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Re: Please help me improve Wind Stability


Sep 23, 2001

 


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

#6116 Sep 23, 2001

I have a G11, loaded only with a C8. When doing CCD imaging at 2"

per pixel or even a bit at twice that I notice that if there is even

a slight breeze, it will trail the stars a bit. I noticed it a

couple weeks ago when there was just a real slight breeze that would

rattle the leaves and move a hair or two on my head. I was using the

mount tightned up a bit, but not cranked all the way down as it seems

to stall my motors when slewing if I do that. I also use a light

weight dew shield doubling the length of the tube. Have the tube

balanced in RA and DEC. And use an 11lb weight. The camera weight is

not real significant, but adds a 6 inches of length to overall

package.



Can you ever get away from that problem with this or any mount?



Kevin



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

#6118 Sep 23, 2001

I have a G11, loaded only with a C8. When doing CCD imaging at 2"

>per pixel or even a bit at twice that I notice that if there is even

>a slight breeze, it will trail the stars a bit. I noticed it a

>couple weeks ago when there was just a real slight breeze that would

>rattle the leaves and move a hair or two on my head. I was using the

>mount tightned up a bit, but not cranked all the way down as it seems

>to stall my motors when slewing if I do that. I also use a light

>weight dew shield doubling the length of the tube. Have the tube

>balanced in RA and DEC. And use an 11lb weight. The camera weight is

>not real significant, but adds a 6 inches of length to overall

>package.

>

>Can you ever get away from that problem with this or any mount?

>

>Kevin



Ok, this answers my question to you in my previous reply. This shouldn't

be the case. There are a lot of variables in every set up so it's kind of

hard to speculate what the exact cause is. Since you mentioned that you

adjusted the worm tension, I might suggest that reducing the tension will

introduce some backlash making the ota subject to a small amount of easy

movement despite how tight the clutches are. You may want to check to

see if the worm gear is too loose. I'm using a C11 & Megrez 80 weighted

with about 40 lbs on RA and 7 lbs on RA and have no problems with

stability. Outside that explanation, maybe someone else could suggest another

possibility?



--

Roth Ritter

DNA Communications

www.DNAcommunications.com



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

#6120 Sep 23, 2001

Mr Ritter's suggestion that you check the worm is a good call, I

hadn't thought of it, but possibly if you tighten up here things will

improve. You need to follow standard worm adjustment precautions and

make sure that your tightest spots are not too tight for the scope to

track.



The obvious other thing to do is aerodynamic. Ditch the dew shield

and get a Kendrick strap (assuming you don't have some ambient light

that the dew shield screens). I found a dew shield unnecessary with

kendrick equipment in my 8" days. Clearly the problem is wind power

in relation to the inherent mass of your setup, and if you double the

wind power caught by the ota you have halved the stability of your

mount, so it's kinda like you're using a c14 or bigger--without the

benefit of an extra counterweight.



But I dare say the effect is even worse than a doubling, because the

moment arm effect or leverage of the large extension will be hard to

counter on your mount. The fact that your dew shield is light might

actually make things worse, giving you all the leverage effect w/o

extra mass to resist movement. Maybe our resident engineers would

have some thoughts.



BUT, now that I own a c14, I need a Kendrick AND a dew shield. But I

get away with an insulating layer that covers 50% of the OTA and pokes

past the corrector plate by about two inches. No real aerodynamic

effect, but on a corrector plate like that you need to keep the heat

going into the metal casting, not out into space. Not a problem with

your c8.



Regards,



Greg Nowell

--- In Losmandy_users@y..., Roth Ritter rritter2@b...> wrote:

> >I have a G11, loaded only with a C8. When doing CCD imaging at 2"

> >per pixel or even a bit at twice that I notice that if there is

even

> >a slight breeze, it will trail the stars a bit. I noticed it a

> >couple weeks ago when there was just a real slight breeze that

would

> >rattle the leaves and move a hair or two on my head. I was using

the

> >mount tightned up a bit, but not cranked all the way down as it

seems

> >to stall my motors when slewing if I do that. I also use a light

> >weight dew shield doubling the length of the tube. Have the tube

> >balanced in RA and DEC. And use an 11lb weight. The camera weight

is

> >not real significant, but adds a 6 inches of length to overall

> >package.

> >

> >Can you ever get away from that problem with this or any mount?

> >

> >Kevin

>

> Ok, this answers my question to you in my previous reply. This

shouldn't

> be the case. There are a lot of variables in every set up so it's

kind of

> hard to speculate what the exact cause is. Since you mentioned that

you

> adjusted the worm tension, I might suggest that reducing the tension

will

> introduce some backlash making the ota subject to a small amount of

easy

> movement despite how tight the clutches are. You may want to check

to

> see if the worm gear is too loose. I'm using a C11 & Megrez 80

weighted

> with about 40 lbs on RA and 7 lbs on RA and have no problems with

> stability. Outside that explanation, maybe someone else could

suggest another

> possibility?

>

> --

> Roth Ritter

> DNA Communications

> www.DNAcommunications.com







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

#6134 Sep 24, 2001

Don/Roth,



Thanks for the replies. Actually I have my worm quite tight. It

reduced the "pe" dramatically. It is actually a bit to tight. If I

crank down tightly on the clutches, my motors will stall when I try

to slew at the highest speeds.



Actually I was wondering whether the package was too light as well.

Matter of fact, I wonder how that effects PE. Because I have been

seeing about 8-10 seconds total with c8 measured with CCD camera.

But with C11 awhile back, and meade 9mm dual cross hair dual circle

reticle that was very well calibrated with double stars, I measured

PE in the range of 6".



I have noticed two things for sure. The sticktion is worse with the

8". Also it tougher to balance the tube as there is quite a range of

weight movement where it seems to be in balance. With the C11/21 lb

weight, it was a matter of 1/4" on balance bar that would change it.

This arises from the G11 being generally tighter more massive than

GM8 I used to have. That mount with C8 was like the c11 was with

G11. Balance point was very distict.



Kevin

--- In Losmandy_users@y..., gnowell@w... wrote:

> Mr Ritter's suggestion that you check the worm is a good call, I

> hadn't thought of it, but possibly if you tighten up here things

will

> improve. You need to follow standard worm adjustment precautions

and

> make sure that your tightest spots are not too tight for the scope

to

> track.

>

> The obvious other thing to do is aerodynamic. Ditch the dew shield

> and get a Kendrick strap (assuming you don't have some ambient

light

> that the dew shield screens). I found a dew shield unnecessary with

> kendrick equipment in my 8" days. Clearly the problem is wind

power

> in relation to the inherent mass of your setup, and if you double

the

> wind power caught by the ota you have halved the stability of your

> mount, so it's kinda like you're using a c14 or bigger--without the

> benefit of an extra counterweight.

>

> But I dare say the effect is even worse than a doubling, because

the

> moment arm effect or leverage of the large extension will be hard

to

> counter on your mount. The fact that your dew shield is light

might

> actually make things worse, giving you all the leverage effect w/o

> extra mass to resist movement. Maybe our resident engineers would

> have some thoughts.

>

> BUT, now that I own a c14, I need a Kendrick AND a dew shield. But

I

> get away with an insulating layer that covers 50% of the OTA and

pokes

> past the corrector plate by about two inches. No real aerodynamic

> effect, but on a corrector plate like that you need to keep the

heat

> going into the metal casting, not out into space. Not a problem

with

> your c8.

>

> Regards,

>

> Greg Nowell

>

> --- In Losmandy_users@y..., Roth Ritter rritter2@b...> wrote:

> > >I have a G11, loaded only with a C8. When doing CCD imaging at

2"

> > >per pixel or even a bit at twice that I notice that if there is

> even

> > >a slight breeze, it will trail the stars a bit. I noticed it a

> > >couple weeks ago when there was just a real slight breeze that

> would

> > >rattle the leaves and move a hair or two on my head. I was

using

> the

> > >mount tightned up a bit, but not cranked all the way down as it

> seems

> > >to stall my motors when slewing if I do that. I also use a light

> > >weight dew shield doubling the length of the tube. Have the tube

> > >balanced in RA and DEC. And use an 11lb weight. The camera

weight

> is

> > >not real significant, but adds a 6 inches of length to overall

> > >package.

> > >

> > >Can you ever get away from that problem with this or any mount?

> > >

> > >Kevin

> >

> > Ok, this answers my question to you in my previous reply. This

> shouldn't

> > be the case. There are a lot of variables in every set up so it's

> kind of

> > hard to speculate what the exact cause is. Since you mentioned

that

> you

> > adjusted the worm tension, I might suggest that reducing the

tension

> will

> > introduce some backlash making the ota subject to a small amount

of

> easy

> > movement despite how tight the clutches are. You may want to

check

> to

> > see if the worm gear is too loose. I'm using a C11 & Megrez 80

> weighted

> > with about 40 lbs on RA and 7 lbs on RA and have no problems with

> > stability. Outside that explanation, maybe someone else could

> suggest another

> > possibility?

