Noisy EXOS 2 PMC8?


Steve Siedentop
 

Moving to a new thread with a relevant subject line to facilitate further discussion, searches, organization, etc.

Question from Pete Turner...

How loud is the EXOS2GTmount with PMC-8?  The videos that I have viewed show it to be very quiet.  The mount I got is anything but. It sounds a lot like my old Celestron CG5-GT.


Response from Steve

Hi Pete -

When ES visited our astronomy club to demo the EXOS 2 PMC8 a couple of years ago, I definitely remember it being quieter than my CG5 which sounded not quite like a coffee grinder.

Any chance you could post a video or just audio?

I don't recall Brian's EXOS 2 PMC8 being terribly loud either when we've been out.  Brian, thoughts?

-Steve


Scott - Moron Astronomer
 

My first one was noisy. There was something wrong with it. Sent it back and it came back smooth and quiet.


Wes Mcdonald
 

The exosII is very quiet.  A smooth humming sound with musical qualities when you manually rotate the axes.  If it is making a hacking noise it means the motor is stalling.  Mine did that under certain circumstances.  The cause was binding in the gear train owing to the mesh adjustment.  If you are hearing loud hacking noises then that is the root cause of your inability to align...or do anything.  If your scope is way out of balance you could also cause this stalling to occur.  Have you balanced things?  How heavy is the scope you have on it? If you are balanced and the mount is hacking instead of humming then you need to adjust the gear mesh or send it back for adjustment.

Wes


Peter Turner
 

I have attached two videos to show slewing in each direction.  The total weight of the FCD-100 plus eyepiece and finder scope I estimate to be 22-23 pounds.  The mount is balanced.

Pete


Wes Mcdonald
 

Hi Peter

Well I can't say it sounds bad.  Its hard to hear but it is not hacking the way mine did when it stalled.  If you use the keypad to move it around, with rate set to 9, do you hear the musical notes step up as it goes through a series of ascending rates and then down again as it stops?

Now this is the part you probably don't want to hear.  When I tried to use it with a scope that weighed in at about 23# I had some pointing problems.  But I never really used it much to see was it my head or the mount.  I did get a pretty good alignment once with the heavy scope using a polemaster.  My overall stick time with the sky and this mount has just been too danged limited.

With any luck I will get some outside stick time this wednesday.  Then next week I'm heading out to a dark sky site for a few days for more fun I hope.  I will wring out the alignment procedure then.  I have to tell you though I have spoken to Jerry about alignment and am satisfied the thing works just fine -- notwithstanding my own problems.  Lots of others are using this thing.  In the end if you just cannot get it to do then it should go back for a checkup.

One thing I did the other day in my study was to run through the alignment procedure a number of times.  While I don't like the way it selects stars for me, it always went through and after the third star solved for the mount model matrix.  After that it moved around per plan, although I can't vouch for its accuracy.  Jerry published a presentation he made at AHSP earlier this month (its in the groups.io) in which he says in the video goto accuracy should be achievable to 5 arc minutes.  That should be plenty to have things in the eyepiece.   Wednesday I won't have my polemaster so I will be relying on the 2 and 3 star alignment algorithm.  I hope I can see the danged stars with the full moon and obstructions where I am.

Up to now my primary scope/mount has been a Meade LX200 10" SCT fork mount.  It took me a long time to learn to get a polar alignment with it on a wedge.  In the end I had to resort to a polemaster which did the trick.  With the EXOS II the polemaster will allow you to get a very good polar alignment.  I believe the correct approach is to do the polar alignment with the polemaster then set the mount precisely at its home position, recycle the PMC and explorestars and then do a one or more star alignment to clean up any little errors.  At least I think that is what worked for me with my heavy old Newtonian on the EXOS II.  I do remember the tracking error was very small but frankly I can't remember if the gotos were great or not.  In my view these two performance parameters are related and interdependent buy one is not sufficient for the other.  Atleast a great PA still might have bad gotos if the mount is not precisely aware of its orientation.

By the way is the timebase for your computer right on?  Need for it to be pretty close to on.

TLDR.  Lots of BS, not much light.

Wes.


Peter Turner
 

Wes,

Unfortunately the videos don't do the noise justice on the email.  They are much louder on my iphone.  I'm going to record my CG5-GT tomorrow and compare them.

