RIP CG5 :(

[FrenchyArnaud]

Well, that's it. It had to happen one day: my trusty CG5GT, circa 2006, died tonight. In the middle of imaging, PHD2 suddenly screamed at me that it was not able to do enough corrections in dec anymore and a rapid inspection revealed that the dec axis has gone for good; the motor makes a weak whine but nothing moves, so either the motor is dead or, much more likely, the mechanical drive has failed. Either ways, it's almost certainely the end of the road for my first "real" mount, that will have served for a solid 15 years inc. about 7 at my service. 

I have begun the built of a custom high specs GEM a few weeks ago but it will not be in service before several months (possibly just in time for the next clear night, forecasted in november 2024) and I really don't have the funds to replace the mount or hurry the build, so for now it's lights out for me... Bit gutted really, but it's less serious than a heart attack I guess.  I will strip it down (again) to see if it is salvageable but my instinct says this time, it's RIP CG5. 

[JeremyS]

Sorry to hear that!

I hope you get it working again 🤞🏻

[Grump Martian]

What a loyal servant. Feel for your loss.

[RobertI]

Sorry to hear about that. I hope it’s salvageable but sounds like it’s given good service. Perhaps it can have a second life as a non-goto mount driven in RA only - someone would love it - perfect for visual, probably ok for solar system imaging. 🙂

[Carbon Brush]

Sorry to hear the mount has failed.
I think the long service life shows the build quality. 
Should you decide it is scrap, then please let me know. I have one in (differently) non running order so am interested in making a package.

 

[malc-c]

May be worth doing an autopsy on the mount to find out what the cause of failure is and if it's something that can be fixed.  If the mount hasn't been serviced or checked in those years it could be something simple as a gear meshing issue or bearings needing lubrication.

[FrenchyArnaud]

On 04/04/2023 at 11:11, malc-c said:

May be worth doing an autopsy on the mount to find out what the cause of failure is and if it's something that can be fixed.  If the mount hasn't been serviced or checked in those years it could be something simple as a gear meshing issue or bearings needing lubrication.

Yes it's in the books, just waiting to have dry weather now to uncover it and take everything indoors which is a bit of an undertaking. 

I'll do it "just in case" but not holding my breath. As I already said elsewhere, i see it as an autopsy, not a rescucitation attempt, i really do not hold any real hope. 

Edited April 5, 2023 by FrenchyArnaud

[SteveNickolls]

Sorry to hear your CG5 may be no more, my own CG5- 'Lazarus' is also 2006 vintage and has served well over the years. I wonder how many AM5's will be operational and reach 2040, I don't think I will be. 🙃

As others have said check everything in case a resurrection can be performed.

Cheers,

Steve

[FrenchyArnaud]

Yesterday was dry so I took everything down and performed the autopsy. 

The CG5 drive train is :

Stepper > integrated cogs gearbox > braket > cogs > worm > axis. 

As soon as I took the mount off the pier I knew something was physically broken inside, it was obvious a heavy part was moving freely and knocking and I could hear smaller parts dancing around. 

It turns out that the gearbox on the stepper had sheard off. It is fixed to the stepper axis by two MINUSCULE screws, about 1.5mm x 5mm. One screw broke clean (i suspect metal fatigue as in effect, these 2 tiny, tiny screws must absorb all the effort of the mount forever)

That in turn freed the bottom plate of the gearbox on one side, warping it; the second screw followed, the motor fell in the casing, the outer case of the gearbox sperated from the bottom plate and all the cogs, bushes etc went flying in the plastic outer case of the mount. 

The caustiously optimistic good news is that this catastrophic failure MIGHT not be terminal. 

I was able miraculously to collect all of the bits of the gearbox and extract the broken screw bits from the bottom plate. I was also able to unwarp it (more or less)

I very cautiously drilled 2 new holes and reassembled as tightly  as I could. By eye it LOOKS ok. I will clean everything of and check/service the RA assembly as well in case it's having the same impending failure and try if it works once reassembled. I am not sure at all my gearbox work comes anywhere near expected tolerances and it will work again, but how much more dead than dead  can I make it? 

If you ask me, having all of the torque transmitted to these 2 ridiculous screws inside the gearbox is a major design flaw. All the rest is pretty sturdy, it's obvious that this is a really weak point in the drive. 

