LX200 Balancing, Loading Limits, & General Stats

       

Subject: Procedure for Balancing the OTA --part 1 of 2   

From: Doc G

For much more on the technical side of the LX200 and CCD imaging visit my website. Note: a new window should open over this one.

Here is a technique that works fairly well toward getting near balancing perfection.

First the gross unbalance needs to be removed. I do this by pointing the tube and fork south and adjusting the Losmandy 2D bar front to back so that the tube balances fairly well when pointed to the southern horizon. Then point the tube to the zenith and screw the weight toward or away from the tube to get reasonably good balance in that position.

When this is done, the tube is close to balance about the Dec axis. Now you have to rotate the fork about the RA axis. If the load on the telescope is reasonably well distributed about the RA axis, you will have reasonable balance. If the balance is off by quite a bit you may have to move one of the attachments closer to the RA axis or add some weight on the light side to balance the tube.

If you repeat this process several times you should approach good balance. I recommend doing this by hand and not using the Balance option since it is hard to evaluate when balance is obtained and the severe wobbling is hard on the drive.

Subject: LX200 Balancing Procedure --part 2 of 2   

From: Jon Brewster <jon_brewsterhp.com>

> Does anyone have a basic lay-out (step by ..) On how to
> Balance the scope on a wedge in both axis?

I balance in 3D (2D DEC plus RA). To get more precision in balancing DEC, use the RA bearings for the out of balance telltale since they have less stiction. See:

<http://www.proaxis.com/~sandstone/Astro/Modifications.htm#2-DWeightSystem>
  for 2-D balance equipment description.

1. remove main dust cover from corrector plate (its very heavy). If the sun is still out, watch out! Make sure all observing gear is on the scope.
2. set and lock DEC to +90 and move RA such that fork is
3. horizontal and unlocked then balance in RA with Velcro ankle weight (or something) on east (non-motorized) fork. A small amount out of balance towards the East is OK to pre-load sidereal tracking.
4. leave DEC lockedat +90 and rotate in RA till the forks are vertical. Adjust 2D weight for least weight farthest out on spindle using unlocked RA for telltale.
5. set and lockDEC to 0 while leaving RA alone (unlocked, forks vertical). OTA should be horizontal E/W now. Slide spindle along OTA until balanced about RA in this configuration.
6. unlock RA and DEC and place OTA in many positions checking for balance. It should be perfect.

Subject: Simple Balance Technique --part 3 of 3   

From: Ric Ecker <astrovikingjuno.com>

I balance my LX200 using a combination of 2-D weights, slider weights, and dew shield (if needed). Whatever weight you add to the back of the scope, i.e., camera, imager or large diagonal and eyepieces, you need to add weight to the corrector end. A flexible dew shield works good for large back accessories.

Guide scopes or piggy-back cameras on top of the scope needs weights on the bottom of the scope. Equal weight on top must have equal weight on the bottom plus, the distance from the main scope tube must also be the same, hence the 2-D weight system. To begin balancing the system, point the scope straight up and loosen the Dec. lock. Move the 2-D weight in or out on the all-thread rod, add or remove weights to get a good balance like a tetter-tauter. Once this is balanced you should be able to move the scope in the forks and the scope should still point straight up. Move the scope level and move the weights forward or backwards to balance. Your scope should now be in perfect balance in the forks. No matter where you put the scope (Dec. lock loose) the scope will stay in that orientation.

Adding a pound weight to the Dec. arm will help balance the scope in R.A. Add enough weight to help the drive but don't try for perfect balance because you need some extra weight on the worm gear so you eliminate any backlash or dead band. Add the weight to the lower Dec. arm opposite of the Dec. motor.

I generally balance the guide scope first than add the cameras and dew shield. Light weight CCD cameras might not need the dew shield. I carry enough weights to balance any accessories that I have.

Subject: Balancing LX200 with a 3D Balance System --part 1 of 2   

From: Jon Brewster <jon_brewsterhp.com>

> Am I correct that when the scope is in balance and the Dec
> Lock is loose the scope can be pointed in any direction and
> stay there?

Yes, but you'll have to go to a 3D balance system. Usually, I have to add an ankle weight to the east fork arm. My full procedure is:

1. remove main dust cover from corrector plate (it's very heavy). If the sun is still out, watch out!
2. set and lock DEC to +90° and move unlocked RA such that the dec axis is horizontal then balance in RA with Velcro ankle weight on east (non-motorized) fork. A small amount out of balance towards the East is OK to pre-load sidereal tracking.
3. leave DEC locked at +90° and rotate 90° in RA till the forks are vertical (one above the other). Adjust 2D weight for least weight farthest out on spindle using unlocked RA for telltale.
4. set and lock DEC to 0° while leaving RA alone (unlocked, forks still vertical). OTA should be horizontal E/W now. Slide spindle along OTA until balanced about RA in this configuration.
5. unlock RA and DEC and place OTA in many positions checking for balance. It should be perfect.

