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GEM28 Experience?

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48 replies to this topic

#26 snlian

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Posted 21 October 2021 - 10:37 PM

Kevin, this is very interesting! I had the same issue with my GEM28 (except for the gear switch), and I can completely confirm the beneficial effects of your proposals.

 

Unfortunately, I seem to have a further severe problem with my GEM28. While trying different DEC backlash adjustments, I noticed that in some circumstances the DEC gear switch on my GEM28 would not engage in a specific rotational segment of the DEC axle anymore. I opened the DEC housing and measured the distance between the DEC worm gear and the DEC gear while the gear switch was disengaged. The distance varied during a full rotation of the DEC axle by about 0.2 - 0.3 mm. This lead to the conclusion that the DEC shaft in my case seems to be slightly tilted, wherein the tilted DEC shaft kind of staggers while it rotates, thus varying the distance between the DEC gear and the worm gear. I confirmed that the distance variation is not caused by a geometric/dimensional aberration of the DEC gear itself by also directly measuring the distance between the outer circumference of the DEC shaft and a fixed reference point, say a specific location on the gear housing. Result: The same variation of about 0.2 - 0.3 mm. This makes it quite difficult to find the right DEC backlash adjustment, i.e. the sweet spot, between an engagement between the DEC gear and the DEC worm gear that is not too tight when reaching the smallest distance therebetween and an engagement between the DEC gear and the worm gear that does not have too much play when reaching the largest distance therebetween.

 

Not knowing if the tilt of the DEC shaft can be corrected by adjusting the shaft nut of the DEC shaft at all, do you or anybody else know if there is a trick to loosen the shaft nut? I suppose, a special tool is used for "normal" assembly (which I don't have). I tried to use a pair of scissors to engage the two openings arranged on the outer axial end face of the shaft nut with the tips of the scissors. Unfortunately, I was not able to rotate the shaft nut since it seems rather firmly tight.

 

Thank you!

man I have the exact same issue with my gem28, have you fixed it?



#27 donsinger

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Posted 22 October 2021 - 11:24 AM

Seems like these new ioptron mounts are snake bit


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#28 Thilo

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Posted 13 November 2021 - 05:47 AM

man I have the exact same issue with my gem28, have you fixed it?

Sorry for the late response. Are you still struggling with the problem or have you found a solution in the meantime?

After disassembling and reassembling the DEC unit of my GEM28 (instructions from iOptron see: https://www.ioptron....nAdjustment.pdf), I was able to significantly improve the DEC shaft tilt. In the end, I tightened the shaft nut much less than the factory setting. However, a slight tilt remains. This is not so bad if the pressure of the worm is set correctly, as Kevin describes above, e.g. https://www.cloudyni...nce/?p=11376523 and https://www.cloudyni...nce/?p=11377449. Now the DEC guiding on my GEM28 works as expected and I am very satisfied.

If you need more detailed information you can pm if you like.


Edited by Thilo, 14 November 2021 - 05:39 AM.

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#29 trycatchfinally

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Posted 23 November 2021 - 02:32 PM

Sorry for the late response. Are you still struggling with the problem or have you found a solution in the meantime?
After disassembling and reassembling the DEC unit of my GEM28 (instructions from iOptron see: https://www.ioptron....nAdjustment.pdf), I was able to significantly improve the DEC shaft tilt. In the end, I tightened the shaft nut much less than the factory setting. However, a slight tilt remains. This is not so bad if the pressure of the worm is set correctly, as Kevin describes above, e.g. https://www.cloudyni...nce/?p=11376523 and https://www.cloudyni...nce/?p=11377449. Now the DEC guiding on my GEM28 works as expected and I am very satisfied.
If you need more detailed information you can pm if you like.


Hi,

I was wondering what guiding numbers are you getting in RMS error? I'm getting interested with this mount because of the size and weight.

Thank you

#30 SingleShotDuker

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Posted 23 November 2021 - 10:45 PM

Hi,

I was wondering what guiding numbers are you getting in RMS error? I'm getting interested with this mount because of the size and weight.

Thank you

 
Just recently purchased the GEM28, and I can tell you this mount is a GEM! Super silent slewing, and lightweight. Currently carrying a Zenithstar 73 no issues. I shared a screenshot of the PHD2 guiding, with a total RMS error of .68"
 
GEM28 Guiding

 

 


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#31 midnightsnacks

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Posted 11 January 2022 - 10:05 AM

The Gem28 is my first mount, upgraded from a Skyguider pro.
It likely would be an excellent mount for my needs if it worked as it should.

