Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Rebuilding my "50 Cent" 20 Inch String Telescope

ATM reflector
  • Please log in to reply
22 replies to this topic

#1 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 05 December 2020 - 01:03 PM

I'm in the process of rebuilding my 20" string scope for the third time now (Version 1 build thread here) since first light in August of 2006. Version 2 was not too complicated, involving getting the primary mirror re-figured to f3.4, and shortening the poles and strings.

 

My current objective is much more ambitious, given realization that in my waning years of observing I'd rather spend more time looking and less time finding things – and lug around a lighter telescope. 

 

My plan could be called an extreme makeover as I intend to replace all wood components with aluminum. My original scope weighed in at 133# with the "50 cent" mirror being 44# itself. Version 2 was basically the same weight as I only hacked off a short section of the metal poles.  I'm hoping to achieve some weight loss on each of the three main components I break the scope down to for transport (ground board, mirror box and secondary cage). I carry the mirror separately as I'd likely break my back lifting the mirror box with the mirror installed. This has been quite manageable so far.  Another reason of using aluminum is to have a structure with more precise right angles and parallel dimensions, important I presume for the most accurate motorized tracking.

 

I'm sticking with the same string design but plan on adding motors, encoders and Sidereal Technology controller system to spend less time finding things and more time looking at things. This will be a stretch of my electronic and mechanical design skills (hence my sharing on this Forum for feedback and advice), but this is a well established system with users all over the world and not coincidentally the designer/manufacturer is a fellow club member.

 

Build plan/schedule is:
1. New mirror box
2. Pole and string holders integrated into mirror box
3. Design and fabricate side bearings
4. Rocker box and ground board
5. Secondary cage (not a priority at this time)

 

This is Version 1.0. which had a focal length of 100” requiring the ladder you see. Going up and down the ladder all night got old – and as I got older less fun. Re-figuring the mirror to f3.5 in V 2.0 meant I only occasionally had to use a step stool. In this rebuild I'm hoping to shave an inch or so off the lower components and get the scope even lower to the ground.

 

At OSP small.jpg

  • ad701xx, PrestonE, Dale Eason and 3 others like this

#2 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,544
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 05 December 2020 - 03:11 PM

 

I'm in the process of rebuilding my 20" string scope for the third time now (Version 1 build thread here) since first light in August of 2006. Version 2 was not too complicated, involving getting the primary mirror re-figured to f3.4, and shortening the poles and strings.

 

My current objective is much more ambitious, given realization that in my waning years of observing I'd rather spend more time looking and less time finding things – and lug around a lighter telescope. 

 

My plan could be called an extreme makeover as I intend to replace all wood components with aluminum. My original scope weighed in at 133# with the "50 cent" mirror being 44# itself. Version 2 was basically the same weight as I only hacked off a short section of the metal poles.  I'm hoping to achieve some weight loss on each of the three main components I break the scope down to for transport (ground board, mirror box and secondary cage). I carry the mirror separately as I'd likely break my back lifting the mirror box with the mirror installed. This has been quite manageable so far.  Another reason of using aluminum is to have a structure with more precise right angles and parallel dimensions, important I presume for the most accurate motorized tracking.

 

I'm sticking with the same string design but plan on adding motors, encoders and Sidereal Technology controller system to spend less time finding things and more time looking at things. This will be a stretch of my electronic and mechanical design skills (hence my sharing on this Forum for feedback and advice), but this is a well established system with users all over the world and not coincidentally the designer/manufacturer is a fellow club member.

 

Build plan/schedule is:
1. New mirror box
2. Pole and string holders integrated into mirror box
3. Design and fabricate side bearings
4. Rocker box and ground board
5. Secondary cage (not a priority at this time)

 

This is Version 1.0. which had a focal length of 100” requiring the ladder you see. Going up and down the ladder all night got old – and as I got older less fun. Re-figuring the mirror to f3.5 in V 2.0 meant I only occasionally had to use a step stool. In this rebuild I'm hoping to shave an inch or so off the lower components and get the scope even lower to the ground.

