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Reworking an old Meade Starfinder mount

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#1 Garyth64

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Posted 20 October 2018 - 10:50 AM

A few years ago I picked up an old Meade Starfinder mount.  It’s the one that has tapered housings on each axis.  It had 1" shafts and a CD.  I thought it would be good for my 6" and smaller scopes.

I soon found out that the CD didn’t work.  The mother board was bad.  So it got placed in a corner of the garage.  (Not as punishment, but just to be out of the way.)

 

file photo.jpg

. . . file photo

 

A couple of months ago, I came across a declination tangent arm for this mount.  After I installed it, I was still faced with a CD that didn’t work.  I wanted a mount to help take the work load off of my CG5 with dual axis controls.

 

tangent arm.jpg

 

As of this writing, I’m having the CD assembly reworked.

 

More to come . . .


Edited by Garyth64, 20 October 2018 - 10:51 AM.

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#2 Garyth64

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Posted 20 October 2018 - 10:54 AM

There was a lot of drag on the shafts.  It took a lot of effort to rotate either shafts.  So I took it all apart, and it did come apart very easily.
I found a black grease on the plastic bushings, and cleaned it all up.  I replaced the old grease with some pink stuff my dad had.  That didn’t work, there was still too much friction.  I took it all apart again and cleaned up the pink stuff.  Just for the heck of it, when I reassembled it this time, I didn’t put anything on the bushings at all.  It actually seemed to help, but still not good enough, and took it all apart once again. 
When I removed the bushings and cleaned the housing, I noticed that there were some dimples made with a punch where the bushings sat.  I guess these were to keep the bushings in place.  I felt that they were pinching the bushing and causing too much friction, so I filed them smooth.
After putting it all back together, I noticed a big difference in the shaft movement.  It was much better.  And after another disassembly I put a little light weight oil on the bushings.  That made another big improvement.
I’d like to replace the plastic bushings with metal ones.

 

This mount has a large RA setting circle, but a small DEC circle.  I had larger 6" setting circle so I replaced the small one.  I came up with a bushing with a 1" ID, and a 1-1/2" OD, and it will work fine.  A minor problem was that there wasn’t an indicator for the large DEC circle.  I made a 6" semicircle, drilled and tapped a hole on the housing, and bolted the new indicator to the housing.

 

setting circles.jpg

drill and tap.jpg

dec indicator plate.jpg

 

More to come . . .


Edited by Garyth64, 20 October 2018 - 09:16 PM.

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#3 Garyth64

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Posted 20 October 2018 - 10:57 AM

The mount head has a built in curve for an 8" to 10" scope.  That wasn’t going to work for my purposes, so I squared everything up.  Now all I have to do is attach different tube rings for the scope I’ll put on it.  (Caution, doing this is irreversible, and I don’t have a problem with that.)

 

Usually a Starfinder mount is found with a newt sitting on it.  I wanted to use it for some of my refractors too, and set it on top of one of my homemade tripods.  But the way the mount hub is made it is for sitting in a metal pier.  To sit on top of the tripod, I had to drill and tap a hole up thru the hub.  Piece of cake, and it works as intended.

 

I also made an declination adjustment.

 

dec adjustment.jpg

 

The ring gear assembly has 3 small lock screws that hold it onto the 1" shaft.  In getting them loose, I thought I was going to break the allen wrench.  They are also set in pretty deep.  I replace them with longer ones.

 

new set screws.jpg

 

I’ve always like the looks of this mount, and it seems very solid as long as it isn’t overloaded.  But that can be said for many other mounts.  Hopefully, these modifications are for the better, and think that I brought an old mount back to life.

 

I am looking forward to installing the new CD, and making an update.


Edited by Garyth64, 20 October 2018 - 09:18 PM.

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#4 Garyth64

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Posted 20 October 2018 - 12:10 PM

In having the CD reworked, the original MB and motor is being replaced.  It will have an Arduino Uno 3 and a Adafruit Motor Shield.  The stepper motor is an Airpax K82256-P2, which is rewired to operate in parallel bipolar mode. The programming is being done with Arduino IDE.

The CD will also be able to slew a little back and forth to center an object like on an old CG5.

 

I have no idea of what all that is smile.gif


Edited by Garyth64, 20 October 2018 - 12:11 PM.


#5 Tenacious

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Posted 20 October 2018 - 02:32 PM

Nice find.  I like the mods you've made, especially the larger dec SC.

