iOptron CEM26 stops tracking at specific angles in Dec

[deanchapman2705]

Hi everyone,

I have had my new setup for a little while now and managed to get my first image with it of the Rosette Nebula a couple of weeks ago!

Recently, I was trying to image the Orion nebula but when I used the ASIAIR to slew the mount to M42, it then had a mind of it's own and kept slewing past Orion (which at the time, was right next to meridian position) and before I could find the power switch to the mount in time, the mount ended up hitting itself causing the gears inside to make a horrible grinding noise for at least 2-3 seconds. I'm guessing the syncing of the mount to the ASIAIR didn't quite work perhaps? I powered it back on and put the RA axis back to a safe angle and tried again. It then worked perfectly and even got a couple of exposures with decent guiding before the clouds came across (in fact, even better guiding than before).

I tried getting some more exposure time the following night and came across a problem... When the DEC axis rotates to a certain angle, it will beep and turn off the tracking itself. I cannot then turn the tracking back on as it will repeat itself.

At this point, I assumed I had damaged the main worm gear inside the RA head as that is what came to a stop and grinded. I took apart the RA section of the mount to see how the gears inside looked and they seemed fine. That's when I realised that the RA gears weren't the problem, it is actually the DEC axis that is damaged somehow (even though it could move freely when the RA axis got stuck).

    

So I took apart the DEC cover instead and the gears looked fine again. Assuming it was the main worm gear, I got a sharpie and drew a line of the area that the tracking does not want to work in (which is shockingly ~220 degrees of the DEC axis). I would slew the DEC axis using the hand controller 360 degrees and it would still fail in the exact same area. So... it must be the main worm gear then right? If it was the small, brass coloured, worm drive below, then it would fail little and often, not throughout a huge angle of the DEC axis as marked. Well apparently not, if I undo the clutch and rotate the worm gear freely (separately to the small worm drive below) to the unmarked area of the main worm gear that would work before, it would then fail (so it would then not correspond with my markings).

   

Then I took off the backplate below which revealed the DEC motor and again, I cannot see anything wrong. The belt feels like it has the right tension.

I can't tell if this is the motor that is used for tracking and slewing. I left it tracking for an hour and the belt had not moved at all but I'm not sure if it was too small of a difference to have noticed or not. Are there separate motors? One for tracking, the other (in the picture) for slewing at faster rates? Just weird how only the tracking fails at curtain points but can slew the DEC 360 degrees perfectly fine with no change in noise to hint any straining.

Any ideas?

Thanks,

Dean

Edited February 4, 2023 by deanchapman2705

[Which one is Polaris]

The terrible grinding noise is usually just the stepper motors jumping steps if the axis can't turn for any reason.

Normally no damage is done, you just lose the current position and have to setup again.

Note that the mount will beep and stubbornly 'fail to move' or 'not Track' if it thinks you are at the Meridian.

Ii is worth checking that the worm engagement to the main gear is not too tight.  Mesh adjustment procedure is simple.

Edited February 4, 2023 by Which one is Polaris

[drjolo]

Just an idea - maybe try to do factory reset of the HC. It does not seem to be mechanical issue, at least basing on your description. If you can rotate the Dec stepper shaft with your fingers (when power is off) then the worm gear is most probably fine. 

Edited February 4, 2023 by drjolo

[Elp]

Was you using version 2.0 10.46 of the app by any chance?

[deanchapman2705]

1 hour ago, Which one is Polaris said:

Note that the mount will beep and stubbornly 'fail to move' or 'not Track' if it thinks you are at the Meridian.

I think this is the case. If I put the DEC to the area that it will not track and then set it as home position, it will track fine. So there is no physical damage then as it's software, Phew!

In fact, if I unlock the DEC clutch and rotate it so the middle of the working area lines up with the centre of the worm drive, the edges of the "Stops tracking" line up exactly with where it stops tracking (where it thinks the limit is for the meridian flip).

So I must have forgotten to set the mount's home position on the hand controller before I started. Just that it was timed so perfectly with me potentially damaging the mount that I thought that was the cause haha. 

Sorry, I'm still new to this but why is there a limit for the DEC axis though? Surely it would need it for RA axis as that would have helped prevent what happened the other night where the mount hit itself?

Is there a way to expand the limit area or even remove it?

Edited February 4, 2023 by deanchapman2705

[Which one is Polaris]

9 hours ago, deanchapman2705 said:

Sorry, I'm still new to this but why is there a limit for the DEC axis though? Surely it would need it for RA axis as that would have helped prevent what happened the other night where the mount hit itself?

Is there a way to expand the limit area or even remove it?

I get into trouble at high Declinations, so the limits are good. 

You can tell the mount what its behaviour should be at the Meridian.  I have my CEM26 set to Stop, which helps.  Or I start imaging just past the meridian.  I am always near to the mount (mobile setup) so can just do the flip manually and check the new alignment to the target.  I often rotate the camera.

I am buying a Pier Extension for my new Mount as it seems to help a lot with avoiding collisions.

[Elp]

I asked my previous question because on two different mounts (azgti and gem28) with two different asiairs I've had strange gotos with the latest update. Like the mount going in the completely wrong direction even though the home position was correct, it's even gone to the right position on first slew, then second iteration adjustment during plate solve started going somewhere else. Is your asiair also set to auto meridian flip when it's running a plan?

[Dinglem]

Hi @deanchapman2705 my small portable setup is a CEM26 and ASIAir, because I setup each time I have found that everytime I use it, on power up, I need to check the co-ordinates are correct for the mount, I then set it to track and move the mount a bit manually, I then tell it to park.

If anything as moved I can then undo the clutches and set it back to the correct park position. It then appears to work perfectly.

I bought the mount second hand and found I needed new drive belts as the ones on it were damaged, I presume from continuing to run when hitting the stops. I've also found that I have to regularly check the Dec axis for slippage as the grub screws in the side of the black ring work loose (in your picture the one with the 4 small bolts in).