> >

> > --

> > Roth Ritter

> > DNA Communications

> > www.DNAcommunications.com



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

#6140 Sep 24, 2001

Hello Mr 1231:



Your sticktion on the g11 is worse with the 8" because you have less

leverage. You have to exert more force at the tip of the shortened

lever--the end of the shorter ota--to "break" the sticktion and once

it starts to move its harder to stop. Best you write to Mr Losmandy

and ask for the UHMW pads which I have heard are now going for $20 a

pair but are still worth it, ALTHOUGH, I've read here with

Gemini and Skywalker type set ups the nylon is preferable.



So speaking of sticking, I'm sticking with my recommendation that you

ditch or radically shorten your dew shield and get the kendrick.

The wind will half as much to push on and many times less

leverage vis a vis the rotation points of the mount. Then

all these leverage issues won't be working against you.

Best wishes,



Greg Nowell



-







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

#6145 Sep 25, 2001

Kevin,

Your description suggests that your breeze is very slight and

therefore the movement of the scope is surprising. Do you get any

clue from the nature of the star trails? For example, trailed in RA

or DEC, or more random vibration? This might help to decide whether

you are suffering backlash oscillation in RA or DEC(ie mount not

unbalanced to remove this) or vibration of scope on mount. I'm

surprised that you have stiffness against RA and DEC rotation when

the clutches are released, sufficient to cause you problems in

checking balance. If the scope itself is vibrating on the mount you

might try a Hargreaves strut (see S&T Sept 2001, p114). Certainly in

stronger winds I've found a similar problem (10" sct) with a long dew

shield in place - can be fixed also by erecting a wind break (shade

cloth works well).



Serena

--- In Losmandy_users@y..., _kevin1231@e... wrote:

> I have a G11, loaded only with a C8. When doing CCD imaging at 2"

> per pixel or even a bit at twice that I notice that if there is

even

> a slight breeze, it will trail the stars a bit. I noticed it a

> couple weeks ago when there was just a real slight breeze that

would

> rattle the leaves and move a hair or two on my head.

>

> Can you ever get away from that problem with this or any mount?

>

> Kevin



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

#6149 Sep 25, 2001

One of the big advantages of the Hargreaves Strut for SCTs is that

you don't need the tub ring. In the case of a Meade 12 SCT mounted

on a G-11 the mounting bracket is at the end of the tube, eliminating

one part, see p. 115. I haven't used the Hargreaves stut but at the

last WSP the wind at the waterline was strong enough to cause

vibrations. People were setting up near their RV or other structures

thereby limiting their view. Ive been looking for a solution and this

is it. I'm currently ordering the parts. By the way the S&T article

gives stock numbers for the parts.



--- In Losmandy_users@y..., "Serena" Serena.Steuart@b...> wrote:

> Kevin,

> Your description suggests that your breeze is very slight and

> therefore the movement of the scope is surprising. Do you get any

> clue from the nature of the star trails? For example, trailed in RA

> or DEC, or more random vibration? This might help to decide whether

> you are suffering backlash oscillation in RA or DEC(ie mount not

> unbalanced to remove this) or vibration of scope on mount. I'm

> surprised that you have stiffness against RA and DEC rotation when

> the clutches are released, sufficient to cause you problems in

> checking balance. If the scope itself is vibrating on the mount you

> might try a Hargreaves strut (see S&T Sept 2001, p114). Certainly

in

> stronger winds I've found a similar problem (10" sct) with a long

dew

> shield in place - can be fixed also by erecting a wind break (shade

> cloth works well).

>

> Serena

>

> --- In Losmandy_users@y..., _kevin1231@e... wrote:

> > I have a G11, loaded only with a C8. When doing CCD imaging at

2"

> > per pixel or even a bit at twice that I notice that if there is

> even

> > a slight breeze, it will trail the stars a bit. I noticed it a

> > couple weeks ago when there was just a real slight breeze that

> would

> > rattle the leaves and move a hair or two on my head.

> >

> > Can you ever get away from that problem with this or any mount?

> >

> > Kevin



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