 

 

Very nice, , i salute your ingenuity & craftsmanship !

 

I too am pursuing my ultimate scope for my "waning years of observing" as you put it :)

 

Based on my experience I don;t think you will lose that much weight replacing wood with aluminum, unless you really skeletonize structures to the max to get a stiffness equivalent to the wooden parts.  My binoscope is almost all Al, and it will not be that light. But it will be on wheels just because it is too big to carry anyway so weight is not a huge factor.

Ideally an Al structure can be lighter than wood, i can easily visualize each part of your scope being a stressed-truss structure containing lots of  triangles.

. To do that i would want access to a good TiG welder and a variety of Al structural shapes & thicknesses.  All of my Al comes from the local scrapyard, so sometimes i have to deal with what is available.

 

Good luck with the project. looking forward to see what you do.

CS

Bob


  • Augustus likes this

#3 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 05 December 2020 - 04:36 PM

 

Based on my experience I don't think you will lose that much weight replacing wood with aluminum, unless you really skeletonize structures to the max to get a stiffness equivalent to the wooden parts.  

I think you're probably right, though even a modest weight loss will satisfy me. The original scope was built in the era of big beefy dobs. I used 5/8" plywood for most pieces.  I'm thinking the mirror box will end up being about the same but the rocker box/ground board I am designing should be significantly lighter.

 

As with my original build the key to transporting the scope is being able to break down into manageable components - which also easily fit in the back of my TUV (telescope utility vehicle).

 

.....David



#4 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 05 December 2020 - 04:40 PM

First order of business was to deconstruct the scope. Some parts were salvaged and passed on to fellow club members for their projects, and others shredded,

 

shredded scope small.jpg

 

then cremated...

 

cremating scope small.jpg


  • JohnnyMac, Shmals, Bob4BVM and 1 other like this

#5 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 06 December 2020 - 12:43 PM

My woodworking tools and skills are going to help somewhat in dealing with aluminum parts, but beyond sourcing and cutting to size I'm paying others to do the welding and machining necessary.

 

First piece to take shape was the mirror box frame.  The finished size was based on snugly fitting the mirror cell inside.  Material is 1” x 2” x1/16” aluminum.

 

Mirror Box small.jpg

 

Once the frame was completed I had to install blocks and plates (I'm making these terms up) at precise places for eventual pole and string holders.

 

Mirror support pieces small.jpg

 

While I created make-shift pole holders out of a plastic plumbing piece and a large bolt for the mirror box in the original scope, for this upgrade I had these (female) pole holders machined out of aluminum stock. Their finished sizes varied in height based on where they would be attached to the mirror box in order for the  dimension of the extended poles to be the same. 

 

Mirror Box Fasteners small.jpg

 

My technique for setting up this string scope is to screw the poles (which have a bolt on one end) deep enough into the female pole holder on the mirror box for the top of the pole to fit underneath the secondary cage (male) pole holder while the strings are attached but not under tension.  Then I unscrew the pole until all the strings are under tight tension – at which point the secondary mirror is the proper distance from the primary mirror.

 

mirror box done small.jpg

 

Mirror box done - and passes first setup test!

 

First Setup Test small.jpg


Edited by David N, 06 December 2020 - 01:15 PM.

  • ad701xx and JohnnyMac like this

#6 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 07 December 2020 - 12:54 PM

With the mirror box done I could turn my attention to the rocker box, or as I now think it more appropriately should be called: the roller bar frame.  This is a mock up using plywood and the pillow block bearings and roller bars I'll be using.

 

Roller Box Mockup small.jpg

 

Using the side bearings from the old scope I was able to get an idea of how the mirror box would fit and work on the roller bars and determine final dimensions of the roller bar frame.

 

Rocker Box mock up small.jpg

 

Quite pleased and relieved with how it's come together so far.

