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DIY mounts


Guest peepshow

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Guest peepshow

Anyone actually built either a Eq mount or a barn door tracker from scratch?


 


How did you make the worm and wheel or get the measurements of the barn door spot on?


 


Have you made a mark 2 version or up to mark 99 !


 


I think a DIY galaxy etc etc  is more interesting if you created it yourself ! :) ..........


...........sticking my neck out here, which is  my parents bit of DIY :D


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When I built mine many years ago I used a threaded rod bent round a tree trunk of 12" in diameter.


 


Edit


 


It could have been 24" in diameter I cannot remember.


Edited by Doc
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Hi Richard,

In the previous thread (smaller than a pound coin) you asked about periodic error. Because of the imperfect match between my diy worm and wheel I have an acceleration/deceleration over the 186 second rotation period of the worm. This isn't noticeable in wide shots at about 1 minute. Shot below taken with 50mm lens (f4, iso800, 70x62 sec). At 300mm I limit exposure times to about 40 secs, take lots of frames and stack them in Deep Sky Stacker. Beyond about 60 secs polar alignment and speed variation due to temperature change on the 555 timer pulse circuit start to show up aswell.

  

 

13041426614_eff56baca1.jpg
 

Edited by Werisit
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And here's a shot of M35 taken with a 300mm lens (f5.6, iso800, 50 sec x 10 frames).

As I mentioned previously I am working on a MK 2 version. This uses a threaded rod 3/8 x 40 tpi moving a nut, pulling a cable wrapped around a pulley. I'm hoping this will eliminate the periodic error. I also plan to build in a polar scope.

 

13041231313_403c6be589.jpg
 

Edited by Werisit
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I am in the process of building a largish split ring mount.


I will probably make all the worms myself when the time comes.


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Guest peepshow

Graham, would like to see your progress on those DIY worms. You must have a nice machine shop.

 

Mick, if you used a 20TPI screwed rod running at 1 RPM the dia would be just under 23 inches.

 

Alan,  it might have helped  you to run the screw at a slight angle to the curved rack to improve contact.

There is a better 555 circuit I have somewhere using 2 x 555 for greater stability.  I'll dig it out and post it.

 

Re your second version, the bigger the pulley the better.  Also if its multi stranded cable there maybe very slight drive speed variations as the strands make contact erratically with the pully.  I would have a think about this.....maybe a single strand galvanised wire?

 

As I said, my previous tracker had hinges and I believe these were responsible for the errors.

Here is a single 5 minute exposure.  If you enlarge it you will see very weird star shapes due, I am sure, to hinge 'wobble' during that 5 minutes. 

My mark 2 version will not have this, but probably some other trouble. :)

 

11476512536_101b016b46.jpg
 

 

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Hello Graham. I'd not heard of a split ring mount so have just looked it up. I've got a 10" Dob that'd go well on one of those. Maybe the next project. 


 


Richard. You raise some interesting points. Maybe an un-bound guitar string? I probably won't do any more work on the current star tracker. It has exceeded my expectations but I think it's pretty much reached its limit. I suppose I just fancy making something new aswell.  The dual 555 timer circuit may well be the answer to control Mk 2.


I Like your Pleiades shot. Ok there's some star distortion but you've got some nice nebulosity. Five minutes unguided is pretty good going.


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Guest peepshow

Alan, as I understand it, as a worm and wheel is fixed dimensionally then one needs a slight variable freq drive to accomodate any tiny error from it's correct radial size.
In my case I do use a crystal controlled oscillator as a very stable drive but not having any worm and wheel
my tracker has mechanical adjustments on all it's important dimensions.

Re your polar scope, Alan...in my new tracker version I allowed the main steel shaft to protrude out from the main body by 4 inches.
Onto this will be mounted a laser whose beam is offset 45 minutes of arc from the shaft's axis.
By rotating the laser mounting around the shaft to the correct RA when aligning to Polaris, I should improve on my previous polar alighnment.

If the laser shines out to only 500 ft, then if my eye is, say, 2 inches away from it, the end of the beam will be within approx 1 minute of arc from Polaris.  

Well that's what I hope for.  :D  

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Guest peepshow

Sorry, I forgot to post piccy of the laser PA.  The steel shaft of the main camera platform runs along the bottom and the laser is the black object at the top. 

Various screws to lock it to the shaft allowing rotation.

 

 

13078927713_8943444e32.jpg
 

Edited by peepshow
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These barn door trackers you keep making with threaded rods ect.


Why dont you use an eccentric cam to raise the mount platform.


Far more controllable and smoother plus will have the added benefit of being able to track for hours not minuets.


I have a design for one here I did a while back.


Edited by Graham
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Guest peepshow

Well Graham, an eccentric cam's profile would have to be extremely accurate, wouldn't it, for long exposures with


longer focus lenses which I am attempting ?  It's that profile that rather puts me off.


 


Does your design track well?


 


My tracker is a double type 3 and with the correct dimensions should ( :rolleyes:)


track for 1 hour with only a 1 arc second error using a crystal controlled drive.


 


Maybe cams are the way to go but that profile might be a pain for me to get spot on over tracking time.


 


BTW, a type 4 tracker has nil error after 2 hours with only 1 arc second error at any one time......so it is said. :)

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Well Graham, an eccentric cam's profile would have to be extremely accurate, wouldn't it, for long exposures with

longer focus lenses which I am attempting ?  It's that profile that rather puts me off.

 

Does your design track well?

 

My tracker is a double type 3 and with the correct dimensions should ( :rolleyes:)

track for 1 hour with only a 1 arc second error using a crystal controlled drive.

 

Maybe cams are the way to go but that profile might be a pain for me to get spot on over tracking time.

