G11 Tracking Problems

[Eris]

Hi everyone,
I am seeking advice from all of you who have had experience with the Losmandy G11 mount with a later Gemini 1 upgrade (Din plugs) re tracking issues. I am running level 4 Version 1.04.
The problem I am having with the mount (carrying a C11 with an Atik One 6 and autoguider) is that it's not tracking properly and I am getting star trails with just 3 second exposures. The combined weight of the CCD camera and a counter balance on the scope is approximately 2.4 kg
Using the hand controller in "All Speeds" mode I can slew in both axes, although motion in Dec is very temperamental and sometimes just doesn't want to work at all. I have checked and double checked connections.

Tonight I dispensed with the autoguider and just used an illuminated eyepiece to see if there was any improvement without the added load. No luck.
To check motion of the mount I turned off the drive switch and allowed a star to drift along a cross hair in the eyepiece. I then turned the mount back on expecting the drift to stop but the star tracked about 45° off the line.

What I have done so far
• Mount is accurately polar aligned
• Scope setup balanced in both axes
• Powered up from a mains supply transformer running at 12.1volts at 4
amps (measured not under load)
• All connectors RA & Dec din plugs and power connections etc cleaned
with IPA
• Hand controller adjustments set for current UTC/date/my longitude
and latitude and nearest time zone +10 ACDT
• Checked that the mount is working as a G11

• Recently added fresh battery inside Gemini unit


Remaining options being considered
• Upgrade power supply to (Powertech 13.8 volt 5 Amp regulated DC
supply) - I would prefer a higher voltage say 15 volts but can't locate
one as yet
• Search for replacement Dec din plug

I would very much appreciate it if anybody can help me resolve this problem as it has been the cause of very considerable and ongoing frustration. I won't even dare mention the 'G' word which is the next massive headache in waiting.
Thanks in advance to all of you who can help me out with this problem.

[Octane]

Is the Gemini set to G-11 and not something else in the mount parameters? Is the tracking rate set to 1x sidereal? Perhaps reset everything to defaults? Is there adequate power supply to the Gemini? Remove the software gremlins from the equation before looking at hardware-related issues.

H

[Octane]

Sorry, didn't read your full post before replying. You've covered the basics. Hrm.

H

[dimithri86]

I cant remember exactly what my symptoms were, but I was using a modified laptop power supply and having random problems. Since I moved to a lab supply at 16 volts and it improved (still havent got it working properly, due to difficulties getting it polar aligned and im short on time)

May not be your problem, but its good to have a bit higher voltage, since low voltage causes a multitude of random and intermittent problems.

Just out of interest, how did you verify it was polar aligned?

[spiezzy]

I am running mine at 15,5 V when I ran it at 13.5V I was having slight issues with tracking .
also check your worm gears that they are not to tight I have a obvision worm on the RA and the adjustment on the end of it sometimes tightens up this caused a tracking issue for me a while ago just some thoughts hope you sort it out there a great mount
cheers Pete

[Peter Ward]

The only way you will get drift at 45 degrees from either RA or Dec axes is absolutely tragic polar alignment or the Dec axis motor is for some reason being driven.

Assuming the latter, then simply disconnect Dec motor (just unbolt it, but leave the electronics connected ) and observe whether the Dec motor cog is turning and that any drift is no longer present.

If no drift then you'll need to determine the cause of the Dec motor being driven. Gemini does have a Comet tracking feature, which you should be able to reset by going back to default values on everything, and re-entering your user data.

[Eris]

Hi again everyone.

Firstly thank you for your initial replies. The main suggestions seem to be pointing to :-

• insufficient power
• poor polar alignment
• problems with the Dec axis motor

Re insufficient power, I am thinking that this may be part of the issue. When I initially measured the voltage of the transformer it came out to 12.1 volts with the mount under no load. Having said this I have used the word may because this same power supply has worked before in combination with the added load of a SBIG ST2000 and DSLR.

As for polar alignment I am confident the scope is accurately polar aligned. The C11 lives permanently in a shed with a roll off roof and has been used for guiding before. In the good old days I polar aligned through the polar axis scope on the Losmandy and there was no way it was not pointing on or very close to the SCP. Being the nervous type I recently purchased Polemaster from Gamma Electronics which really took the strain out of my back and helped me refine polar alignment further. So polar alignment is very close if not spot on (under a minute of arc).

Thanks Peter for your points about issues regarding the Dec axis motor. As mentioned earlier in the first post, Dec axis motion is temperamental and sometimes does not work at all when slewing in 'All Speeds'. This problem has only happened over the last couple of weeks.

Tonight weather permitting, I will test these ideas re issues with the Dec motor although I'm not feeling too confident about the current weather forecast.

[Peter Ward]

Just so we are clear....with a polar aligned telescope, motion in DEC over a short period can only occur if something is moving the DEC axis.

The RA gear running fast or slow matters not....as it simply cannot drive a telescope in DEC (i.e the 45 degree departure you describe)

Apart from the DEC motor (could be a rogue input from the autoguider) , an imbalance and slipping clutch would also do it. The latter is more common than you'd think, as oil does separate from the bearing grease over time, and ends up on what should be a dry clutch pad. Even with high clutch pressures, the clutch can never be properly locked, and the 'scope may slowly sag to the "heavy" end. Simple fix is to clean the clutch pads with isopropyl.

[Eris]

Hi Peter,

Thanks again for your suggestions. I haven't had a chance to test the Dec motor/tracking yet - another cloudy one. Re clutch slippage I am starting to wonder if this may turn out to be the problem. The mount has been living in an insulated shed equipped with a small cooling air conditioner for about 10 years now. Up until last year the roof was insulated as well with 50 mm Styrofoam sheets which was brilliant for keeping out the heat. It kept the interior very cool on hot days. This insulation was unfortunately blown off in a storm and I have been temporally making do with thin shielding on the roof and an insulating blanket over the scope and mount. However, I have noticed that in spite these temporary measures and with the air conditioner running the temperature in the observatory on hot days still got into the upper 30's. So the point I am trying to make is that if it is clutch slippage it may have come from oil separating from the grease as you suggest onto the clutch pad in a heated environment over the summer.

If the Dec test does not work out I may be forced to take this next step to try and solve the problem and yes of course replace the roll off roof insulation asap.

I have found this website below which I hope will guide me through the procedure if I go ahead.

https://seeingstarswi.wordpress.com/astro-gear-projects/re-greasing/losmandy-g-11-telescope-mount/

Also, if re-greasing bearings is required is there a recommended type of grease which must be used with this mount?

[spiezzy]

Super lube is the best and can with stand very high heat mine has been in my Observatory in 40 + outside and must be around 48 in the obs and the grease has never run you can get it on Ebay
cheers Pete

[lazjen]

You might also be able to source it from local locksmiths as well.

[cfranks]

Eris,
I don't live too far from Mt. Barker and could bring my Gemini-2 to isolate one potential source of your problem. I've also got plenty of Lubriplate as I bought 2x 10gm tubes which turned out to be 2x 10oz tubes! Send a pm if interested.
Cheers

[Eris]

Thanks for the input guys.

[cfranks]

Hi eris,

I tried to reply to your PM but get this message: "Eris has chosen not to receive private messages or may not be allowed to receive private messages. Therefore you may not send your message to him/her."
My email is cfranks (at) internode (dot) on (dot) net

Cheers

[wasyoungonce]

Eris its not power...I run mine fine on 12V.

If your getting trails at 3 seconds in tracking...I guess you mean it's unguided and you get star trails! If it's unguided and trails then the alignment must be off.

Normally DEC shouldn't be doing much when guiding if it is then the alignment is not right. You said without guiding it drifted off....its gotta be alignment.

Clutches should be tight but enough to allow slip if bumped.

You might want to check your Gemini settings and divisors are correct. Use Gemini ASCOM, (https://groups.yahoo.com/neo/groups/Gemini_ASCOM_Driver/conversations/messages)it makes this easy. If they are correct can you change your divisor to speed up the Ra?

The only other thing is its slow in Ra....although lets not go there yet!

[Eris]

Thanks Charles I'll try and fix this up.

[Eris]

Thanks for your reply Brendan. I'm pretty sure the polar axis is aligned on the pole but I will recheck this.
My 12 volt supply has also worked well in the past so I'm assuming it may not be a power issue.
I am still thinking it may likely be a slippage issue that Peter has pointed out. However, I will recheck everything especially polar alignment before I start pulling things apart.

[wasyoungonce]

Also check your Gemini settings.....this is a must!

I did fix a Gemini that had slow Ra, only seen one with that issue, but you never know and this would be the last thing to look at, but checking Gemini divisors settings etc against the manual is definitely a must.

Have a look at Gemini FAQs (http://gemini-2.com/faqG1.php) for manuals etc.

[Eris]

Will do. Thanks again for your suggestions Brendan.

[sharpiel]

Please let us know what the originating problem was and your solution Eris.

[Eris]

Hi just an update if anyone's wondering about what progress has been made re the tracking problems on the G11.

Firstly many thanks to Charles (for his time and expertise) who came over and worked with me on the problem.

We pulled both RA and Dec axis apart and cleaned the pads etc of oil as Peter had predicted. However, we were unable to free up the bearings embedded within the polar axis shaft itself.

Also Charles noted that even though the polar axis knob was on tight there was still a fair amount of 'looseness' still remaining when attempting to turn the scope by hand. We were able to improve on this tightening by removing the polar axis scope which is now not required owing to PoleMaster working at the other end.

Charles mentioned that although the pins had been cleaned between the hand controller and the Gemini there could still be corrosion remaining preventing a good connection. Moving the pins in and out of their sockets again several times in RA and Dec has helped and movement in both axes seems fixed.

I am hoping these measures have gone a long way in fixing the problem but as on many occasions before clouds have prevented me doing a further polar alignment and a star tracking test. So until then I am waiting for the next clear night to be sure it is fixed.

[Octane]

Well done!

I also spent several hours today dismantling my G-11 (the first time I've done it in ten years of owning it). I washed and cleaned everything with detergent, then, rubbed dry with rubbing alcohol. I applied lithium grease to all the bearings.

I also installed the encoder set that I've had sitting around doing nothing for the past 6 or 7 years.

Now, my back hurts, haha.

H

[Eris]

I know what you mean. For me it's my neck.