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iOptron GEM45G RA motor clicking....after flip jammed it against the tripod!

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#1 cwmtocol

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Posted 21 January 2021 - 10:53 PM

Hi everyone,

 

My first post although have being going VA and AP for years. Embarrassing that the first post is a query on a schoolboy error.

 

APT crashed, reloaded a previous live feed image, plate solved against that although was moved to another target and the goto kept going way past meridian. 

Instead of stopping it, disengaging RA lock and manually going back to home position and starting again, I hit goto and sure enough it kept going the same direction for a new target (that I thought would allow it to back away) and pushed hard against the tripod leg for about 7-8 seconds.

New mount, new camera (upgrade) and on a 1-day old TS 86SDQ. Took a while for frustration to subside given what could have happened when new things were assembled.

 

However, guiding was fine after, as was imaging, no damage to camera, focuser (3 inch brute) or tilting etc. 

 

The RA motor however has a loud periodic clicking sound caused by it pushing against the tripod leg. It still rotates, but the clicking is worrying me. Slews to targets OK too. the zero position was way out, had to manually reconfigure that. I hope the worm did not keep turing while the gears were jammed.

 

Did anyone have this happen to any mount before? It was a direct cause of the crash against the leg. I have not opened it up, but I dont have a tear down image post for the ioptron GEM45 mounts. Is there one available or has anyone opened up their GEM45 to mod or fine tune it? 

 

I hope it is a gear or worm mesh, but it works just fine. I do not want to use it again until I know what the issue is.

 

Thanks for any help. 

 

 



#2 Cfreerksen

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Posted 21 January 2021 - 11:03 PM

I would seriously doubt it. My experience with steppers is they don't provide very much torque. If the gear was fully meshed and it hit tripod it would just lose steps and not know where is was anymore. I'm not sure what your ticking sounds like but my CEM60 and CEM40 make a bit of noise while tracking and I can here guide pulses when guiding.

 

Chris



#3 cwmtocol

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Posted 22 January 2021 - 12:25 AM

Thansk Chris,

 

I also hear those very tiny ticks when guiding etc. and the various tones of the axes operation, but these noises are another level. I might try capture a vid over the weekend. To anyone who hears it, it sounds like piece of wood stuck/plastic in the spokes of a bicycle wheel, if that makes sense. And it only happened after the collision with the tripod leg which is what worries me. It made a high pitched whine and sounded very stained when it was trying to push through the tripod leg, with some clicks heard during that process too.

 

I wish I could take the cover off, but unlike astro baby tutorials for other mounts, I dont want to 'unhook' something inside by accident. I assume they are straight forward assemblies like most mounts in this category.



#4 cwmtocol

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Posted 22 January 2021 - 04:44 AM

Actually, does anyone know where to covers are on the GEM45 to see inside the motor/gears? Are they the black covers or the the panels on the red colored parts?



#5 ryanha

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Posted 22 January 2021 - 11:50 AM

Hopefully you just marred a tooth on the belt.  Here is a doc with instructions on belt tensioning and you can see which cover to remove to take a look: http://www.ioptron.u...Tension_Adj.pdf

 

You should also do a backlash test in PhD and see if it may have stretched your belt.  This is an easy thing to fix if that is the problem (replacing the belt).

 

And Ill say the obvious which is that I a paranoid about tripod collisions so anytime I engage/disengage the clutch I do a "search zero position" command just to be safe.

 

--Ryan


Edited by ryanha, 22 January 2021 - 11:53 AM.


#6 cwmtocol

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Posted 24 January 2021 - 03:16 AM

Thanks Ryan,

 

Before seeing your reply, I did open up the RA motor cover to do some look-seeing. I've attached 2 images and a video in this google drive link here:

 

 

 

https://drive.google...ncj?usp=sharing

 

 

So, there is a frayed part and a slightly flattened or bumpy (depending on which side of the belt you look at).

From experience, did the very strained push against the tripod leg cause some of the belt  composite to be permanently deformed in one area?

 

When I run the mount, that area causes a slip or bump in the overall drive every time is passes over the larger toothed gear that likely meshes with the main large gear. I am guessing, but i assume this issue is with the bely deformity?

 

I haven't had a chance to test the guiding yet. But I get every third or second sub (240s exposure), the others have a teardrop start caused by the slight slippage I think. It manifests as a small double star beside the main star, which is not real and appears in the same direction and on the same side of every star. If I dump these subs, the rest are fine. I could play with exposures and minimize the number of slipped-induced dropped subs, but my current targets have darks and everything ready, and I would prefer to fix the main issue.

 

I can remove and get into the DEC axis motor if I wanted to. Interestingly the GEM45G has the CEM40 motor and board in the mount, guess they are one and the same.

what I cannot do is find a way to slide off the DEC motor assembly with the counterweight shaft, so that I can remove the cover for the RA motor. The rotating shaft and all the DEC/CW assembly prevents the RA cover (with is central opening) from coming off!


Edited by cwmtocol, 24 January 2021 - 03:16 AM.


#7 cwmtocol

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Posted 24 January 2021 - 06:12 AM

One other detail re the video. the louder metallic noise is exacerbated because the metal top cover to the worm assembly (which cannot be accessed unless the assembly with counterweight shaft etc can be removed) is unscrewed and loose. when all assembled, the click noise sounds more like a thud that a metallic clash in the video.

 

I'll try the belt tensioning too, thanks for those instructions. I already tested the mesh gear tightening, but that had no influence.



#8 Cfreerksen

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Posted 24 January 2021 - 10:21 AM

You have a bad belt. Just google the number on the belt and order one. The belt is not special from Ioptron. I just saw someone who posted a very similar video on Facebook and his was missing one of the teeth.

 

Chris


Edited by Cfreerksen, 24 January 2021 - 10:22 AM.


#9 ryanha

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Posted 24 January 2021 - 10:28 AM

You have a bad belt. Just google the number on the belt and order one. The belt is not special from Ioptron. I just saw someone who posted a very similar video on Facebook and his was missing one of the teeth.

 

Chris

Agreed, you should get a new belt.  I bet iOptron will send you a new one if you ask them. 

 

My guess is that iOptron selected the belt so that it would be "sacrificial" relative to the gears.  That means that in the event of a tripod collision it would be the belt that soaks up the damage to protect the gear.  But I can't say for sure.  But either way a new belt is the way to go.

 

Thanks,

--Ryan



#10 ryanha

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Posted 24 January 2021 - 10:35 AM

Oof, I just watched the video.  That sound is not good.

 

When chasing down gearing issues you want to try to figure out what is the period of the click and what it corresponds to.

 

The belt is moving too quick for me to tell for sure whether the click/thud aligns with the period of the belt rotation or if it is off cycle.

 

Maybe do it more slowly and see. 

 

It also appears that maybe your motor shaft is slightly bent. Can't say for sure in the video, but you should look at that too.

 

If the click/thud is aligned with the belt, that is a good first step.  If it is not, then you probably also have a gear issue in addition to the belt.

 

I am not sure if the gears are user-serviceable but I have found iOptron to be somewhat responsive via e-mail, so if you do find it is a gear issue you might reach out to them. 

 

Sometimes you have to re-forward the mail to them a couple times over the course of a week or so for them to reply.

 

--Ryan



#11 cwmtocol

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Posted 25 January 2021 - 03:11 AM

thank everyone. Last nights imaging on rosette nebula was fruitful, the alternative tensioning proposed here (using a screwdriver to push back the gear mounting before retightening) did help and reduced slack in that RA belt.

I'll get a vid at slower rate and define exactly the periodicity in relation to the missed tooth .Maybe all this will be useful to someone else down the line too.

For what its worth, here is a typical 240 s sub and another that shows what I get on every third sub. It is like clockwork and when I sit beside it, it times to exactly that point. They are .fits files and accessible under the same link:

 

https://drive.google...ncj?usp=sharing

 

Out of 40 subs, I had to dump exactly 12.

I have not integrated these, but i will see if some hot pixel correction or sigma-kappa clipping could remove these.

 

Next step is to order the belt, fix that, and see if the motor shaft is bent, or if that is caused by the periodic slippage.

 

Can i slip off the belt without getting access to the larger to other gear? What you see in the video/pics is as far as it is possible to open in this mount. I cannot locate the route to lift of the front DEC assembly.



#12 cwmtocol

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Posted 26 January 2021 - 05:15 AM

Curious side note: 

When imaging rosette, I tried PPEC algorithm in PHD2. Since it depends on PEC and assessment of worm etc. it was probably not ideally calibrated, quite a lot of excursions way outside the track bullseye.

The lights in the link in earlier post shows some horizontal banding (looks like read noise, but not likely with my camera) and this is exacerbated in stacking. I put in a stretched image of 30, 240s subs as a jpeg where you can see this.

 

Questions: given I have a periodic dodgy belt that causes a jump every 240*3 = 720s at normal sidereal tracking rate, is this banding likely due to PPEC algorithm? You can see the effect of the belt on the sub in the shared link (fits files), where the star shifts. The banding appears in every light sub.

Assuming non-optimal PPEC algorithm setup, and guiding response time of 2000 ms (with exposure looping of 2 s), can this algorithm provide horizontal banding in RA?

 

https://drive.google...ncj?usp=sharing

 

Since causing this issue with with RA belt, these types or errors have appeared for the first time in years. 

Next clear night will revert to well calibrated hysteresis for RA guiding to see if it is the mount as the fault. But I am curious if anyone has had this horizontal banding due to settings/algorithm in PHD2 specifically?

 

Thanks. Have a good weekend.




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