome the inertia. So you

want the clutches tighted down firmly, not a strap wrench, but firmly.

If it's a used mount you might want to make sure that the clutch

surfaces are clean and that the previous owner didn't lube them

(which would cause slippage and therefore pointing inaccuracy).



Along these lines you want to be balanced pretty well because, if the

whole arrangement is sesverely out of balance, it will contribute to

clutch slippage on the out of balance axis.



If you are using, say, a refactor with a three degree field at 25x to

do the alignment stars your sense of the center point may be off and

feeding bad information into the pointing model. So make sure you

use a crosshair or fairly high magnification eyepiece (such as 10mm)

for the actual centering before "zapping" a star.



regards

Greg N













--- In Losmandy_users@yahoogroups.com, "Tom Picciani" tpicciani@...>

wrote: >

> If your scope is an sct you might be getting mirror flop. If the

> errors occur after a flip, I'd suspect this, especially if after 2

or > three short movements things settle down. What scope are you using?

>

>

>

>

> --- In Losmandy_users@yahoogroups.com, "macdonjh" macdonjh@>

> wrote:

> >

> > Hi all,

> >

> > I think I know what's going on and how to fix it, but I'd like

some > > confirmation...

> >

> > I had my G-11 out this weekend and experienced a bit of trouble.

> > Small slews (say within Leo or within Virgo) were fine. But if I

> > performed a meridian flip, or slewed from western Leo to Eastern

> Virgo

> > the scope would end up pointing well away from my target. I

would > > regain pointing accuracy by doing a sych on a bright star and

then > go

> > on about my business. Ideas?

> >

> > When I set up I got polar aligned with the PAS, balanced the

gear, > > tightened the clutches and alt-az knobs, and built a model with

> four

> > stars (one west, three east of the meridian). Initially, I

slewed > and

> > found objects within a 30' AFOV (good enough for me that night).

> > However, later on that same night, after adding a few more stars

to > > the model, I started having trouble with slews.

> >

>







----------------------------

#41887 Feb 23 1:57 PM

Another place to look for slippage is the servo gearbox to Oldham coupler connection. I had pointing problems after upgrading my gearboxes, and found that the grub screws on the Oldham connection had come loose, as I was a bit conservative when tightening them.



Easiest way to check this is to remove the worm cover and manually slew back and forth. Any looseness in the coupler will be obvious as slop in the drive chain.



Cheers

Rod

--- On Tue, 24/2/09, gnowellsct tim71pos@...> wrote:



> From: gnowellsct tim71pos@...>

> Subject: [Losmandy_users] Re: Please help confirm my theory

> To: Losmandy_users@yahoogroups.com

> Received: Tuesday, 24 February, 2009, 9:45 AM

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

> Jeeze that would have to be pretty severe

> mirror flop. I would

>

> double check to make sure that the time is correct on your

> paddle and

>

> also your location as accurate as you can make it. Paddle

> times can

>

> get out of whack due to daylight savings and that will

> introduce a

>

> big error. A failing paddle battery can contribute to time

> issues

>

> that affect pointing accuracy.

>

>

>

> You also want to have your clutches tight for gemini. If

> you have

>

> them loose you might get the motors turning without the

> rest of the

>

> mount moving with them until you've overcome the

> inertia. So you

>

> want the clutches tighted down firmly, not a strap wrench,

> but firmly.

>

> If it's a used mount you might want to make sure that

> the clutch

>

> surfaces are clean and that the previous owner didn't

> lube them

>

> (which would cause slippage and therefore pointing

> inaccuracy).

>

>

>

> Along these lines you want to be balanced pretty well

> because, if the

>

> whole arrangement is sesverely out of balance, it will

> contribute to

>

> clutch slippage on the out of balance axis.

>

>

>

> If you are using, say, a refactor with a three degree field

> at 25x to

>

> do the alignment stars your sense of the center point may

> be off and

>

> feeding bad information into the pointing model. So make

> sure you

>

> use a crosshair or fairly high magnification eyepiece (such

> as 10mm)

>

> for the actual centering before "zapping" a star.

>

>

>

>

> regards

>

> Greg N

>

>

>

> --- In Losmandy_users@

> yahoogroups. com, "Tom Picciani"

> tpicciani@. ..>

>

> wrote:

>

> >

>

> > If your scope is an sct you might be getting mirror

> flop. If the

>

> > errors occur after a flip, I'd suspect this,

> especially if after 2

>

> or

>

> > three short movements things settle down. What scope

> are you using?

>

> >

>

> >

>

> >

>

> >

>

> > --- In Losmandy_users@

> yahoogroups. com, "macdonjh" macdonjh@>

>

>

> > wrote:

>

> > >

>

> > > Hi all,

>

> > >

>

> > > I think I know what's going on and how to fix

> it, but I'd like

>

> some

>

> > > confirmation. ..