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

Subject: Balancing LX200 with a 3D Balance System --part 2 of 2    

From: Dave Schanz <dave23schvalleytranscription.com>

I found this very helpful to getting started balancing my scope:
 <http://www.starizona.com/basics/balfork.html> Note: shoudl open a new browser window over this one.

Subject: Balance at High Declinations    

From: Manning Butterworth <mbemailsubscriptionsearthlink.net>

It will seem more difficult to balance at high declination because the moment arm of your off-center weight (the guide scope in this case) effectively becomes larger. When your scope is pointed straight up, (high declination) the moment arm through which gravity can act is at maximum, so any imbalance is most noticeable there.

The solution is simply to find the right amount of weight placed in the right positions on the opposite side of the scope. I use two Meade counterweight sets. I like their clean, low profile design which ensures they clear the fork base. I use one rail mounted on the bottom on the opposite side from the declination drive and the other rail mounted on the bottom in the middle. I use one of the weights on the offset rail to better balance the scope rotationally, but that weight also contributes to offsetting whatever is on top of the scope. In my case, all the rest of the weights go on the center rail. Their position along the rail is determined mostly by what is on the back of the scope. The amount of weight on the rail is determined by what is on the other side (top) of the scope.

If your guide scope is on a rail, you may (depending on the design) be able to adjust its position longitudinally along the OTA, but its weight and distance from the OTA centerline are fixed. The product of those two numbers must equal the equivalent product of the counterweights on the other side of the scope and their distance from the OTA centerline. If you use a counterweight design in which you can adjust the counterweight's distance from the OTA centerline, you can change that distance or the amount or weight or both, to achieve balance.

Bottom line, it sounds like you need more weight on the bottom of your scope. Point the scope up and add weights until it balances. Then, point the scope at the horizon and position the weights longitudinally along the OTA so that it again balances. Then, it will be balanced at any declination.

Subject: Dew Shield Counterweight    

From: Scott Baker <scottb80cts.com>

To balance my 10" with a dew shield, take a look on my web page under "LX200 Projects" to see how made a ring weight to fit on the back of the scope: <http://www.starcrwzr.com/weight.htm>

Subject: Symmetrical Balancing Device --part 1 of 2   

From: Doc G

Matt Considine wrote:
> It would seem that OTA balance could be more easily maintained
> with a counter-weight system that went *around* the tube,
> preferably towards the front. This would be in contrast to designs
> in which the counterweights are slung along a guide rail
> underneath the OTA. The advantage would be an ability to create
> a weight configuration that mimics what is at the eyepiece/camera
> end but provides symmetry about the pivot point of the RA/Dec
> axes. So, as one went to different sky coordinates, one wouldn't
> need to rebalance. Nor would balance get out of whack during a
> long exposure.

Again, Matt, you are excellently perceptive. The balancing of the telescope with weights requires that the added (balancing) weight be of the correct weight and placed at exactly the right point in space. If a minimum of added weight is desired it is necessary to have the weight move both along the length of the telescope OTA and in and out from the OTA axis.

If the weights are confined to rails along the length of the telescope, like the basic Meade rails and weights, is generally possible to get balance, but it will usually require several weights placed so as to establish a virtual weight with the proper strength and direction vector.

A 2-D weight system like the Losmandy and several others usually enables placing the weight at close to the correct position and thus optimizes the amount of weight used.

You suggestion to be able to place the weight ahead of the front of the OTA is a very good one. Basically, when you add stuff to the back of the OTA, you need to add weight to the front of the OTA. If you could move the weight more forward, you would need a smaller weight. I have played with this sort of weight system. I added a rail to a 12" LX200 at the bottom and to the top. Each rail extended about 6 inches in front of the front of the OTA. This indeed made it possible to get excellent balance with smaller weights, thus reducing the load on the mount.

However, after considerable experimenting with different weight placements on these experimental rails, I found that the two dimensional weight sets such as are available from Losmandy and others were very satisfactory.

My telescopes all have a Losmandy rail system on both the top and the bottom of the OTA. Then by judicious placement of accessories and attachments on these rails, it is possible to get close to balance without added dead weight. Then a small weight set can be used to tweak up the final balance.

In summary, I now feel that careful placement of accessories and a small weight set, such as the Losmandy set can give very satisfactory results. Still, if you add accessories only to the back end of the telescope, which is quite reasonable with cameras and CCD imagers and color wheels and the like, Then the very best place to put the weight is on a bar extending in front of OTA as you suggest. I do not know of a commercial weight set system that provides this feature.

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Subject: Symmetrical Balancing Device --part 2 of 2     

From: Matt Considine <mattconsidine.net>

Balancing the tube of the 10" LX200 has always bugged me. With a camera body, Lumicon GEG, extension tube and ST-4 hanging off of one end, a dovetail bar+threaded weight hanging off the front struck me as a less-than-ideal solution. While I have used this, it still struck me that as the scope worked through R.A., the balance point would shift, aggravating whatever shortcomings the stock Dec bearings had to begin with.

A solution I came up with is "SymBaD" (symmetrical balancing device :) ). I picked up a piece of 3/4" melamine (sp?), about 24 inches to a side. This is a pressboard-like product with a smooth (laminated?) surface on each side. Any stiff piece of wood would work, I'm sure. Out of this I cut a ring, with an inside diameter of 11 7/8" and an outside diameter of 16". In this I cut 16 half-inch holes, evenly spaced around the ring and at what would be a diameter of 14" if all the circles had been drawn before cutting.

At Home Depot, I bought a few packs of 1 1/2" corner braces (Stanley, IIRC). Taking 6 of these, I mounted these to the 6 holes in the corrector-end of the OTA. Sliding the ring over the corrector-end of the scope, I marked the outlines and holes of the braces on the ring. At the hole marks, I drilled through the ring, so that the ring could be attached to the braces with small bolt+washer+lock washer+nut combinations.

Now, I took a bunch of 2" x 1/2" hex bolts and a bunch of 1/2" nuts, also found at Home Depot. I placed these around the ring as symmetrically as possible to balance the above mentioned setup. (I also tried 3" bolts, but these added more weight, and I wanted better "granularity" for adjusting the weights.) If I recall, 14 of the nut-and-bolt combinations were required. Using Doc's measurement of the weights of the fork arms, I've got a 2.5 pound weight for the east fork arm (though Bruce Johnson's elastic+scale approach seems intriguing).

I have yet to rigorously test this setup. It seemed that there was still going to be some unbalancing, but it (qualitatively) didn't seem to be as much. And it made more sense to me to have counterweights organized symmetrically around the mechanical axis of the OTA. If nothing else, it killed a rainy afternoon :)

Hope this helps someone. If anyone can see problems or improvements, please let me know.

Subject: LX200 Max Weight Loading -- part 1 of 5    

From: Roger Hamlett <ttelmahntlworld.com>

----- Original Message -----
From: David Samuel
> I purchased my 12" LX200 during the later half of this year and do have the
> steel ball bearings on the Dec. axis. I will be putting a Vixen DED108SS
> tube assembly on the 12". It is a 108mm f/5 refractor which weighs about
> 6kg-7kg (I am guessing and may be wrong by a couple of kilograms). The
> Losmandy dovetail system and rings will weigh 2.7kg (6lbs according to the
> Losmandy web site), and Meade told my dealer that the 12" is rated to take a
> maximum payload of 22lbs (10kg). This 10kg should include the
> counterweights, refractor, camera, etc. So I will probably be overloading
> the 12" a little bit. The LX200 is on a wedge (have not yet polar aligned it
> properly). I am not sure what effect the extra weight will have on the life
> or operation of the LX200 mount?

This is where reducing the maximum slew rate is critical. The standard fast slew, is pretty 'hard' on everything, especially when accelerating and decelerating. The 'rated load', is (since it does not say otherwise, with the full slew rate still used. In terms of the loads on the motors and gears, you can run with a lot more weight, without increasing the actual loads on the motors by bringing this down. The 'caveat', is that it has to be set everytime the scope is used. I have a simple 'batch' file, that sends an 'initialization' sequence to the scope from the laptop, cutting the slew rate, and setting the time to an accurate clock. Glad you already have the better bearings. Otherwise high loads can lead to accelerated wear on the shafts.

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

Subject: LX200 Max Weight Loading --part 2     

From: Doc G

That is a lot of weight you are adding. I have always recommended no more that about 12 to 14 pounds of added equipment and additionally a 3D weight set so you can balance this weight with significantly less added counterweight. With a 3D weight set you can usually get by with less than an equal amount of weight in the counterbalance.

I think you are pushing the limit for the 12" since the OTA is already heavy. The mechanics of the 8, 10 and 12 are all the same. Do your polar alignment with the added weight in place. The added weight will change the RA axis of the scope from the unloaded position.

