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A smart barn door tracker

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#1 arun289

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Posted 16 April 2018 - 01:09 PM

Hi,

 

I would like to share my design of a smart barn door tracker. It is an isosceles barn door tracker with tangent error correction through a Arduino micro-controller. I have shared all the details about the tracker including the mechanical design, electrical circuit and the software source code here:

https://barndoor.spa...ference-design/

 

The other entries in the blog describe the principles and design of a barn door tracker. Also included is an online calculator which helps in calculating various parameters while designing a barn door tracker. The blog is here:

https://barndoor.space/

 

barndoortracker-s.jpg

 

M46 and M47 shot with this tracker.

135mm lens, ISO800, 15sec X 200 subs (50 minutes) exposure. Cannon 500D.

 

m47m46-cropped-s.jpg

 

Comments and suggestions most welcome.

 

Regards,

Arun

 


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#2 Ed Jones

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Posted 16 April 2018 - 06:04 PM

Simpler yet would have been to make a tracker with no tangent error.   I'd like to see someone put an auto-guider on a tracker, that would be really cool. 



#3 mark cowan

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Posted 16 April 2018 - 06:32 PM

Is that not done just by curving the threaded rod?  (Obviously you then have to turn a nut not the screw itself...)


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#4 arun289

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Posted 16 April 2018 - 09:39 PM

Simpler yet would have been to make a tracker with no tangent error.   I'd like to see someone put an auto-guider on a tracker, that would be really cool. 

A curved bolt barn door tracker can be made with no tangent error. But it is inherently more difficult to build. It requires some very good DIY skills. The idea behind my project was to keep the mechanical design extremely simple. To allow a build with very little fabrication. Almost everything is commodity components.

 

Regarding the auto guider, it is in my wish list smile.gif But this would require a very high quality build of the base system. 

 

Regards,

Arun



#5 arun289

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Posted 16 April 2018 - 09:42 PM

Is that not done just by curving the threaded rod?  (Obviously you then have to turn a nut not the screw itself...)

Yeah, a curved bolt barn door tracker has no tangent error. But as you mentioned, we need to turn the nut and not the screw in that case. This requires the motor to be coupled to the nut through a gear and cannot be directly driven. This requires some very good DIY skills. The idea behind my project was to use off the shelf commodity components and keep fabrication to the minimum.

 

Regards,

Arun


Edited by arun289, 16 April 2018 - 09:47 PM.


#6 Ed Jones

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Posted 16 April 2018 - 09:45 PM

Mark that how I do it but the Arun's method is fine too.  Now if you would stick an auto-guider on it you might be able to do longer exposures or longer focal length lens.  



#7 mark cowan

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Posted 16 April 2018 - 09:58 PM

Yeah, a curved bolt barn door tracker has no tangent error. But as you mentioned, we need to turn the nut and not the screw in that case. This requires the motor to be coupled to the nut through a gear and cannot be directly driven. This requires some very good DIY skills. The idea behind my project was to use off the shelf commodity components and keep fabrication to the minimum.

 

Regards,

Arun

I understand what you're doing and approve, I was just responding to Ed.  I think it would lend itself to autoguiding just fine but I'd have to think about how it would work for a while.  ;)



#8 Geo.

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Posted 18 April 2018 - 01:11 PM

Arun, nice project. You may want to take a look at the Arduino Button.h library. It really can save a lot of coding for switch control inputs. Example from my RA code:

 

Button button1 = Button(5); //setup your button pins
Button button2 = Button(4);

 

void loop() {
motor.step(1);
motor.setSpeed(motorSpeed);
if(button1.isPressed()){
    motor.setSpeed(motorSpeed * 2); // i.e. 150 RPM
  }
else {
    motor.setSpeed(motorSpeed); //i.e. 75 RPM
  }

 

The button call takes care of debounce, acceleration ramping and pin change of state. My code for a simple RA sidereal drive is about 30 lines and 15 more to add a Dec drive. As my input pins are pulled high, the SPST switches just pull them low. Thus implementing ST-4 is simply a matter of wiring a parallel plug. I'm now porting the code to the TB6612FNG motor shield from an L293 driver.

 

Presumably, you would only guide in RA as Dec is fixed. So a 50mm finder based guide scope, board camera and PC or Phablet (https://www.cloudyni...android-device/). Looks like a lot of expense and complexity for a SCOTCH mount! OK, I get motorizing the barndoor rather than using hand power and a stop watch. And using math to overcome the inherent inaccuracy of the straight screw goes along with the minimalism of the barndoor. But the whole concept is lightness and economy. 

 

Better you pick up a CG-5 used for $125. Add a simple Arduino based stepper drive system (Nano & TB6612FNG motor shield) with a ST-4 interface, a standalone NexGuide camera for another $150-60 plus couple  K code and have something you can mount a camera or a scope and still have portability.. 


Edited by Geo., 18 April 2018 - 01:38 PM.


#9 arun289

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Posted 21 April 2018 - 12:31 PM

Arun, nice project. You may want to take a look at the Arduino Button.h library. It really can save a lot of coding for switch control inputs. Example from my RA code:

 

Button button1 = Button(5); //setup your button pins
Button button2 = Button(4);

 

void loop() {
motor.step(1);
motor.setSpeed(motorSpeed);
if(button1.isPressed()){
    motor.setSpeed(motorSpeed * 2); // i.e. 150 RPM
  }
else {
    motor.setSpeed(motorSpeed); //i.e. 75 RPM
  }

 

The button call takes care of debounce, acceleration ramping and pin change of state. My code for a simple RA sidereal drive is about 30 lines and 15 more to add a Dec drive. As my input pins are pulled high, the SPST switches just pull them low. Thus implementing ST-4 is simply a matter of wiring a parallel plug. I'm now porting the code to the TB6612FNG motor shield from an L293 driver.

 

Presumably, you would only guide in RA as Dec is fixed. So a 50mm finder based guide scope, board camera and PC or Phablet (https://www.cloudyni...android-device/). Looks like a lot of expense and complexity for a SCOTCH mount! OK, I get motorizing the barndoor rather than using hand power and a stop watch. And using math to overcome the inherent inaccuracy of the straight screw goes along with the minimalism of the barndoor. But the whole concept is lightness and economy. 

 

Better you pick up a CG-5 used for $125. Add a simple Arduino based stepper drive system (Nano & TB6612FNG motor shield) with a ST-4 interface, a standalone NexGuide camera for another $150-60 plus couple  K code and have something you can mount a camera or a scope and still have portability.. 

Thanks!

Connecting ST-4 in parallel is a really cool idea.

Thanks for pointing to the button library.

 

Regarding the economy, the electronics involved is not very expensive though. Clones of the arduino and the DRV8825 is available for less than $10 in India.

 

Regards,

Arun



#10 tommm

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Posted 22 April 2018 - 09:03 AM

Simple and inexpensive solution for someone who knows a bit about software/arduino and wants to take some low power photos with a camera. Regarding curved rod, it's generally easier and more desirable to do things in software than hardware. And easier to modify later.  Easier to tweak constants in the code than tweak the bend in the rod. Can do it at night while you are using the tracker. Nice work Arun!


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#11 555aaa

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Posted 22 April 2018 - 03:07 PM

Nice project. With guiding one would be schlepping their laptop around. At that point the Arduino isn't really needed any more, you can control the stepper driver via a Windows program that either uses a USB parallel port emulator or via a fancier motor driver. With windows one can also write an ascom driver for it that can link to the guide sw to eliminate the ST4 port. The ASCOM mount driver is non trivial however.
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#12 Geo.

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Posted 23 April 2018 - 10:00 AM

Thanks!

Connecting ST-4 in parallel is a really cool idea.

Thanks for pointing to the button library.

 

Regarding the economy, the electronics involved is not very expensive though. Clones of the arduino and the DRV8825 is available for less than $10 in India.

 

Regards,

Arun

My comments were addressed more at the idea of guiding a barn door. I draw the line at and optical finder!


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#13 tommm

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Posted 23 April 2018 - 10:10 AM

Arun, your present design would make a nice school project. Combine coding with astronomy, and it is relatively low cost, just make a wedge to mount it on rather than using a tripod.


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