Edited April 10, 2023 by FrenchyArnaud

[malc-c]

Glad to hear you managed to find out what had failed and that the mount can have a second lease of life simply replacing a couple of small screws.  Without the ability to see the structure of the broken screws you can only speculate that the screws failed through fatigue, but one aspect that may have contributed, based on the image of the rig above, is that the manufactures may not have anticipate the torque needed to move such a rig, and simply chose screws that would handle the mass of a range of OTA's that were originally supplied with the mount.  Again, this is just speculation, and who knows if those screws would still have failed for a casual observer who just used the same OTA for visual and kept the mount inside when not in use ?

[FrenchyArnaud]

1 hour ago, malc-c said:

 Again, this is just speculation, and who knows if those screws would still have failed for a casual observer who just used the same OTA for visual and kept the mount inside when not in use ?

That's a valid point. This particular mount was supplied with a C8N intented mostly for visual use and even though it's obviously much heavier than the 130pds i use, it is probably marginally lighter than the 130 geared up for AP; crucially the 130 is outdoors on the pier 24/7 under a cover so it's possible that the wind has put a lot of stress on the assembly day after day. 

The screws I have fitted are much sturdier though, so if the thing restarts and runs more or less smoothly I think it will hold. 

Plan B is to do an onstep conversion. Like an upgrade / intermediate step towards the GEM i am building anyway. 

[FrenchyArnaud]

Ok so after very careful reassembly... well not careful enough apparently. Turns out the vynil/plastic primary cog of the gearbox was damaged in the process - it's missing 1 tooth. I am very confident i can put the mount back in service if I can find a replacement. Any ideas where to find that? 

[RT65CB-SWL]

13 hours ago, FrenchyArnaud said:

Ok so after very careful reassembly... well not careful enough apparently. Turns out the vynil/plastic primary cog of the gearbox was damaged in the process - it's missing 1 tooth. I am very confident i can put the mount back in service if I can find a replacement. Any ideas where to find that? 

Maybe a local engineering workshop or watch/clock maker maybe able to fabricate one [or the complete set] for you. 

I did see on ''AstroBiscuit' [aka @rorymultistorey here on SGL] YouTube channel a few months ago, he visited the guy who tunes-up mounts. Unfortunately I cannot remember the guys name. Sorry about that.

Have you looked at AliExpress? - it is surprising what you can find/buy there if you have not visited the site before.

Edited April 11, 2023 by Philip R

[RobertI]

1 hour ago, Philip R said:

Unfortunately I cannot remember the guys name. Sorry about that.

I think it’s these guys:

https://www.darkframeoptics.com
 

[iapa]

3 hours ago, RobertI said:

I think it’s these guys:

https://www.darkframeoptics.com
 

Check feedback on several of the forums on this site. Quite mixed.

[carastro]

Not being at all into engineering I have been reading this thread as I used to own a CG5 GT.   I guess 3D printed cogs are not going to be an option?

I know a guy who built a complete EQ Mount 3D printed and it works and guides well (he is actually a member of this forum but not active these days).

Carole

Edited April 11, 2023 by carastro

[FrenchyArnaud]

5 hours ago, RobertI said:

I think it’s these guys:

https://www.darkframeoptics.com
 

I contacted them - twice- MONTHS ago as I was interested in having this very mount serviced and put back to specs. They never even answered. So tbh I will not even bother  My custom made GEM will be in serice before they just respond to the messages  

[FrenchyArnaud]

1 hour ago, carastro said:

Not being at all into engineering I have been reading this thread as I used to own a CG5 GT.   I guess 3D printed cogs are not going to be an option?

I know a guy who built a complete EQ Mount 3D printed and it works and guides well (he is actually a member of this forum but not active these days).

Carole

I discussed it with a buddy of mine who does a lot of 3D print and he thinks it's simply too delicate a part to sustain any chance of it taking on the forces. In the meantime I have found job lots of similar cogs used for RC models and printers and there is a good chance one within the job lots would do the job as it is apparently a common model (24-12, 2.5mm bore)

However, as I have the electronics and motors ready to go for the mount I am building, and this gear box is only 50:1, I am ore and more interested in simply shoving my own motors and PCB and converting the mount to a system I trust more and would give better precision. I can symply clone my pcb/motors when build time comes. I am undecided yet. 

[malc-c]

I've very little experience of 3D printing, but it's possible to have prints done in metal.  I googled "3D printed metal gears" and found this

I have no idea if they can do one offs or won't entertain private orders and are more geared up (sorry couldn't resist) for bulk orders form large companies

I did have some servo gears made in SLS Nylon for use with servos to switch points on model railway layouts

 

With careful design of the layout I managed to 21 sets for £55 shipped from 3D print UK  

I have no idea if the torque in the servos is any more or less than the gears in the mount, but it may be worth a punt without loosing too much money

[FrenchyArnaud]