 

 

 

 

 

 


  • ad701xx likes this

#7 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 08 December 2020 - 04:32 PM

For my azimuth bearing/ground board I'm going to use a "Lazy Susan" turntable. Specifically, a "TamBee Heavy-Duty Mute 24 Inch Aluminum Lazy Susan Bearing Turntable Ring Swivel Plate Hardware for Heavy Loads", purchased off Amazon.

 

Shown here overlaid on my old traditional ground board it will be slightly smaller but I hope and believe should work OK.  I could have gotten one larger, but as I shopped the prices started rising exponentially for anything over 24".  

 

lazy susan.jpg

 

It moves smoothly on a ring of ball bearings and is rated for loads up to 800 lbs. I removed the tiny feet on either side exposing threaded through-holes which will come in handy for attaching to the roller bar frame and proper legs.

 

This is not a novel idea as I've come across several other scopes using a similar azimuth bearing.  I'd be curious to hear from anyone using a similar turntable with comments on how it's worked out.

 



#8 TopherTheME

TopherTheME

    Viking 1

  • *****
  • Posts: 629
  • Joined: 11 Feb 2011
  • Loc: SE Michigan

Posted 09 December 2020 - 10:09 AM

I use the same kind of Az bearing for my dob buts it's only 20in diameter. It does work well but if you want to smoothly track planets you'll need to take it apart, clean it out, and then re-lube it with some better grease. Otherwise the motion can be kind of gritty at high powers. You may also want to consider adding a friction pad of some sort as the scope will be pushed around very easily.

#9 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 09 December 2020 - 11:47 AM



I use the same kind of Az bearing for my dob buts it's only 20in diameter. It does work well but if you want to smoothly track planets you'll need to take it apart, clean it out, and then re-lube it with some better grease. Otherwise the motion can be kind of gritty at high powers. You may also want to consider adding a friction pad of some sort as the scope will be pushed around very easily.

I've had those thoughts about friction pads in the back of my head for both the altitude and azimuth bearings. But, I'm also expecting that when the belts, pulleys, and gears are in place they will serve to control the bearing from free-wheeling movement or backlash when tracking and smooth out normal movement. 

 

My system will also have bearing "clutches" so I can disengage from motor control and manually move to an object and the controller will know at all times where I'm pointed and reengage tracking when I let go. [I hope I'm describing that correctly as I'm still learning how this all will work.]

 

I haven't inspected the turntable yet to see if it's possible to take apart. It does appear that the track of ball bearings is exposed so maybe one could lube this model without taking apart.

 

Thanks for the feedback......David



#10 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 10 December 2020 - 01:13 PM

With the roller bar frame done, I space out and attached the pillow block bearings then added some shelves to hold the motors and gear drives, and to secure the turntable.

 

Roller Bar Frame Shelves small.jpg

 

For stability, I'm going with four adjustable feet.

 

Turntable Feet.jpg

 

Everything fits great and under weight the turntable rotates smooth and effortlessly. 

 

Complete bottom components.jpg

 

So essentially I've finished rebuilding my scope and can use as is - but now the challenge begins to add the motors, gears and other stuff to turn into a go-to and tracking telescope. 


Edited by David N, 10 December 2020 - 01:18 PM.

  • Shmals likes this

#11 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 10 December 2020 - 04:23 PM

Getting my head wrapped around what's necessary to mechanically move my telescope simultaneously in two directions "hands free" has taken some time, but fortunately several RCA members much smarter than me on this subject have documented and left helpful nuggets on the internet about their projects for novices like me.

 

The path I'm taking has been most influenced by Howard Banich's latest upgrades to his 28 inch scope, one many of us recall enviously inspecting at multiple Oregon Star Party walk-abouts. If you want to learn more about the evolution of his scope, I'd encourage you to visit his website

 

I'm starting with the altitude drive and with Howard's help, I've created this annotated photo of his latest iteration which I had to dissect in order to understand the mechanics of it all. Don't get hung up at the moment about the "clutches" as I'm just beginning to understand them and will deal with that down the road.

 

Atitudedrivecloseup labels - small.jpg

 

To get a handle on exactly what parts I need and how my altitude drive system will be put together I did a sketch showing the miscellaneous parts on the lower part of the system. This also illustrates how the mounting blocks will need to be fabricated so as to assure the overall shaft is parallel to my roller bars.

 

Altitude Schematic small.jpg

 

I'm still waiting on a couple of parts before heading over to my machinist with the box of parts and these illustrations to try and explain what I need him to fabricate.  If I had the proper tools and skills I could probably do this myself, but alas, I took band in high school rather than metal shop, and there was no such thing as computers and robotics at the time.


  • ad701xx likes this

#12 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 12 December 2020 - 01:09 PM

Help!

 

These are the NEMA 17 planetary gearbox 40:1 reducers I want to use in my drive systems.

 

Planetary Gear Box.JPG

 

I need to find what I think is called the "Sun gear" that will fit into the 3 gears (Planet gears?) inside the gearbox.

 

Gear Reducer Input End.jpg

 

I'm having a devil of a time finding such a part on the web. The first unit I ordered (off eBay) didn't have one so I returned it. I then ordered a NEMA 23 unit from a different vendor which had such an input shaft/gear - so I know they exist. Looks like this:

 

gear.jpg

 

I didn't like the size and weight of the 23, so returned it asking they send me a 17 instead and very clearly asking for confirmation it had the input shaft/gear. No reply to my question but I did just get the 17 and alas it doesn't have the input shaft/gear.  I've since messaged over a dozen different vendors asking about the gear and they all say "doesn't come with one and don't have as separate part."  Kind of baffling to me what good this unit is to anybody without a matching input gear.

 

Anybody know what I'm looking for and where to find?

 

Am I going to have to have one machined - if that's possible and not outrageously expensive? And if so, how would I go about figuring out what diameter the gear needs to be and how many teeth?

 

Just one of many scavenger hunts involved in building a complicated scope.

 

Thanks in advance.........David



#13 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 16 December 2020 - 11:29 AM

My headache may soon be over as I eventually heard from the folks I purchased the gearbox from that they will be able to get the gear I need from their supplier. This was after trading several messages and photos that I'm sure had to work their way back and forth through Chinese translators.  I'm hopeful, but not confident I'll get the right part.

 

Why in the world they don't sell the input gear with the gearbox is beyond me, though I speculate these 'resellers' are getting these units as surplus from the manufacturer - and they are surplus because they don't have the gear.  Anyway, here's hoping they come through.

 

In the meantime I started a separate thread asking for advice on this issue.  Got enough feedback and advice to convince me to give up on this gearbox and purchase something or someplace else - which I plan on doing if the above promise doesn't work out.

 

Meanwhile, I have all the other azimuth drive parts necessary and will be taking to my machinist to start fabricating necessary mounting blocks.

 



#14 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 16 December 2020 - 05:22 PM

Project today was to finish the parts for the roller bar in the altitude drive system (see earlier post with labeled photo).

 

These parts (in concert with a separate encoder yet to come) constitute the "clutch" that will allow me to manually move the scope up or down and the controller to follow and know where the scope is pointed. When I let go the motors/controller take over and tracking continues from that new spot in the sky. 

 

If you don't want this feature in a motorized scope, then you would just affix the belt pulley to the roller bar and use a controller keypad or computer program to move the scope.

 

This is how I've come to understand and explain the principle of the clutch.

  • When the clutch is not engaged the altitude drive motor turns the belt pulley which turns the roller bar and the controller/computer is used to manage the movement of the scope.
  • When the clutch is engaged the roller bar pulley spins freely and the movement of the scope is under human control. 

In order for the scope to move freely under human control the pulley bore is slightly larger than the roller bar (3/4").

 

In order for the motor drive to raise/lower the scope the pulley needs to be firmly married to collars affixed to the roller bar. 

 

This is accomplished by some mechanism to 'push' the pulley into the collar - and conversely be slippery enough to allow the bar to spin while the pulley remains frozen in place.

 

'Slippery' is achieved by attaching pieces of Ebony Star (or suitable replacement) to either side of the pulley and placing companion Teflon washers on the roller. I drilled the center hole in the laminate and then free-handed the circle with tin snips.

 

Pulley Clutch - small.jpg

 

This adhesive worked great attaching the laminate to metal. 

 

Adhesive - Small.jpg

 

These are all the pieces on the roller - spaced out for clarity.

 

Roller Bar Drive Components - small.jpg

 

The adjustable width clamp on the far left is the key part.  This part is fixed to the roller bar while at the same time pushing the wave spring into the Teflon washer/pulley/washer and the fixed collar.  When adjusted properly it will exert enough pressure for the pulley to act as if it is fixed to the roller bar and thus allow the drive motor to move the telescope altitude bearings - and also allow the Teflon to slide over the laminate without the pulley moving when moving the scope manually.  The adjustable clamp is itself pretty clever. The left collar is threaded into the right collar - and you can release the right collar from the bar and turn one way or the other to adjust the tension on the spring while the left collar remains fixed in place, then retighten to the collar.

 

Make sense?  Took me quite a while.


Edited by David N, 16 December 2020 - 07:52 PM.


#15 grzesznypl

grzesznypl

    Viking 1

  • *****
  • Posts: 600
  • Joined: 07 Apr 2019
  • Loc: Jackson Heights, NY ... for now

Posted 20 December 2020 - 11:46 AM

Are you familiar with Low Rider concept of Reiner Vogel? That would allow you to completely eliminate any ladder climbing during night. Lowrider_prinzipk_e.jpg

Attached Thumbnails

  • Lowrider_prinzipk.jpg


#16 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 20 December 2020 - 02:34 PM

Are you familiar with Low Rider concept of Reiner Vogel? That would allow you to completely eliminate any ladder climbing during night.

Yes I am familiar with the concept and have observed through Dan Gray's 28" string scope  (the inspiration and mentor to my original string scope) which incorporates a similar approach.  

 

Once I get this build finished and everything working like I hope, I will then decide whether or not to rebuild the secondary cage and perhaps incorporate this concept at that time if I'm still inconvenienced by having to lift my feet off the ground to look through the eyepiece.  Wouldn't be an issue if I were 6'4" instead of 5'9". smile.gif

 

Thanks for your comment.........David


  • grzesznypl likes this

#17 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 21 December 2020 - 11:57 AM

With my altitude drive system designed and components on hand or waiting to be machined, time to move on to designing and building the azimuth drive system.

 

What I've decided to do is use basically the same components I'm using on the altitude drive roller, with some slight modifications. This is the plan:

 

Azimuth Drive Components.jpg

 

The most crucial and yet to be designed component is what I'm calling the drive roller. Some folks use belts and pulleys to move the azimuth and that is a fallback for me, but I'd prefer to keep moving parts to a minimum and keep a low profile that I can tuck within the roller bar frame. So, I'm taking a possibly more novel and problematic path which is that the drive roller will be making direct contact with the turntable. To be successful I need to conquer what I'm advised are two major considerations.

 

1)  Traction / Friction / Stiction - In order to ensure accurate azimuth movement and tracking, the driver roller needs to remain in CONSTANT contact with the turntable, without balking or skipping as it is commanded to move, and not slip when commanded to stop. The turntable is an aluminum surface and I'm not yet sure what to use for the roller. Maybe aluminum, Delrin. plastic, rubber or YTD?  My thoughts:

  • Scuffing up the surface of the turntable and an aluminum roller to create a sandpaper on sandpaper effect.
  • Applying sandpaper to the turntable and using either an aluminum or rubber roller.
  • Applying Velcro to the turntable and roller.
  • Other suggestions?

2) Binding between the roller and turntable - I didn't understand this concern until I got this explanation from Howard, who's general design I'm following:

 

About binding - think about the circle the inside edge of the drive wheel makes as it goes around the top of the turntable compared to the larger circle the outside edge of the drive wheel makes. These two arcs have different diameters, and because the drive wheel is solid, after a few rotations the inside edge of the drive wheel will have travelled a shorter distance than the outside edge. This causes binding that will either release itself with a lurch or even stop the drive until you release the binding. 

He dealt with this issue by putting a crown on his drive roller. My thoughts on that:

  • Probably wouldn't work if I went the Velcro route because I need a smooth surface to affix the Velcro.
  • Might work without Velcro in concert with some YTD treatment I end up doing to the turntable surface.

And he suggested another possible option if I wanted to maintain a smooth surface on the roller edge that makes contact with the turntable thus maximizing contact surface area for Velcro or whatever other treatment I end up with on the two surfaces - and that is to put a slight taper on the drive roller. My thoughts on that:

  • Would require me to do math to calculate proper angle - just one more headache.
  • Probably makes the most sense if crowned rubber roller doesn't work with a scuffed turntable edge.

My preference would be a solution that doesn't involve gluing some material to either the turntable or roller that will collect dust, peel off or otherwise give me a headache down the road. Next step is to do some experimenting with different materials and treatments and see what works best. 

 

I'm interested in hearing from others who have dealt with this issue - or have thoughts or suggestions.


Edited by David N, 21 December 2020 - 12:10 PM.


#18 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 25 December 2020 - 02:28 PM

Up to this point I have been planning on tucking all the motors and controllers within the roller bar frame and under the mirror box. I thought it was about time to see if that was possible, so I laid out most all the pieces and adjusted until I came up with this arrangement.  

 

Motor Controller Layout Small.jpg

 

 

Looked great - BUT I had failed to account for the swing of the mirror box which crashed into the azimuth shaft bearings. So, giving up a precious inch or so of eventual eyepiece height, I moved the roller bars closer together which raised the mirror box swing enough to clear the bearings. 

 

I am going to mount each motor/gearbox/shaft assembly on a separate strip of aluminum and then mount that to the equipment shelf to accommodate future fine tuning of the alignment of the whole assembly with less hassle (i.e. relocate two screws rather than eight).  


Edited by David N, 25 December 2020 - 02:29 PM.

  • ad701xx likes this

#19 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 29 December 2020 - 05:55 PM

 

Looked great - BUT I had failed to account for the swing of the mirror box which crashed into the azimuth shaft bearings. So, giving up a precious inch or so of eventual eyepiece height, I moved the roller bars closer together which raised the mirror box swing enough to clear the bearings.

After stewing and being a little depressed over the prospect of adding an inch of eyepiece height, I conferred with some fellow local scope builders and one offered an interesting solution, cut a notch (?) in the frame where it passes over the drive shaft. With some hesitation I marked and bored an oversize channel (?) in the frame.  Need to do a little touchup filing, but it works great and I can keep the scope as low to the ground as possible!

 

 

Frame Notch.jpg

 



#20 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 02 January 2021 - 08:07 PM

I have been fretting for some time on getting an azimuth drive roller machined, mainly because of my hesitation to visit my machinist who is a no-masker. So, in the middle of the night (when ATM'ers do their best thinking), I had a vision of this:

 

Oreo.jpg

 

....which set off a light bulb. I could mill something like this out of wood on my lathe, get an o-ring of the proper diameter to put on the roller and at least prove the concept before eventually getting the piece made out of some other material.

 

I refreshed my lathe technique and perfected my design on some soft fir.

 

Fir rollers.jpg

 

...then glued up some solid oak scraps and with the correct size o-ring produced a perfect roller.

