Exos-2 PMC-8 - pier extension & axes stabilty


Jennifer Shelly
 

I am going to preface this post with some information about me. The Exos-2 PMC-8 is my first mount. I began my journey with astrophotography a few months ago. I know enough about computers and electronics to be dangerous. Please keep this in mind if you respond.

I own a Exos-2 PMC-8 and I was wondering if it would be possible to get/add a pier extension to give my telescope some additional travel on the RA axis. If so, can someone provide me with some suggestions on how I can accomplish this.

Also, I have noticed that both axes have some wobble when the clutches are locked. The RA axis has the most wobble. Is this normal? If not, what can I do to add stability?


Jennifer Shelly
 

I forgot to let you guys know my name is Jennifer.


Steve Siedentop
 

The pier extension for the Orion Atlas EQ-G fits the Meade LXD-75, which the body of the EXOS-2 is based on.  It might be worth checking out to see if it fits the EXOS 2 as well.

-Steve

On Mon, Jun 11, 2018 at 1:01 PM drunkendogg@... [ESPMC-Eight] <ESPMC-Eight@...> wrote:
 

I forgot to let you guys know my name is Jennifer.


r_hoskin@...
 

Jennifer,

I have an EXOS-2/PMC-8, too.  If the clutches are locked, the wobble you are feeling will be the play between the worm and ring gears on each axis.  The two sets of teeth have either moved apart in use (the worm gear clearance is adjustable), or they left the factory like that.

My own mount arrived with very little play on either axis, but after some use, the RA loosened up. If you contact ES customer service, they can send you instructions on making the adjustment.  This problem recurred on mine after adjustment, and it is currently in Springdale (at ES's request!), undergoing what I fervently hope is a rejuvenation.  YMMV.

There is always going to be some imperfection in the way the ring and the worm interact on this design of mount, so some play will come with the territory.  If it's more than you're comfortable with, you can either adjust it yourself (ES can provide instructions, and Google is your friend), or you can ask ES if they'll do that for you. 

I think the key thing is whether the amout of play you're experiencing is stable, or increasing.  If it's stable and the mount is otherwise performing for you, perhaps you're ok.  If it's increasing/recurring (like mine was), you should probably reach out to ES CS and get some help.

The other thing is that, because of that pretty-much-inevitable mesh imperfection, people  developed the technique of balancing their scope 'east-heavy'.  Basically forcing the motors to drive 'uphill' all the time, so that the flanks of the gear teeth always mesh the same way, reducing backlash/play.  You will probably want to look into that as well. Lots of threads on that over on Cloudy Nights.

Hope this helps! 

- Bob


Jennifer Shelly
 

Thanks Bob. I will definitely contact ES.


Jennifer Shelly
 

Thanks Steve I will check it out.


Jennifer Shelly
 

Bob - Could you send me the instructions ES sent you to adjust your worm and ring gears?


Robert Hoskin <r_hoskin@...>
 

Ok.  I'll send you a note separately - but I'm surprised.  You didn't get helped?




From: "drunkendogg@... [ESPMC-Eight]"
To: ESPMC-Eight@...
Sent: Sunday, June 17, 2018 3:00 PM
Subject: [ESPMC-Eight] Re: Exos-2 PMC-8 - pier extension & axes stabilty

 
Bob - Could you send me the instructions ES sent you to adjust your worm and ring gears?



Jennifer Shelly
 

Bob -

First and foremost...Thank you. Thank you. Thank you. That is just what I needed.
I have performed the adjustment and it made a huge difference.

I did not get a chance to call ES before the weekend.  I did not want to call without being in front of my mount in case they wanted to do some troubleshooting. 

I found this website helpful to visualize what I was going to do.


Thanks again.

Jennifer



r_hoskin@...
 

Jennifer,

You didn't waste any time :-)   You're most welcome.  Glad it worked out for you, and happy to help. 

Do keep an eye on whether the adjustment lasts, though.  That was the issue that sent mine back to the shop... 

- Bob


Jennifer Shelly
 

I called ES last week and obtained clarification on how to determine where the high point is on the worm assembly.

For those interested here are some pointers.
* The high point will be the spot that has the most friction when manually rotating the axis by hand
* The high point should have the least amount of wobble/backlash
* Backlash can be observed by looking at the axis when giving it a little shake and/or by looking at the gear that you are manually turning by hand
* Rotate the axis by hand 180 degrees to find the low point.
* The low point should have the most wobble by observing the axis whilst shaking and/or by looking at the movement of the gear which will show the most movement.
* Only make adjustments at the high point
* If you have a lot of friction the you will need to back out the two end adjustment screws a tiny bit at a time and and rotate the the low spot and check for wobble
* You will likely have to do this as many times as it takes to get to an acceptable amount of wobble at the low point. It might take 5-10 times.
* BE PATIENT because this is a time where patience is indeed a virtue.

*


hubbell_jerry@...
 

Hi Jennifer,

There are actually 2 modes that the wheel can be out of round (run-out) in terms of the mesh adjustment. One mode has 1 low and 1 high spot, the other mode has 2 low and 2 high spots per revolution. I have attached a drawing which shows this.

I would assume that typically any mount will have both modes of run-out at the same time, but one mode may be more pronounced than the other. It is important to understand this when you are adjusting your mount as you may find the first spot to adjust to, but you still could have another high friction spot that will cause some more binding (although maybe not as bad). 

I hope this helps clarify what you may find in your adjustment. I will try and update the knowledge base article I have already posted 


To include this information also.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


Jennifer Shelly
 

Thanks Jerry. I noticed something like that when I was making adjustments, but I thought my mind was playing tricks on me.

I did read that article and unfortunately the link to the Losmandy mount was not helpful because it did not pertain to the Exos-2. It looks different and I did not see where the Exos-2 had the option to move the worm blocks. I suggest adding a link with pictures of for Exos-2 to the knowledge base article.