Star Tracking

Projects General Guidance
1

Hello guys!

I'm trying to make a star tracking device for my camera.
My regular setup (20mm ultra wide lens) can make 25seconds exposure without any star trail but after that world is spinning and I lost all sharpness.

My goal is reach the 2+ minutes exposure for now.

But I'm not building a barn door tracking system.
It's big, heavy and useless (if you are planing much longer exposure is different story of course).

This is Vixen Polarie

Very portable and effective way to make long exposure like 5 minutes.

This is Chinese YSF rotator. "Smallest" tracker on market right now.

My plan building the same. Nothing fancy, no extra setting, no LCD, or WiFi connection or remote... anything.
Just 4 leds that will show me the time of exposure and on-off switch.

And this is my first prototype ;D

It's work but big and need perfection touch"es"

  • I already have Arduino nano
  • DRV8825
  • Nema 14 7,4v motor but I'll change it with smaller one.
  • 1/65,1 gearbox (or reduction gear, not sure about name)
  • I'm planing to use green laser pointer to align northern star.

I don't know how to code but there is a lot of work around and found my way some how.

I already bought this motor.
https://www.aliexpress.com/item/1PCS-Japanese-Original-FDK-7-5-degrees-35MM-Two-Phase-Four-Wire-Circular-Stepper-Motor/32896036269.html?spm=a2g0s.9042311.0.0.13524c4da11SAK
If you have any suggestion under 10$ I'm open for it.

If I think about this motor;
7,5 degree, total 48 step motor.
I do some math.
Earth making 360 degree spin every 1436 minutes (86160 seconds).
Which mean 0,004178 degree every second.

My motor give me every step 7,5 degree
Driver give me 1/32 micro stepping
Also 1/65,1 gearbox for slowing the motor and reduce vibration.

A believe if I give every 0,85 second 1 pulse that will make approx. 0,004 degree.

At this point am I missing or forget any step?

And yes there is a lot of topic about barn door tracking but I didn't find this kind tracking.
Also searching and reading older topic for good advices.

Thanks for help anyway.!

2

I would suggest you get a better motor. one that has 200 steps per revolution. the one you show has 48. that means each step has to rely on micro-stepping. it is better to not rely on micro-stepping if possible.

the gearbox with 65:1 reduction is OK

count the teeth on the large gear. the page is wrong if it says 14.4:1 it is more like 80:1

80 teeth, 200 steps, quarter step
80200quarter step (4) = 64,000 steps per revolution
360 / 64,000 = 0.005625

1/8 step = 0.0028125 stepper per revolution.

3

I'm running motor very slowly that's way I don't need a too much steps but yes past a couple days experience says don't trust on micro stepping. Especially if you are using cheap driver like DRV8825 or TMC2100 (TMC2100 is good but Chinese copy are not).
Well actually I'm looking a motor right now.
If I can found a 200steps motor I like to use it.

Gearbox isn't a problem. I already have a couple different stuff.

First prototype I used this DC motor gearbox.

But this is big and doesn't have a flat surface. Kind a weird shape.

I found another DC motor in my garbage with gearbox on it.

It's small and I can put on top the stepper motor.

This way I can make whole system way more compact size.
Like 80x80x80mm which probably I can't found a plastic box like this shape but it's ok. Smallest always better.

Also tooth are metal not plastic. Which is great!
You can buy this gear parts on aliexpress but it's too expensive. But you can buy 1RPM DC motor with gearbox on it much more cheaper :grin:

4

Also about motor steps.
200steps is great OK but I must use micro-stepping.
Stepper motors are very strong they hit like a hammer every step. Micro-stepping make them very soft, smooth steps.
I don't care about sound but vibration is most important issue.
Soon or later I can make the right hardware, code and spin but with vibration all of work will be useless.

5

If the purpose of the project is to rotate a camera in sync with the movement of the earth so that you can take a long single exposure without the stars seeming to move then I suspect a stepper motor is not appropriate because they ALL move in jerks.

IMHO a very low-geared DC motor with a suitable speed control system would be much more suitable. These small gearmotors are widely available and some have very low gearing.

A stepper motor would be more suitable for a system where you take a separate exposure after every step and amalgamate the images afterwards.

...R

6

Robin2:
If the purpose of the project is to rotate a camera in sync with the movement of the earth so that you can take a long single exposure without the stars seeming to move then I suspect a stepper motor is not appropriate because they ALL move in jerks.

IMHO a very low-geared DC motor with a suitable speed control system would be much more suitable. These small gearmotors are widely available and some have very low gearing.

A stepper motor would be more suitable for a system where you take a separate exposure after every step and amalgamate the images afterwards.

...R

Purpose of project is correct.

DC motor is easy but is it work? I'm not sure about that.

I need 0,25RPM speed but DC motor can't run this slow.
I have to use 2 gearbox or a custom gearbox (which isn't easy) to make it super slow.

Here is a Vixen Polarie inside look.

I'm not an expert but there is 6 wire on motor. It can't be a DC motor right?
If they can make it with stepper motor, I can ;D

---Also;
Is it possible to cut stepper motor shaft?
With metal saw very slowly and gently.

7

Stick with the stepper, it's what everybody else does. I submit that the only requirement of the stepper is that the aforementioned jerks are less than the maximum exposure allowable for a fixed camera, and they should all pass that by miles.

8

Yes I can cut the motor shaft and make it smaller

750×1000 157 KB

9

Just had another thought. How many degrees of rotation will your camera need? If you just want a few minutes of exposure time I suspect the number of degrees will be small. The earth rotates 360° in 1440 minutes so it will only move 1.25° in 5 minutes. (Assuming my maths is correct).

What about using a screwed rod and a lever to move the camera - I think it would be a lot more precise for small movements.

An M6 screw has a pitch of 1mm so the 200 steps of a motor would each move 0.005mm - and with micro-stepping the motion per step would be very much smaller.

...R

10

Sorry but I couldn't picture it.
You mean like a slider?
https://www.proaim.com/media/wysiwyg/Images/Camera-Sliders/Curve/Proaim-Curve-120-Curved-Camera-Slider-on-2-tripod.jpg

BTW this is my code

void setup() {                
  pinMode(2, OUTPUT); //Direction
  pinMode(3, OUTPUT); //Step
  pinMode(4, OUTPUT); //MS0
  pinMode(5, OUTPUT); //MS1
  pinMode(6, OUTPUT); //MS2
  pinMode(7, INPUT_PULLUP); //Button
  digitalWrite(2, LOW);
  digitalWrite(3, LOW);
  digitalWrite(4, HIGH);
  digitalWrite(5, HIGH);
  digitalWrite(6, HIGH);
}

void loop() {
  if(digitalRead(7) == LOW)
  {
  digitalWrite(3, HIGH);
  delay(1);          
 digitalWrite(3, LOW);
  delay(0);
  } 
}

Extremely simple ::slight_smile:
But works just fine I guess.

I have a simple cable remote for my camera.
There is 3 wire GND / Focus / Shutter
I'll make some modification to use it with camera and trigger for system.
When I stop shooting also motor will stop.
Very simple setup, no extra hardware needed.

But I also wanna add leds to system that will show me how long I'm shooting.
I wrote an another basic code. It's work standalone but I couldn't combine with motor.

void setup() {  
pinMode(8, OUTPUT); //Green LED
pinMode(9, OUTPUT); //Yellow LED
pinMode(10, OUTPUT); //Yellow LED
pinMode(11, OUTPUT); //Red LED

}

void loop(){
digitalWrite(8,HIGH);
digitalWrite(9,LOW);
digitalWrite(10,LOW);
digitalWrite(11,LOW);
delay(25000);
digitalWrite(8,HIGH);
digitalWrite(9,HIGH);
digitalWrite(10,LOW);
digitalWrite(11,LOW);;
delay(15000);
digitalWrite(8,HIGH);
digitalWrite(9,HIGH);
digitalWrite(10,HIGH);
digitalWrite(11,LOW);;
delay(20000);
digitalWrite(8,LOW);
digitalWrite(9,LOW);
digitalWrite(10,LOW);
digitalWrite(11,HIGH);
delay(9999999);
}

When system triggered;
First 25 seconds green led will on that's mean I'm in safe exposure zone.
Between 25-40 seconds first yellow led ON
40-60 seconds yellow led ON
After 60 seconds later only red led ON which mean danger zone.

11

sebatiantr:
Sorry but I couldn't picture it.
You mean like a slider?

I have something very much simpler in mind. Think of this diagram as looking up from the bottom

CameraScrew.png

...R

CameraScrew.png

12

OK I see it now.
This is technically a motorized camera slider.

1280×720 58.8 KB

Yes it might work for short exposure like 1-2min or more. I don't know.
But this is not a stable work.

System looks very simple but keeping camera stable will be very difficult.
Also I want as soon as possible small thing that going to my bag and easy to set for shooting.

This video show how easy to use of this YSF rotator

I want that easy even more easy ;D

I'm doing it.
I'll do some hardware modification today.

Actually I'm all done I just have a problem with size and combine that 2 codes.
That's way I'll cut the motor shaft and also probably will do a custom gearbox for smaller size.

13

sebatiantr:
OK I see it now.
This is technically a motorized camera slider.

My diagram is a rotator, not a slider..

Why would it be any more difficult to keep the camera stable? That only depends on the mounting pivot.

...R

14

Robin2:
My diagram is a rotator, not a slider..

Why would it be any more difficult to keep the camera stable? That only depends on the mounting pivot.

...R

When motor start turning, screw will turn.
Nut will not turn because lever holding it. This way nut will slide up and down which makes lever and camera make movement in up and down or left or right you name it.

I don't know how this will turn the camera.

15

sebatiantr:
or left or right you name it.

I have been under the impression that you want to rotate the camera left to right (or right to left?

Cut out a piece of cardboard in the shape of my diagram for the camera and lever. Put your finger on the pivot point and move the of the lever (where the nut is).

...R

16

google barn door tracker. that is what you are describing.

Size is dependent on skills of builder. Smaller than a camera is possible.
Before you get too far, is battery power important ?
A stepper will need a small car battery due to inefficiencies of the motor.

A DC gear motor with encoder would be a better choice.
If the camera is balanced well on the mounting, then a small motor is all that is needed.
Not sure if they make a servo with a super high encoder.

17

Robin2:
I have been under the impression that you want to rotate the camera left to right (or right to left?

Cut out a piece of cardboard in the shape of my diagram for the camera and lever. Put your finger on the pivot point and move the of the lever (where the nut is).

...R

When I move lever camera will move with it.
This is exactly a slider. Technically yes it will move left or right axis and might do what I want but this is not rotator it's slider.

@dave-in-nj
I don't want a barn door. it's big.
Also I don't need a 3 hours of exposure. 1-5minutes super fine for me.

I'm using my camera battery. Sony NP-NW50 7.4v 1000mAh.
It's enough for over 2.5 hours work also I can charge it very easily.

18

Please re-read my post.
I said that you guys are talking about the design of a barn door tracker.

If you are saying yoy have seen barndoor trackers that are large, i understand.
If you are saying do not feel that your build skills are not up to making a barn door that is the size of a deck of cards, i can understand that too

There is no physical reason one cannot be made that is the size of a deck of cards. A floppy drive has way more parts than you need and is a huge empty cavity.

The barn door tracker is designed for short times. 3 to 5 minutes....
This does not mean that a barn door is the best. A rotating mount with worm gear is also a choice. The worm is for longer times, possbly hours
The worm can be made as small as a barn door if your build skills are up to it.

19

This is smallest star tracker;

This is regular DIY barn door tracker;

How we can compare of size of these two ;D

It's not about the size. Barn door doesn't have any shape. You can't put in a backpack and go outside.
But if I can make it a cube it can be fit anywhere. More important It will be solid.
I'll not care about edges, sharp screws, nail, bump, metal parts etc.
Just a simple box.

lets forget about barn door system.
I'm already working on something.

Can we back to my codes?
How can I combine with both motor and LED parts?

20

sebatiantr:
When I move lever camera will move with it.
This is exactly a slider. Technically yes it will move left or right axis and might do what I want but this is not rotator it's slider.

How can the camera slide if it is fixed to a rotating pivot.

This is getting ridiculous.

...R