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Az Mount Pro Azimuth Motor replacement

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23 replies to this topic

#1 Eddgie

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Posted 05 December 2022 - 06:14 PM

First thing first.  Please do not respond with questions or comments until I have completed this, and there are about 15 pictures and some commentary. 

 

By not interrupting the flow, it will make it easier for others to follow this procedure if they ever have to replace a motor.

 

Before I get into that, some general thoughts on the Az Mount Pro design and engineering.

 

I greatly admire the design of this mount. It is compact and well laid out. All of the materials appear to be good quality.  The circuit board has good packaging and is well finished. 

 

The mount is mechanically a beautiful piece of work. The biggest upgrade vs the MiniTower pro is the azimuth axle bearing. The Minitower Pro used small needle bearings. This mount uses a large tapered bearing.  This bearing is by itself able to easily support the payload rating of the mount by a factor of 3 or 4 times. This would be the size bearing you might expect to see on a golf car front axle.  For this reason, there should be zero concern about having perfect balance in azimuth. The bearing is absolutely oversized for any load that you could put on it up to the load rating.  Why people obsess over the need to perfectly balance this mount is beyond me.   Previous to this Az Mount Pro, I had another one, and I ran my 8" f/2.8 scope on it whiteout a counterweight with no problems.  The only reason why azimuth balance would be important is if the mount  is not level or the tripod is deflecting and the motor stalls when it has to push the off balance weight up hill.  The Altitude balance would be more important and here, I would say that you want to be somewhat close. 

 

The motor mounting is elegant but unnecessarily complex. I will get to that when I am doing the photos.

 

About belt skipping.  I have heard people say that they heard the belt cogging. I can just about totally assure you that this is not happening. If you hear a sound like a belt cogging what you are hearing is the worm gear teeth being deflected out of the worm wheel and the rapid RumpRumpRump is the sound of the teeth on the worm gear skipping across the teeth of the worm wheel. This is from insufficient tension on the spring that holds the worm gear in mesh.  This spring should be kept fairly tight. I would say that one turn from motor stall is about as much as you should allow. If you go to far, if you are out of balance in DEC or you bump the mount in Az and it skips, you can damage the worm gear.

 

 

I have to resize every picture so I might not finish this today or even tomorrow, but I will get started today.

 

Again, please hold comments or questions so that the flow is un-interrupted. If you have a burning question, please PM me.
 

 

Thanks.



#2 Eddgie

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Posted 05 December 2022 - 06:22 PM

Step 1.  Remove the balance shaft lock collar, compression ring and the clutch. All come off counterclockwise.  Be aware that there is a washer behind the clutch and if you tip the mount towards this side, it can fall off.

 

Remove the four hex screws that hold the cover on to expose the top of the az axle and the retaining ring.

 

Cover removal.jpg


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#3 Eddgie

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Posted 05 December 2022 - 06:26 PM

Next, use your handset to rotate the mount so that the small hex head screw is at an angle that allows you to go in with a hex wrench and using a hex head wrench, loosen the screw that holds the bearing preload retaining ring. Because the head of this screw can be slightly below the level of the hole in the housing, I recommend one of the hex wrenches with the rounded splines at the long end because these let you come in at an angle. It is only necessary to back it out a turn. You can see my wrench in the picture.

 

Bering Retainer.jpg


Edited by Eddgie, 05 December 2022 - 06:27 PM.

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#4 Eddgie

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Posted 05 December 2022 - 06:29 PM

You will need a pin spanner wrench to remove the retaining ring. You can buy sets on Amazon.  Be sure that it has 90 degree tips and will open to about 1.5 inches.

 

 

Bearing retaining ring.jpg

 



#5 Eddgie

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Posted 05 December 2022 - 06:32 PM

Once the retaining ring is removed, turn the mount on to a side (remember the washer behind the clutch can fall out..) and pull the foot down a bit. It may be a bit snug, so just wiggle a bit and it should pull free, but don't use too much force. It is necessary to get this to come free but not with so much force that it can crack the bottom covers.

 

Base clearance.jpg


Edited by Eddgie, 05 December 2022 - 08:17 PM.


#6 Eddgie

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Posted 05 December 2022 - 06:38 PM

Now, remove the six hex head screws that hold the covers in place. Four on the U shaped motor case and four on the motor board/control panel. It will be necessary to partially remove the motorboard to extract the Azimuth axel and worm wheel.

 

Base cover removal.jpg



#7 Eddgie

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Posted 05 December 2022 - 06:41 PM

It will be necessary to pull the motorboard up out from the base. It is in a shallow slot so only about 10mm and it will pull up. You may need to side walk it out. It has to tip away from the axle to allow clearance for the worm wheel.

 

This done, the axle with worm and bearing can be extracted. This picture does not show the motor board tipped back, but that is because I put it back into the slot to avoid stress on the wiring. 

 

Axel removal.jpg


Edited by Eddgie, 05 December 2022 - 06:42 PM.


#8 Eddgie

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Posted 05 December 2022 - 06:44 PM

This is the board so you can see how it comes up slightly and twists out. There is enough slack in to tilt it away from the housing, but best to put it back in when the axle is out. 

 

 

Attached Thumbnails

  • motor board.jpg

Edited by Eddgie, 05 December 2022 - 06:45 PM.


#9 Eddgie

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Posted 05 December 2022 - 06:51 PM

In this picture you will see three holes.  For now, of interest are the two very small holes. These holes allow you loosen the set screws that hold the pivot pins for the motor assembly in place.

It is not necessary to remove these screws completely. Just back them out maybe a turn and a half. You will be able to see the tip of your wrench if you look into the bottom but the screw heads are mostly blind.  You can kind of see them with a flashlight, but if you fish around a bit, you should get your wrench into them.

 

Motor Pin Screw location.jpg

 

 



#10 Eddgie

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Posted 05 December 2022 - 06:56 PM

Next, using the larger hole, remove the grub screw in the deep hole that is used to access the worm gear tension spring and be prepared to back this out, but before you do, you want to be looking into the mount at the spring.  Grasp the spring with your fingers to keep it from falling into the housing and then back the adjuster out from the housing until you can get the spring off of its shoulder and put it aside.

 

Gear lash tension spring.jpg

 

 



#11 Eddgie

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Posted 05 December 2022 - 07:03 PM

Now we are getting into the tedious part of the job. As I said in my first post, while the design here is quite elegant, it seems (to me) to be unnecessarily complex. I have worked on a great variety of electro-mechanical devices and for the life of my, I can't figure out why they chose this particular way to mount the motor/worm assembly. I think it could have been easier, but it is what it is. 

 

 

Plugs removed.jpg

Note that after the plugs are removed, you can see the pivot pin bearings. Sadly, these bearings have to be backed out to remove the assembly. It is not difficult, but it is tedious. The next step will show you how to proceed but getting these rings out is the goal.

 

 

 



#12 Eddgie

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Posted 05 December 2022 - 07:06 PM

The bearings retainers you can see in the photo above are held in place by set screws located inside the base. There is one on either side of the motor assembly. I am just going to call them Left and Right, but they have no real designation.

 

Do not completely remove the screws. Just back them out a turn or a turn and a half. 

 

Left side:

 

left bearing retaining ring.jpg



#13 Eddgie

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Posted 05 December 2022 - 07:07 PM

Right side:

 

Right bearing retaining ring.jpg



#14 Eddgie

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Posted 05 December 2022 - 07:12 PM

I should say this before going any further.  I tried to get these pins out without having to do this but I was unsuccessful. I used a powerful magnet on the side of a hex wrench and attempted to get the pins out from the side by touching only the pin and pulling it out from the side through the bearing, but I was unsuccessful doing this. This means that I am going to proceed by removing the bearings.

 

To remove the bearings, use a pin wrench (I doubt that it is essential) to loosen the bearing retaining ring and then I used a ball point pen to back both of the bearings out of the sides.

 

 

Attached Thumbnails

  • Bearing retaining ring.jpg

Edited by Eddgie, 05 December 2022 - 07:16 PM.


#15 Eddgie

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Posted 05 December 2022 - 07:24 PM

Once the retaining rings are clear, the motor is almost ready to come out, but to get it out, the pins on both ends need to be removed. There is not enough clearance if you just remove one or the other. Both have to come out. 

 

 

The best way to do this is to grasp the motor worm assembly and move it along the axis so that the casting pushes the bearings out towards the side. This will just loosen them and will not push them far enough out. It may also be necessary to use a thin blades screwdriver to work separate bearings from the carrier casting.  You will notice that the casting has a round protrusion on either side that will go into the bearing hole and just keep working them until they are as far into the hole as possible.

 

Be aware that there is a small bronze bearing on either axle pin.  In this picture you can see the bronze bearing and the pin.  Again, this is rather fiddly but with some patience you will get the bearings pretty far into the holes. 

 

Brone bearing.jpg


Edited by Eddgie, 05 December 2022 - 07:24 PM.


#16 Eddgie

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Posted 05 December 2022 - 07:29 PM

If you are lucky, you will be able to get the bearing to come off of the pivot pin and fish it out with a small hex wrench. 

 

If not, you may be successful getting it out with a magnetic retrieval tool. I could not find mine, so I McGivered one using some powerful magnets on the side of a hex wrench to get the pins out. I don't know if this will work for you but the goal is to get both pivot pins out. Both must be out to remove the assembly.

 

McGiver .jpg



#17 Eddgie

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Posted 05 December 2022 - 07:33 PM

That was the tedious part. From here out, it is smooth sailing and the great news is that assembly is very straight forward.

 

Now that you have the pins, the motor assembly will lift out. Here you may want to go back to the motor board and remove connector and start the connector through the holes in the housing. 

 

 

Motor free.jpg

 



#18 Eddgie

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Posted 05 December 2022 - 07:35 PM

Cables connector simply pulls out of the plug. Two holes, one by the board, and one down in the motor assembly hole visible in the picture above.

 

Connector.jpg


Edited by Eddgie, 05 December 2022 - 07:35 PM.


#19 Eddgie

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Posted 05 December 2022 - 07:40 PM

Almost done.  The motor is held on to the casting by two screws. These are slotted so that the belt tension can be adjusted so remember that for re-assembly.

 

Motor Screws.jpg



#20 Eddgie

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Posted 05 December 2022 - 07:46 PM

Congratulations.

 

 

Congratulations.jpg

 

This is not a difficult job, but as can be seen, the method used for the pivot seems overly complex. I think it could have been done in a manner that would have allowed very easy motor removal, but I think someone was just showing us what interesting engineering would look like. Maybe there is a reason, but I have worked on hundreds of different electro-mechanical devices in my lifetime (many years of that professionally) and I am at a loss as to why it was made in such a complex fashion.

You are done now though and I open this up for questions. 

 

I will probably do a different thread on re-assembly to touch on the adjustments for the motor/worm lateral play, but for now, this is everything you should need to know to get the motor out. 

 

I hope this is useful for someone. 

 


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#21 bthrel

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Posted 05 December 2022 - 07:49 PM

Looking forward to part two, especially the adjustment part. excellent tutorial

 

Thanks

 

Brian


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#22 Eddgie

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Posted 05 December 2022 - 07:51 PM

And as for my absolute certainty about belts slipping, it is almost impossible to back drive a worm gear.  If you hear ratcheting from your mount for any reason, I can guarantee it is the worm gear deflecting out of mesh with the worm wheel. If you every hear this sound, it is vital that you immediately increase the tension using the provided adjustments. The tension should never be allowed to be so loose as to have the gears come out of mesh when bumped or used in normal load ranges. 

 

Note that when you adjust the tension, you are also closing the gap between the end of the tensioner screw and the motor/worm assembly. You want that end of the screw to be a hard stop for the motor assembly pivot range so that it can't pivot so far as to un-mesh the gears. You should never back that screw down so much that the worm is not overlapping the teeth in the wheel when you manually compress the spring. 

 

(I say this because many people that have been troubleshooting the jump in the view have been backing out these screws. As I said elsewhere, I do not think this is a worm adjustment issue. I think it is the board or the stepper. If you have backed out your screw in an attempt to fix the jumping, then my advice is to tighten it all of the way in, then turn it out a turn or a turn and a half a most. This post can't act as a stop if it is backed away too far.)


Edited by Eddgie, 05 December 2022 - 07:56 PM.


#23 ngc7319_20

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Posted 05 December 2022 - 08:19 PM

Fantastic how-to manual!  Thanks!!!

 

The obvious question... why are you replacing the azimuth motor?  What happened to it?  What could be done to prevent the issue or extend the motor life?

 

....Why people obsess over the need to perfectly balance this mount is beyond me.   Previous to this Az Mount Pro, I had another one, and I ran my 8" f/2.8 scope on it whiteout a counterweight with no problems.  The only reason why azimuth balance would be important is if the mount  is not level or the tripod is deflecting and the motor stalls when it has to push the off balance weight up hill. 

 

I usually set up on grass, and I feel that having a good azimuth balance gives me more accurate go-to.



#24 Eddgie

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Posted 05 December 2022 - 09:39 PM

Several people (including myself) have mounts that do not track smoothly that we can see when viewing at high powers.  The mounts develop a "tick" where it runs for a second or two, then jumps, then runs for a second or two, the jumps and on and on.

 

Most of the attempts to fix this have focused on balance and playing with the worm gear mesh tension spring. I tried all of those things but could not make any improvement, and really had as strong doubt that this had anything to do with the problem.

 

One of the things I wanted to check was belt tension but when I went to do this, I could feel the jump in the stepper motor. I could feel some micro steps than the big jump.

 

I probed the input to the stepper and sent it to iOptron because I was not sure if it was the motor driver or the stepper.  They showed it to an engineer and he said he thought it was the stepper. I removed the stepper and the motor driver board and sent them to iOptron and they will investigate further.

 

If the problem is the stepper motor, then others that are out of warranty will be able to diagnose the problem and order a stepper and replace it.


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