43 replies to this topic

[SeaBee1]

I mean, really... we pay our hard earned dollars for equipment and we have reasonable expectation that this stuff will do as advertised, right? And not just astronomy equipment, I find this problem with everything... but I digress... this is about astronomy equipment, and specifically my RA drive for "The Beast".

 

I bought the drive on the recommendation from another CNer, who also had one and I am sure his worked right out of the box, as it probably does for most people. However, from the first time I used mine, I knew something wasn't quite right. Keep in mind that I am a newbie, and still finding my way around, but I KNOW if the drive is supposed to put an object in stop motion, then it should never leave the center of view... it's supposed to track the object. Mine did not, I was constantly pressing the 8X button to slew RA in order to re-center an object. OK, I thought, maybe it is just THAT object... tried it on planets, the moon, M42, solar... same result. OK, now I am sure it's the drive. At this point, most sane people would contact the vendor and request a replacement. I never claimed to be COMPLETELY sane...

 

What was I going to do? And at this point, my return option had spoiled, so I was left to deal with a defective drive. Fortunately, all my career has been spent repairing and modifying mechanical and electrical equipment, and most of the time with minimal training on the equipment. Time to dig in and figure it out.

 

So my first thought was "There must be a pot for the manufacturer to dial in the speed". So, in light of that, the following is presented as a resource for anyone facing the same issue with the RA drive of their mount...

 

 

^^^ The first thing to do is pop off the buttons. I didn't do this first and the cover wouldn't release. They come off much like the keys of a computer keyboard.

 

 

^^^ Step 2 -  remove the screw that holds the DC connector. There is another on the underside, but you can leave that one alone.

 

 

^^^ Finally, remove the 4 screws that hold the cover in place.

 

 

^^^ You will find 2 long and 2 short screws. The short ones go into the top 2 holes near the On/Off and North/South switches.

 

 

^^^ After removing the cover, boom, there she is!

 

I only had a short session on the 24th while doing some solar observing, and turning the pot clockwise made the difference. It's not completely fixed, clouds rolled in before I could finalize my adjustment, but I am so close now, I could probably leave it alone... took about 10 minutes for the solar disk to go from centered to touching the field stop while using my 14.5mm eyepiece.

 

And to add this: this has not been intended to slam any vendor. I am sure this vendor makes fine equipment, and had I called their CS dept., they would have made it good. I do hope this will be helpful for anyone experiencing the same issues I did.

 

Clear skies guys!

 

CB

[kfiscus]

What about drilling a small access hole/fine-tuning port in the front cover?  It looks like a clear shot.  You'd not have to take anything apart again.  (None of this suggestion works if the pot cannot be adjusted with a tool instead of a finger.)

Edited by kfiscus, 25 September 2016 - 09:22 PM.

[SeaBee1]

Hi Ken, I did consider drilling a hole, and I may still do that, but my hope is that once I set it, I can forget it. It looks like the hole would be right where the "O" is, making it nearly invisible. With the right size hole, adjusting with a screw driver would be no problem.

 

It's a thought...

 

Thanks for stopping by!

 

Best regards!

 

CB

[Scott in NC]

Wow, that's great that you figured that out!  I would have been left scratching my head. 

 

BTW, this thread may be very helpful to someone else with a similar issue in the future.  Do you mind if I change the title so that it can be more easily found during a future search?  If you can come up with something suitable, I'd be glad to assist with changing it to that.

[GrandadCast]

This box (from what I see here and not knowing the model) appears to only have sidereal (stars) and not solar (planets). They require different rates. So this box if set as design, the planets are going to drift. So, if your up to it you can added a switch, single pole single throw with a resistor. This will connect the resistor in parallel with the pot. One end of the resistor goes to the center arm of the pot and the other end to the center pole of the switch, the other pole of the switch will go to one of the other pot connection (depending on its design). When the switch is thrown it will reduce the pots residents a bit. You will have to experiment for the resistor value needed. Any way once you find the value, you would have solar and sidereal settings with a flip of a switch. This switch with a resistor added to a pot is common with electronic devices. 

Jess

Edited by GrandadCast, 25 September 2016 - 11:20 PM.

[SeaBee1]

Wow, that's great that you figured that out!  I would have been left scratching my head. 

 

BTW, this thread may be very helpful to someone else with a similar issue in the future.  Do you mind if I change the title so that it can be more easily found during a future search?  If you can come up with something suitable, I'd be glad to assist with changing it to that.

 

Absolutely Scott! I posted it to help others. How does "Tweaking the Orion RA drive sidereal rate" sound? Or something along those lines?

 

Thanks!

 

Best regards!

 

CB

[SeaBee1]

This box (from what I see here and not knowing the model) appears to only have sidereal (stars) and not solar (planets). They require different rates. So this box if set as design, the planets are going to drift. So, if your up to it you can added a switch, single pole single throw with a resistor. This will connect the resistor in parallel with the pot. One end of the resistor goes to the center arm of the pot and the other end to the center pole of the switch, the other pole of the switch will go to one of the other pot connection (depending on its design). When the switch is thrown it will reduce the pots residents a bit. You will have to experiment for the resistor value needed. Any way once you find the value, you would have solar and sidereal settings with a flip of a switch. This switch with a resistor added to a pot is common with electronic devices. 

Jess

 

Hello Grandad! I am very much a newbie when it comes to the astronomical stuff, i.e. sidereal versus solar rate. I can grasp the concepts once explained, so thank you, I did not know there would be different rates.

 

My original conclusion that something was off was due to both stars and planets were drifting, so I figured the rate was not set right at the factory. The lit for the drive did not indicate ONLY stars would be tracked. Good marketing on their part, bad for the newb consumer like me.

 

I like your idea of adding a switch and resistor, and thank you for that. Makes sense, now that I realize that stuff moves at different rates. Why the heck didn't the manufacturer just add this as a feature?

 

Man, I love this site!

 

Thank you guys!

 

CB

[Scott in NC]

 

Wow, that's great that you figured that out!  I would have been left scratching my head. 

 

BTW, this thread may be very helpful to someone else with a similar issue in the future.  Do you mind if I change the title so that it can be more easily found during a future search?  If you can come up with something suitable, I'd be glad to assist with changing it to that.

 

Absolutely Scott! I posted it to help others. How does "Tweaking the Orion RA drive sidereal rate" sound? Or something along those lines?

 

Thanks!

 

Best regards!

 

CB

 

Done!

[DAVIDG]

 I've worked on number of these units and unless your  design is much different then the ones I have worked on, you didn't adjust the speed. The speed is determined by the frequency of a crystal in the circuit and that is fixed.  The circuit takes the crystal frequency  which is in the mega hertz range and divides it down to make the frequency needed to run the motor at Sidereal rates. When you hit the fast or slow button you changing a binary divider used to change the frequency.  By using a digital circuit to divide the frequency you can get very precise tracking rates that  do not  change with temperature.  Since your dividing down a huge number ie the crystal frequency is in mega hertz and your dividing it down to hertz any error in the exact crystal frequency results in an  extremely small error in the finally frequency  that you'll never see it. 

   What I believe the pot that you adjusted is doing is setting a reference voltage, that is used to determine when the batteries  is low and that causes the LED in the middle of the buttons to turn red and flash.

   I think the reason why your getting better tracking is that you might have done a better job in polar aligning you scope. Also the difference between Solar, and Sidereal rates is 4 minutes in 24 hours, so unless your doing long exposure astrophotography or observing an object over many hours you wouldn't see the drift. The difference in the rate that the planet are moves in also very small and you don't need a different tracking  rate. Only the Moon has difference in rate that you can easily see and it moves it's diameter against the background stars in about  an hour.   Any short term drift is usually caused by poor polar alignment or something loose in the mount or motor connection.

 

                      - Dave  

Edited by DAVIDG, 26 September 2016 - 10:06 AM.

[SeaBee1]

 I've worked on number of these units and unless your  design is much different then the ones I have worked on, you didn't adjust the speed. The speed is determined by the frequency of a crystal in the circuit and that is fixed.  The circuit takes the crystal frequency  which is in the mega hertz range and divides it down to make the frequency needed to run the motor at Sidereal rates. When you hit the fast or slow button you changing a binary divider used to change the frequency.  By using a digital circuit to divide the frequency you can get very precise tracking rates that  do not  change with temperature.  Since your dividing down a huge number ie the crystal frequency is in mega hertz and your dividing it down to hertz any error in the exact crystal frequency results in an  extremely small error in the finally frequency  that you'll never see it. 

   What I believe the pot that you adjusted is doing is setting a reference voltage, that is used to determine when the batteries  is low and that causes the LED in the middle of the buttons to turn red and flash.

   I think the reason why your getting better tracking is that you might have done a better job in polar aligning you scope. Also the difference between Solar, and Sidereal rates is 4 minutes in 24 hours, so unless your doing long exposure astrophotography or observing an object over many hours you wouldn't see the drift. The difference in the rate that the planet are moves in also very small and you don't need a different tracking  rate. Only the Moon has difference in rate that you can easily see and it moves it's diameter against the background stars in about  an hour.   Any short term drift is usually caused by poor polar alignment or something loose in the mount or motor connection.

 

                      - Dave  

 

Dave, thank you very much for your response! Although, it isn't exactly what I was hoping for, if you know what I mean! As a newbie to this type of equipment, I must defer to your experience. At any rate, here are some points to ponder:

 

1.) Your comment about polar alignment is a valid one, although, I always set the scope up the same way and I don't think my polar alignment is better or worse in this case or at least not by much. And yet, I will not claim to get it perfect every time. Only that the amount of drift has always been consistent.

 

2.) So noted on the solar and sidereal rates, so not really an issue. Which would explain why I experienced the same drift for solar system objects and stellar.

 

3.) I did double check to make sure the mechanical connection from the motor to the RA shaft was tight, and also to make sure the clutch was tight. That all seems good.

 

4.) I am now baffled as to why the drift APPEARED to diminish as I adjusted the pot. Wishful thinking maybe?

 

For Scott: Not sure now if this thread is really beneficial for what I thought it might be. I will probably do some more experimenting to verify what I thought I saw, and add my observations to this thread.

 

Thank you guys for your interest and response!

 

Best regards!

 

CB

[DAVIDG]

 CB, 

 You can confirm that your unit uses a crystal vs a resistor/capacitor as a  time base  by removing the small circuit board that the switches are mounted too. The crystal will be  thin silver metal rectangle  about 3/4" long and about 1/2" wide with two wires coming from it. It might have plastic insulation around it. Here is a link to what they typically look like http://media.digikey...1.05 SERIES.JPG

 If it uses a crystal as a time base then all the drives rates are done digitally and the only way to change them is to install a different crystal with a different frequency since there is a micro controller that is programmed  to make the needed pulses at the correct frequency to drive the motor uses the crystal frequency as a time base.

   Also these units are designed for certain mounts and motor combinations so a unit designed for say EQ-3 type mount may not work with say EQ-5 mount since the gearing on these mounts have different number of teeth on the RA gear.  So be sure you have the correct motor and controller for your mount.  

   If the motor and controller are correct,  and your close to having the scope polar aligned correctly when I have experienced drifting issues it has been a loose mechanical connection, especially with the  external clutches. If you hit the slewing buttons and the objective in the eyepiece doesn't move almost instantly then you have play or slippage some were in the system. 

 

                 - Dave 

Edited by DAVIDG, 27 September 2016 - 09:56 AM.

[evan9162]

Also, you need to watch the tracking for at least 20-30 minutes (or more), as the worm period of the CG4/EQ3 is 10 minutes.  During that 10 minute period, it may be slow or fast, depending on mechanical inaccuracies in the machining of the worm.  There may be slow spots or fast spots.  What matters is the overall drift in RA over the course of 1/2 hour or more.

 

The best place to track this is with a star at the meridian, at 0* declination.  If you are reasonably polar aligned, drift due to polar misalignment will be in declination.  Very long term drift would be due to improper RA tracking, and short term drift (especially if it's fast sometimes, and slow other times) is due to PE in the worm/worm gear.

[SeaBee1]

 CB, 

 You can confirm that your unit uses a crystal vs a resistor/capacitor as a  time base  by removing the small circuit board that the switches are mounted too. The crystal will be  thin silver metal rectangle  about 3/4" long and about 1/2" wide with two wires coming from it. It might have plastic insulation around it. Here is a link to what they typically look like http://media.digikey...1.05 SERIES.JPG

 If it uses a crystal as a time base then all the drives rates are done digitally and the only way to change them is to install a different crystal with teh different frequency since there is a micro controller that is programmed  to make the needed pulses at the correct frequency to drive the motor uses the crystal frequency as a time base.

   Also these units are designed for certain mounts and motor combinations so a unit designed for say EQ-3 type mount may not work with say EQ-5 mount since the gearing on these mounts have different number of teeth on the RA gear.  So be sure you have the correct motor and controller for your mount.  

   If the motor and controller are correct,  and your close to having the scope polar aligned correctly when I have experienced drifting issued it has been a loose mechanical connection, especially with the  external clutches. If you hit the slewing buttons and the objective in the eyepiece doesn't move almost instantly then you have play or slippage some were in the system. 

 

                 - Dave 

 

Hi Dave! I just looked per your suggestion... dad burnit... there's a crystal on the board... well... It would seem I only thought I had fixed it. I am pretty sure my polar alignments have been good. I am pretty sure that the clutches and all the mechanics are good. The unit is advertised as compatible with a CG-4 (EQ-3), which is what I am using. Slewing with the 8X button starts instantly.

 

And this only leads me to one conclusion: a defective unit that I can't return.

 

Such is life...

 

Thank you Sir for helping me sort this out!

 

Best regards!

 

CB

[SeaBee1]

Also, you need to watch the tracking for at least 20-30 minutes (or more), as the worm period of the CG4/EQ3 is 10 minutes.  During that 10 minute period, it may be slow or fast, depending on mechanical inaccuracies in the machining of the worm.  There may be slow spots or fast spots.  What matters is the overall drift in RA over the course of 1/2 hour or more.

 

The best place to track this is with a star at the meridian, at 0* declination.  If you are reasonably polar aligned, drift due to polar misalignment will be in declination.  Very long term drift would be due to improper RA tracking, and short term drift (especially if it's fast sometimes, and slow other times) is due to PE in the worm/worm gear.

 

Hello Evan! This is something I have not tried. Next clear night that I can get out, I will look into this.

 

Thank you for the info!

 

CB

[DAVIDG]

 If you were just looking at the motor shaft and not at a star when you tried the 8X slewing, it could still be something mechanically loose. Your motor is turning at a speed of around 1/10 rpm so a small amount of play can take a few minutes to get taken up and by that time the star has drifted out of the field.  You could also have play in the worm gear  that drives the main gear of the scope. Like I said a small amount of play can take  awhile to be taken up and the scope to start to track. So don't toss the controller just yet. The other  issue could be the plug for the motor. The unit uses a stepper motor which has four windings. If the plug was loose and only three winding were working the motor would still run, just slower then it should. If you put your hand on the motor  you should feel the pulses and they should be regular and smooth. If you feel it jump then you might have a bad connection at the plug. 

 

                  - Dave 

Edited by DAVIDG, 27 September 2016 - 09:57 AM.

[Geo.]

A couple of things come to mind. The EQ3-2's RA crown has 130 teeth. The CG-4's RA crown has 132 teeth. That's about a 1.5% error or 46' an hour.

 

I'm a bit surprised that Orion is still selling a stepper driver based on frequency dividers, when speed functions can be easily handled by the firmware coding. This greatly simplifies things.

 

[evan9162]

A couple of things come to mind. The EQ3-2's RA crown has 130 teeth. The CG-4's RA crown has 132 teeth.

 

Huh.  The mounts appear to be completely identical, wonder why they would make such a change between the two brands?

[SeaBee1]

 If you were just looking at the motor shaft and not at a star when you tried the 8X slewing, it could still be something mechanically loose. Your motor is turning at a speed of around 1/10 rpm so a small amount of play can take a few minutes to get taken up and by that time the star has drifted out of the field.  You could also have play in the worm gear  that drives the main gear of the scope. Like I said a small amount of play can take  awhile to be taken up and the scope to start to track. So don't toss the controller just yet. The other  issue could be the plug for the motor. The unit uses a stepper motor which has four windings. If the plug was loose and only three winding were working the motor would still run, just slower then it should. If you put your hand on the motor  you should feel the pulses and they should be regular and smooth. If you feel it jump then you might have a bad connection at the plug. 

 

                  - Dave 

 

I have checked this both on stellar and solar system objects, not observing the shaft, all slews have been instant. There is virtually no slop or backlash in the mechanics of the mount, this I am confident of.

 

The plug for the motor could very well be the issue. I have not checked this. However, I have checked the motor for operation while tracking and I could definitely feel the motor stepping. I did not notice any stalling or jumping, BUT, I did not do an extended check on this, only to verify that the motor was indeed stepping while tracking. I will look into this a bit further.

 

Thank you Dave for the info!

 

Best regards!

 

CB

[SeaBee1]

A couple of things come to mind. The EQ3-2's RA crown has 130 teeth. The CG-4's RA crown has 132 teeth. That's about a 1.5% error or 46' an hour.

 

I'm a bit surprised that Orion is still selling a stepper driver based on frequency dividers, when speed functions can be easily handled by the firmware coding. This greatly simplifies things.

 

P1015483 copy.jpg

 

Hi Geo! Forgive my newbishness here. How would 46 arc minutes difference appear visually? The reason I ask is this: as I observe, while the drift does not appear the same as if I did not have the RA drive installed, there is a noticeable drift over, say, a 2 minute time frame, from centered to edge of field using a 7mm eyepiece on a stellar object. Does that sound right?

 

Thanks!

 

Best regards!

 

CB

[SeaBee1]

 

A couple of things come to mind. The EQ3-2's RA crown has 130 teeth. The CG-4's RA crown has 132 teeth.

 

Huh.  The mounts appear to be completely identical, wonder why they would make such a change between the two brands?

 

 

And that is probably the $100 question!

 

Best regards!

 

CB

[DAVIDG]

 Jupiter is about 35 arc seconds in diameter, so you would see the star drift by about one Jupiter diameter in an hour if the drive so setup for 130 teeth on the RA gear vs 132. So much less then what you were seeing.

 

               - Dave 

[SeaBee1]

 Jupiter is about 35 arc seconds in diameter, so you would see the star drift by about one Jupiter diameter in an hour if the drive so setup for 130 teeth on the RA gear vs 132. So much less then what you were seeing.

 

               - Dave 

 

Oh my, no, the drift is way worse than that. Not sure what I am going to find. It may be a couple of weeks before I can do any more troubleshooting as my work schedule is becoming more brutal through the end of the month. I will be working the next 2 weeks without a night off, maybe longer. I will post any findings here, when I have something.

 

My sincere thanks to you and everyone else for the help!

 

Lots of things to check...

 

Best regards!

 

CB

[DaveJ]

No, a drift of over 60 TIMES Jupiter's diameter. DAVIDG mixed up arcseconds and arcminutes.

[DAVIDG]

 The only other crazy thing that comes to mind is the possibility is  that the North/South switch was in the South position which would run the drive backwards. 

 

                     - Dave 

[SeaBee1]

 The only other crazy thing that comes to mind is the possibility is  that the North/South switch was in the South position which would run the drive backwards. 

 

                     - Dave 

 

Yep, that was one of the first things I double checked when I noticed the problem. I even flipped the switch to see what would happen...

 

At this point, I am leaning on maybe a bad connection at the motor, but who knows   

 

I will try to check some things over the next few days if my schedule doesn't get too bad.

 

Thanks again!

 

CB