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RA motor drive for Celestron Astromaster 130 EQ mount

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#1 abordage

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Posted 27 June 2022 - 03:03 PM

Hi all;  I recently got a Celestron Astromaster 130 EQ scope for a very good price. Everything is great except the DC Right Ascension (RA) clock drive that came with it. Strangely enough the mounting hole for attaching the clock drive to the mount's RA  shaft is on the wrong side of the mount....for the mount to turn the RA shaft in the right direction to track the celestial objects the clock drive needs to be set to the "S" (South position, for Southern hemisphere observers). Okay, no problem, I dont mind setting it to the S position. However one more problem....with a new (Energizer) 9V battery inserted into the clock drive the RA shaft of the DC drive turns okay, however when attaching the clock drive to the mount (assuring that the flat side of the DC motor drive shaft is aligned with the screw of the coupler that connects to the mount's RA slow-mo shaft and that the screw is firmly tightned) and after powering on the DC drive and waiting up to an hour and watching, the DC motor shaft is no longer turning, thus the slow-mo shaft is not turning and the scope is not tracking at all.To me it seems that the DC drive just does not have enough torque to drive the scope. I have tried turning on the DC drive both with the scope attached to the mount (counterweights also on), and I have tried it without the scope and no counterweights....still no luck. I have also tried it with the mount's RA lock knob both tightened, and loosened....again...no luck.

Does anyone have a solution to this? Or should I look for a different type of clock drive. Thanks. Adrien


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#2 Skywatchr

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Posted 28 June 2022 - 08:34 AM

Hi all;  I recently got a Celestron Astromaster 130 EQ scope for a very good price. Everything is great except the DC Right Ascension (RA) clock drive that came with it. Strangely enough the mounting hole for attaching the clock drive to the mount's RA  shaft is on the wrong side of the mount....for the mount to turn the RA shaft in the right direction to track the celestial objects the clock drive needs to be set to the "S" (South position, for Southern hemisphere observers). Okay, no problem, I dont mind setting it to the S position. However one more problem....with a new (Energizer) 9V battery inserted into the clock drive the RA shaft of the DC drive turns okay, however when attaching the clock drive to the mount (assuring that the flat side of the DC motor drive shaft is aligned with the screw of the coupler that connects to the mount's RA slow-mo shaft and that the screw is firmly tightned) and after powering on the DC drive and waiting up to an hour and watching, the DC motor shaft is no longer turning, thus the slow-mo shaft is not turning and the scope is not tracking at all.To me it seems that the DC drive just does not have enough torque to drive the scope. I have tried turning on the DC drive both with the scope attached to the mount (counterweights also on), and I have tried it without the scope and no counterweights....still no luck. I have also tried it with the mount's RA lock knob both tightened, and loosened....again...no luck.

Does anyone have a solution to this? Or should I look for a different type of clock drive. Thanks. Adrien

With the motor NOT on the mount, put a mark on it to index it and power it on.  Let it go for about an hour, then see if the shaft turned.  If so, the RA gear on the mount is too tight and needs adjusting.  The slo-mo knob should turn quite easily.



#3 abordage

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Posted 30 June 2022 - 02:36 AM

Skywatchr, thanks for the reply. Yeah , I already tried unmounting the DC motor, marking the marking the motor shaft, powering it on and watching...it turns nicely. With the ota installed on the mount and the counterweights on the RA slow-mo control knob is rather stiff to turn, regardless if the RA shaft locking knob is just snug tightened or completely loose, and when I remove the ota and counterweights the RA knob turns smoothly.Unfortunately the Astromaster EQ mount does not have adjustment screws for meshing the slow-mo worm gear with the RA shaft spur gear. You may be right in that the RA spur gear is too tight against the RA spur, unfortunately I cant do anything about that. UnlessI can find a different RA motor with more torque I will have just have to use the mount without the motor, or I could try using a much smaller and lighter ota.....



#4 Skywatchr

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Posted 30 June 2022 - 07:58 AM

I've never had one of these mounts apart, so I don't know how the polar axis is assembled. But it points to the axis bearing(s) having slop allowing the gear to move and put too much pressure (weight) on the worm.  No doubt it uses some sort of plastic sleeve bearings.

The 9v battery probably doesn't have enough current to overcome the draw of the motor under load because of the bearing load.  And I doubt the drive is made to be able to handle much more current like using an AC to DC 9v adapter with at least 2A output current.  The adapter (or battery) doesn't "push" the current out, the motor circuit draws what it needs.  If the motor circuit "wants" 1A, that's all the adapter lets out.

Take the cover off the drive and see if you can find the specs on the motor that is in there.  It should have the voltage, current, and RPM either stamped in to the motor cover, or a label.  You'll have to pull the motor out of the plastic housing to see it.  It "may" be a 12vDC motor running on 9v.




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