14 replies to this topic

[Piet Le Roux]

I recently acquired a 10" LX200R on a LX200GPS SMT mount, after updating the firmware tp 4.2G patch ver. 22 I did a reset and both drives went to a value of 30, The mount is in Az/Alt and I then did drive training, the values are now 72 and 99. I assume the default value is 30 so are my training values acceptable? At what value should one consider to adjust endpoint play on the drives? 

[OzAndrewJ]

Gday Piet

The average train values for LX200s sits between 50 and 75.

If the motor carrier is firmly fixed to the frame, then it is unusual

to have endplay on the worm bearings or the carrier bearings

unless they have been damaged.

Nearly all lash comes from the motor gearbox, and that cannot be tweaked.

Andrew Johansen Melbourne Australia

[Piet Le Roux]

Thanks Andrew, so I must check the retaining screws of the motor carries....especially the one with a 99 value. 

[OzAndrewJ]

Gday Piet

The normal causes of large lash ( in order ) are

1) The 2 large screws holding the carrier to the casting

2) Endplay in the worm itself ( brg failure )

3) Endplay in the worm carrier ( tiny bearings )

 

If its (2), they used to flood it with loctite so adjusting in situ

may be a problem. When my bearings collapsed, i had to use

a blowtorch and 2 handed "Tbar" ( about 12" each side )

to get it released.

 

Andrew Johansen Melbourne Australia

[Piet Le Roux]

Thanks Andrew,

I did find that the 2 large screws holding the carrier to the casting to be a bit loose, the 3 allan head screws holding the motor were very loose. I am hearing a high pitch noise emanating from the RA drive I don't know if this is normal or a sign of bearing failure? Do you have photos and information on the procedure of replacing the worm bearings, it sounds like a challenging exercise! I will do another drive training session and see what the results look like.

 

PS does a training value of 99 qualify as a large lash? 

Edited by Piet Le Roux, 15 February 2025 - 11:04 PM.

[OzAndrewJ]

Gday Piet

For bearing failure, you remove the transfer gear from the motor

and back off the grubscrew that prevents the worm carrier from springing away from the worm

Now, with the worm free, use the transfer gear to rotate the worm.

It should be buttery smooth.

You will also note in PIC1 there is an oring and it has a semi spherical spigot that the

connector plate sits on.This stops it moving laterally but allows it to slightly pivot.

When this is fitted, the 4 screws that hold it are used to set the gap between

the transfer gears. It is trial and error but normally you adjust it bit by bit until

when you slide the Xfer gear onto the shaft, it needs a tiny bit of force to make it mesh.

It then effectively rocks on the spigot with the oring giving a spring load.

Its crude, esp if the gears arent exactly the right dia as it means they dont mesh

perfectly square.

I have more photos of the assy but its pretty simple

Re the worm, one bearing ( at the transfer gear end ) is flanged and the other is std.

The end screw pushes onto the std bearing and this preloads the worm

against the flanged bearing.

 

I would not classify 99 as "large", but a bit above average

Last time i measured mine, i got 76 and 80.

 

Andrew Johansen Melbourne Australia

 

 

 

 

 

[Piet Le Roux]

Did another drive training session and the training values are 73 and 95, I don't think its is going to be a problem because I had it on a test run a week back with the default values, 30 and 30 and it was accurate enough. If the results get worse than 100 I will consider to replace the bearings. The problem that I now picked up is that the scope does not travel well and went out of collimation on my last trip to a farm outside the city, a trip that I have done numerous times with my LX90 without any problems. As soon as the weather improves I will do the collimation again and try to place more tension on the set screws by giving each an equal clockwise turn and then re check the collimation. These old girls can keep you busy! 

[OzAndrewJ]

Gday Piet

If you run patched firmware, you can also do daylight training tests using a camera feed.

My PEC editor has a dedicated traing screen

It does the same process as Meade but you can adjust speed and distance moved out/in

It runs as many times as you want so

out right, back left, centre, out left, back right, centre repeat

This allows you to get a better average of whats going on

esp based on speed used.