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Subject: LX200 Max Weight Loading --part 3     

From: Roger Hamlett <ttelmahntlworld.com>

First, in determining the max weight loading, are you working Alt/Az, or Polar mounted?.

If the former, you can go higher in weight, than with the latter. The problem is that when polar mounted, weight mounted up on the tube, exerts a considerable torque between the two main base bearings. The bearings are strong, but eventually this can lead to vibration problems. The next part is whether you can counterbalance the weight. Remember that the available moment arm 'below' the tube, to place a counterweight for masses above, is fairly short, unless the counterweight is going to foul the forks. You _must_ counterbalance well, and because of the short moment arm, the counterbalance may need to be significant 'doubling' the problem...

The next part is inertia. You can reduce the motor problems by limiting your slew speed (keeping the setting down to say 4, allows a lot more weight to be carried, safely, than if the slew is left at it's default setting.

The next part, is how heavy the refractor is. Though some parts are 'fixed' (the lenses...), some designs are significantly heavier than others.

The next part, concerns how it is mounted. Good rigid mounts, will add yet more weight...

Finally, there is a question on how old the LX200 is?. The newer ones, have needle roller bearings, for the Dec axis. This is a mod that many people fitting a lot of weight have found necessary. So. If the 6" scope if carefully mounted, and reasonably light of it's type, kept as close to the LX200 as you can. Then you are careful to counterbalance it well (2D counterbalance below the tube of the LX), and keep your slew rates low, it is reasonable achievable, but you need to be 'considerate' of the LX, if you are not to have problems...

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Subject: LX200 Max Weight Loading --part 4  

From: Doug Groesbeck

> My concern is that as it is on a wedge, the whole weight issue
> is distorted over to one side of the RA bearings. This together
> with the extra work the RA motor has to do has made me
> reconsider doing this.

I think that you need to look at this from two aspects. The first is the load to the drive motors. As has been noted elsewhere in the Archives and member's websites, the LX200's motors and gearboxes seem flimsy and weak until you look at the final gear ratio output -- that little assembly actually generates a fair amount of torque for its size! But you have to work within limits of not overstressing it, so you must balance the load they have to move. If the load is properly balanced, there is no effectual change to the amount of load that the motors are required to move; i.e. the amount of mass can increase, but balanced mass is effectively naught when it comes to stress on the drives.

The other aspect is the amount of increased mass the mount must carry, and that's where I think that you'll start hitting some walls. The 22lb. load limit that David mentioned as being the Meade recommended maximum load centers more around this aspect. While it may be mechanically possible to put more mass load on the drives, the bearings (both Dec and RA) and the forks have to bear that mass. The newer models with roller bearings in the Dec axis can negate some (even most, to a limit) of that load with their better load/friction surfaces than other types of sleeve bearings. But on a wedge, the upper and lower RA bearings are really going to be taking some lateral torque stresses that roller bearings aren't designed to take. There also may be some flexure problems with the forks if the load gets excessive.

So it may be possible to put a total additional mass of 30-35lbs. on an LX200 *if it is properly balanced* without undue stress on the drive motors. More than that may begin to overload the mount itself, though, to the point where it will eventually begin to cause problems with the bearings.

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

Subject: Max Weight Loading --part 5 of 5 

From: Greg Pyros <greggregpyros.com>

> From: Edward Registrato
> Is an 8lb weight (TeleVue 85 scope) plus a CCD (Meade 416XTE) too much
> weight to piggy back onto a 10" LX200 scope which has the Meade under scope
> weight system as the offset?

I use a TV-85 with STV autoguider piggybacked on my 10" LX200 with Pictor 1616XTE, color wheel, and flip mirror with no problems whatsoever. But balance is critical when doing this.

What I did was to modify the stock Meade weight system slightly to make it a 2D system to balance the scope when aimed both vertically and horizontally.

You can see the modification by going to my web site at:
<http://www.gregpyros.com/> and clicking on the "Customizations" link. Or direct: counterweight mods are on the second row down on the right side. I've updated it a bit since the pictures, but you get the idea.

Subject: Weights of 10" & 12" Classic Mounts & OTAs  

From: Doc G

My values are as follows:

10" mount (forks and base with electronics) = 34 lb.
12" mount (forks and base with electronics) = 36 lb.

10" OTA (f/6.3 version) = 28 lb.
12" OTA (f/10 with front cap) = 36 lb.

10" complete (f/6.3 version) = 62 lb.
12" complete (f/10 with front cap) = 72 lb.

I think the f/6.3 version is a bit heavier than the f/10 version because of the larger secondary structure. There are still some minor discrepancies, but I would say we are close enough.