Declination Axis Balance

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Graeme1858 Great Britain
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Declination Axis Balance

#1

Post by Graeme1858 »

I've put my "grab and go" refractor onto my CGX mount, on the observatory pier and I have been enjoying the wider field of view. For some reason now it is impossible to balance the Declination axis. I can move its position in the saddle so that it is in perfect balance when sitting horizontally, but then when I push the front of the telescope up it drops back down again. Similarly, when I push the front down it comes back up again.

It's not the weight of the cables because I have redressed them into a loop that remains the same length and doesn't touch the floor wherever the telescope is pointing..

I feel I'm missing something simple because it was ok. But the return to horizontal torque is enough to scupper all attempts at calibrating the guiding which leaves me limited to 30 second exposures.

If anyone could point out, to coin a phrase, the bleeding obvious, for me, I would be most grateful.
Graeme

──────────────────────────────────────────────
Celestron 9.25" F10 SCT, CGX Mount.
StellaMira 110mm ED APO F6 Refractor, AVX Mount
ASI1600MM Pro, ASI294MC Pro, ASI224MC.
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.
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https://www.averywayobservatory.co.uk/
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KathyNS Canada
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Re: Declination Axis Balance

#2

Post by KathyNS »

Declination needs to be balanced in two dimensions. One dimension is the fore-and-aft balance that you can adjust by sliding the dovetail forwards and backwards. This is done with the scope horizontal, as you describe.

You also need to balance it laterally. This is done with the scope in the Home position (pointing at the pole). Imbalance in this position is caused by the load not being symmetrical on the mount. The OTA by itself is usually pretty balanced, but if you have a finder or guider on it, or a diagonal with eyepiece (SCT or refractor), or the focuser (Newtonian), or any other similar external load, those loads will pull the centre of gravity off-centre. You need to rotate the OTA in the mounting rings until the centre of gravity is on the centreline of the dovetail. It will not be on the axis of the OTA, but as long as it is on the centreline of the dovetail, it is balanced.

After you get declination balanced in both dimensions, then you can adjust the counterweights to balance RA.

The objective in balancing is to put the combined centre of gravity of the whole movable load exactly at the intersection of the RA and dec axes.
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DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
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Re: Declination Axis Balance

#3

Post by Graeme1858 »

Ah, yes, brilliant! Thanks Kathy. I have heard of the procedure you describe but it's never been an issue before with the 9.25 SCT. But now I'm using a lighter telescope, it would appear, it makes a big difference. And to confirm, the problem started when I changed the camera angle rotation, before the filter wheel and guide camera were opposite the focuser, now they're the same side.

I'll have another look at it tomorrow. Thanks again.
Graeme

──────────────────────────────────────────────
Celestron 9.25" F10 SCT, CGX Mount.
StellaMira 110mm ED APO F6 Refractor, AVX Mount
ASI1600MM Pro, ASI294MC Pro, ASI224MC.
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.
──────────────────────────────────────────────
https://www.averywayobservatory.co.uk/
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Re: Declination Axis Balance

#4

Post by KathyNS »

If you can get the filter wheel and guider to balance each other again, you should be good to go. If not, a flaw in my procedure is that most SCTs do not use rings in which they can be rotated. If all else fails, you can get add-on counterweights to help balancing the rig. Magnets are handy as counterweights if you have a steel tube. Or you can get clamps that fit onto a dovetail, to hold counterweights that can be adjusted on a threaded rod.
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DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
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OzEclipse Australia
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Re: Declination Axis Balance

#5

Post by OzEclipse »

I use a four-step balance.

1. With the counterweight bar horizontal and the OTA horizontal, adjust and balance the counterweights on the counterwight shaft.

2. With the counterweight bar horizontal and the OTA horizontal, I slide the OTA until the OTA is balanced.

3. I turn the declination axis 90o so that the counterweight shaft is horizontal and the optic axis vertical and balance if possible.

4. I turn the RA axis so the counterweight shaft is vertical and check the balance in two directions. If the first three were done correctly, thee should be no problem.
Joe Cali (OzEclipse)

34 South - The Hilltops Observatory
Hilltops region, Young, New South Wales, Australia. [148E, 34S]


Amateur astronomer since 1978.....Web site :http://joe-cali.com/.....Total & Annular Eclipses Observed:18
Scopes: ATM 18" Dob, Vixen VC200L, Hand Made 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, Coronado PST
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Re: Declination Axis Balance

#6

Post by KathyNS »

OzEclipse wrote: Mon Feb 03, 2025 9:49 am I use a four-step balance.

1. With the counterweight bar horizontal and the OTA horizontal, adjust and balance the counterweights on the counterwight shaft.

2. With the counterweight bar horizontal and the OTA horizontal, I slide the OTA until the OTA is balanced.

3. I turn the declination axis 90o so that the counterweight shaft is horizontal and the optic axis vertical and balance if possible.

