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Equipment Discussions >> Mounts

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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5739449 - 03/17/13 07:10 PM

Gday Rick

Quote:

I will try to reverse the sign of dec as soon as I can get a clear night. Fully overcast tonight.




Overcast is good
as you can waste time indoors with a beer and cheese whilst watching TV if reqd.
Use a planetarium to display the night sky for your location.
Adjust the time in the planetarium to find when Sirius is at the meridien.
( The actual date/time you get is immaterial, ie it doesnt need to be current. )
Now go to yr mount ( it can be set up anywhere and pointing anywhere )
Put the DEC head to polar home and start the Hbx.
When it asks for time, use the date/time you found in the planetarium.
Do a one star align.
Just hit enter when it asks to centre polaris.
The next star will be Sirius
When it slews to it and asks you to centre it,
your OTA should be pointing vertical and the DEC readout of the OTA
( from the setting circles ) should be the same as Sirius.

Lots of tests can be done this way without needing clear sky.

Andrew Johansen Melbourne Australia


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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5741834 - 03/18/13 09:44 PM

Quote:

Now go to yr mount ( it can be set up anywhere and pointing anywhere )




Except the bearings that hold my motorized head at the angle of my latitude (note the large shaft protruding to the right in my photo) are permanently mounted outside.

Not say that I couldn't design a similar experiment with the head sitting flat on some kind of stand.

But the beer and cheese is sounding more appealing right now!

Edited by ricknau (03/18/13 09:47 PM)


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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5741902 - 03/18/13 10:03 PM

Gday Rick

Quote:

Except the bearings that hold my motorized head at the angle of my latitude (note the large shaft protruding to the right in my photo) are permanently mounted outside.




So take the beer and cheese outside on a tray
All i'm pointuing out is that for this level of diagnostic work,
you dont need a clear sky, or even the ability to see stars.
We are only trying to test if changing the DEC ratio sign
gets you into the ballpark.
Faking the time, to put a known target in a known position
makes it easy to see how close it is getting.

Andrew Johansen Melbourne Australia


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5742622 - 03/19/13 10:47 AM

Thanks Andrew, like the beer and cheese idea, I'm learning so much reading this thread. Good stuff.

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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5744139 - 03/19/13 10:20 PM

Quote:

All i'm pointing out is that for this level of diagnostic work,
you dont need a clear sky, or even the ability to see stars.
We are only trying to test if changing the DEC ratio sign
gets you into the ballpark.
Faking the time, to put a known target in a known position
makes it easy to see how close it is getting.




Ok, I'm slow but I get there! I must say that while I missed a chance 2 nights ago, last night was big rain. Tonight is good though and I've given it a go with the sign of Dec reversed. I did it without the OTA. That made it much easier to set up.

Here's what happened. After doing a motor calibration I set the mount at polar north and did Easy Align. It looked like the the RA fairly nailed Sirius' RA but the declination motor had the imaginary tube pointed roughly 160-170 deg out. I was encouraged by RA and decided to return the dec sign to +. Did easy align again. This time it pointed to roughly 2/3 of the way between Sirius and Procyon. Returned once again to polar north. Redid easy align. It pointed to the same place between Sirius And Procyon.

Things of note: At one point the Autostar crashed. Running off the battery pack with AA batts. Battery readout says batts at 100%

Work night so I couldn't keep beating at it. Off to bed now

Edited by ricknau (03/20/13 07:06 AM)


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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5745419 - 03/20/13 03:36 PM

Gday Rick

When you did the 360deg test, what speed did you use???
Ie did you do the DEC axis slew at MAX, then drop back???
Just wondering if the encoder is miscounting at high speed.
Maybe put the Hbx into "quiet mode" and retry the dummy align.
In this mode, the scope goes slow enough to ensure the encoders read quickly enough for a speed feedback loop to work, vs max, which just runs at raw voltage and the encoders try to just maintain a count.

Andrew Johansen Melbourne Australia


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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5746168 - 03/20/13 08:24 PM

HOLY COW! I can't believe what a dumby I am! Started shopping for a new worm gear for RA thinking the tripod-head built in worm gear is kind of crude (possible warped) and those bearings aren't made to support so much weight cantilevered out at my latitude angle. The motor does strain mightily. To begin with I looked at the invoice for the worm gear I bought for the dec axis. And lo and behold I see that that SOB has 120 teeth! Not 100! I can't believe I didn't remember that number correctly! Well my mind just must not be what it used to be! They say the mind is the second thing to give out as you age!

Well this will most assuredly fix that axis. The RA 360 deg test indicated that I have the number of teeth correct for that axis. (Why didn't I test both axes?) And my easy align test yesterday indicates that the RA is probably working OK.

Sorry to all you guys I lead on a goose chase. I'll report back in day or two with my new results.

Edited by ricknau (03/20/13 08:31 PM)


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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5746348 - 03/20/13 09:32 PM

Gday Rick

Quote:

(Why didn't I test both axes?)




Too much beer and cheese before you got
to that part in the instructions

Anyway, see how the new numbers go and you should find it will work.
Also, can you fit the 120 toother to RA and 96 toother to DEC??
If so, you will get a better feedback ratio for tracking in RA.