 

I have a 6", f/8 Newtonian (Harden Optical) with great optics that is Dob mounted.  It is very comfortable, easy to use and one trip through the back door.  Occasionally though, I think it would be nice on a GEM that tracks (with rotating tube rings, of course).  Funny how my preference seems to be evolving toward equatorials.


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#6 jcricket

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Posted 20 October 2018 - 05:47 PM

Well done!

I didn't quite follow what you did to be able to make it mount to another hub. Any pics possible?



#7 Garyth64

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Posted 20 October 2018 - 09:31 PM

Well done!

I didn't quite follow what you did to be able to make it mount to another hub. Any pics possible?

I drilled and tapped a hole for a 5/16 bolt, that extends down thru the hub in the tripod.  The mount rests on a plate that holds the legs together.  You can see the plate in post 3 pic 1.

 

Maybe these pictures will help

 

bolt for hub 1.jpg

bolt for hub 2.jpg


Edited by Garyth64, 20 October 2018 - 09:57 PM.

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#8 apfever

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Posted 21 October 2018 - 08:27 AM

I also made an declination adjustment.

Latitude adjustment?



#9 jcricket

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Posted 21 October 2018 - 10:01 AM

I drilled and tapped a hole for a 5/16 bolt, that extends down thru the hub in the tripod.  The mount rests on a plate that holds the legs together.  You can see the plate in post 3 pic 1.

 

Maybe these pictures will help

 

attachicon.gif bolt for hub 1.jpg

attachicon.gif bolt for hub 2.jpg

Good idea!

Thanks for the pics!!!


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#10 chuck52

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Posted 21 October 2018 - 10:19 AM

I also like the mods you have made to your mount. I have been working on the same mount off and on for the last six months. My plan is to mount my Celestron 6 inch refractor on it. Removed the stock tube cradle and replacing with a flat plate .Replacing both ra and dec axis with stainless shafts. I will be using a 7 inch diameter aluminum pier (portable).I have not checked out the clock drive yet. It is also battery powered. Im thinking if its bad I will replace current motor with an ac version. Also looking at making a home brew declination drive. Cant wait to see more pictures with your update!


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#11 Garyth64

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Posted 21 October 2018 - 11:14 AM

Latitude adjustment?

Yes, when I want to make an alignment to my latitude, I can loosed the bolts, make the adjustment, and retighten everything. 


Edited by Garyth64, 21 October 2018 - 11:14 AM.


#12 jcricket

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Posted 21 October 2018 - 11:38 AM

I also like the mods you have made to your mount. I have been working on the same mount off and on for the last six months. My plan is to mount my Celestron 6 inch refractor on it. Removed the stock tube cradle and replacing with a flat plate .Replacing both ra and dec axis with stainless shafts. I will be using a 7 inch diameter aluminum pier (portable).I have not checked out the clock drive yet. It is also battery powered. Im thinking if its bad I will replace current motor with an ac version. Also looking at making a home brew declination drive. Cant wait to see more pictures with your update!

I used one of these mounts years ago with a D&G 5" f/12 refractor. I did find a different steel tube for the pier, but other than that I used it as a stock unit. It worked very well for that application. 


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#13 chuck52

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Posted 21 October 2018 - 01:43 PM

Posts regarding these mounts don't seem to come up very often. Reassuring to know the mount will handle a 5 inch f12. I had read somewhere that when sizing a pier it should be at least the same diameter as the objective in the scope.Dont know if its true or not but that's what I follow. Like Garyth64 I had looked into replacing plastic bushings with metal but abandoned that idea when trying to figure out how to align bore both ends of ra or dec casting. I really like the larger declination circle mod and the dec adjuster Garyth64 completed.Seeing this thread has sparked a renewed sense to get it done on my own mount.Fantastic!


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#14 Garyth64

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Posted 22 May 2019 - 06:26 PM

I got back to working on this mount.

 

The original mother board was fried, and the motor just wasn't working.

 

As you can see, there's new electronics and a new motor with a belt drive.  thanks George.  I can  use the 12v battery pack, or hook it up to my lawnmower battery.

 

new electronics 2.jpg

 

I am also able to make fine adjustments in the CD to keep objects centered in the fov with the use of those yellow buttons.

 

new electronics 1.jpg

 

 

This will be great for outreach programs, or moving around my yard.