>

> > >

>

> > > I had my G-11 out this weekend and experienced a

> bit of trouble.

>

> > > Small slews (say within Leo or within Virgo) were

> fine. But if I

>

> > > performed a meridian flip, or slewed from western

> Leo to Eastern

>

> > Virgo

>

> > > the scope would end up pointing well away from my

> target. I

>

> would

>

> > > regain pointing accuracy by doing a sych on a

> bright star and

>

> then

>

> > go

>

> > > on about my business. Ideas?

>

> > >

>

> > > When I set up I got polar aligned with the PAS,

> balanced the

>

> gear,

>

> > > tightened the clutches and alt-az knobs, and

> built a model with

>

> > four

>

> > > stars (one west, three east of the meridian).

> Initially, I

>

> slewed

>

> > and

>

> > > found objects within a 30' AFOV (good enough

> for me that night).

>

> > > However, later on that same night, after adding a

> few more stars

>

> to

>

> > > the model, I started having trouble with slews.

>

> > >

>

> >

>

>

>

>

>

>

>

>

>

>

> .

> .

> .

> .

>

>

>

>

> .

>

>

>

>

> .

> .

>

>

> .

> .

> .

>

>





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----------------------------

#41889 Feb 24 3:00 AM

--- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@...>

wrote: >

> Jeeze that would have to be pretty severe mirror flop. I would

> double check to make sure that the time is correct on your paddle and

> also your location as accurate as you can make it. Paddle times can

> get out of whack due to daylight savings and that will introduce a

> big error. A failing paddle battery can contribute to time issues

> that affect pointing accuracy.

>

The battery of course is not in the paddle, but in the main control

unit. See the schematic near the bottom of:

homepage.ntlworld.com/john.moore88/designs/designs_index.htm



Regards

John Moore



----------------------------

#41892 Feb 24 6:04 AM

Thanks for the suggestions, all. Greg, the clock and location were

both set correctly, but that has caused me trouble in the past (so now

I pay attention when Gemini tells me what time it thinks it is and

where it thinks it's located). I don't suspect mirror flop for this

trouble: I've had my C11 for a bit more than a year and haven't

noticed mirror flop affecting pointing.



I bought the mount used and owned the mount for 2-1/2 years My

suspicion is grease migrating to the clutch pads. I was planning to

grab one of the rebuild instruction files from the archives, find a

tube of Slick 50 and take the mount apart next weekend.



----------------------------

#41896 Feb 24 11:36 AM

Mobile One synthetic grease is also an excellent choice.



Tom P.

--- In Losmandy_users@yahoogroups.com, "macdonjh" macdonjh@...> wrote:

>

> Thanks for the suggestions, all. Greg, the clock and location were

> both set correctly, but that has caused me trouble in the past (so

now

> I pay attention when Gemini tells me what time it thinks it is and

> where it thinks it's located). I don't suspect mirror flop for this

> trouble: I've had my C11 for a bit more than a year and haven't

> noticed mirror flop affecting pointing.

>

> I bought the mount used and owned the mount for 2-1/2 years My

> suspicion is grease migrating to the clutch pads. I was planning to

> grab one of the rebuild instruction files from the archives, find a

> tube of Slick 50 and take the mount apart next weekend.

>



----------------------------

#41914 Feb 25 6:00 PM

Although it is tempting to think well I'll do everything at once, the cautious approach here

is just to clean the bearing pads with alcohol and make sure the are totally dry and free of

grease (the surfaces of the mount too). One of the lead ways that grease gets on the pads

is by accidental contamination when someone has the mount apart to grease other areas.



To control for these variables it is probably better just to clean the pads and clutch

surfaces and put it all together and see if the system works better. That way, if you decide

to do a full lubrication and end up contaminating the pads again, you'll at least have an

idea what is happening. That's the way I see it, maybe others would disagree...



regards

Greg N



--- In Losmandy_users@yahoogroups.com, "macdonjh" macdonjh@...> wrote:

>

> Thanks for the suggestions, all. Greg, the clock and location were

> both set correctly, but that has caused me trouble in the past (so now

> I pay attention when Gemini tells me what time it thinks it is and

> where it thinks it's located). I don't suspect mirror flop for this

> trouble: I've had my C11 for a bit more than a year and haven't

> noticed mirror flop affecting pointing.

>

> I bought the mount used and owned the mount for 2-1/2 years My

> suspicion is grease migrating to the clutch pads. I was planning to

> grab one of the rebuild instruction files from the archives, find a

> tube of Slick 50 and take the mount apart next weekend.

>



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