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"East Heavy"

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#1 Danoglide63

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Posted 11 September 2019 - 02:21 PM

Hello everybody,

I read in a post here about off balancing your telescope in the mount. "East heavy" was mentioned but I'm confused....does this mean with the telescope laid over RA to the East it's heavy or the weights are on the East and they are heavy?

 

Thanks!

Dano



#2 zxx

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Posted 11 September 2019 - 02:30 PM

Whatever is east, scope or weight



#3 wrnchhead

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Posted 11 September 2019 - 02:34 PM

Yeah before it passes the point that line from dead south to dead north, you want the counter weight side heavy and then when it crosses over to the west side of that line, you want it scope side heavy. And this is not a massive imbalance, just enough to keep the gear train engaged to prevent backlash from affecting the tracking

Edited by wrnchhead, 11 September 2019 - 02:35 PM.

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#4 rgsalinger

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Posted 11 September 2019 - 03:34 PM

Well, I've never thought that east heavy is necessary. The RA axis is always driven when the mount is tracking, there is always friction and there is no such thing as perfect balance. That means that some net force is always being applied to it. RA guiding is slowing down and speeding up the mount. The mount never reverses direction in RA. The mount does reverse direction in DEC (even though it shouldn't) from time to time and that's where you will see backlash if you are not properly polar aligned.

 

Of course backlash is an issue with regards to slewing a mount because the mount may need to reverse direction at some point. You can observe backlash with an eyepiece but note that with your mount balanced it's only when actually moving the mount toward the east.

 

 

I've owned 5 mounts over the past 18 years and never once tried to unbalance one to improve my guiding. I'm happy with my results. I also note that I can't find a manual for a mid priced or expensive mount that recommends this practice. I would expect that such a simple palliative would be in every manual if it was necessary. I've looked just today at both of my mounts, the EQ6 pro, the Celestron CGX and the iOptron CEM60.

 

So, I wonder where this recommendation is coming from?


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#5 Devonshire

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Posted 11 September 2019 - 03:42 PM

Whether you need to do this or not depends on whether you are doing AP or working visually.  It may also depend on the quality of your mount's gears and whether they are spring-loaded or not.  For AP, and not having spring-loaded gears, I certainly need to be East-heavy.

 

Balancing East-heavy is easy. 

Begin by balancing your mount evenly.  Slew to your target.  Then, simply stand in front of your mount’s RA axis, with your back to North, and your face to south.  Make sure that the things on the left of the RA axis are heavier than the things on the right.  That’s all there is to it. 

If the weights are on the left, move them down the weight bar by an inch or two.  If they’re on the right, move them up. 

 

Done.


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#6 freddie

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Posted 11 September 2019 - 03:50 PM

Or even easier, don’t worry if the weights are on the left or right, just move them slightly east wherever they are.


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#7 Danoglide63

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Posted 11 September 2019 - 04:41 PM

I found this video online, makes it easy and kind of backs up what others have said. My objective was to solve the problem I had last night. It was my third time using PHD2 and after calibrating it was slightly off what was acceptable. I then ran guide assistant and failed gear backlash. This got me wondering if I was too light, too heavy or just right and the gear slop was the problem. A East heavy weight is to load up the gear and take up the slack.

I have a Celestron AVX  mount.

Dano

 

https://www.celestro...quatorial-mount


Edited by Danoglide63, 11 September 2019 - 04:42 PM.


#8 zxx

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Posted 11 September 2019 - 04:55 PM

I found this video online, makes it easy and kind of backs up what others have said. My objective was to solve the problem I had last night. It was my third time using PHD2 and after calibrating it was slightly off what was acceptable. I then ran guide assistant and failed gear backlash. This got me wondering if I was too light, too heavy or just right and the gear slop was the problem. A East heavy weight is to load up the gear and take up the slack.

I have a Celestron AVX  mount.

Dano

 

https://www.celestro...quatorial-mount

That is likely your DEC backlash. Try guiding DEC in one direction. That works best with my CGEM DX.


Edited by zxx, 11 September 2019 - 04:58 PM.

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#9 dmdouglass

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Posted 11 September 2019 - 05:38 PM

The term "East Heavy" is sort of a "misnomer"...

A better way would be to say "Tail Heavy" or "Counter Weight Heavy"

But remember.... only by a "little bit".


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#10 rgsalinger

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Posted 11 September 2019 - 05:45 PM

Visual or not, spring loaded or not, the only backlash you have to be concerned about when tracking is on the DEC axis because, as I said the RA axis never reverses direction. Can any of you posting something contradicting that premise point to a manual or a book about astronomy that's authoritative and explains how you can have RA backlash in a balanced GEM when it's tracking? The only exception that I know of would be the situation where you used a guide rate of more than 1X. If you did that then you sure could have backlash. That's why it's recommended to use a number between .5 and 1.

Rgrds-Ross


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#11 kingjamez

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Posted 11 September 2019 - 06:09 PM

The term "East Heavy" is sort of a "misnomer"...
A better way would be to say "Tail Heavy" or "Counter Weight Heavy"
But remember.... only by a "little bit".