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#15 steveob

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Posted 20 February 2020 - 08:30 PM

Hi Garyth64, I have the same mount, a second hand purchase from many years ago, happily takes my 8" Newtonian, and luckily it is nice and smooth on both axes. It came with the original Meade 6" Sonotube but I drilled through and mounted the dovetail saddle when I got the 8" as finding larger straps was impossible. This is easily removed for when using the Meade

 

Not so lucky, the motor never worked from day one. I tried on and off over the years, recently found a replacement power IC and re-soldered it to the board and got the motor running but there is no regulation on the speed, the motor spins way too fast, I estimate it will do a full rotation of the scope in about 51 minutes.....

 

Not knowing enough about electronics my dabbling goes no further.

 

I can rig up a bracket to mount a new motor to the existing gearbox, and I have a speed controller that I can put to use, what sort of rotation speed is needed to drive the worm gear?

 

I used the speed controller on the existing motor and at 4% on the speed controller the motor turns at approx. 600rpm, the worm gear then turned 1 revolution in 1min 54seconds.

 

There are 144 teeth on the main axis wheel, so if 1 revolution of the worm gear turns the wheel 1 tooth, 1min 54 seconds x 144 teeth = 1 axial revolution in 4.8 hours.

 

if the axis needs to turn 1 revolution in 24 hours to track objects then 24/4.8 = 5, meaning I need a motor that turns at 1/5 of 600rpm = 120rpm.

The no load speed of the original motor is 2700 rpm

 

Do my numbers make sense?

 

Any advice on what sort of motor would be possible to substitute, I guess if at 50% on the speed controller the motor turned 120rpm, that would be ideal as I would have the range to speed up or slow down the motor.

 

Thanks

 

Steve

 

speed controller
Album: Motor Drive
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#16 Garyth64

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Posted 20 February 2020 - 09:59 PM

I ended up buying an AC replacement original set up from another Starfinder mount.  It works just fine now.

The belt drive thing just wouldn't track, and I don't know why.  I'm no electronics guy.

 

If the gear has 144 teeth, you need a motor whose final output is 1/10 rpm.


Edited by Garyth64, 20 February 2020 - 10:00 PM.


#17 steveob

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Posted 21 February 2020 - 08:15 PM

Thanks Garyth64, I'll take a look at a possible replacement, and 1/10rpm sounds about right, it was doing 1 revolution in just under 2 minutes and I estimated it needed to be 5 times slower, ie 1 revolution in 10 minutes.
Thank you for your advice

#18 Tom Stock

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Posted 04 July 2021 - 07:04 AM

How is the project going?

 

I just purchased one of these old mounts. Its not in my hands yet but I'm going to rebuild it because I love friction clutches and setting circles.  The 6" dec circle will be a great project for my mini lathe and another fixed circle for the pointer is a great idea! 

 

I was really not excited about the DC drive, I'm assuming mine will be dead also.  I looked around in my parts bin and found a 1/10 RPM synchro ac motor.

 

One issue is a rusty and pitted dec shaft.

 

Is it possible to replace that shaft or is it pressed i to the saddle?

 

How is the tangent arm installed?

 

Thanks!


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#19 Garyth64

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Posted 04 July 2021 - 09:47 AM

With putting in an original AC CD, I've really had no problems with it.

 

The only little nuisance was getting the scope to balance.  With the clutch engaged, it's hard to get it balanced correctly.  To loosen the clutch screws the plastic housing has to be taken off.  But I obtained a cover off a yoke mounted Starfinder, which has a large hole to access the clutch screws. (Or I had thought of putting in about a 2-1/2" hole in the back of another housing.)  So I loosen up the clutch screws, balance the mount, and then retighten the screws.  It only has to be done once, unless I change OTA's or add accessories.

The rusty and pitted shaft should work just fine.  It may just not look pretty.lol.gif

 

The tangent arm is an original assembly.  The shaft and telescope mounting plate is pulled out of the mount.  The tangent arm is  slid over the shaft and then the shaft is slid back down into the mount.  It should have a thin plastic washer.  The tangent arm bracket just bolts onto the mounting plate.  It may already be predrilled and tapped.


Edited by Garyth64, 04 July 2021 - 09:50 AM.


#20 Tom Stock

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Posted 08 July 2021 - 10:36 PM

With putting in an original AC CD, I've really had no problems with it.