4. I turn the RA axis so the counterweight shaft is vertical and check the balance in two directions. If the first three were done correctly, thee should be no problem.
That's pretty much what I do, except that I always do step #1 last. Whatever actions you take for step #3, whether rotating the scope in its rings, moving the guider around, or moving camera loads, are almost certain to change the position of the centre of gravity perpendicular to the RA axis, requiring an adjustment of the RA balance.
Image
DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
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Re: Declination Axis Balance

#7

Post by Graeme1858 »

KathyNS wrote: Sun Feb 02, 2025 11:40 pm If you can get the filter wheel and guider to balance each other again, you should be good to go. If not, a flaw in my procedure is that most SCTs do not use rings in which they can be rotated. If all else fails, you can get add-on counterweights to help balancing the rig. Magnets are handy as counterweights if you have a steel tube. Or you can get clamps that fit onto a dovetail, to hold counterweights that can be adjusted on a threaded rod.

Cheers Kathy

My problem is with the refractor. The SCT was ok because I used it, for most of the time with an OSC camera and the Dec axis was balanced on both lines of symmetry. The refractor has a ZWO focuser off to one side and the camera sensor rotation needs the camera, the OAG camera and the EFW to be rotated. I'm going to have a look now and rotate the camera, the OAG and the EFW to get a good balance. Then all my imaging will be done at that rotation in future!
Graeme

──────────────────────────────────────────────
Celestron 9.25" F10 SCT, CGX Mount.
StellaMira 110mm ED APO F6 Refractor, AVX Mount
ASI1600MM Pro, ASI294MC Pro, ASI224MC.
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.
──────────────────────────────────────────────
https://www.averywayobservatory.co.uk/
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Re: Declination Axis Balance

#8

Post by Graeme1858 »

OzEclipse wrote: Mon Feb 03, 2025 9:49 am I use a four-step balance.

1. With the counterweight bar horizontal and the OTA horizontal, adjust and balance the counterweights on the counterwight shaft.

2. With the counterweight bar horizontal and the OTA horizontal, I slide the OTA until the OTA is balanced.

3. I turn the declination axis 90o so that the counterweight shaft is horizontal and the optic axis vertical and balance if possible.

4. I turn the RA axis so the counterweight shaft is vertical and check the balance in two directions. If the first three were done correctly, thee should be no problem.

Cheers Joe

It was step 3 that was missing from my procedure.
Graeme

──────────────────────────────────────────────
Celestron 9.25" F10 SCT, CGX Mount.
StellaMira 110mm ED APO F6 Refractor, AVX Mount
ASI1600MM Pro, ASI294MC Pro, ASI224MC.
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.
──────────────────────────────────────────────
https://www.averywayobservatory.co.uk/
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Re: Declination Axis Balance

#9

Post by Graeme1858 »

Well I spent a hour or so balancing and tweaking and re-balancing until I was happy. The telescope stayed where I put it, clutches off, wherever I put it.

The sky was clear after sunset tonight so I fired the rig up and ran a PHD2 calibration. Same result! The calibration movement was not happening even with a calibration ms step of 2000.

So here's 7 x 30 seconds on Praesepe as a consolation prize.

M44.jpg
Graeme

──────────────────────────────────────────────
Celestron 9.25" F10 SCT, CGX Mount.
StellaMira 110mm ED APO F6 Refractor, AVX Mount
ASI1600MM Pro, ASI294MC Pro, ASI224MC.
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.
──────────────────────────────────────────────
https://www.averywayobservatory.co.uk/
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Re: Declination Axis Balance

#10

Post by Graeme1858 »

Well I posted in the PHD2 Group and the excellent Bruce came to the conclusion that my mount is receiving the push commands but the motors are not moving the telescope.

So I raised a ticket with Celestron and got the following response:

CPWI has a PHD2 emulator (PHD2 Server) built in, which is how you connect to NINA. Please follow the steps below to interface the to NINA:
1) Connect mount, and other accessories to CPWI and do an alignment (even a quick align is fine)
2) go to the CPWI menu and turn on PHD2 Server and turn off High-precision Slew and Meridian flip (since these will be controlled by NINA)
3) turn on NINA and connect mount (CPWI or Device hub -> CPWI) and then tell the guider you are connecting to PHD2 (but do not have PHD2 running)
4) NINA will display an error that PHD2 is not found and then 1-2 seconds later will have a message that the guider is connected. This is normal behavior
5) You can then start/stop guiding and dithering in the Sequencer and set up meridian flip rules in the settings tab. The reason you have these settings off in CPWI is to prevent NINA/CPWI from fighting each other or getting into a feedback loop if the SSAG is more than an arcminute misalligned. Better to keep the SSAG doing guiding and let NINA handle the plate solving, dithering, and flip

CPWI has a PHD2 server. This is news to me.

Does anyone know where this option is in the CPWI menu?
Graeme

──────────────────────────────────────────────
Celestron 9.25" F10 SCT, CGX Mount.
StellaMira 110mm ED APO F6 Refractor, AVX Mount
ASI1600MM Pro, ASI294MC Pro, ASI224MC.
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.
──────────────────────────────────────────────
https://www.averywayobservatory.co.uk/
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