Not at all, it means East heavy. It can be counter weight heavy or telescope heavy, which ever is on the east side of the pier.
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#12 kingjamez

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Posted 11 September 2019 - 06:11 PM

Visual or not, spring loaded or not, the only backlash you have to be concerned about when tracking is on the DEC axis because, as I said the RA axis never reverses direction. Can any of you posting something contradicting that premise point to a manual or a book about astronomy that's authoritative and explains how you can have RA backlash in a balanced GEM when it's tracking? The only exception that I know of would be the situation where you used a guide rate of more than 1X. If you did that then you sure could have backlash. That's why it's recommended to use a number between .5 and 1.
Rgrds-Ross

It’s not about backlash from reversing directions. It’s about slop in the gear mesh which can cause bounce opposite the direction of movement. If you are west heavy the weight will bias the RA gear on the leading edge of the slop between the gears. This causes the weight to be actually causing the rotation around the polar axis and the worm gear is “stopping” it from moving. When perfectly balanced the RA gear can slightly bounce between the slop. When east heavy the weight keeps the RA gear on the trailing edge of the worm and the motor is doing the driving of the movement of the mount.

If there is zero slop between the RA and the worm, this doesn’t apply. It’s not backlash exactly but both effects are from the same source.

Edited to be less argumentative and add explanations.
-Jim

Edited by kingjamez, 11 September 2019 - 06:41 PM.

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#13 OldManSky

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Posted 11 September 2019 - 06:26 PM

Just for another "contrary" view...

I don't east-heavy balance.  I balance normally.

My mount behaves the same in RA as it approaches the meridian, as it crosses it, and after a flip.

I get that some mounts may benefit from it.  Mine doesn't. 

I tried doing it -- made no difference whatsoever.


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#14 rgsalinger

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Posted 11 September 2019 - 06:27 PM

Interesting discussion to me.

 

So, the "slop" is sufficient to overcome the force of the motor and actually reverse the direction or slow down the RA rate to the point where guiding is affected? I would have expected that all that would happen is that the motors would have to deliver more torque to keep the rate constant.

 

I thought that someone was going to make a periodic error argument - you can see that it goes up and down. That basically what you are talking about but the amount of up/down never gets sufficient (on any mount I've worked with) to reverse the direction.  

 

If you've done the science then you've done the science with your mount. I've found the opposite to be true - as balance gets worse, the guiding gets worse.

 

Why not give iOptron or Skywatcher a call and see what they recommend. I have an unending supply of hats to eat.

 

Rgrds-Ross


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#15 WadeH237

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Posted 11 September 2019 - 06:53 PM

On a mount with backlash, when you run east heavy, the gears load in such a way that that motors are pushing the load up, against gravity.  On a mount with backlash that is west heavy (at least west heavy enough to matter), then the gears are loaded such that gravity is driving the load, and the motors are acting as a brake.

 

This may or may not matter on an individual mount basis.  You will just need to try it and see if it makes a difference.  My older CGE mounts had plenty of backlash, but they worked reasonably well if there were east or west heavy.  Running them perfectly balanced was a problem if there was any wind at all.  I'd get barbell shaped stars, presumably with the mount alternating how the gears were loaded.

 

The other thing to keep in mind, is that when diagnosing elongates stars, it's critically important to understand whether the elongation is in the RA axis or declination axis.  I've spent plenty of time troubleshooting the RA axis without success, only to discover that the problem was in declination.  And if the problem is in declination, the fiddling with the RA balance won't help.


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#16 dmdouglass

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Posted 11 September 2019 - 07:16 PM

Not at all, it means East heavy. It can be counter weight heavy or telescope heavy, which ever is on the east side of the pier.

I thought about it...  and you are right. I stand corrected.

From my observing spot (backyard)... 90 % or more of my targets are on the East side, and thus it is the counterweight side (lower end) that wants to be "slightly" heavy.

 

Another important point on this (balancing) is the other axis.  And a good reference there (and this one works) is "camera heavy", and again, only slightly.  I guide in both axis, but my DEC is almost always a very flat (well, almost) line.  I could only "wish" for that kind of result in RA..... but its close.


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#17 Devonshire

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Posted 11 September 2019 - 07:40 PM

+1 for WadeH237

 

Has nothing to do with the RA motor reversing or not.  It has to do with whether the worm drive is lifting or lowering weight.  In the 'brake' (lowering) scenario, you can have a stick-slip action that affects tracking. 

 

And yes, camera-heavy can be good, too - but there it's more a case of preventing the DEC gears from rocking against each other as the scope nears vertical.


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#18 wrnchhead

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Posted 11 September 2019 - 07:55 PM

Also, I forgot to do the east heavy thing a couple times, and I when I corrected it, it did make a difference.