 

BTW, a type 4 tracker has nil error after 2 hours with only 1 arc second error at any one time......so it is said. :)

 

Richard.

No idea if it tracks well as I never got round to building it.

The engineering behind it is sound so there is no reason why it should not track all night with total accuracy. 

The Cam profile you would have to get laser cut to keep it to a tight enough tolerance.

It does have the useful advantage of being infinitely controllable using a stepper motor.

Could even use PHD to make it guide. :lol:

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Laser polar alignment Richard. Yep, could be a simpler solution than an optical device. I'll log that idea.


Graham, that's an interesting idea. Any chance of putting a diagram on here to show how it works? 


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Laser polar alignment Richard. Yep, could be a simpler solution than an optical device. I'll log that idea.

Graham, that's an interesting idea. Any chance of putting a diagram on here to show how it works? 

 

Hi Alan

Simple enough idea.

 

BARN%20DOOR%20TRACKER%201.jpg

 

Exploded parts view.

 

BARN%20DOOR%20TRACKER%202.jpg

 

Close up of the cam and roller. ( lower plate removed for view )

 

BARN%20DOOR%20TRACKER%203.jpg

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Thanks Graham. Now I see. Calculating the curve on the snail cam would be fun. I'm learning a lot here.


Richard, I googled type 3 barn door tracker and found some pictures and diagrams. I'm beginning to understand the attraction of this type of mechanism now. 


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Guest peepshow

Thanks for the drawings, Graham.


The cam will have the same problem that single arm barn doors have.


Namely, as the platform opens the cam's profile is driving it at a slowly changing angle,


leading to an unwanted  change of tracking speed.


 


This means that the cam cannot be a linear type but would have to be designed to take this angular


change into account.


As Alan said, calculating the cam's curve would be fun. :)


 


Alan. the type 3 barn door overcomes this problem by the one sliding section  which slows the camera


platform down as the other section is increasing it. 


One exactly  balances the other, providing  the dimensions are  correct.  Not too easy to obtain.


Edited by peepshow
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Been reading Dave Trott's article on the double arm and its fascinating stuff.


I must do a redesign on mine to incorporate his findings.


Still like to use the cam method just need to incorporate a second hinge point and sliding plate.

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Guest peepshow

Graham, whichever way you go I would advise you to make  the critical dimensions adjustable.


 


Two of these are in the 12 inch region and to get to within 1/64th of an inch is pretty good going


without adjustment.


 


BTW my sliding contact is a thin round edged brass section sliding onto a glass flat, all greased up to minimum friction.


...........one needs to avoid any slight juddering caused by friction,  'slip and lock, slip and lock.'


 


I think that you will find that your cam will require a large torgue in order to raise the camera


with maybe a heavyish lens and mount etc.


  The standard barn door lifting screw only requires a low torque for quite heavy lifts.


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1/64 of an inch, that is a positive mile to me. I work to 1/1000 of an inch unless it needs to be precise :lol:


But joking apart that is sound advice.


Instead of sliding plates why not use bearings between the plates to stop any sticksion or if that is getting away from the ideals of a barn door tracker then at least use Teflon plates.


Problem with grease is it attracts dirt and moisture like the plague so all you good work and intent could be undone in a matter of minuets on a damp or breezy night.


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Guest peepshow

Well Graham I was trained as a toolmaker so 1/10000 is happy hunting ground for me too. :)


 


Bearings between the plates......You may find that this introduces yet another changing angle


to contend with. When in the down position the two platforms are near parallel to each other.


As they raise an angle opens up between them due to the 2 inch offset of the hinges in a type 3.


 


BTW, re torque.  If your cam, say, worked over say 2 hours for a revolution, in this same time the standard


1 RPM screw would revolve 120 times.....less torquie requirement.


 


OK on grease.  Point taken.  One can get paranoid over trackers I guess. :D


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"Bearings between the plates"......You may find that this introduces yet another changing angle


to contend with. When in the down position the two platforms are near parallel to each other.


As they raise an angle opens up between them due to the 2 inch offset of the hinges in a type 3.


 


Yup did not explain that too well.


Thinking in terms of using small bearing as a wheels to eliminate the friction between the 2 plates.


The pivot end would have to be raised by an equal distance to keep the plates conformity to the spec.


 


I do love chucking ideas about with other engineers, you never know what tangent it could spark off.


Edited by Graham
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Lathes are dead long live 3d printing - just joking lads 


 


Arn't Engineers great - Worked for Brush for 5yrs - Engineers came up with a great idea to "float" very large Generators on air to move them outside the build building(N Sea contracts) - It worked a treat except they forgot the height measurements and had to dismantle the front of the building to get it out  :)​ 


 


been following your discussion with interest nice to see head banging at work.


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Guest peepshow

Well Clve, re your floating Brush generators.  Engineers can both adopt things  and adapt situations at the blink of an eye, hence taking the building partly down.  Were rollers considered?


 


 Others would have stripped the generators all down and bankers would have


 liquidated the company. :D


 


Re 3D printing one will  never get the smell of oil, nor the shining curl of steel cuttings coming off a lathe.


The excitment of knocking off the  saddle drive just in time before the tool hits the chuck. :)


 


The whistles blown for tea break................ !


 


 


 


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True but it wasn't the Eng who took the front of the building down - they were in a room being given a lecture by the MD who arrived in his little  Armstrong Siddeley car (very nice)


 


Unfortunately 3D printing can do things that a Lathe(CNC or otherwise) could never do - build the complete item without waste and not using multiple parts - but the rest,as you say, is true - oil ,tool going across rooms by apprentice mishap  and no soul  :)


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