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Trouble with Autostar GOTO

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#26 OzAndrewJ

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Posted 20 March 2013 - 02:36 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

#27 ricknau

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Posted 20 March 2013 - 07:24 PM

HOLY COW! I can't believe what a dumby I am! :foreheadslap: 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. :D

#28 OzAndrewJ

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Posted 20 March 2013 - 08:32 PM

Gday Rick

(Why didn't I test both axes?)



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

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

#29 ricknau

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Posted 21 March 2013 - 05:47 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. :grin:

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! :(

#30 OzAndrewJ

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Posted 21 March 2013 - 04:18 PM

Gday Rick

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

#31 ricknau

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Posted 22 March 2013 - 04:58 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?

#32 OzAndrewJ

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Posted 22 March 2013 - 05:25 AM

Gday Rick

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

#33 ricknau

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Posted 22 March 2013 - 05:43 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. :(

#34 ricknau

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Posted 29 March 2013 - 10:54 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!






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