Andrew Johansen Melbourne Australia

[Piet Le Roux]

Good day again, I am still struggling to get the training values of my Alt/Dec drive down, it is staying around 90-100 although I have removed the drive and  checked all bolts, the worm gear feels lose but you dont know what happens under load. Something els that has now presented itself and that is a Knockin noise comming from the drive at times, I am thinking this could be of pit marks in the bearing, at times it is so bad that it is causing vibrations in the eyepiece. Does someone know the type of bearings that I can replace the bearings with on a 10" LX200ACF, are they both the same or do I need two types? I would like to have the bearings in hand before I attempt to remove the old ones. 

[OzAndrewJ]

Gday Piet

If you cant get lower than 90, then its possibly the gearing in the gearhead

and that is not user servicable.

Re the knocking noise, if you can see it in the EP

it could be teeth in the gearbox or it could be a worm bearing

tho the worm bearing only rotates once per 8 mins

so normally only gives a "knocking" sound if running at high speed.

I have the part nos for the worm shaft bearings if reqd

Basic form is R188A and FR188A   ( after that, material and seals etc is to your choice )

but i would be looking more at the gearbox

If its as clear as you say, grab an unguided log in polar that shows the period

and from that, you can work backwards

 

Andrew Johansen Melbourne Australia

[Piet Le Roux]

Thank you Andrew,

I have taken the drive apart again and disassembled the gearbox, no visible damage, all the gears look fine but then I did a careful inspection of the worm gear and yes there are definitely some roughness at a few points when I rotate the gear while applying a bit of pressure! I will first try to get the bearings locally and then attempt to disassemble the worm gear.....any tips to help me there? 

Edited by Piet Le Roux, 25 February 2025 - 03:08 AM.

[OzAndrewJ]

Gday Piet

Two possible problems come to mind, neither critical.

1) The PEC sensor may be too close to allow the flanged bearing to be removed

A sharp chisel or razor blade can normally break it free without damage

Refitting is not critical, as long as it is close under the magnet,

as a refingerprint routine can then recalibrate the setup precisely.

2) The end plug seems to be fitted with so much loctite, it could hold the Queen Mary

I had to use heat and a 12" TBar to get mine moving.

There is nothing inside the housing at the plug end that is affected by the heat

but it was an absolute b@st@rd to get loose on two i have worked on

Andrew Johansen Melbourne Australia

[Piet Le Roux]

A bit of luck! My endplug were secured with beige stuff, not loctite, little bit of heat gun and a big screwdriver and it came loose without a problem, the sensor came off with a Stanley blade. I am waiting for a local supplier  to come back to me about the bearings but if he doesn't today I will order them via Amazon. 

PS Andrew please explain what is  "a refingerprint routine" and how is it done?

Edited by Piet Le Roux, 25 February 2025 - 08:08 AM.

[OzAndrewJ]

Gday Piet

 

Are the bearings slightly rough???

Just slip them onto the worm shaft and spin it whilst providing some axial load.

Mine were like they were full of gravel :-)

 

Re fingerprinting, it is Meades method to synchronise the three turn

PEC model when rebooting, using only one sensor on the worm.

If you look at your PEC model in my PEC editor, in the header you will see 3 numbers

all around 51200 ( listed as "Synch Counters" ) The sum of all three should be 51200*3

There is an option in my PEC editor to reset the fingerprints.

You run this and on next boot, it will refingerprint the setup.

 

Just for info, one "perfect" turn of the worm requires 51200 encoder ticks between firings of the sensor

but the sensor is on the worm and the encoder is on the motor.

The PE inside the gearbox means the motor desynchronises from perfect relative to the worm

but it does resynch after 3 revs of the worm.

Thus the "measured" ticks change between each of the three revs ,

and can be used to pattern match the worm to the stored model.

 

Andrew Johansen Melbourne Australia

[Piet Le Roux]

My R188ZZ and FR188ZZ bearings arrived this week and I replaced the bearings of my Alt/Dec drive, the loud knocking sound that came from the drive appears to be much less, I did drive training and the results looks positive : the training value of the Alt/Dec drive came down with more than 20 arc seconds and is around the 70 to 74 mark. So my training values at present are Ra/Az 69 and Dec/Alt 74 so just in what I would call the "safe zone". It looks like the weather will be  accommodating tonight so we may see how she does with a few gotos. 

Edited by Piet Le Roux, 05 March 2025 - 10:32 AM.