Author Topic: Celestron AVX Rebuild  (Read 1412 times)

revekosque

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Celestron AVX Rebuild
« on: December 24, 2017, 04:32:31 PM »
Ok people, I will post this, since I believe it's applicable.

I've never really been happy with my Celestron AVX bracket.  Most of us know what a disaster that they are, or at least most of them.  The design is far from world class, it's a bottom dweller.  I've really wanted to send out my mount for a HyperTune, but spending nearly $500 for that support for an $800 or $900 mount only seems a waste.

I've discovered a better way!

http://rocketsparrow...estron-avx.html

This gentlemen detailed the breakdown of the AVX bracket and the way he went on rebuilding it into something such as it ought to have been to start with.  Anyone who has or has had an AVX, also has gone to perform the gear net adjustments know how greasy these things happen.  Well, when you put into the guts of it, you'll find it's even worse, possibly because there's too much grease, or, on the R.A. axis on mine, nearly none in any way!

I spent this afternoon doing so 'cleaning', for lack of a better term.  It took me around three hours or so.  The instructions are fairly detailed, you can see my comments at the end of the blog, and you might want to read these before you start, there's some things he missed, or even forgot to put in.

But if you have an AVX bracket, and have some basic hand tools, including a good set of Metric Allen Wrenches, you need to be able to get this done in a few hours, most certainly a Saturday or Sunday afternoon.  I'm hoping that this can make the AVX a better bracket for those who have one.

Oh, by the way, I can actually balance in Dec now, in addition to R.A.!!  Could not do that before!



ithoclirans

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Re: Celestron AVX Rebuild
« Reply #1 on: December 28, 2017, 07:59:07 PM »
Quote
I've never really been happy with my Celestron AVX mount. We all know what a disaster they are, or at least most of them.

Perhaps more accurate to say some AVX's are problematic. Mine has the sticky grease but it actually guides very well.

Good to have the strip down reference though if it ever does need attention.

Patrick Zhu

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Re: Celestron AVX Rebuild
« Reply #2 on: December 31, 2017, 06:40:18 PM »
Thanks for sharing this, Gary! This is going to come in handy for when I strip down my mount.

breakagalkit

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Re: Celestron AVX Rebuild
« Reply #3 on: January 10, 2018, 10:41:46 PM »
I just took the gearbox apart tonight, tightened up the play in the gears and regreased. I tested it with motor speed set to 3 and I could see both gears actually move instantly when I pressed a directional button. Before it would be at least a 1 second delay. Hope this improves things a bit at least. Might have to move on to this next.
Question: do you use the anti-backlash on the hand control? I've heard some say it helps with guiding, others say it interferes with guiding.

ifaclidis

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Re: Celestron AVX Rebuild
« Reply #4 on: January 10, 2018, 11:51:18 PM »
Quote
I just took the gearbox apart tonight, tightened up the play in the gears and regreased. I tested it with motor speed set to 3 and I could see both gears actually move instantly when I pressed a directional button. Before it would be at least a 1 second delay. Hope this improves things a bit at least. Might have to move on to this next.
Question: do you use the anti-backlash on the hand control? I've heard some say it helps with guiding, others say it interferes with guiding.

Jarrett, one thing you want to make sure is that there IS some backlash in the gearing, you need to have that, and it's very easy to mash the two gears together and tighten everything down.

As to the Anti-Backlash control, I don't use it, so I can't really say.

lorndwatassi

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Re: Celestron AVX Rebuild
« Reply #5 on: January 11, 2018, 02:26:17 AM »
Quote
I just took the gearbox apart tonight, tightened up the play in the gears and regreased. I tested it with motor speed set to 3 and I could see both gears actually move instantly when I pressed a directional button. Before it would be at least a 1 second delay. Hope this improves things a bit at least. Might have to move on to this next.
Question: do you use the anti-backlash on the hand control? I've heard some say it helps with guiding, others say it interferes with guiding.

If your guiding with PHD, you must have "backlash compensation" disabled in the HC.

The part# for a replacement bearing, taken from another tear down is, Part# bearing 51107. Google it, there are many suppliers on the cheap!

Here is yet another detailed tear down of the AVX...https://www.flickr.c...N04/14934150119

hiswacoka

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Re: Celestron AVX Rebuild
« Reply #6 on: January 11, 2018, 05:29:06 PM »
Quote
If your guiding with PHD, you must have "backlash compensation" disabled in the HC.

Could you please explain why?

As I observed, "backlash comp." is momentary increase of motor speed when slewing opposite direction.
If there is backlash, not compensated mechanically, and if right value chosen in HC,
then this feature improves guiding.

However the best is to adjust gears and make backlash as low as possible.

P.S. I agree that wrong value of backlash compensation in HC can make guiding with PHD like a pain.

Jeff Ramirez

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Re: Celestron AVX Rebuild
« Reply #7 on: January 22, 2018, 07:56:17 PM »
Backlash compensation in the HC does exactly as you say, but it depends entirely upon the mount being at one end or the other of the backlash gap when it is applied. For mounts with a lot of stiction, this is probably not a problem since the OTA will tend to stay put after a DEC move. However, depending on balance, OTA orientation, etc. the mount can fairly easily drift into the middle of the backlash gap following a DEC move. When the next backlash correction is applied, it will overshoot. This is typically not a problem visually but can wreak havoc while guiding.I have successfully used backlash compensation while guiding so it can be done and as such the idea that it "must" be disabled is not true. But using it will require some careful experimentation to ensure that the amount of compensation is consistently correct. It is also important to remember that PHD2 also does backlash compensation, and it adjusts the value on the fly. This feature assumes that there is no HC compensation enabled, and if both are enabled, they can fight each other. I prefer to let PHD2 handle backlash compensation since it be constantly monitoring it and making adjustments as the OTA orientation changes.Tim

Christopher Mendez

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Re: Celestron AVX Rebuild
« Reply #8 on: January 30, 2018, 07:28:05 AM »
Quote
Quote

If your guiding with PHD, you must have "backlash compensation" disabled in the HC.

Could you please explain why?

As I observed, "backlash comp." is momentary increase of motor speed when slewing opposite direction.
If there is backlash, not compensated mechanically, and if right value chosen in HC,
then this feature improves guiding.

However the best is to adjust gears and make backlash as low as possible.

P.S. I agree that wrong value of backlash compensation in HC can make guiding with PHD like a pain.
There is an option in PHD to handle backlash but I never use it or take the recommendations to enable it after running the GA. You certainly don't want to have both enabled (HC and PHD). You can try one or the other, it'll either makes things better or...not?

outatnoha

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Re: Celestron AVX Rebuild
« Reply #9 on: January 30, 2018, 11:21:19 PM »
I missed there is an option in PHD.
Since PHD does pulse guiding (correct me please if I wrong), it can compensate backlash only by longer pulse duration. Slow way.
Other side, mount compensates it by initially higher speed of motor for several milliseconds. Faster way.

Kyle Johnson

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Re: Celestron AVX Rebuild
« Reply #10 on: January 31, 2018, 03:22:37 AM »
Quote
I missed there is an option in PHD.Since PHD does pulse guiding (correct me please if I wrong), it can compensate backlash only by longer pulse duration. Slow way.Other side, mount compensates it by initially higher speed of motor for several milliseconds. Faster way.
True. But there should never be fast deviations that require fast corrections when guiding in DEC. With good PA, DEC just comes along for the ride. The only deviations would be due to drift which happens slowly. A second or two to take up backlash should not impact guiding quality at all.Tim

Robert Spencer

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Re: Celestron AVX Rebuild
« Reply #11 on: January 31, 2018, 06:05:21 AM »
Quote
Backlash compensation in the HC does exactly as you say, but it depends entirely upon the mount being at one end or the other of the backlash gap when it is applied. For mounts with a lot of stiction, this is probably not a problem since the OTA will tend to stay put after a DEC move. However, depending on balance, OTA orientation, etc. the mount can fairly easily drift into the middle of the backlash gap following a DEC move. When the next backlash correction is applied, it will overshoot. This is typically not a problem visually but can wreak havoc while guiding.
I have successfully used backlash compensation while guiding so it can be done and as such the idea that it "must" be disabled is not true. But using it will require some careful experimentation to ensure that the amount of compensation is consistently correct. It is also important to remember that PHD2 also does backlash compensation, and it adjusts the value on the fly. This feature assumes that there is no HC compensation enabled, and if both are enabled, they can fight each other. I prefer to let PHD2 handle backlash compensation since it be constantly monitoring it and making adjustments as the OTA orientation changes.
Tim

Well I had set them on on the HC before and feel like I had better guiding results, then I turned them off and I think it has been worse since. Could obviously be other factors of course though.

I hope to get out tonight after tightening up the gears last night and test with and without anti-backlash on in the HC and see if it is better or worse.

wordpuzzlesubc

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Re: Celestron AVX Rebuild
« Reply #12 on: February 08, 2018, 02:09:43 AM »
Gary, thanks for pointing this out (and your comments in the blog) ...
As you know - I've never opened up my AVX, but it's nice to think I could one day.

Jason Pederes

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Re: Celestron AVX Rebuild
« Reply #13 on: February 09, 2018, 10:49:33 AM »
Well, I regreased the gearboxes with white lithium grease. I attempted to unscrew the bolts on the clamps, but they were SO tight.