Advice for someone considering purchasing a well used AP900GTO


George Lutch
 

I am considering purchasing a well used AP900GTO CP3 with hand controller and am in need of advice on what to check on the actual mount prior to purchase. I want to be sure there are no major issues with it.  Any advice would be appreciated.


Emilio J. Robau, P.E.
 

Greetings George,

I purchased a used 2003 2004 vintage AP900 and after a break in period for me that entailed getting used to it and switching out an older CP2 unit for a used CP3 unit I think I have it performing pretty well.   The main thing to look for after your observe the general condition is the serial number.    AP had an enhancement (or fixed an issue with counterweight up guiding) that was deployed after a certain serial number.   I don't recall the number but will look it up for you and post later.   If you can get a mount with a serial number higher than the magic number you are one step ahead of me.   I love my mount and I picked it up with a whole bunch of stuff and it looked brand spanking new.   It was primarily used by a visual observer so the wear was significantly less than say my 1600 in the observatory which is deployed every single moment in the fall through spring that I can get to collect data all night long.

I think the main thing is the serial number that indicates whether or not it has the dec fix.

I don't think you can go wrong with any AP 900, 1200, 1100, and 1600 mounts.  They are electro mechanical works of art.   

I don't think you have to upgrade the CP3 to CP4 since the CP3 allows you to deploy a model from APCC and you really want that functionality, so you will need to purchase APPC if you don't already have it.   Highly recommended contribution to Ray's artwork in my opinion.

My AP900 points as well as my 1600 which has the CP4 box.   Sometimes I just shake my head and don't believe that NINA does not have to make a correction on a nearby slew or just one correction when slewing across the sky on the plate solves.   Amazing performance.

You can take the cover off of the gear box and take a look at the condition of the gears and the actual lube itself.   Mine was older and caked on.  I purchased the kit and re-applied the lube and it sounds better.  You could take off the box itself and take a look at the main gear as well as the worm, but that is somewhat invasive to someone who already may have the PEC programmed and does not want you messing with it.  

After using my 900 without the through mount routing of wires, I can say that I would be satisfied with a 1200 also.   I like the through mount functionality for the wiring, but have come to learn that it is not that huge of an issue to control the cords,  This is especially true if you purchase a Pegasus power box, which I did and it is definitely one of y favorite gadgets and allows for a very graceful control of the cords.

Finally, I want to add that I power my mount separately from everything else connected to the camera, heater, focuser and so on and so forth.   I have found that the heaters draw some amps and mess up the mount a bit from time to time so I run separate power.  Some will tell you that it is not necessary and their systems work through the power box, but mine does not.

Don't think twice, buy the thing.


Steve Salvo
 

I believe Not all of the older mounts needed the DEC upgrade, only those mounts that showed tracking issues. George can certainly further explain if needed.

I have an older AP900GTO no issues, amazing mounts!

Steve


On Apr 12, 2022, at 15:29, George Lutch <glutch@...> wrote:

I am considering purchasing a well used AP900GTO CP3 with hand controller and am in need of advice on what to check on the actual mount prior to purchase. I want to be sure there are no major issues with it.  Any advice would be appreciated.


Roland Christen
 

Make sure the Dec is balanced and it will track well. RA is not as important to get the balance just right.

Roland

-----Original Message-----
From: Steve Salvo via groups.io <sws105@...>
To: main@ap-gto.groups.io
Sent: Tue, Apr 12, 2022 2:51 pm
Subject: Re: [ap-gto] Advice for someone considering purchasing a well used AP900GTO

I believe Not all of the older mounts needed the DEC upgrade, only those mounts that showed tracking issues. George can certainly further explain if needed.

I have an older AP900GTO no issues, amazing mounts!

Steve


On Apr 12, 2022, at 15:29, George Lutch <glutch@...> wrote:

I am considering purchasing a well used AP900GTO CP3 with hand controller and am in need of advice on what to check on the actual mount prior to purchase. I want to be sure there are no major issues with it.  Any advice would be appreciated.

--
Roland Christen
Astro-Physics


Emilio J. Robau, P.E.
 

Steve,

I think you are correct.  I have not tried to guide counter weight up just in case.  I have not tried to run a mile lately, just in case.