What do you mean by "solving for the mount model matrix".  I did not get any messages after I hit Synch on the third star.

With respect to your questions about polar alignment; it was a visual alignment rather than using the polar scope.  It was difficult to see Polaris in the polar scope as I think it was probably too early in the evening.  I'm still trying to get the hang of the polar scope as it's a little different than doing it on my Celestron mounts.  It was also my impression that polar alignment wasn't that critical for visual observing. My time on the Android tablet agrees with my iphone as it gets its clock from the network.  I suppose after I connect to PMC-Eight-xx the time could vary a little as there is no internet connection.

I'm going to use the mount again Tuesday night.  We had some clouds tonight and last night, however the forecast for tomorrow is clear.

Pete


Wes Mcdonald
 

Peter

If you go to settings there is  button to show the alignment data.  It starts out as all zeros and is updated after the last star is synched.  You can do this inside and watch the result.  Just press sync each time the procedure moves the mount to the next star.  There is also a button to reset alignment data which restore it to all zeros.  These are what I meant by a mount model matrix. Alignment calculates a transformation matrix which converts the desired pointing angle into the proper mount position given there is error in mechanical alignment.   If the mount were perfectly polar aligned and level and the time were perfectly known by explorestars then the only transform needed would be motor count to ra-dec -- a transform that could be hard coded into the software.  No doubt this transform is known and used initially by the explorestars.  But with errors in polar alignment and time one has to apply corrections.  This is what the 3 star computes.  

I agree peeping through the polar scope is next to impossible for me.  That is one reason why I sprang for a polemaster.  Look it up, it is really the way to go .  You get polar aligned in 10 minutes and use your computer screen.  Easy.  The standard CGEM mounting adapter is correct for the EXOS II.

Coarse alignment is OK for visual but without pretty good alignment gotos will not be in the eyepiece.  And dim objects cannot be seen in the finder.  Thus a pretty good coarse align is needed.  If the coarse alignment is fair, and you can find the object in the finder, then after centering in the eyepiece the object will hang out there  pretty good as the rates of tracking are right....but since the PA is not spot on the object will be sliding slowly out and you have to adjust both the DEC and RA  position to keep centered.  

So this is the real problem with doing a 2 or three star alignment. When you start out with a plopped down mount poorly aligned it is easy to have 5 or more degrees of error.  That  of course puts any alignment star out of the main eyepiece FOV. Then you have to use the finder and identify the correct star and use the controls to move it to the center of the eyepiece.   This needs to be pretty danged accurate for the synch to solve for that matrix.  It is best to have a illuminated crosshair eyepiece, though for visual after alignment one can do well enough if you eyeball center with a pretty high power eyepiece.  I like to use something like magnification of 100 which is a 26mm in my lx200.  (You know the magnification = scope focal length / eyepiece focal length.)  So the first challenge is to identify the correct star in the finder field of view and the second is to get it close to the dead center of the eyepiece.  BTW sometimes I go all the way out to very low power (like 40 or 50) at first, center that and change eyepieces to get closer.  In my experience if you want your gotos to place you in the eyepiece FOV you need to take the time to center the star in the main eyepiece and not just in the finder...the finder just has too much error relative to the  main telescope line of sight.  Do this three times with three stars and things should be plenty good for visual.  

Your cell phone can really help with your coarse  alignment.  Use it as a digital level to set your scope at the correct angle = your lattitude.  Don't use only the mount scale it is not accurate.  Use the phone's compass  to point things to true north...make sure that is correct and not magnetic.  When that is all about right Polaris will be in view of a lowish power eyepiece ( mount in home position PMC8 off).  You will know you have polaris by a couple of means.  First it will be the brightest star in the eyepiece and second, if you boost the mag enough you will see it is a binary (Polaris B -- actually it is a ternary system but you can't see the other).  Seems to me the companion is blueish in color and pretty close to Polaris A .  As polaris is close to the NCP you can rotate the scope in RA and polaris should rotate in a circle which stays in the FOV of a low power eyepiece.  When this works you are pretty danged good.  If you can see polaris in the eyepiece but it rotates out you are still pretty good.  So you can fiddle with your ALT and AZ mount adjustments to make it rotate better  or just set the mount at home and turn on the PMC8 and run the 2 or 3 star alignment.

