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Equipment Discussions >> Mounts

Pages: 1
dickbill
scholastic sledgehammer


Reged: 09/30/08

CGEM RA stopped working...and solution
      #5653979 - 01/31/13 10:05 AM

Almost Brand new mount. Factory settings indicate hand control version 4.19. Without any previous warning, last night I could not complete the 2 stars aligns. The RA would not move while declination still worked.
I spread the pin, no effect, did a factory reset, no effect. I considered the return at this point.
But, i still could hear the RA gear trying to engage with a faint 'nk...nk...' every time i pushed the hand control button. I powered on/off the mount several time with no results and finally ressorted to the old car starter method:

I flapped pretty hard with my fingers on the mount panel (the side where the connectors are) to introduce some energy in the system, while the mount was stuck slewing a star, and the RA re-engaged!
After that I completed the alignement with no more problem.

Is it humidity? the cold? I thought tonight i should put an electric heater straight under the mount while it is still covered to warm up the electronic.


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM RA stopped working...and solution new [Re: dickbill]
      #5653993 - 01/31/13 10:15 AM

Where are you located? I could be the cold. The worm may have bound up slightly stalling the axis. You might need to increase the worm spacing a very small amount. If it is very cold it could also be grease stiffness that stalled the axis.

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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM RA stopped working...and solution new [Re: EFT]
      #5654064 - 01/31/13 10:48 AM

Well, the guys in Canada are going to laugh, I am in Dallas, Tx. Last night was maybe in the 40s, ~6-10C, definitively above freezing anyways.

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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM RA stopped working...and solution new [Re: dickbill]
      #5654266 - 01/31/13 12:46 PM

I'm not going to laugh. I'm in Phoenix and it is about the same, and it's too darn cold.

I could still be an issue with the cold though. You heard the spur gear clicking which suggests that the worm was stalled. When the worm is very close to the stalling point on the ring gear then it can take very little temperature variation to get it to stall, especially if you had just taken the mount outside and it had not acclimated yet. That would still be the first suspect in my book. Stiff grease is less likely at that temperature. Because you could still hear that there was power going to the motor, it is much less likely that it was a problem with the electronics.


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM RA stopped working...and solution new [Re: EFT]
      #5654402 - 01/31/13 02:10 PM

So the worm was sorta glued to the gear and with the stiffened grease it couldn't start rotate...
But if the binding force is so great, how could a relatively weak flap (maybe a two-pound force but no more) distributed on the side of the mount, break that 'bound'? By resonnant forces, since the mount was still attempting to move in RA while i flapped it?

Also why isn't the declination axis ever affected?
There are lots of similar stories on the net, it's always the RA that is affected. Is it what the CGEM dx is supposed to adress, in delivering more power, the dx would ensure that any binding would be overcome, isn't it dangerous for the gears to apply too much power?


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM RA stopped working...and solution new [Re: dickbill]
      #5654517 - 01/31/13 03:19 PM

Quote:

So the worm was sorta glued to the gear and with the stiffened grease it couldn't start rotate...
But if the binding force is so great, how could a relatively weak flap (maybe a two-pound force but no more) distributed on the side of the mount, break that 'bound'? By resonnant forces, since the mount was still attempting to move in RA while i flapped it?

Also why isn't the declination axis ever affected?
There are lots of similar stories on the net, it's always the RA that is affected. Is it what the CGEM dx is supposed to adress, in delivering more power, the dx would ensure that any binding would be overcome, isn't it dangerous for the gears to apply too much power?




Depending on how well (or how poorly) a mount is balanced, there can be a lot more force applied to the gears in the RA than the DEC in most cases. The reason the RA was affected could be as simple as the adjustment of the gear spacing in two axes not being the same. Part of the idea of the DX is that it might have overcome this stiction whereas the CGEM might not. Like I said, I think that at that temperature, the grease was probably not a major factor, but it can still be a contributor in general due to the lack of quality and over abundance of grease used.

Think of the gear spacing as a zone in which the gears do not have too much stiction or too much backlash. With the stock gears in the mount, this zone is relatively wide (compared to high precision gears). It is still quite small measurement wise, but if you are on the tight side of the zone, very slight differences in temperature, balance, grease, etc. can make a big difference. If you are on the loose side of the zone, these things will have far less impact. The force that you gave it may simply have been just enough to break the stiction and allow the gears to start turning again. But if the spacing were very slightly closer, this might not have worked. This zone of adjustment also helps to account for the slight high spots in the ring gear which inevitably exist as well and you may have been on a high spot when the worm was bound up.

Is it dangerous to apply more power? Yes and no. The advertised idea of the CGEM DX, i.e., that it allows you to use the mount less well balanced, is bad. A less well balanced mount is still not going to perform at its best. However, having more power can be helpful and the DX does seem to run the motors better than the standard CGEM because of it. There is little to be worried about in regards to damaging the primary mount gears because of more power. The worm and ring gears, along with the motor and worm spurs, are very course gears and very difficult to damage as a result and these motors will not apply enough force to damage them. The motor gearbox is another story though. The smallest gear in the gearbox is nylon for two reasons, noise reduction and safety. If too much power is supplied, the nylon gear can be stripped and I have seen this happen with a jammed axis. That's why you should never keep applying power if an axis (or worm) is jammed. The motor contoller continues to increase the power to the servo until it breaks free, stips the gear or causes some damage to the electronics. That's how most servo systems work. Over time, a poorly balanced or overly stiff system where more power is being supplied to the motor to overcome these problems, will likely wear out faster. So operating a poorly balanced mount is still not a good idea.


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CGEM RA stopped working...and solution new [Re: EFT]
      #5654556 - 01/31/13 03:36 PM

Thanks Ed, your comment is very instructive. I think i'm gonna put a heater under the mount tonight for a couple of minutes. Maybe it was a high spot as you said but i won't take a chance.

I wonder if those who have the RA axis problem, had it in winter, or at least during cold weather. That would be an interesting statistic to know.

Edited by dickbill (01/31/13 03:37 PM)


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