Jump to content


Photo

Varying the RA drive rate on a DS-10

This topic has been archived. This means that you cannot reply to this topic.
16 replies to this topic

#1 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 25 June 2009 - 12:03 PM

I have an old DS-10 mount for visual observing. It tracks a bit slowly, however: at magnifications over 100x, this is noticeable. I have read on the web that Orion and later JMI and a few others produced a smallish unit (usually named "___trak") that would both allow one to run the AC mount from a 12-volt battery and also vary the speed. There seem to be multiple variations of these, including many that would run both RA and Dec drives and respond to autoguiding commands. That's far more than I need; I am just wondering about varying my RA rate. Has anyone used one who could give me more information?

#2 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15794
  • Joined: 06 Jul 2007

Posted 25 June 2009 - 04:11 PM

I have an old DS-10 mount for visual observing. It tracks a bit slowly, however: at magnifications over 100x, this is noticeable. I have read on the web that Orion and later JMI and a few others produced a smallish unit (usually named "___trak") that would both allow one to run the AC mount from a 12-volt battery and also vary the speed. There seem to be multiple variations of these, including many that would run both RA and Dec drives and respond to autoguiding commands. That's far more than I need; I am just wondering about varying my RA rate. Has anyone used one who could give me more information?


Depends on how slow your drive is. Any drive corrector will work (a fancy name for a variable frequency inverter) if it is not too far off. Problem is, they are right hard to come by these days. You might call JMI and see if they have any left. Other than that? Hit the Astromart. Are you sure what you are seeing is not the result of polar misalignment?

#3 Jimmy2K63

Jimmy2K63

    Surveyor 1

  • *****
  • Posts: 1651
  • Joined: 26 Apr 2009

Posted 25 June 2009 - 04:46 PM

You could build one yourself or get an old power inverter and dissect it - may just have to put a variable resistor on it. One of the guys in our club built one for me - think he used a 555, and there were a couple of externally mounted power transistors on it. Even had a coiled cord and a couple of pushbuttons on a handset.

#4 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 25 June 2009 - 05:47 PM

Hey, Uncle Rod, Jimmy2K63,

The lag is only in RA, and I tried JMI first (they essentially don't deal in these any more at all). I plan to open the drive up on my next cloudy night and see if there is something else mechanical going on. Barring that, finding a working drive corrector that I can connect the AC cord to seems like the best solution. Anything in particular I should look for or avoid?

I'm an electrical novice (being generous with myself) and am hesitant to build. I've heard that S&T published plans a while back but don't know if that's true. If I could find instructions that I could read (with pictures), I would probably try to build one.

#5 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 25 June 2009 - 05:53 PM

Nice blog, Jimmy. Enjoy that new scope! Congrats on getting a model with an accurate goto!

#6 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15794
  • Joined: 06 Jul 2007

Posted 26 June 2009 - 08:41 AM

Hey, Uncle Rod, Jimmy2K63,

The lag is only in RA, and I tried JMI first (they essentially don't deal in these any more at all). I plan to open the drive up on my next cloudy night and see if there is something else mechanical going on. Barring that, finding a working drive corrector that I can connect the AC cord to seems like the best solution. Anything in particular I should look for or avoid?

I'm an electrical novice (being generous with myself) and am hesitant to build. I've heard that S&T published plans a while back but don't know if that's true. If I could find instructions that I could read (with pictures), I would probably try to build one.


To avoid? I doubt you'll have the luxury of doin' that. If you find a working drive corrector, just get it. ;)

Well, yeah, that was the second option I was gonna give you...there are still sets of schematics/plans for drive correctors. They are _not_ overly complicated devices...but...yeah...hit Astromart, CN Classfieds, your local club, etc.

#7 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 26 June 2009 - 04:25 PM

Thanks. Posting hopefully, as I write.

#8 Jimmy2K63

Jimmy2K63

    Surveyor 1

  • *****
  • Posts: 1651
  • Joined: 26 Apr 2009

Posted 26 June 2009 - 08:49 PM

I think any drive correcter you find should be fine if it has accomodation to plug an AC cord in it. Synchronous motors don't draw much at all. I have one, but it goes with my Astrola mount if/when I sell it. You should be able to find one on one of those places too - was a very popular item.

#9 Joe F Gafford

Joe F Gafford

    Vanguard

  • -----
  • Posts: 2088
  • Joined: 15 Dec 2006

Posted 29 June 2009 - 12:44 AM

Alterf,
Avoid any used Meade drive correctors. They are inherently unstable due to cheap circuit design. I got my DS-10 new in 1984 with the astrophoto package. I replaced the circuits inside the drive corrector that came with it with one of my own design. Any drive corrector with 110v output should work. Repack the drive gear in the clock drive. I replaced the 3" gear assembly that was in mine with a 6.6" one. My 10" scope does not resemble the DS-10 I started out with.
Joe.

#10 rmollise

rmollise

    Hubble

  • *****
  • Posts: 15794
  • Joined: 06 Jul 2007

Posted 29 June 2009 - 07:04 AM

Alterf,
Avoid any used Meade drive correctors. They are inherently unstable due to cheap circuit design.


Actually, those Meades should be fine for visual use, which is what he wants. At this point in the drive corrector game Beggers Cain't be Choosers, I fear. :lol:

#11 Joe F Gafford

Joe F Gafford

    Vanguard

  • -----
  • Posts: 2088
  • Joined: 15 Dec 2006

Posted 29 June 2009 - 07:34 PM

Alterf,
Avoid any used Meade drive correctors. They are inherently unstable due to cheap circuit design.


Actually, those Meades should be fine for visual use, which is what he wants. At this point in the drive corrector game Beggers Cain't be Choosers, I fear. :lol:

Yeah, and they really heat up the motor. Find one that has a sine output or a 66% duty cycle square output. The 100% duty cycle Meade correctors will cause gear strippage in the motor due to overheating.
Joe.

#12 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 30 June 2009 - 02:41 PM

My initial attempts have drawn no response at all. I will keep trying. Yes, someone must have one.

#13 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 30 June 2009 - 02:44 PM

I'm interested in why you replaced the gears. I've had clouds ever since I opened and adjusted the gears, so I've been unable to test it out, but I moved the worm closer and tightened the clutch up a bit. Now I need to try it out. I suppose it is possible that I am experiencing very poor machining. I watch for 30 minutes and the drive appears to lag. Perhaps if I watched for another 30 it would speed back up?

#14 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 30 June 2009 - 02:50 PM

All of your comments have been very helpful. Someone suggested I contact the local ham radio folks. I did, and the fellow I spoke with suggested that my AC outlet may not be putting out a full 120V. I haven't tested that yet, but how would I resolve that? He suggested a variac. Of course, his point is that increasing the voltage would speed up the motor. That's true, right? Used variacs are not that expensive, but I really don't want to burn the thing out and I have no idea what the motor will take. Any thoughts on that?

#15 jrcrilly

jrcrilly

    Refractor wienie no more

  • *****
  • Administrators
  • Posts: 33958
  • Joined: 30 Apr 2003

Posted 30 June 2009 - 02:58 PM

his point is that increasing the voltage would speed up the motor. That's true, right?


Not likely. It's a synchronous motor. If the voltage were so low that the motor couldn't operate at the correct speed it would stall and burn up fairly quickly.

#16 Joe F Gafford

Joe F Gafford

    Vanguard

  • -----
  • Posts: 2088
  • Joined: 15 Dec 2006

Posted 30 June 2009 - 08:43 PM

I watch for 30 minutes and the drive appears to lag. Perhaps if I watched for another 30 it would speed back up?

You have a 1/10th RPM motor. Any differences will happen within the 10 minutes, it is called periodic error. If it is still slow, you may have worm to worm gear facing problems. Be sure there is plenty of thick grease on the worm and on the teeth around the worm gear.

Also check and remove grease between the clutch pads in the worm gear assembly and replace those 3 dang clutch screws with screws with small knobs and tighten LIGHT HAND TIGHT. Too tight will damage your drive if something binds. Not enough friction on the clutch coupled with friction in the RA axis will slow you down. You will have to cut a ~ 4" circular hole in the back of the cover to accommodate the knobs
Remove the worm gear assembly and the clamp and pull out the Tee and check, clean, and lube the 2 teflon bearings with grease. You might do this on the DEC axis in the Tee as well. You should be able to spin both axis easily with your finger with nothing attached if properly lubed.

This is a CAD representation of the mount. You don't have to remove the backplate to service. The RA tangent motor is a JMI one.
Joe.

Attached Files



#17 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 02 July 2009 - 01:03 PM

You have a 1/10th RPM motor. Any differences will happen within the 10 minutes, it is called periodic error. If it is still slow, you may have worm to worm gear facing problems. Be sure there is plenty of thick grease on the worm and on the teeth around the worm gear.

Also check and remove grease between the clutch pads in the worm gear assembly and replace those 3 dang clutch screws with screws with small knobs and tighten LIGHT HAND TIGHT. Too tight will damage your drive if something binds. Not enough friction on the clutch coupled with friction in the RA axis will slow you down. You will have to cut a ~ 4" circular hole in the back of the cover to accommodate the knobs
Remove the worm gear assembly and the clamp and pull out the Tee and check, clean, and lube the 2 teflon bearings with grease. You might do this on the DEC axis in the Tee as well. You should be able to spin both axis easily with your finger with nothing attached if properly lubed.


Thanks, Joe. Yes, it is periodic error. I was able to watch the movement in RA closely since and see it slow in one part and speed up in another. For part of the period, the tracking is very close to perfect (at least, visually).

I will re-lube, as you recommend. There is a slight bit of grease on things, but there is also a dried residue of something that looks like it has been on there a long time.

Thanks for advice on this project. The mount is very easy to use and thus far seems an excellent value for backyard visual observing. Updates to come.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics