Barn door tracker

[happy-kat]

EDIT: I think my errors are coming in from trying to keep the clock face and the absolute angle in synch. When I rewrite the software to drive a stepper I won't have to worry about that.

I know this was a conversation early last year, but did you make any progress into rewriting to drive a stepper please?

Finally built my barn door but I am already thinking about motorising it and on the research side of choosing between a mechanical servo motor or electronically arduino driven stepper motor solution.

[Ags]

No, I have been distracted by other projects. I have been doing some experiments with supershort subs at f1.8 with just the manual barn door :-)

[JamesF]

I have been doing some experiments with supershort subs at f1.8 with just the manual barn door :-)

Old stick-in-the-mud that I am, I always like to use a camera, too

James

[happy-kat]

Thanks for replying.

I have tried to use mine but more days inside thinking then evenings actually using it.

It is working well though so I guess I am being impatient thinking about motorising it.

Have any image to share of your supershort subs?

[Ajohn]

Might be of use to some people. While nosing around for a diy eyepiece calculator I came across this collection of SCOTCH mount links  no idea why it's called a barn door. I have seen some barn doors but never a type 3 etc.

http://www.astronomyboy.com/barndoor/links.shtml

The few I tried are still live.

Not sure how it will work out photographically but the pole star round here is  a problem at times. For visual use I set the wedge according to the scale on it.  Orientated the mount with a compass taking care to level the platform and then used star drift to get the compass alignment correct. It may be possible to do the same thing with a camera using magnified live view. It doesn't take long with a bit of practice. In fact after a while I forgot the compass and lifted the lot up and turned it to get close. I still use a compass and level to align go to mounts. Maybe every one is aware of the star drift method but with all of the aids around now maybe not.

I'm pretty sure Meade made a finder with a built in polar alignment reticule at one point. I don't think anyone does now, just polar scopes. I'm a little dubious about comments like just look along the hinge and line it up especially for exposures that need a more complicated scotch mount. Those do reduce the need for rewinding though.

John

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[Ags]

Old stick-in-the-mud that I am, I always like to use a camera, too

James

 

That's what I've been doing wrong!

Thanks for replying.

I have tried to use mine but more days inside thinking then evenings actually using it.

It is working well though so I guess I am being impatient thinking about motorising it.

Have any image to share of your supershort subs?

Nothing to show, just trying out ideas for a trip to dark skies later this year.

[happy-kat]

Just downloaded the source code, nothing like jumping in at the deep end! Thank you for sharing it, have it loaded into Eclipse. Not doing anything clever just want to see if can change it to go anti-clockwise as that is how I turn my handle.

[Ags]

It was the first android app I ever wrote, there are many errors to fix and improvements to make. I intend to make a version 2 sooner or later.

[Ags]

@Ajohn: I use an RDF for polar-aligning my barn door...

I had a go at imaging part of the dipper last night. From my back yard, so plenty of city orange muck. I took 20 lights, 30 sec, f2.5, iso200, 50mm. And darks and flats and all that. Post processed (if you can call it that) in Canon DPP. And 50% cropped to get rid of the worst gradients.

I don't think I get better results at f2.5 than at f1.8. The stars look astigmatic at the edges either way, and I end up cropping this away (not to mention cropping away the gradients), so why not just go for the fastest setting? Then I can cut the sub length down to 20 seconds, which is good because I find my concentration starts fading after the tenth sub :-)

Plate solver: http://nova.astrometry.net/user_images/594037#annotated

[happy-kat]

Your stars are neat, from my back garden I have found the filter I bought has really helped the background though I recall you have a gradient removal fix to smarten your images.

Have you made a longer handle for your tracker?

[Ags]

Yes, I have a background extractor, but I'm not entirely happy wih its performance yet. I also think the stars look ok, especially as the image has been cropped quite a bit. I was hoping to get a bit of diffraction dazzle around the 4 dipper stars, but I lost that in post-processing. I might have more luck from a darker site.

I still have the short handle on the barn door - I keep meaning to add a 2-3cm to it.

My daughter has a farm with very dark skies (I though the skies at her last farm were pretty dark, but she says the new place is much darker...). I am thinking of buying a heritage 130p to keep at the farm, what is your opinion of that scope?

[Ajohn]

That's better than I expected.

A 50mm should be ok with 10 sec exposures according to DSLR pundits without guiding. I did try that at ISO 200 F2.8 just on a tripod hoping to catch some milky way at a reasonably dark site but it only caught brighter stars. So far the conditions haven't been suitable to try again at higher iso - i'm not in the same area very often.

John

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[happy-kat]

The scope is very compact and pretty sturdy construction.

I often sit it on something the height of a bucket and I sit on a plastic garden chair.

The helical focuser does the job but it does not lend well to finite miniscule adjustment which I find sometimes slightly frustrating finding that sweet spot, I have seen a diy focuser from an old prime lens which I would like to do.

Overall though it is just right for what we wanted to have as first telescope, well made, sturdy, compact and decent apperature.

[Ags]

I extended my turning handle with the help of a tasty magnum bar :-)

Unfortunately, that is as long as I can make it, otherwise it hits the knob in the background.

It doesn't look solidly engineered, but it should do the job, especially now that I've applied a spot of oil to the mechanism!

[happy-kat]

I bet that will make the handle easier to hold and turn.

[Ags]

Well... I am starting the next phase of my barn door efforts. I am planning on a motorized isosceles triangle design (so both the drive stepper motor and the nut it threads into will pivot versus their arms). I'm looking at this motor, which seems to provide enough torque for a reasonable load and to avoid the barn door sticking:

https://iprototype.nl/products/robotics/servo-motors/stepper-motor-4.8kg-cm

It does 1.8 degree steps, but I can go even finer with this widget, which can subdivide the 1.8 degree steps into 32 substeps:

https://iprototype.nl/products/robotics/drivers-controllers/drv8825-steppermotor-driver

Somehow I need to connect these to a programmable controller (rasperry Pi?) with settings for drive / fast-forward / rewind. 

It is a very ambitious project for me, as a simple resistor dew strip is already challenging my fabrication abilities (best to start small  ).

[happy-kat]

I got this one almost the same motor here

These are the two guides I am using to base my build on.

here and here.

I chose Arduino as it was going to work out cheaper then Rpi and I found those two sites both with code I could use.

Never done anything like this before (build or code wise) but nothing ventured nothing gained... hopefully all the parts I chose will be OK, haha

[Ags]

Good links, thanks for that. I was also looking at the EasyDriver so it seems it is a small world.

https://iprototype.nl/products/robotics/drivers-controllers/EasyDriver-stepper-motor-driver

A circuit diagram and some example code is a big help. I would like to add a bluetooth module so I can control the device from my phone :-)

If my metal lens hood arrives this week, I will have a go at building my resistor dew strip - I will really need that for my dark sky trips later in the year. That should give me the confidence to go ahead with this one.

[Ags]

Looking at the design on:

I would think that it is a mistake to place the camera, ball head etc on the outermost part of the arm. It should be placed as close as possible to the axis to reduce load and vibration.

Using a dual lever design for the barn door seems unnecessary as the inaccuracy of the traditional Haig design can be fully corrected in software. It's easier to correct for a simple Haig design than to correct for a dual lever system.

Aside from those two changes, I think I will follow the design pretty closely - at least as far as the wiring goes.

[happy-kat]

Agree that is not an ideal build (but hats up for sharing the project).

I am only using either site for the electronics, my actual barn door and mount is already built and proven.

My aim is 3 switches, on/off and fast/slow and forward/reverse.

It took me a lot of work days googling to get eclipse working for Arduino and have added the improved stepper libraries.

[Ags]

Yes that was the first of the two designs you sent earlier. I am so happy someone posted a design with a circuit diagram, and that your second link added further information to this. The circuitry was always going to be my downfall. If we are sharing more or less the same circuit, we can maybe also share the software side of things too. I do plenty of development work in my day job so I'd be happy to contribute on the software side.

[happy-kat]

Thank you for the offer, I have no skills to return the favour other than my ability to search on google.

Whilst I have bought all the bits my first step will be using my breadboard to make a simple led circuit with switch, I don't want to fail this project because I did not prepare enough.

My eventual plan is to build the code in stages so I can see where it failed, so first off will be can I start the motor, then start by switch etc. Though when I come to actually do it I may end up doing it different to how I see it now.

I am also hoping to get the rpm right through managing the speed in the code, I also plan to be able to set the maximum open and closed size so the motor doesn't keep going in forward or reverse mode and that was on one of the links.

When I can fit this project in, it will be slow I think as I have an immediate project that needs attention.

Looking forward to starting it though.

I will try and update my thread later once my last cog arrives.

[happy-kat]

The code for both builds is fully available on either link, the one with the photo you posted is the one I plan to use.

I thought if I followed the design it would work OK.

That reads so naive!

Anything I get to work I will share too.

[Ags]

Very sensible to stick to a proven design!