 

The only little nuisance was getting the scope to balance.  With the clutch engaged, it's hard to get it balanced correctly.  To loosen the clutch screws the plastic housing has to be taken off.  But I obtained a 

 

Thanks I finally have the mount. I disassembled the clock drive and everything seemed to be intact. I removed the clutch and worm gear, and powered up the drive.  Worm is rotating at 1/10 RPM as expected so that is good.  It's an odd drive.  You can see the motor sort of briefly stop and start to keep the average speed at 1/10 RPM (I verified the RPM with a stopwatch).  It does it so quickly it's hard to see.

 

Mechanically the mount needs a little cleanup work. The dec shaft is rusty, so I will probably put it in my lathe and run sand paper over it to remove the rust and pitting and then polish it up on a buffing wheel.  It only seems to be the exposed part of the shaft that is rusty so that is the only part I'll work on.

 

It was disassembled and missing some grub screws, but everything else (nylon washers, etc) seem to be here.  I remember drooling over these old mounts in S&T back in the 90s so it's fun to finally have one.  I do like these type of mounts.  Settings circles work well enough for me.   Slow motion controls would be a plus but not needed.

 

I haven't had a chance to inspect the plastic shaft bearings yet but I've read about these being replaced with bronze bushings.  Any info on that would be appreciated.  I could probably turn a set down which are close in OD on my mini lathe to make them fit if necessary.

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Edited by Tom Stock, 08 July 2021 - 10:37 PM.

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#21 Tom Stock

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Posted 09 July 2021 - 05:31 AM

I found replacement bushings here:
https://www.mcmaster.com/1281N28/
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#22 Geo.

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Posted 09 July 2021 - 10:26 AM

It's become much simpler to convert these mounts to stepper drive and retain DC operation. 

 

For Garth's conversion we used a Arduino mini Pro with a Atmel 358P microprocessor, a step motor driver and a simple enough circuit. 

 

DSkyDetails.jpg

 

The problem is that the C++ code has to be rewritten and tested for every different mount configuration and scratch circuit building is time consuming.  Roman Hujer has designed a circuit board to tap into the power of the Espressif ESP32 microprocessor (https://www.aliexpre....27424c4d7F3QyS). This PCB is intended to support goto operation, but it works just as well for a simple RA drive.

( https://easyeda.com/...an/onstepshield ). The cost is comparable to the Arduino, build time is minimal and the software is easy configured to any mount. 

 

As a mental exercise I worked what a minimum configuration for non-goto RA would look like. 

 

SimpleRAsm.jpg

 

EasyEDA requires a minimum order of five, but the Gerbers are free. Garth's motor was a used Vextra NEMA 11 with a 18:1 gearbox. MJPA.com may still have some for $9. Otherwise there's a similar motor on Amazon for $30.  https://www.amazon.c...5843908&sr=8-20 So for about $50-60 we can build an accurate tracking drive. 

 

And a hand control. 

 

RA HBX.jpg

 

Have fun.

 

 

 

 

 


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#23 Tom Stock

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Posted 12 July 2021 - 01:03 PM

Yeah thats not a bad solution, and I like the cute little stepper. 

 

Another option is Meade's Polaris RA drive, which has a potentiometer for speed adjustment, N/S switch, runs on a single 9V battery, no C coding required, easy to mount and draws only 29mA

 

It's also about $50.

 

Fortunately the original drive appears to be working fine in my case.


Edited by Tom Stock, 12 July 2021 - 01:04 PM.

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#24 technogeek001

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Posted 30 July 2021 - 04:36 PM

I'm glad I came across this thread!

I just purchased a 10" StarFinder for what I though a good price and in very good condition for it's age. The extra filters and lenses it came with would have been worth the price.

It currently seems to track well (it has the AC motor) and has had a "push to" installed.

Getting ready to add a 2" Crayford Focuser and clean the mirrors. May have them recoated if needed.

I'm glad to see that when I'm ready, I can breath even newer life into it at what looks like a reasonable cost.


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#25 Tom Stock

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Posted 30 July 2021 - 08:33 PM

I'm glad I came across this thread!

I just purchased a 10" StarFinder for what I though a good price and in very good condition for it's age. The extra filters and lenses it came with would have been worth the price.

It currently seems to track well (it has the AC motor) and has had a "push to" installed.

Getting ready to add a 2" Crayford Focuser and clean the mirrors. May have them recoated if needed.

I'm glad to see that when I'm ready, I can breath even newer life into it at what looks like a reasonable cost.

Great set up. For visual use I definitely prefer push-to over go to.




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