Andrew Johansen Melbourne Australia


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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5746951 - 03/21/13 06:47 AM

Can't swap them. The RA worm gear is built into the old tripod head. Was thinking of abandoning that built-in gear and fashoning an external one. Reason being (beyond getting better ratio) is that that rotation exerts a bit more resistance than I think ideal. Plus the resistance varies with the period of the worm. The sound goes weeee uuuh weeee uuuh weeee uuuh when it rotates at high speed. But it does rotate. And if it does "count" properly I'll probably live with it, at least for now. Hopefully it won't harm the motor itself. All these issues with that axis is why I focused there and ignored the beautifully engineered and expertly fabricated one-off dec axis.

EDIT: of course there is that pesky problem of the sidereal tracking rate being off a little. I might have to break open the head and recount the gear teeth. Ugh! Means complete dismantling!

Edited by ricknau (03/21/13 06:53 AM)


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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5748068 - 03/21/13 05:18 PM

Gday Rick
Quote:

EDIT: of course there is that pesky problem of the sidereal tracking rate being off a little. I might have to break open the head and recount the gear teeth. Ugh! Means complete dismantling!




Not required.
You noted its a 96 tooth worm.
Armwave calc means 4deg per tooth.
If you did the RA spin test on a fixed landmark,
the the Az readout would have shown a 4deg error per error in toothcount.

Andrew Johansen Melbourne Australia


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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5749089 - 03/22/13 05:58 AM

Yes, thanks for that reminder. Thank goodness. I sure didn't want to have to break the entire assembly down. I see looking at a document by Michael Weasner that the tracking rate can be adjusted by direct input. So if the error persists after I get everything else fine tuned then I will try to fix it that way.

Here's a new question for you... I took great care to get my RA and dec axis to be 90 degrees apart. But I didn't do the same for the OTA vs the dec axis. To my way of thinking, since the tube doesn't spin on it's own axis (is not controlled by the Autostar), that axis (it's line of sight) is not required to be at exactly 90 degrees from the dec axis for the Autostar's positional calculations to work. Correct?

Edited by ricknau (03/22/13 06:16 AM)


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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5749102 - 03/22/13 06:25 AM

Gday Rick

Quote:

Here's a new question for you... I took great care to get my RA and dec axis to be 90 degrees apart. But I didn't do the same for the OTA vs the dec axis. To my way of thinking, since the tube doesn't spin on it's own axis (is not controlled by the Autostar), that axis (it's line of sight) is not required to be at exactly 90 degrees from the dec axis for the Autostar's positional calculations to work. Correct?





Incorrect. If the OTA isnt square, then depending on where you
align/ synch in the sky, you wil get errors in RA as you slew in DEC.
Ie imagine you set the weightbar horizontal
and then line yr OTA up on the pole.
Now spin the RA 180deg.
Are you still on the pole ??????
There is a section in the LXD75 manual on how to get yr OTA "mechanically" aligned correctly

Andrew Johansen Melbourne Australia


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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: OzAndrewJ]
      #5749109 - 03/22/13 06:43 AM

Ugh! Not what I wanted to hear! Well it should be darn close to 90, so first I'll do my checkout with the new dec ratio to validate that improvment. And then after seeing how accurately it can GOTO various sky objects I will tackle that adjustment. It shouldn't be a biggie to fine tune that. Just requires some shims.

Today being Friday I'll have time to play over the weekend... if not raining. Actaully I can adjust that angle with the head indoors.

Off to work now.

Edited by ricknau (03/22/13 06:47 AM)


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ricknau
member


Reged: 02/26/11

Re: Trouble with Autostar GOTO new [Re: ricknau]
      #5765953 - 03/29/13 11:54 PM

WOO HOO!! I got it working! Had to wait till this weekend since last week was a weather bust. What was the problem? BOTH axes had to have their sign reversed. (That, plus I got the dec ratio corrected.)

Started out having the same old error. Easy Align tried to go to Sirius but stopped off the mark by many degrees. But this time the dec was right on. I could drive right to the target with RA only. Tried several times and each time the RA error got worse. Dec was dead on every time. I finally deduced that the stop point was working it's way eastward while the stars worked their way westward. I also deduced that the sidereal tracKing was in the wrong direction. (Remember I metioned that "pesky problem"?) So I reversed the sign of the RA. Did Easy Align and this time the RA moved in the opposite direction but stopped where it seemed like it might be close. But the dec was now pointed way off, like in the complete opposite direction! ARRGH! The declination had been working perfectly! Then I figured "what the hell", even though the dec had been right on the money, flip the sign anyway. And sure enough, BINGO!, it went right to Sirius. I finished Easy Align with the second star and I was off to the races!

OMG how cool! I was scooting from object to object. How sweet! This is going to be so productive! My daughter will be in town from NYC in about a week, near the new moon. She has been my viewing buddy since she was about 10. She's going to love this.

Thanks to you guys, especially Andrew, for giving me troubleshooting ideas and stimulalting my thought processes. I wish you good luck and clear skies!

EDIT:
BTW, apparently my OTA is darn square to the DEC axis. I think I was due some good luck!

Edited by ricknau (03/30/13 09:18 AM)


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