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Why does my Titan w/ Gemini 1v4 go the wrong direction when attempting an alignment star?

+1 vote

I picked this up used and in very good shape as far as I can tell. It goes the wrong direction with every alignment attempt.

I kept getting reset messages and realized this wasn't normal, that's when I found the battery was dead. I replaced that and manually reset the works just to be thorough, then I entered time (UTC and UTC date for that UTC time), my site name, lat/lon, time zone, home position, CWD. Yes, the RA cable goes to RA motor, and the DEC to the DEC..the RA cable is so short it barely reaches the fixed position for the RA motor anyway.

I have a roughly decent first polar on it I think, it should at least go somewhere near Regulus when I tell it to, I figure.

Instead, it goes the wrong direction. The RA seems to be correct, it tilted to scope on the E side consistent with aiming at Regulus W of the meridian, but the DEC went wonky and pointed way N. This is consistent with every attempt.

I've checked the troubleshooting page and not seen anything I didn't set, now my remaining question is about the gearbox replacement. My gearboxes say S162 and look like this...My gearboxes look like this

asked May 11 by MtnGoat (130 points)
edited May 11 by MtnGoat
Success! I took your comments on trying different mount types to heart. I tried the MI250 setting, rebooted, and then reset the CWD home position.

On it's first align try both axes went the correct direction, but not far enough. Then I recalled a conversation about gear ratios and some 25:1 setups vs 50:1, and decided it now looked like the ratio was too low. So I dialed in the Titan 50:1 mount option, again rebooted and reset home.

This time "Align to Bright Star - Regulus" went the correct direction AND far enough to put me within a couple degrees of Regulus. I was *thrilled*. Then I just hit a few more stars and added them as additional aligns, and started getting really good gotos. Last night I had a 9mm 100 deg ocular in the 14, which runs about 400x...and all the GOTOs were near center field of the 15' true FOV. I'm impressed and thrilled. Thanks for the suggestion which led to the resolution!

Next issue...what do I reset as I'm iterating to get the polar nailed?

1 Answer

0 votes
I can't tell from the photo, but it maybe that you have a non-stock gearbox. McLennan brand has been used quite a bit, which reverses worm direction. In that case, you'll need to make configuration changes on your Gemini. If both gearboxes are custom, you can use MI-250 as the mount type with Gemini, as that reverses both axis but keeps most other settings nearly the same. You may want to also adjust the default safety limits, as they might be different for your mount.
answered May 12 by paul_kanevsky (3,810 points)
Hi Paul, thanks for the comment.

From the conversion notes on the site, I'd think the hole in the worm gear covering needs to be enlarged for the mods to accept the other gearbox. Plus they describe drilling out the 'ears' on the gearbox to get the spur gear placement correct. These boxes look like the ones on the L parts page, to me anyway.

Can I just go into setup and change the encoder sign on the DEC axis? If so, do I restart the mount or do the changes take place upon entry?

I'm also wondering about the ratios. I have the full finned motors, which I think makes them the last stepper version of the maxxons. I can't find how many ticks they're supposed to have to check what's entered in my system.

This is an extremely frustrating problem. No matter what I do this happens, I've had the mount for 8 weeks now and it's still unusable no matter what I do. It must be something simple but i've checked and rechecked and used an increasing amount of poor language lately. lol. Tomorrow I pick up the 14" I bought this mount for, and that's going to put the frustration level over the top. I was sure I'd figure it out in two months. Nope. I'm a noob to Losmandy but have years on Autostar and Celestron systems, so I know the basics and then  some about what is going on, so this is especially vexing.
You can change just the sign, if you want.  All motors sold by Losmandy, and all gearboxes have the same ratios, but all bets are off if these are custom on your mount.