Losmandy G11 slewing the wrong way.

[AlexN]

Hey all,

Just trying to get all the computer nonsense out of the way before I get out under clear skies, and I've run into an interesting one...

When I connect to my G11 from the computer, Stellarium shows the reticule pointing at the SCP, The mounts location and time were sent to the mount via GeminiTelescope.NET ascom driver.

The planetarium and Gemini controller both think the telescope is in the same location, and time zone.

When I pick a star in the east and tell the scope to slew there, the mount goes to the exact location of where it should be, but in the western sky.

its like its somehow mirrored? its very strange.

When the slew occurs, the reticule in stellarium is moving from the SCP, out to the east to a declination of 0, but the mount is heading west.

Anyone experienced this before?

Alex.

[pmrid (Peter)]

Alex, that behaviour you describe is what happens when your software is being told somehow that it is in the northern hemisphere. I'm afraid you're going to have to go through every setting to find it.

[Mosc_007 (Charles)]

From memory Losmandy has a Switch on the motherboard to select Northern or Southern hemisphere.

Clip from the G11 manual.


Northern/Southern hemisphere operation

When using your Losmandy G-11 in the southern hemisphere, there is a need to reverse the motors. In some mounts this is accomplished by installing a reversed motor. In the G-11 the direction the drive motor moves the telescope is within the control of the user. Changing from northern hemisphere to southern hemisphere requires changing the polarity of the drive motor. To do this:

1. Remove the cover of the electronic box by removing the four screws (one in each corner).

2. Locate the north/south switch (labeled N/S) just to the right of the ON/OFF switch.

3. Change the switch from “N” to “S” setting. NOTE: If the “N” or “S” is not visible, the N position is away from the edge of the circuit board; S is toward the edge.

4. Replace the cover.

The direction of the drive motor is now reversed and will work in the southern hemisphere. Changing from the southern hemisphere to the northern hemisphere requires flipping the switch from the “S” to “N” setting.
For quick changes, press one of the R.A. buttons while powering up the drive. Which R.A. button do you press? It depends on the directional setting of the R.A. switch (see the section on R.A./DEC REVERSE). The best way is to do it by trial and error; press one button while powering up the drive. If it does not work, turn the drive off and try the process again while pressing the other R.A. button.

The hand controller allows you to move the telescope in R.A. and DEC using the corresponding motors. This includes fine corrections for guided astro-photography and minor adjustments for centering objects in the field of view. The buttons on the hand controller are intentionally labeled rather simply. This is due to the fact that the direction of motion of the mount varies depending on how the telescope is oriented. Furthermore, these buttons are user definable to eliminate confusion when guiding. For more information, see the section on R.A./DEC Reverse.

Once again, to move the telescope at the 16x speed WITHOUT changing the guide setting, press the button that corresponds to the direction you want to move the telescope. While holding the button down, press the opposite directional button. For example, if you want to move the telescope west, hold the west button down and then press the east button. Conversely, if you want to move the telescope east, hold the east button down then press the west button. This fast-set function also works in declination.

[Star Catcher (Ted Dobosz)]

Originally Posted by AlexN

Hey all,

Just trying to get all the computer nonsense out of the way before I get out under clear skies, and I've run into an interesting one...

When I connect to my G11 from the computer, Stellarium shows the reticule pointing at the SCP, The mounts location and time were sent to the mount via GeminiTelescope.NET ascom driver.

The planetarium and Gemini controller both think the telescope is in the same location, and time zone.

When I pick a star in the east and tell the scope to slew there, the mount goes to the exact location of where it should be, but in the western sky.

its like its somehow mirrored? its very strange.

When the slew occurs, the reticule in stellarium is moving from the SCP, out to the east to a declination of 0, but the mount is heading west.

Anyone experienced this before?

Alex.

I have experienced this. From memory, it happened when the battery was on its way out. As suggested you need to go through all settings and double check battery voltage. From memory I had a weird disconnect between time zone and my actual latitude and longitude i.e. one went back to factory default and the other stayed as I entered it.

Ted

[wasyoungonce (Brendan)]

Alex

Peters post is spot on. There is no N/S switch in the Gemini its on the 492DD controller. N/S is set by the local lat/long/DTG/timezone you input. Remember "-ve" for latitude.

See here for entering DTG Gemini style. (link at bottom of page. DTG format is for G1, the G2 is input differently). You already know this but its always good to check these. Also check local Lat/long/timezone as these can conflict throw off planetarium programs.

Also check you have Ra on Ra axes and visa versa DEC....an oldie but goodie. Bad battery in the Gemini2 and 1 can cause loss or corruption of data so check battery

Stallerium is a pretty stable program id expect it to be correctly using the Gemini settings but do check

[TrevorW]

Try cold restart on the mount also if you haven't already use NINA, manual slew to target, then plate solveand plate solve. I use Gemeni net Ascom in NINA and sometimes have issues with the mount slewing wrong way even though everything is set for my location in the mount and NINA

[multiweb (Marc)]

Just another obvious thing to check is that you didn't mix RA and DEC cables.

[wasyoungonce (Brendan)]

Originally Posted by multiweb

Just another obvious thing to check is that you didn't mix RA and DEC cables.

Don’t know how many times I’ve done that. Wot an idiot I am. Also check modelling pointing. It’s possible a bad pointing model point has been added (can you deleted starts that are way off!). Might be best to build another new model just do a 3 star and on subsequent warm boot synchronise to a known good star and it’ll update the new model.

If at worse resort to Gemini ASCOM of just HC (non ASCOM) and check modelling pointing accuracy is ok. If so there is possible wrong data being sent to the Gemini throwing off modelling.

Also check Gemini ASCOM isn’t throwing in spurious location data on connect! It’s like finding a holy grail but in most cases the fix is simple cannot see the tress for the woods.

Lastly reset it all start again this time don’t use a planetarium 3rd party program and build a model one step at a time for this.
Lastly check the Gemini RTC Clock Is accurate and not drifting.

If no joy and it’s a continuous issue then let’s cross that hurdle vehement ween we get there. I have a metrology setup to count Ra rate to very accurate values over let’s say an hour or more. To 3 decimal places. Do

So I can confirm Ra rates snd correct slewing etc happy to test for free for you!.

Cheers Bren.

FWIW

[AlexN]

Originally Posted by wasyoungonce

Cheers Bren.

The issue was a fair bit more obscure than expected.

Replaced the battery (CMOS was resetting on every startup)
Geolocation was correct (In NINA, Stellarium and the Gemini computer)
Cables from RA/DEC were correct

Still - the issue remained...
I did some further digging, and it turns out that my mount has the McLennan gearboxes fitted, which reverse the motor rotation. This, combined with the fact that the Gemini.NET ASCOM driver didn't know that, was the cause of the issue.

Under the Gemini Options in the ASCOM driver, I changed the mount type to custom, modified the RA and DEC Worm to axis wheel ratio from 360:1 to -360 to 1 and boom. We slew and track in the correct direction.

The other thing I discovered, is that my mount has axis encoders, which I was using, however, they do not seem to do their job fantastically, so if I do a push to a target, the alignment goes off by a mile... I unchecked the 'Use Encoders' box in the ASCOM drivers, and that sorted out a lot of my pointing accuracy issues.

So, as a result, after a number of hurdles jumped through and a lot of testing, I got out under the sky last night for the first time in a decade, collected 3.3hrs of reasonable data and produced an image!

Couldn't be happier.

Thanks for all your suggestions, I did try them all!

The solution came from a member on the Gemini group on Groups.io, he basically read my post and said

Here's my assumption... Your mount is OLD, was originaly a 492 and later upgraded to gemini, and your motors have a gearbox on them that says McLennen. If those things are correct, put a - in front of the 360 in your drive ratios and the problem will be fixed.

He proceeded to email me about 30 documents about maintenance, gemini tweaking, mount upgrades/installation processes, guiding tweaking/fine tuning etc...

Amazing guy...

He did however mention you Bren, he gave me your email and said you're a top bloke and and would no doubt be able to resolve the issue!

[wasyoungonce (Brendan)]

Originally Posted by AlexN

…….
I did some further digging, and it turns out that my mount has the McLennan gearboxes fitted, which reverse the motor rotation. This, combined with the fact that the Gemini.NET ASCOM driver didn't know that, was the cause of the issue.

He did however mention you Bren, he gave me your email and said you're a top bloke and and would no doubt be able to resolve the issue!

Ahh that’ll be Michael. The McLennan gearbox trick. Another oldie but goodie. Michael is pivotal in mechanics of of mounts. He’s don’t a lot of work and mods/tweaks and has written comprehensive guides. I’m more electronics nerd. I just don’t get the hands on he does.

Glad it’s sorted I pay him to say nice things about me! Hahaha

Cheers