CEM26 backlash

[Endolf]

I got the CEM26 at the beginning of the month, the weather being what it is I've only had 1 evening with it. I noticed the guiding (especially in dec) was not great.

I took a look at adjusting the backlash yesterday and noticed that both axis have terrible slop in the mesh, I tried adjusting it, but it seems to not have any effect, only making the motor stall if it's too tight (so it's doing something), also, doing it too tight means the clutch won't disengage. The videos attached are *after* I tried to adjust it, but as I mentioned, it's made no difference, this is as bad as it originally was.

My first setup uses an EQ6-R pro with my 8" newt on the top, so this mount was supposed to be for the SharpStar, so I didn't need the payload of another EQ6, but I'm beginning to doubt my choice.

I've contacted the vendor and they seem to suggest that this amount of slop is fine, but it's certainly not what I get on the EQ6 and it's not what a friend of mine sees on his AVX.

If the balance is off center, then the gear would be on one side of the worm, and it would be solid for a bit, but as each axis goes over the top, it would suddenly jump, which would ruin the guiding at that moment.

 

 

 

[Dinglem]

@Endolf that certainly doesn't look acceptable to me, I'd be asking the vendor for a replacement. If that was the same I'd return it and get my money back. I'm pleased I've seen this as I was considering getiing one of these or the GEM28 for a lightweight setup. I too have the EQ6R-Pro and after a bit of tweaking there's virtually no play in the gears. I shall wait to see what others say when they start using theirs.

[david_taurus83]

Apart from in built WiFi I'm guessing these are exactly the same (mechanically) as the CEM25P. I wouldn't worry about the apparent play in the mesh. What you don't want is the spring load too high as it will indeed stall the motors. The Dec axis on mine did require the cover to come off and get the screwdrivers out. For starters the belt was a lot looser than the RA. I followed the PDF guides regarding tuning out the play in both housing and belt. We shouldn't really have to be adjusting brand new gear but they are low end astronomy mounts at the end of the day. Once you get them tweaked, balanced and polar aligned well, they are very good. I see regular RMS values of 0.5" and last night I seen peak to peak errors of less than 1 second. 

 

CEM25_Play_Fixing.pdf CEM25_Belt_Tension.pdf

[Endolf]

Thanks, I've started surgery.... 

I can confirm that the mesh between the worm and main gear is fine, as is the belt tension. The issue is that the main gear "floats" on the axis. I need to dig more in to the guts, but that gear rotating is exactly where the slop is.

[david_taurus83]

3 minutes ago, Endolf said:

Thanks, I've started surgery.... 

I can confirm that the mesh between the worm and main gear is fine, as is the belt tension. The issue is that the main gear "floats" on the axis. I need to dig more in to the guts, but that gear rotating is exactly where the slop is.

That doesn't sound good at all.

[Endolf]

Especially not in both axis....

[Endolf]

So I've managed to fix one axis, the video is from before. There are 2 grub screws around the collar that the gear bolts to, and these grip the tube the polar scope runs through. I just tightened them up and now the gear doesn't rotate, so the whole thing is nice and solid.

The other axis looks more tricky, as the issue is the shaft that the belt joins to and runs through the clutch can move laterally in it's bearings, this is where the slop is coming from. I might see if the pulley can be moved along the shaft a little. I'm not sure at this stage. I'll take another look tomorrow.

 

[david_taurus83]

That's really shocking! The second looks like end float play like you get on an EQ5 worm.

[Endolf]

I've managed to reduce the end play, but not remove it. It's an improvement though. Found there was a grub screw in the pulley. Loosened it up, moved the pulley up the shaft a bit and tightened it back up.

Just need some clear skies now....

[StuartJPP]

I briefly owned  an iOptron ZEQ25-GT from new a few years ago, it had horrendous backlash in dec, mostly cause by a loose grub screw connecting the motor shaft to the pully gear, sad to see they still arrive in such poor working order.

 

 

 

Hope you get it sorted.

[Endolf]

Indeed, I thought iOptron were supposed to be better than SW....

[spongebobscaredypants]

This is very interesting.  I've been looking for reviews about this mount in a search for a future replacement for my iPolar SGP.  I had to deal with the same problem with the SkyGuider pro and tighten some screws up to fix the backlash.  Thanks so much for sharing this. 

I hope you are able to come up with a solution to fix the problems!

Best wishes!

[Feccy]

Funnily (well not really) enough I received my CEM26 last week and had the identical issue - 2 grub screws on the RA axis not tight - I was wondering why after a 3 star alignment why my GOTO was off so much! Not good really on a brand new mount. Luckily the experts on the iOptron FB group came to the rescue. Clouds now forecast for the next 5 days!. Hope you get going OK

[Paul1]

Hey,

Here the same story a lot of backslash on the RA Axis I contacted Ioptron but still got no answer after two days.

Regards 

 

 

[Feccy]

1 hour ago, Paul1 said:

Hey,

Here the same story a lot of backslash on the RA Axis I contacted Ioptron but still got no answer after two days.

Regards 

 

 

This was the problem on mine - quick tighten and all good

 

[Endolf]

I did the same thing, they all seem to be coming like this at the moment.

[Paul1]

I tried that but still the same, he will go back on Tuesday.

[larstronomie]

On 23/02/2021 at 23:28, Endolf said:

So I've managed to fix one axis, the video is from before. There are 2 grub screws around the collar that the gear bolts to, and these grip the tube the polar scope runs through. I just tightened them up and now the gear doesn't rotate, so the whole thing is nice and solid.

The other axis looks more tricky, as the issue is the shaft that the belt joins to and runs through the clutch can move laterally in it's bearings, this is where the slop is coming from. I might see if the pulley can be moved along the shaft a little. I'm not sure at this stage. I'll take another look tomorrow.

 

Did you get the counter-weight shaft holder off easily? I did this yesterday and had to use a lot of force in order to get the counter-weight shaft holder off. Once I finally got it off I was able to move the RA-axis even with the clutch enabled? (Only the black axis, the metal disk stayed where it was). Once tightening the screws and putting everything back together I couldn't move the RA axis anymore with the clutch enabled? Is this normal? It had me kinda worried. 

[SwimmingFish849]

23 hours ago, larstronomie said:

Did you get the counter-weight shaft holder off easily? I did this yesterday and had to use a lot of force in order to get the counter-weight shaft holder off. Once I finally got it off I was able to move the RA-axis even with the clutch enabled? (Only the black axis, the metal disk stayed where it was). Once tightening the screws and putting everything back together I couldn't move the RA axis anymore with the clutch enabled? Is this normal? It had me kinda worried. 

When I first took mine off it took a lot of force, after a while it does come of easier. 

I've found those little screws keep coming loose over time though so I contact ioptron and they recommended using some Loctite Threadlocker Blue 242 

I applied that last night so let's see if it helps! 

[larstronomie]

13 hours ago, SwimmingFish849 said:

When I first took mine off it took a lot of force, after a while it does come of easier. 

I've found those little screws keep coming loose over time though so I contact ioptron and they recommended using some Loctite Threadlocker Blue 242 

I applied that last night so let's see if it helps! 

Hey thanks for your response! When you took it off were you able to move the other end quite freely aswell? It had me quite worried that I was able to move it while the clutch was on. 
It was not the actual metal colored gear (behind the cover) that was moving though. Once I put everything back together I couldn't move it anymore and everything seems fine to me. Haven't tested it yet though. Only this part was moving (with clutch enabled):

 
 

[larstronomie]

Happy to report mount is still working perfect.

[SwimmingFish849]

On 28/07/2022 at 21:54, larstronomie said:

Hey thanks for your response! When you took it off were you able to move the other end quite freely aswell? It had me quite worried that I was able to move it while the clutch was on. 
It was not the actual metal colored gear (behind the cover) that was moving though. Once I put everything back together I couldn't move it anymore and everything seems fine to me. Haven't tested it yet though. Only this part was moving (with clutch enabled):

 
 

If I'm honest I didn't try moving it when I had the front off. If everything feels solid now it's back together you should be golden though