Lowest Cost DIY 2 Axis Autoguiding Setup?

[bobro]

Previously I posted my efforts at a DIY autoguiding setup https://stargazerslounge.com/topic/285181-diy-eq2-economy-autoguiding/

This setup used a Raspberry PI and Lin_guider for guiding, driving DC Economy RA motors for RA and DEC and works well.

As an alternative (and simpler/lower cost setup) the PI/Lin_guider combination has been replaced by PHD2 running on the laptop and an Arduino Nano acting as an Ascom interface to drive the Economy RA motors in a similar (though not identical) way to an ST4 interface. This is a potential, and very low cost, way for someone with a basic reflector scope without Goto to upgrade to a single or dual-axis guided system. It does require some DIY skills though. Note the motors cost about £30 each and are simple DC - not stepper motors. Some scopes come with a single RA motor.

Only 3 batteries in the setup : PC, RA motor (PP3), and camera. The DEC motor is driven by the Arduino output and hence the PCs USB output.

Code for the Arduino is at : https://hackaday.io/project/4386-arduino-st4-telescope-control

Testing so far has shown the setup produces a similar guided result to the PI/Lin_guider config. Having PHD2 on the laptop provides a very good set of utilities for polar alignment etc. Although Astro Photography Tool is used on the PC, any image capture method could be employed.

There's not a great deal in the sky other than small galaxies I can image at present, so apologies for the lack of images. Galaxies images are composed of 300 second subs.

If there's interest I can post more details.

 

[SteveBz]

HI Bobro

I love these little spring galaxies.  Not so little really, just far far away.

I've got my arduino guider working with some home made code. I have a couple of issues. One is that my Arduino now does everything I can throw at it so I need to be able to deal with contention. The other is that my camera really is not sensitive enough even with the gain turned right up. I don't know if I can do a mechanical mod to it to up it's sensitivity.  Otherwise I need to bite the bullet and she'll out for a proper guide cam.

Good luck with the weather. Have you seen iTelescope? I haven't tried it as it involves money but you can rent telescope time in other clear locations on a monthly basis.

Regards

Steve.

[adder001]

Thats brill. Thanks for the info

[bobro]

1 hour ago, SteveBz said:

Otherwise I need to bite the bullet and she'll out for a proper guide cam.

Yes, I found it slightly tricky trying to find a suitable guide star when imaging the Virgo galaxies - my thoughts also turned to a proper guide-cam. QHY5-II perhaps. Glad you have your Arduino guider working - a great little device! Must admit I don't find using an online telescope too interesting - a bit like downloading someone else's images. DIYing is more fun for me!

[SteveBz]

2 minutes ago, bobro said:

Must admit I don't find using an online telescope too interesting - a bit like downloading someone else's images. DIYing is more fun for me!

I agree, however the renowned Damian Peach swears by it.

Regarding finding a guide-star, the experts on this site all say you shouldn't have to use guide rings, but I was running around (on tiptoe), pulling out the guide cam, inserting an eyepiece, finding a star optically with the guide rings, thinking about re-installing the finderscope on the guidescope, trying not to hit the telescope, centring the star, reinserting the guidecam, re-finding focus on the guidecam, and then guiding.  But after all the faffing, it worked. And I was so chuffed, but then the software was playing up and it was midnight, and I was thinking do I really want to debug at this time of night. 

And so I didn't.

Steve.

[bobro]

The AR0130 sensor is used on some guide cameras (e.g. https://www.altairastro.com/Altair-GPCAM-Colour-BASIC-Guide-Imaging-Camera.html ) and is also available as a module, so I've ordered a module from Amazon ( https://www.amazon.co.uk/ELP-illumination-Industrial-Equipment-megapixel/dp/B01HYVF4DK/ref=sr_1_12?ie=UTF8&qid=1493115983&sr=8-12&keywords=ar0130 ) to see how well it works. 

[SteveBz]

19 hours ago, bobro said:

The AR0130 sensor is used on some guide cameras (e.g. https://www.altairastro.com/Altair-GPCAM-Colour-BASIC-Guide-Imaging-Camera.html ) and is also available as a module, so I've ordered a module from Amazon ( https://www.amazon.co.uk/ELP-illumination-Industrial-Equipment-megapixel/dp/B01HYVF4DK/ref=sr_1_12?ie=UTF8&qid=1493115983&sr=8-12&keywords=ar0130 ) to see how well it works. 

Hi Bobro,

Very cool.  That might be the right answer.

I'm about to go down another route. Did you see my post on your other thread regarding stacking in Orion in "Add" mode?  It brought out dozens of stars not visible in the original. Based on this idea and the ideas that:

1) an object doesn't move very much in one second; and

2) my poor cousin of a webcam still takes 30 frames per second.

I could theoretically stack up to 30 frames per second giving essentially one stacked frame every few seconds.  Good enough for guiding. If I also automatically subtract the noise the same way, it could potentially create a slow stream of more sensitive images.  Even if for CPU reasons I can only stack, say five frames every ten seconds, it could make a difference.

I am ashamed to say I have also put the v. v. cheap finderscope that came with the telescope I'm using as a guider, back on to allow me to find stars without removing the camera.

Let me know how the sensor module goes.  How will you mount it?

Steve

[bobro]

16 hours ago, SteveBz said:

Did you see my post on your other thread regarding stacking in Orion in "Add" mode?

Hi Steve,

Yes, I did see your post. I suppose adding images this way is a form of stretching (plus noise reduction) as the resulting image is brighter? Sounds like a lot of processing to real-time stack images for guiding.

Another idea for sensitive guiding is to really reduce the focal length a lot. This site has low cost lenses that could be mounted in a modified OTA:  http://www.astromediashop.co.uk/Components.html

For example, I think your scope has a 50mm lens and 360mm focal length - give f# of 360/50= 7.3. Replacing the lend with an 182mm one would give f#=3.64. As the illumination is a square law it would mean 4 times the intensity of light falling on the sensor, plus a wider field of view, making it easier to find a guide star. Would mean a mod to the guide scope of course. Just an idea....

No idea at present how to mount the AR0130. I'll see how it goes first. Could perhaps get a plastic mount made as I know someone with a 3-d printer. Would need to learn the 3-d software first! 

Bob

[SteveBz]

12 hours ago, bobro said:

For example, I think your scope has a 50mm lens and 360mm focal length - give f# of 360/50= 7.3. Replacing the lend with an 182mm one would give f#=3.64. As the illumination is a square law it would mean 4 times the intensity of light falling on the sensor, plus a wider field of view, making it easier to find a guide star. Would mean a mod to the guide scope of course. Just an idea....

Hi Bob,

Great idea and very cheap.  But as I'd need to destroy my current guidescope by cutting it in half, I'm going to try the stacking or intensifying first.  Actually my current software already does it for finding a star (when there's no time pressure), but not when guiding.  I'd just need to replicate that, maybe two frames at first and see how it goes.  I'd want to do at least one 'guide' every ten to 15 secs.

Steve.