Please Help - Can't Get My Barn Tracker To Work !!!

[Chuleton08]

Hello Everyone,

I've just started my Astrophotography journey, and I've decided to build a DIY barn tracker which I 3D printed. I can't seem to get even a 30 second long exposure without star trails. The big wheel spins once every minute, which is correct, and I'm pretty sure its polar aligned, as when I put my phone with Polaris in Stellarium, it aligns up with everything. Maybe Its not orientated the right way or something. I have attached a photo of the set up, with north being straight on, and east being where the arm is pointing to. I am located near Chichester in the UK if that helps.

If you need more details, please ask and I will try my best to respond.

Thanks in Advance!

Here is the Tracker Set up

https://imgur.com/a/x7LWrA3

[vlaiv]

Do you have any idea if star trails appear in RA or DEC direction?

That would be a good place to start - examine images you took and compare them with stellarium rendering. Determine RA and DEC directions in your image and see if trailing is in RA or DEC.

If it's in the RA direction - then it is drive and my advice for next step would be to make sure you are tracking at sidereal speed.

If it's in the DEC direction - then you have issue with polar alignment, and I'd look into getting it better. One simple trick would be to add a straw or some small diameter tube to your setup so that it's aligned with axis of tracking (aligned with RA axis) and then when you polar align everything - you should be able to see Polaris thru the straw/tube. That should be precise enough for 30s exposures without much trailing.

[Chuleton08]

Thanks Viaiv for the reply,

I have attached an image to here of a 30 sec exposure with the tracking on.

[vlaiv]

4 minutes ago, Chuleton08 said:

I have attached an image to here of a 30 sec exposure with the tracking on.

Do you have any idea what part of the sky you imaged?

From what I can tell - it looks like it's general type of "wobble" - usually because of lack of stiffness and general jaggedness of motion. I'm betting it is in RA direction and it is due to construction of the barn door tracker.

Since you have 3d printer - why don't you try to create motion system that is more suited for 3d printing rather than using bent threaded rod?

On the other hand, if you want to try to fix this, and see if you can improve it. Here is what I would consider doing:

1. Make thicker bearings and apply angle to teeth for more contact / better meshing. That should also reduce any errors (average them out). You can also try herring bone gears (double angled).

So this:

or this:

2. add some bearings on both sides of larger gear to constrain its rotation axis and prevent any wobble.

3. Use "nut" with longer thread - or as long as you can before it starts interfering with curvature of threaded rod

4. Apply lubrication (if you have not done so already)

5. Maybe think of switching to belted drive between stepper and threaded rod instead of use of gears

 

[Chuleton08]

Thanks for all of this. I will definitely try out some of these ideas!

[happy-kat]

Hi

Northern hemisphere which is UK the hinge needs to be aligned at Polaris and the boards facing East. When the motor runs the top board should open upwards and round towards the West.

The camera can point anywhere

Edited June 21 by happy-kat

[Chuleton08]

Hi, thanks for the reply,

On reddit, I found out I was properly polar aligned, and it was more of a mechanical issue instead.

[happy-kat]

If you have a shorter focal length lens I'd start with that, if you have a kit lens try that at it's widest and get a feel for what your tracker can do. Try lengthening the lens and try again. In general pointing East or West keeping below 60 degrees would be less prone to star trails. There's a link to my barn door build in my signature, not sure if that shows in mobile view.

[Chuleton08]

 Yea, someone else recommended me to take photos with a shorter focal length, so im going to see how the tracker works with that. Thanks.