 

Problems
1. The tension knob for the saddle of the DEC catches the top of the DEC unit.
2. The RA axis has considerable play.
3. The battery terminal in the hand control was installed backwards, so the HC won't keep location, date, time etc.

 

Some Solutions and questions.
1. I fixed this with some washers, however, is the problem deeper caused by saddle tilt?
2. Been back and forth with them for well over a month now, basically talking in circles. I tried tightening some bolts and checked the belt tension. The next step is to take the mount apart. I am not comfortable doing this. It sounds like a repair will be costly if I pay for all the shipping.
3. Ioptron said they would send me a new hand controller. This was six weeks ago, so I'm not holding my breath.

 

If anyone has any guidance here, I would appreciate it as the seller, and the manufacturer doesn't seem eager to help me.



#32 Mr.OD

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Posted 11 January 2022 - 10:40 AM

Both axes on GEM28 are spring loaded. The spring is supposed to compensate gear mesh if any needed. Therefore the only play that You should feel is due to spring tension. There is no need to disassemble it unless You are sure there is play between gears and adjustment of spring tension didn’t eliminated it.
Here is good explanation how it works:
https://youtu.be/dqGZEtjeOL0

Edited by Mr.OD, 11 January 2022 - 10:45 AM.

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#33 midnightsnacks

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Posted 11 January 2022 - 01:36 PM

Both axes on GEM28 are spring loaded. The spring is supposed to compensate gear mesh if any needed. Therefore the only play that You should feel is due to spring tension. There is no need to disassemble it unless You are sure there is play between gears and adjustment of spring tension didn’t eliminated it.
Here is good explanation how it works:
https://youtu.be/dqGZEtjeOL0

Such a great video resource. Thank you for sending it our way.

After speaking with ioptron the diagnosis as come back as its true play and not related to spring tension.

 

This is what they provided me as a DIY solution.

 

https://www.ioptron...._Fix_210808.pdf



#34 Tams

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Posted 11 January 2022 - 03:33 PM

The Gem28 is my first mount, upgraded from a Skyguider pro.
It likely would be an excellent mount for my needs if it worked as it should.

 

Problems
1. The tension knob for the saddle of the DEC catches the top of the DEC unit.
2. The RA axis has considerable play.
3. The battery terminal in the hand control was installed backwards, so the HC won't keep location, date, time etc.

 

Some Solutions and questions.
1. I fixed this with some washers, however, is the problem deeper caused by saddle tilt?
2. Been back and forth with them for well over a month now, basically talking in circles. I tried tightening some bolts and checked the belt tension. The next step is to take the mount apart. I am not comfortable doing this. It sounds like a repair will be costly if I pay for all the shipping.
3. Ioptron said they would send me a new hand controller. This was six weeks ago, so I'm not holding my breath.

 

If anyone has any guidance here, I would appreciate it as the seller, and the manufacturer doesn't seem eager to help me.

I have had some of the same issues with my GEM28. At first I thought I was just unlucky and my specific unit was a lemon. But it seems more and more owners of this mount are experiencing the same issues, and other common issues. I have sent my mount back to ioptron (at my own cost even though it is under warranty) to try to fix the issues, but after numerous emails back and forth trying to convince them there is deflection happening in the dec axis (which they flat out deny), I have no confidence that when they return it to me, it will function well enough to justify the amount of money I spent on it.  I have a nexstar se mount that performs better than this GEM28.

 

In my case, the saddle knob actually rubbed the paint off the top of the mount from making contact, regardless of how careful I was about balancing a 12.5lb load.  I was never able to to get an alignment routine to complete successfully. GOTO was useless, and the mount would not hold a target properly even using it just manually to track (i.e. centre a star and  then hit the zero button on the HC to engage tracking).

 

Numerous times while trying to use it, the mount stalled and the HC froze up, which required me to power cycle the mount to get it to respond again. (this was probably due to the saddle knob hitting the top)

 

Ioptron said they would replace the saddle tightening knob with a lever type, and maybe give me a new HC. They refuse to consider that the dec shaft is experiencing any deflection, and that their quality control is complete crap.

 

If anyone reading this is still considering buying one, your chances of getting a lemon are getting better and better the more units they push out.

 

Buyer beware!!!


Edited by Tams, 11 January 2022 - 03:45 PM.


#35 Tom M

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Posted 11 January 2022 - 04:15 PM

I have had some of the same issues with my GEM28. At first I thought I was just unlucky and my specific unit was a lemon. But it seems more and more owners of this mount are experiencing the same issues, and other common issues. I have sent my mount back to ioptron (at my own cost even though it is under warranty) to try to fix the issues, but after numerous emails back and forth trying to convince them there is deflection happening in the dec axis (which they flat out deny), I have no confidence that when they return it to me, it will function well enough to justify the amount of money I spent on it.  I have a nexstar se mount that performs better than this GEM28.

 

In my case, the saddle knob actually rubbed the paint off the top of the mount from making contact, regardless of how careful I was about balancing a 12.5lb load.  I was never able to to get an alignment routine to complete successfully. GOTO was useless, and the mount would not hold a target properly even using it just manually to track (i.e. centre a star and  then hit the zero button on the HC to engage tracking).

 

Numerous times while trying to use it, the mount stalled and the HC froze up, which required me to power cycle the mount to get it to respond again. (this was probably due to the saddle knob hitting the top)

 

Ioptron said they would replace the saddle tightening knob with a lever type, and maybe give me a new HC. They refuse to consider that the dec shaft is experiencing any deflection, and that their quality control is complete crap.

 

If anyone reading this is still considering buying one, your chances of getting a lemon are getting better and better the more units they push out.

 

Buyer beware!!!

While I really like my GEM28 there is definitely something weird going on balance-wise.

 

I did a complete 3D balance in RA & DEC. Everything is fine with the DEC axis horizontal and DEC is fully balanced in Z as well. However if I rotate RA with the OTA above horizontal it seeks to go back horizontal. If I then rotate RA so the OTA is below horizontal the OTA also seeks to go back to horizontal and, to top it off, it behaves exactly the same on either side of the pier.

 

About the only way that can happen is if the CG is below the axis of rotation and since the behavior is the same on both sides of the mount it means the CG has to move. The only way I see that happening is due to flexure. Granted, it's not enough to really impact things and my tracking is decent so I'm no longer chasing it but it's definitely interesting.



#36 midnightsnacks

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Posted 11 January 2022 - 06:05 PM

I have had some of the same issues with my GEM28. At first I thought I was just unlucky and my specific unit was a lemon. But it seems more and more owners of this mount are experiencing the same issues, and other common issues. I have sent my mount back to ioptron (at my own cost even though it is under warranty) to try to fix the issues, but after numerous emails back and forth trying to convince them there is deflection happening in the dec axis (which they flat out deny), I have no confidence that when they return it to me, it will function well enough to justify the amount of money I spent on it.  I have a nexstar se mount that performs better than this GEM28.

 

In my case, the saddle knob actually rubbed the paint off the top of the mount from making contact, regardless of how careful I was about balancing a 12.5lb load.  I was never able to to get an alignment routine to complete successfully. GOTO was useless, and the mount would not hold a target properly even using it just manually to track (i.e. centre a star and  then hit the zero button on the HC to engage tracking).

 

Numerous times while trying to use it, the mount stalled and the HC froze up, which required me to power cycle the mount to get it to respond again. (this was probably due to the saddle knob hitting the top)

 

Ioptron said they would replace the saddle tightening knob with a lever type, and maybe give me a new HC. They refuse to consider that the dec shaft is experiencing any deflection, and that their quality control is complete crap.

 

If anyone reading this is still considering buying one, your chances of getting a lemon are getting better and better the more units they push out.

 

Buyer beware!!!

I had the same issue. Saddle tension knob rubbed the paint off the top of the DEC.

 

I've checked it with and without weight on the saddle, no rubbing with no weight. Does this mean a deeper issue?

 

The rubbing is also dependent on the size of the dovetail plate, the knob needs to be at the specific point of its rotation for it to rub.

 

I have fixed my issue by adding a washer between the tension screw and saddle.

 

Ioptron told me to add 4 washers between the saddle and the DEC or send it in. 

 

I thought my solution was slightly more elegant, that is until I change out the scope.

 

Likely a better solution would be to file down the high points of the knob.



#37 khobar

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Posted 08 April 2022 - 12:42 PM

I know this is a fairly old thread, but I am curious about the way the worm is engaged/disengaged.

 

I have a CEM25p that has spring-loaded "clutch" release/engage, and one of the problems this introduces is the possibility of camming the gear. I have had this happen previously despite being super careful with balance, etc. Ultimately, it damages the worm and/or ring gear necessitating replacement. 

 

From what I've read in this thread and elsewhere, it sounds like the GEM28 uses the same method for engaging/disengaging the worms. Yes?



#38 Thilo

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Posted 15 April 2022 - 05:39 PM

I know this is a fairly old thread, but I am curious about the way the worm is engaged/disengaged.

 

I have a CEM25p that has spring-loaded "clutch" release/engage, and one of the problems this introduces is the possibility of camming the gear. I have had this happen previously despite being super careful with balance, etc. Ultimately, it damages the worm and/or ring gear necessitating replacement. 

 

From what I've read in this thread and elsewhere, it sounds like the GEM28 uses the same method for engaging/disengaging the worms. Yes?

This is correct. The worm is spring-loaded against the worm/ring gear. Recently, I also had the problem of camming the gear when I bumped into the free end of the counterweight rod due to an unintended movement (the mount was loaded and fully balanced). The worm wheel actually jumped by one tooth. I hope no damage was done. An inspection is still pending.


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#39 S_Milliken

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Posted 12 May 2022 - 06:02 PM

The Gem28 is my first mount, upgraded from a Skyguider pro.
It likely would be an excellent mount for my needs if it worked as it should.

 

Problems
1. The tension knob for the saddle of the DEC catches the top of the DEC unit.
2. The RA axis has considerable play.
3. The battery terminal in the hand control was installed backwards, so the HC won't keep location, date, time etc.

 

Some Solutions and questions.
1. I fixed this with some washers, however, is the problem deeper caused by saddle tilt?
2. Been back and forth with them for well over a month now, basically talking in circles. I tried tightening some bolts and checked the belt tension. The next step is to take the mount apart. I am not comfortable doing this. It sounds like a repair will be costly if I pay for all the shipping.
3. Ioptron said they would send me a new hand controller. This was six weeks ago, so I'm not holding my breath.

 

If anyone has any guidance here, I would appreciate it as the seller, and the manufacturer doesn't seem eager to help me.

What do you mean about the battery terminal backwards?  I can't get my new GEM 28 to keep time, and I'm just getting started...



#40 khobar

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Posted 22 May 2022 - 03:00 PM

This is correct. The worm is spring-loaded against the worm/ring gear. Recently, I also had the problem of camming the gear when I bumped into the free end of the counterweight rod due to an unintended movement (the mount was loaded and fully balanced). The worm wheel actually jumped by one tooth. I hope no damage was done. An inspection is still pending.

Thanks Thilo - it's been about a month now - did you do your inspection and what were the results? Good, I hope.



#41 mfinity

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Posted 22 May 2022 - 08:06 PM

I have a GEM28 and it has not been a good experience.  Mount is basically unusable. Ioptron support recommends I take it apart and 'fix' my brand new $2000.00 piece of crap myself, or send it back to them at my cost.

I had my cart full with one of thes mounts until I ran across some of the comments like this.  Thanks, and sorry you are having problems with the mount.  
 

‘’reminds me of a Tommy Boy quote.:
 

“Hey, if you want me to take a dump in a box and mark it guaranteed, I will. I got spare time. But for right now, for your sake, for your daughter's sake, ya might wanna think about buying a quality item from me.”



#42 midnightsnacks

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Posted 30 May 2022 - 07:57 PM

What do you mean about the battery terminal backwards?  I can't get my new GEM 28 to keep time, and I'm just getting started...

The battery terminal was installed with the polarity reversed, so the hand controller wouldn't hold a date and time once the mount was disconnected from a power source.

Open up the hand controller and the circuit board will show where the +/- on the terminal should be. If the terminal matches you're good, if not contact ioptron for a new one.

 

ioptron did replace the hand controller and tuned up the mount for me. Took 5 months and 1000 thousand emails but now its working well. 



#43 JMG62

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Posted 31 May 2022 - 07:57 PM

Hi folks.  I've had a GEM28 for a short time.  It's my first GoTo mount.  I'm primarily a visual observer so I'm not (at this point) too fussed about the subtleties of PEC, the effects of backlash on guiding and things like that.  What I am struggling with is the really poor user manual and the apparent lack of any online resources to help my climb up the learning curve.  I went the GoTo route because I want to spend time looking AT things rather then looking FOR them (thanks Uncle Rod).  However, now I am finding that I am spending the bullk of my time under the stars time trying to get the the blasted thing accurately aligned so it will actually point in the right direction.  Is anyone aware of any iOptron user groups or fora that I could take my beginner questions to?


Edited by JMG62, 31 May 2022 - 07:58 PM.


#44 whooshbang

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Posted 01 June 2022 - 02:22 AM

The battery terminal was installed with the polarity reversed, so the hand controller wouldn't hold a date and time once the mount was disconnected from a power source.

Open up the hand controller and the circuit board will show where the +/- on the terminal should be. If the terminal matches you're good, if not contact ioptron for a new one.

 

ioptron did replace the hand controller and tuned up the mount for me. Took 5 months and 1000 thousand emails but now its working well. 

I have also seen the battery terminal prongs bent down flat where someone pushed the battery in incorrectly. This video shows how to install it correctly.

 

https://youtu.be/VL7gLZc3gfc

 

Thanks



#45 BlueMoon

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Posted 04 July 2022 - 10:09 AM

Glad to have found this thread. I'm vacillating between a CEM26 and a GEM28. My choice may be "an evil of two lessers" now. While I understand mass-produced mounts can have some issues, comparatively speaking, it appears the GEM28 has more of them than the CEM26. I currently own an older SmartEQ Pro+ so I've been through a few iOptron "omissions" in both mechanical and documentary realms.

 

 I've "tuned" GEM mounts for years. Now, my decision is whether it will be simpler to remedy the problems with the more conventional GEM28 or the not-so-conventional CEM26.

 

Clear skies and thanks for all the info.


Edited by BlueMoon, 04 July 2022 - 10:20 AM.

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#46 oldthor

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Posted 10 July 2022 - 04:55 PM

What is going one with the quality of Ioptron mounts? Based on their market share is seems they have quite a high rate of issues compared to other brands. I came close to buying a gem28 but after all the reported issues passed and bought a EQ6R pro instead  while a heavier mount has performed perfectly. Now, looking for a second mount and decided to give the Gem28 another look and nothings changed so disappointing.


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#47 Stevemr2t

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Posted 10 July 2022 - 07:34 PM

What is going one with the quality of Ioptron mounts? Based on their market share is seems they have quite a high rate of issues compared to other brands. I came close to buying a gem28 but after all the reported issues passed and bought a EQ6R pro instead  while a heavier mount has performed perfectly. Now, looking for a second mount and decided to give the Gem28 another look and nothings changed so disappointing.

I had connectivity issues with their newer GEM45 also. Something changed in their electronics or wiring quality between 2020 and 2022 as my older CEM40 and 70 (from 2020) are flawless.



#48 oldthor

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Posted 18 July 2022 - 11:50 AM

Sorry for the late response. Are you still struggling with the problem or have you found a solution in the meantime?

After disassembling and reassembling the DEC unit of my GEM28 (instructions from iOptron see: https://www.ioptron....nAdjustment.pdf), I was able to significantly improve the DEC shaft tilt. In the end, I tightened the shaft nut much less than the factory setting. However, a slight tilt remains. This is not so bad if the pressure of the worm is set correctly, as Kevin describes above, e.g. https://www.cloudyni...nce/?p=11376523 and https://www.cloudyni...nce/?p=11377449. Now the DEC guiding on my GEM28 works as expected and I am very satisfied.

If you need more detailed information you can pm if you like.

Just a shame that Ioptron sells these mounts as a precision instrument and  yet so many are defective out of the box. Worst yet it's become so common place that consumers now just see it as almost normal. I for one won't purchase anything more from Ioptron until they get their act together and consumers should demand credit for having to repair new mounts or send them back, it's the only way Ioptron will fix their quality issues apparently. I think the latest price increases are a slap in the face concidering the quality.


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#49 gcocks

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Posted 20 July 2022 - 08:25 PM

I went back and forth with iOptron support about the DEC performance on my GEM28 within the first 3 months of purchasing it.. I ended up giving up and purchasing a CEM70 and it's worked flawlessly. The GEM28 has been sitting in the corner being used as an overpriced stand for the past year.




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