Emilio J. Robau, P.E.
 

A question for Roland if he is still there relevant to the 900.  What are the knobs that are associated with the axis that seem to be locks but are not really locks. What is their function and how tight do they have to be?


Roland Christen
 

They are shaft dampers with Teflon tips. They should not be tight, but just gently touching. Shaft dampers were commonly used back some 30 years ago to take slack out of shafts that were held by standard ball bearings that were not pre-loaded. The dampers put pressure on the shaft but still allow it to rotate at the sidereal rate. Too much pressure and the shaft will stall the motor.

We recently had an old mount come back where the damper was tightened by a crowbar. It was so tight we could not back it off without using a ton of force. The complaint was that the motors would stall and not track consistently. Yes indeed, that's what happens.

Nowadays mount bearings are preloaded, so no dampers needed.

Rolando

-----Original Message-----
From: Emilio J. Robau, P.E. <ejr@...>
To: main@ap-gto.groups.io
Sent: Tue, Apr 12, 2022 2:55 pm
Subject: Re: [ap-gto] Advice for someone considering purchasing a well used AP900GTO

A question for Roland if he is still there relevant to the 900.  What are the knobs that are associated with the axis that seem to be locks but are not really locks. What is their function and how tight do they have to be?

--
Roland Christen
Astro-Physics


Emilio J. Robau, P.E.
 

Thanks Roland.  I have them snug but not tight.


Christopher Erickson
 

If the knobs are silver they could be the locks for the dovetail for taking the mount into two halves. Those need to be tight.

"Always take the high road. There's less traffic."

-Christopher Erickson
Observatory Engineer
Summit Kinetics
Waikoloa, Hawaii


Virus-free. www.avg.com


On Tue, Apr 12, 2022 at 10:36 AM Emilio J. Robau, P.E. <ejr@...> wrote:
Thanks Roland.  I have them snug but not tight.


Emilio J. Robau, P.E.
 

Thanks Chris,

Roland was able to understand what I was talking about.   They are the shaft dampers.


George
 

Emilio,

 

Touch them…do not snug them.

 

Regards,

 

George

 

George Whitney

Astro-Physics, Inc.

Phone:  815-222-6538 (direct line)

Phone:  815-282-1513 (office)

Email:  george@...

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Emilio J. Robau, P.E.
Sent: Tuesday, April 12, 2022 3:42 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Advice for someone considering purchasing a well used AP900GTO

 

Thanks Chris,

Roland was able to understand what I was talking about.   They are the shaft dampers.


Emilio J. Robau, P.E.
 

Thanks for the clarification.   I will touch and not snug.


George Lutch
 

So much great advice.  I even went back via search and determined the correct grease to use.  The person selling the mount is going to let me test drive it for a week so I should see if there are any issues with it over that amount of time. 
Any advice on adjusting backlash out?


Emilio J. Robau, P.E.
 
Edited

George L,

If you have possession for a while, then for sure get Pempro and test out the PEC to see where you are at.  Pempro has a trial version that you can use.  I would feed the mount a new PEM curve if the owner will allow you to do that.   I am not sure but a trial may be available for APPC.  If you can get a hold of that, build a model and check the pointing.   

Also, just get the grease kit from AP when you purchase it.  Support the locals!  They have a kit that will last say three applications for sure.  I applied it to my 1600 and the 900 and have some left over.

Backlash is an interesting question on these older mounts.  I don't think my 1600 has any backlash.   Also, I think the backlash is also dependent on how well the gears are mashed.   I see APCC has a backlash setting on the initialization where you can set backlash in arc-sec on both RA and DEC.   Mine is set to zero but I often wonder if I can improve the tracking even more by adjusting that variable.   I am curious to see what tests people do to actually determine if a setting other than zero is appropriate.

I also wonder if the backlash setting on Ray's V2 driver sets the variable immediately after you enter the value and close out the ASCOM driver.  Not sure on backlash and interested in any input.


Charles Thompson
 

PHD2 guide assistant has the option to measure backlash. I do not know how accurate it is though. 





Thanks,
Charles

Sent from mobile device.