 

Drive Roller Prototype.jpg

 

The o-ring will stretch quite a bit, so I made the groove in the roller slightly oversized to keep the rubber o-ring in place and allowing it to be slightly compressed on the turntable track to create maximum contact and traction. I fiddled with the tension on my clutch and it rolls great both with and without the clutch engaged. The wood surface also seems to be as effective as laminate in providing 'stiction' in tandem with the plastic washer.

 

Depending on how it performs under weight and power, this may the permanent solution.



#21 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 05 January 2021 - 06:11 PM

In the ongoing challenge to keep the eyepiece as short as possible, I needed to come up with a mounting solution for my gear reducer to align with the drive shaft installation that helps me meet that objective.

 

The solution was a NEMA mounting bracket, a cut-out on the frame shelf, and a spacer/mounting block.

 

AZ Drive Shaft 2.jpg

 

AZ Drive Shaft 1.jpg

 

Will have to fine tune height adjustment down the road, but for now another headache and item to check off the to-do list.



#22 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted 17 January 2021 - 02:30 PM

I made a first attempt at creating an azimuth scope encoder based on design suggested by consulting engineer, mrcotton73 (Sameer).  

 

Secondary encoder diagram.jpg

 

The "scope encoder" will track scope movement via a wheel that is in constant contact with fixed portion of the turntable.  This will allow the SiTech controller to know where the scope is pointed when the azimuth "clutch" is engaged (i.e., the scope is moved manually) and the motor encoder doesn't rotate because the drive shaft is not turning. When you let go of the scope the drive shaft/motor encoder will resume turning/tracking and the controller will recalibrate sky location.

 

This is Prototype #1 I fabricated this morning based on that design.

 

Encoder Wheel - 1.jpg

 

The concept is sound and worked when I held in place.  BUT, I quickly observed a major issue that I need to address, that the wheel would slip/not turn under a little tension which is not good. You want the wheel to be in constant contact with the turntable (in my case) and not slip, otherwise the controller will loose track of where you are in the sky.

 

I know I need a better wheel to begin with. This one is for a toy and the rubber 'tire' actually fits over the inner wheel and thus can slip on the wheel while the wheel is turning.  The tire tread is also too skinny and it has a very tiny axle (also susceptible I expect to bending under tension) that could also be slipping in the wheel, or the encoder. I may need to fabricate one from wood as I did for the azimuth drive wheel, but am hoping to find a solid rubber wheel.

 

So begins another scavenger hunt on Google - any sourcing suggestions would be appreciated. What I'm looking for:

  • solid rubber wheel 1-2" in diameter
  • 1/4 - 1/2" tread
  • axle diameter of 1/8"; 3/16"; or 1/4" (and I think bigger would be best)

 



#23 David N

David N

    Vostok 1

  • -----
  • topic starter
  • Posts: 124
  • Joined: 11 Nov 2003
  • Loc: Portland, OR

Posted Yesterday, 02:46 PM

Major milestone today as I finished installation and successful testing of motors and controller.  Took some troubleshooting to solve a wiring/controller issue of course, but all good now thanks to Taj at SiTech and simply inverting motor/encoder direction configuration.

 

I'm quite pleased that I was successful in my objective of keeping all the motors/gears/wiring on the roller bar deck - with nothing hanging off the scope.  If I had it do over again I probably would have built the roller bar frame just a couple inches longer.  [Note: belt/pulley on far right of lower roller bar is for yet-to-come scope encoder assembly.]

 

Motor Deck.jpg

 

In pervious versions of this scope I used batteries hanging off the mirror box as counterweight. In this version I need to have the battery on the motor deck so I created a cradle to hold my battery in a corner void of the bottom frame. 

 

Battery.jpg

 

Battery Cradle.jpg

 

Next task is to balance the scope and fine tune the clutches.

 

........David


  • grzesznypl likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: ATM, reflector



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics