C8-SGT Drive motor trouble

[Nathan25]

Im having trouble with the RA drive motor on my Celestron C8-SGT. The motor can't cope with the weight of the OTA (and counter wight). I can see the internal shaft moving, but the rest of the fixture remains stationary. Any ideas? Cheers!

Nathan

[iceman (Mike)]

Is it a C8 on it?

btw to the forum?

[Dennis]

Hi Nathan

I haven't a clue about what type of mount/motor the C8-SGT is so can't offer any specific advice. However, I am going to assume that it is a German Equatorial Mount (GEM), not a fork mount.

When tracking at the sidereal rate, the movement is difficult to see as it is only 1 revolution in 24 hours. Does the problem happen also when you slew?

I once had a similar problem with a Vixen GPDX GEM as follows:

MOTOR:

• The RA motor has a drive shaft on which is fitted a gear wheel with a locking collar.
• The gear wheel with collar slides onto the motor shaft.
• The gear wheel collar has a tiny Allen key head grub screw.
• This grub screw, when tightened correctly, grips the motor shaft so the gear wheel turns with the motor shaft.

Q1: If your GEM is similar, is this grub screw loose?

MOUNT:

• The mount has a worm and a worm wheel that is turned by the motor.
• This worm shaft protrudes from the body of the mount.
• A similar gear wheel with collar slips on this worm shaft, again held in place by a grub screw.

Q2: If your GEM is similar, is this grub screw tight, or is the gear slipping on the worm shaft?

If either of these grub screws are loose, it means that the motor shaft will not be able to drive the worm.

Cheers

Dennis

[sheeny (Al)]

Nathan,

I sent you a PM. I hope it fixes the problem, otherwise some of the more serious stuff that Dennis is describing could be more like it.

Did you buy the scope new or second hand?

And again BTW.

Al.

[Nathan25]

Hi Al and Dennis,

Thanks for both your fast replies! Al, i just sent you back a PM. I think its gonna be what you suggested, ie me having the lock levers open rather than locked while having the Go-To operating . Very much looking forward to seeing what this thing can do. Many thanks!

Nathan

[sheeny (Al)]

Nathan,

I've assumed the scope is new to you... if it isn't then my answer will probably seem pretty dumb.

Just to help fault find can you tell us:

Have you used the scope OK and it has ceased to work as it used to?

If you have used it for some time and it now doesn't drive properly, can you describe how you balance your scope when you set it up?

I'm really hoping the scope is new to you and you've simply missed tightening the drive clutches on set up. It's a basic little step that I remember not being well described in the manual - it's almost so basic that I think Celestron assume you know to do it! The drive clutches look like the shaft locks on my old samson EQ mount from 25 years ago. Old my old mount I had to make sure the shaft locks were free so the shafts could rotate before I engaged my motor drives. On the CG5 the clutches actually engage the drive train to the servos, so it is only the gear ratio and the resistance of the servo motors that stop you from pushing the scope around. You need those clutches to be locked (i.e. so you can move the scope) in order for the drives to move the scope... I might stop now... I think I've made something really simple sound more complicated than it needs to be!

Al.

[Dennis]

Originally Posted by sheeny

Nathan,

I've assumed the scope is new to you... if it isn't then my answer will probably seem pretty dumb.

Just to help fault find can you tell us:

Have you used the scope OK and it has ceased to work as it used to?

If you have used it for some time and it now doesn't drive properly, can you describe how you balance your scope when you set it up?

I'm really hoping the scope is new to you and you've simply missed tightening the drive clutches on set up. It's a basic little step that I remember not being well described in the manual - it's almost so basic that I think Celestron assume you know to do it! The drive clutches look like the shaft locks on my old samson EQ mount from 25 years ago. Old my old mount I had to make sure the shaft locks were free so the shafts could rotate before I engaged my motor drives. On the CG5 the clutches actually engage the drive train to the servos, so it is only the gear ratio and the resistance of the servo motors that stop you from pushing the scope around. You need those clutches to be locked (i.e. so you can move the scope) in order for the drives to move the scope... I might stop now... I think I've made something really simple sound more complicated than it needs to be!

Al.

Good pick up Al – it’s often the simple things that get overlooked.

Cheers

Dennis