-------- Original message --------
From: "Emilio J. Robau, P.E." <ejr@...>
Date: 4/12/22 3:53 PM (GMT-06:00)
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Advice for someone considering purchasing a well used AP900GTO

[Edited Message Follows]

George L,

If you have possession for a while, then for sure get Pempro and test out the PEC to see where you are at.  Pempro has a trial version that you can use.  I would feed the mount a new PEM curve if the owner will allow you to do that.   I am not sure but a trial may be available for APPC.  If you can get a hold of that, build a model and check the pointing.   

Also, just get the grease kit from AP when you purchase it.  Support the locals!  They have a kit that will last say three applications for sure.  I applied it to my 1600 and the 900 and have some left over.

Backlash is an interesting question on these older mounts.  I don't think my 1600 has any backlash.   Also, I think the backlash is also dependent on how well the gears are mashed.   I see APCC has a backlash setting on the initialization where you can set backlash in arc-sec on both RA and DEC.   Mine is set to zero but I often wonder if I can improve the tracking even more by adjusting that variable.   I am curious to see what tests people do to actually determine if a setting other than zero is appropriate.

I also wonder if the backlash setting on Ray's V2 driver sets the variable immediately after you enter the value and close out the ASCOM driver.  Not sure on backlash and interested in any input.


George Lutch
 

From watching youtube it appears that you just loosen the adjustment screws on the worm housing and wiggle it followed by applying slight pressure to mesh the gears as you tighten the adjustment screws.


Steven Panish
 

That's basically it.  There is a Gear Mesh doc on the AP website that you should read.  But the gear and worm mate very well...no real pressure needed, just rock the motor box a bit and let it settle in.

Steve

On Tue, Apr 12, 2022 at 7:00 PM George Lutch <glutch@...> wrote:
From watching youtube it appears that you just loosen the adjustment screws on the worm housing and wiggle it followed by applying slight pressure to mesh the gears as you tighten the adjustment screws.



--
PLEASE NOTE MY NEW EMAIL ADDRESS!!!
Due to Google eliminating cheap domain serving, Virginia and I are changing to regular gmail addresses.  The old panishnet address will forward to this address for a short while, but please add the new address, scpanish1@..., to your contact list.


Chris White
 

On Tue, Apr 12, 2022 at 04:45 PM, George Lutch wrote:
So much great advice.  I even went back via search and determined the correct grease to use.  The person selling the mount is going to let me test drive it for a week so I should see if there are any issues with it over that amount of time. 
Any advice on adjusting backlash out?
George,

I've needed to adjust the gear mesh on DEC with my 900.  Just follow the instructions here:  https://astro-physics.info/tech_support/mounts/900gto/gear-mesh-900.pdf

It's pretty easy to do and you'll get a feel for it after a couple of tries. 


Michael Hamburg
 

The AP900 like all AP mounts is a true work of art and engineering. I bought my own used a few years ago and it carries an Edge 11HD and an Orion 80mm ED and a bunch of electronic controls without breaking a sweat. The only thing it cannot do is dissipate clouds.

Best wishes, Michael


On Tuesday, April 12, 2022, 10:12:50 PM EDT, Chris White <chris.white@...> wrote:


On Tue, Apr 12, 2022 at 04:45 PM, George Lutch wrote:
So much great advice.  I even went back via search and determined the correct grease to use.  The person selling the mount is going to let me test drive it for a week so I should see if there are any issues with it over that amount of time. 
Any advice on adjusting backlash out?
George,

I've needed to adjust the gear mesh on DEC with my 900.  Just follow the instructions here:  https://astro-physics.info/tech_support/mounts/900gto/gear-mesh-900.pdf

It's pretty easy to do and you'll get a feel for it after a couple of tries. 


George Lutch
 

I was able to pick it up for a couple days of evaluation.  I adjusted the backlash on the two axis and took a look at the overall state of the mount.  The Dec and RA are stiff with the knobs loose so not sure how to adjust it to allow it to be looser for balancing as well as overall operation during use. The right RA adjustment knob is not seated all the way on the threaded stud and loosening the grub screw does not allow me to adjust that, Can I order a new one.  Chip in the CP3 is a "J" chip so not a V2.  Has several chips in the paint. Anyone know where I can get paint for touchup? I will set it up tomorrow night and do some guiding on it to see how it tracks natively.