A trick I learned to do recently involves the program Sky Safari.  Version 5 for Android is free.  Load it.  It gives you this incredible virtual reality view of the sky.  With my Meade I can place the phone on the wedge which is normal to the mount orientation and adjust the AZ-EL mount knobs to center polaris in the virtual reality screen.  That only happens when the elevation and azimuth of the wedge are pretty danged close to the NCP.   So that's all well and good if you have such a surface -- it's sort of like using the polar scope but it is all virtual and quite easy to do.  That is all well and good when there is a flat surface normal ot the desired line of sight but with our mount this is not the case.  Perhaps you can find some edge of the telescope tube to align the phone with.  Worst case you can stand behind the scope and just sight along it using the Sky Safari virtual reality display as a guide.  Being behind the scope is a pretty good way to get things toward true north using the cell phone.

Good luck.   This all just takes some practice.
Wes


Bert Garrison
 

Not to go off topic...

+1 for the Polemaster!  I have 3 mounts and one Polemaster camera. The adapters they sell make it so easy to move it around from mount to mount.  Every adapter they sell (or at least the ones I bought) comes with a cap that replaces the camera when removed!

Great post Wes!


Steve Siedentop
 

Hi Peter -

To add to the discussion, the PoleMaster camera is a great device for speeding up the process of obtaining an accurate polar alignment.  It's not more accurate than other methods, but it's a lot faster and doesn't require you to get on your knees.  I didn't know the ground was always soggy in Georgia until I started learning how to polar align an equatorial mount.

But...I wouldn't recommend a PoleMaster to someone who isn't imaging.  It's absolutely great to have it and I love mine, but if you don't have a camera in your scope, you don't need it, so don't feel you need to rush out and buy yet another piece of astro equipment to be able to enjoy your mount.

This will make the imagers squirm a bit, but you can quickly "polar-enough" align your mount by centering Polaris in a high magnification eyepiece.  This will get you, at most, approximately half a degree from celestial pole, which is more than sufficient for visual observing with modern goto systems.  Particularly so with ExploreStars which dynamically points both axes to keep the object centered in the eyepiece.

-Steve


Steve Siedentop
 

Back to your noise issue...

Without looking at your mount, it sounds like your mount is adjusted with a really tight worm/ring gear mesh.  The PMC8 uses stepper motors so they'll power through and stop when they can't rather than burning out the electronics like the server motors on other mounts I've owned.

That being said, if you want to adjust some of that noise out, here's a good video that explains how to do that.  The presenter is using a Celestron CG4 mount, but the design is the same as are the concepts of adjustment.  Make the adjustments without a scope or counterweights on the mount.  Also, do so with very small turns of the push/pull bolts involved (that will make sense when you watch the video).  You'll find that it's a fine balance between a quiet mount with some backlash and a noisy mount with almost no backlash.  I prefer something in the middle and adjust my mounts to that preference.

Of course, you can always send it back for adjustment.  However, adjusting your mount is a good skill to have regardless of what mount you own.

https://www.youtube.com/watch?v=sqwVBIkcCjU

-Steve


Scott - Moron Astronomer
 

Steve,

I hope to image at some point so maybe PoleMaster would be a worthwhile investment. Even so, I cannot get the GOTO to work and never have in the year or so I've had my PMC-8. Do you think the PoleMaster would help with that issue?

Scott


Chip Louie <chiplouie@...>
 

Hi Scott,

For the best GOTO accuracy most EQ mounts need only a few bits of information to reliably center an object from a GOTO command. The mount needs to be reasonably well aligned mechanically with the north celestial pole, latitude & longitude information must be correct and very importantly - in the correct format for the system - and the time must be accurate and again in the correct format for the system. For the most part you can easily get the location and time information from your smartphone using one of the many downloadable free GPS location apps. That said the PoleMaster ia an outstanding piece of gear for achieving very accurate polar alignment for imaging or for those who prefer accurate GOTOs. If you are using the mount in PUSH-TO mode and can starhop the PoleMaster is overkill. A trick I show a lot of people without polar scopes is to use a planetarium program and simply hold the smartphone to the RA axis of the mount where the polar scope would go and then center Polaris on the screen, BINGO, close enough for PUSH-TO visual use. Another way to get a reasonably close polar alignment is to level the telescope in RA and DEC using a bubble level on the mount head then just adjust the mount using the ALT and AZ knobs to point the main scope at Polaris using a crosshair eyepiece. This also results in close enough for PUSH-TO visual use. 

Chip

Here is my PoleMaster on an ADM universal prototype mount. 

    

 


 

 


Peter Turner
 
Edited

Thanks to all of you for your suggestions.  I forgot about mounts being off on the latitude scale.  As an example I live at 33 degrees north and my CG5-GT is at 40 degrees north. I'll rotate the mount up and down to find polaris tonight. Since I've always aligned to Polaris with my compass and a quick view through the mount, I don't think I'll be getting the Polemaster until I do more AP.

BTW:  I recorded the sound the scope makes using a recording app rather than video.  I have attached it here.  The second half of the recording is louder than the first half because the alignment routine went to a new star and reversed direction.  Also, I used a decibel meter on the mount from about 3 feet away.  It was 75.9db.  As a comparison, my CG5-GT was 80.1 db.  Although there is a 4.2db difference between the EXOS-2GT w PMC-8 and the CG5-GT, when listening live there doesn't appear to be much difference. 80 decibels is twice as loud as 70db.  For example 80db is equal to: Garbage disposal, dishwasher, average factory, freight train (at 15 meters). . Possible ear damage with 8 hour exposure. 70db is equal to: Passenger car at 65 mph at 25 ft (77 dB); freeway at 50 ft from pavement edge 10 a.m. (76 dB). Living room music (76 dB); radio or TV-audio, vacuum cleaner (70 dB). Noise in the upper 70 decibels is annoyingly loud to some people.


 

Peter,

One more vote towards "Screaming ain't normal".
 
I've had mechanical issues with my EXOS-2, but noise wasn't on the list.  Depending on the speed of the slew, mine is anywhere from almost silent, to a very reasonable whirr.

Best thing is to call ES Customer Service and have a chat with them.  They do try to help with both advice and repair as necessary. 

I've had the covers off and have been through the ajustment routine for other reasons.  I agree with Steve that the CG4 in the video is conceptually similar to the EXOS2 as far as the worm goes, but our mount is a belt drive.  You can't get to the adjustment capscrews on the worm block until you've gotten the motor clamshell open and the motor off its belt and removed - only then are they exposed. 

If you do decide to open it up and do an adjustment, the screws holding my motor clamshell together were Philips #1, and a 100mm driver was required to reach some of them.   The hex keys that came with my mount were fine for everything else. 

The motor is not held in place by the screws visible inside the motor clamshell, rather by a large hex capscrew countersunk deep in the mount casting,  just above your rear (Up) latitude adjustment screw.    When the screw is removed, the motor can be gently  tipped and the belt slid off its pulley.    With the motor removed, you'll see the three adjustment capscrews of the worm block.   The two outside screws and the middle one work against each other to position the block and lock it in place.   Lots of advice and caveats around on how to do that, and I know ES can send you instructions for that. 

Hope this helps


- Bob



On Tue, Sep 25, 2018, at 8:06 PM, Peter Turner via Groups.Io wrote:
Thanks to all of you for your suggestions.  I forgot about mounts being off on the latitude scale.  As an example I live at 33 degrees north and my CG5-GT is at 40 degrees north. I'll rotate the mount up and down to find polaris tonight. Since I've always aligned to Polaris with my compass and a quick view through the mount, I don't think I'll be getting the Polemaster until I do more AP.

BTW:  I recorded the sound the scope makes using a recording app rather than video.  I have attached it here.  The second half of the recording is louder than the first half because the alignment routine went to a new star and reversed direction.  Also, I used a decibel meter on the mount from about 3 feet away.  It was 75.9db.  As a comparison, my CG5-GT was 80.1 db.  Although there is a 4.2db difference between the EXOS-2GT w PMC-8 and the CG5-GT, when listening live there doesn't appear to be much difference. 80 decibels is twice as loud as 70db.  For example 80db is equal to: Garbage disposal, dishwasher, average factory, freight train (at 15 meters). . Possible ear damage with 8 hour exposure. 70db is equal to: Passenger car at 65 mph at 25 ft (77 dB); freeway at 50 ft from pavement edge 10 a.m. (76 dB). Living room music (76 dB); radio or TV-audio, vacuum cleaner (70 dB). Noise in the upper 70 decibels is annoyingly loud to some people.