Some anecdotal field experience.
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#19 skycamper

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Posted 11 September 2019 - 10:33 PM

Ive had the following mounts:

 

CG4/CG5

Vixen GP

Vixen GPDX

LXD75

Losmandy G11

NEQ6 with and without belt modds

Tak NJP

 

Yep I went right down the line, should have just got into an AP or SB mount, anyhow I also am one who never noticed much of a difference in east heavy but Im still doing it.  ...  but then again I dont have an engineers mind and am pretty scatter brained. This could have gone by me weather it helps in guiding or not. I certainly didnt keep great notes when I tried it out....  Sometimes it takes a genius to point out the obvious and the obvious question is , "why this isn't in a manual or instruction booklet" ..... Per Ross.   So im with Ross on this one.  Just doesn't make sense.   


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#20 rgsalinger

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Posted 11 September 2019 - 11:47 PM

First of all, it's an easy experiment to unbalance a mount, so give it a try and see if you get consistently better results by biasing the mount. Don't forget that you will have to stop (if it's a GEM) and rebalance it when you cross the meridian every night.

 

As I said, I find it probative that there is not a peep about doing this in the PHD manual or in any manual that I can find for setting up a GEM. Here's an excerpt from the MaximDL manual "Backlash on the RA axis can become a problem, though, if the mount is poorly balanced, e.g. heavier on the west side". To me this means "balance your mount" for best guiding.

 

The worm is turning the mount using the gear it is meshed with. To rotate any object is to change its direction. To change the direction of an object requires that a force be applied to it. So, in a balanced mount you are never going to be "braking" with the worm at all. Not only do you need to apply force to rotate the system, but you also need to overcome friction. So, I just can't see that the worm in a balanced mount is going to be braking on one side and "lifting" on the other. That implies an imbalance. 

 

So, I think my position is that if you find that you need to unbalance to get better guiding then there's some not so obvious reason for it, but it's not backlash. So, my guess is that what's actually going on relates to the difficulty of accurately balancing a mount under all possible load configurations, particularly when there is considerable friction present during the balancing process.

 

Rgrds-Ross

 

 

 

Rgrds-Ross


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#21 42itous1

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Posted 12 September 2019 - 12:07 AM

Hi Ross

 

Page 13 of the CGEM manual describes balancing in RA with a slight imbalance.

 

https://s3.amazonaws...em11097inst.pdf


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#22 rgsalinger

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Posted 12 September 2019 - 12:32 AM

Then I stand (or post) corrected. Celestron certainly knows more than I do but they are the outlier in suggesting this. At least I know for sure that it's not just on the forums.

Rgrds-Ross


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#23 WadeH237

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Posted 12 September 2019 - 07:45 AM

So, I think my position is that if you find that you need to unbalance to get better guiding then there's some not so obvious reason for it, but it's not backlash.

In an ideal world, I agree with you.

 

In my case, as I described, my CGE mounts needed to be unbalanced when it was windy enough to move the axes within the backlash area.  In calm conditions, they did fine balanced.  Through testing, I determined that there was not a significant difference between east and west heavy in the RA axis (although there were other CGE users that found east heavy to be noticeably better), so I just got in the habit of unbalancing them just a bit counterweight heavy.

 

The declination axis was a much bigger headache.  Unbalancing the declination axis will have a significant effect on the RA balance - to the point where you cannot have consistent RA balance unless the declination axis is well balanced.  The best way that I found to deal with that was to have a slight polar misalignment, so that there would be a small but consistent declination drift.  I would then disable declination corrections opposite the drift.  That gave me good results on calm nights, but wind was still a problem in declination.

 

There are lots of little tricks that you can do to improve the results on a less-than-perfect mount.  What's hard to convey in the forums is that you need to diagnose and recognize the specific problem, in order to know which trick to apply.  It seems that most of the time, people suggest trying things without the "diagnose and recognize" part, until it eventually becomes common lore that just gets repeated without context.


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#24 rgsalinger

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Posted 12 September 2019 - 08:57 AM

Well, rebalancing a mount would still not be my first suggestion to improve guiding. And, I think that the mitigation techniques - belt drive to eliminate the spur gears, magnetic and spring loaded gears make it even less likely that your RA guiding problems will be mitigated by going east heavy. Still, it's trivial to try it and if you don't mind rebalancing after a flip then it's a viable option for an imager. 

 

I thought that it was interesting the Celestron manuals- I checked the CGE pro and the AVX as well - recommended it but I still think that the laws of motion do not permit the worm ever to act as a brake because rotation is acceleration and there is friction present. I wonder how far back that recommendation goes. 

 

Next time I'm at a large star party I'll make a pest of myself and conduct an informal study by asking people what they do. 

 

Rgrds-Ross


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#25 kingjamez

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Posted 12 September 2019 - 09:12 AM

the laws of motion do not permit the worm ever to act as a brake because rotation is acceleration and there is friction present.


What?!? Please tell me what “laws” do not permit the worm to act as a brake. That’s exactly what it does when west heavy. Rotation is NOT acceleration, not that that has anything to do with anything. Acceleration is 2nd derivative of position and the first derivative of velocity.

-Jim
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