Email had 2 attachments:

  • EXOS 2GT recording.wav
      5.3M (audio/wav)
  • EXOS 2GT recording.wav
      5.3M (audio/wav)


Brian Tucker <wd4dx@...>
 

Mine has always been very quiet.  I hear the trademark sound of the motors "singing" when slewing, but it's never had a grinding noise at all.


Peter Turner
 

This comment is a little off the noise issue, however I think I'm going to call ES Customer Service but plan to wait a day or two and use the mount more. I definitely don't want to take the mount apart while it is under warranty.

Last night I got a better polar alignment, but was still unable to see Polaris in the polar scope.  I then used Steve Siedentop's method (which is much more user friendly than a polar scope) and was able to center Polaris. FYI: to get the elevation correct I used the front and back knobs while keeping the mount in the "Park" position. To center it I usedthe twist knobs on either side to center the star and did not use the direction arrows on the tablet. Note to Wes: The resulting elevation was 40 rather than the normal 33 for Phoenix. I going to use a different level to see if the mount's level is causing the elevation to be so far off.

After performing a three star alignment, I constantly got different objects in my finder scope but not the eyepiece.  The average distance from the 8x50 finder's center point was about halfway to the edge of the objective. My finder eyepiece is a 15mm, 1.25" which provides a magnification of 63 with a 58 degree field of view. I do have a 25mm plossl which has a mag of 38.  However it's FOV is only 40 so I rarely use it any more. One thing I am going to do is use my reticle eyepiece to center polaris if I can't view it in the polar scope tonight.

Brian, I hear the motors singing but only if I'm moving the mount at a rate 9, which I rarely do when getting the alignment correct.  When the mount is slewing to an alignment star the motors do not sing.

Pete


Wes Mcdonald
 

Peter

There is something amiss with your calcs.  An 8x50 finder has a focal length probably between 160 and 200 mm. A 15mm eyepiece would have a mag of between 10 and 15.  The fov of a polosi eyepiece would then be it's apparent fov, say 50 degrees, divided by the magnification in this case about 5 to 3.5 degrees.  Perhaps you meant your main scope was at magnification 60?  In that case your 15mm would have about .8 degree fov.  

The following assumes you meant the 15mm was in your main scope.  If the Polaris is out to about a third of the finder then it is about a degree off of center.  That error is about just outside the 15mm eyepiece fov in your main scope (given numbers above). Note that if you used the 25 mm you would have a larger fov than the 15mm even though the apparent fov is less.  That's the eyepiece I would use to get things rolling along.  In fact I would use a 32 or 40 if you have one.  You can buy Meade series 4000 eyepieces for a song and they are decent for the money.  All are about 50 degrees apparent fov....not high tech.  Obvious you can spend a lot more and probably should as you advance.  In fact for shits and grins just to get a couple of low mag eyepieces you might pick up some really really cheap Meade MA eyepieces.  People please don't flame me I know they are very low end but we are talking alignment here.  

If your scope is a 7-8 f# you are going to want some low power eyepieces to view stuff like the double cluster.  Once you get going you.migjt get you some explorescientific 80degree boys at 30-40mm FL.

A telescope is very similar to a boat when it comes to money disappearing.  Haha.  If you want to keep your kids Out of trouble introduce them to astronomy...no money for anything else!

It does not surprise me the elevation scale is off.  That's why it's best to use a digital level like your phone app. But it would be good to get the mount level.  I have found the bubble level is about right...it's difficult to find surfaces to check level on.

The moon was full last night so stars were no doubt tough to see.  Next week things will be way easier.

I finally had a chance to listen to your mount.  Still not sure about it. It seems loud and i must say mine is not objectionable loud...in fact my daughter when she first heard it at the last star party remarked on how soft it was.  So yours is probably not right.  As others have pointed out it is not difficult to adjust.  When I had to do mine I got permission from es to do it and not void the warranty.  It's just faster.  But it is a bit of a pain.

Wes