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DIY EQ2 Economy Autoguiding


bobro

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4 hours ago, bobro said:

Maximum correction - large guiding corrections shouldn't be necessary, though may be calculated due to wind on the mount. Limiting the maximum correction helps stop sending the scope too far off course (it should come back as the wind effect disappears). 500msec is a good starting value for this.

So have I got this right?  I assume that your measurements are in msecs of RA (ie our normal clock and not out of 360 degrees).  Were I to do this manually, if I were correcting at twice Earth speed (ie tracking plus 1), it would need to correct for up to half a second.  You also say that 50 msecs is the minimum useful correction (ie one twentieth of a second at 2x).  So if I were to specify corrections in tenths of a second at 2x Earth speed, that might be a useful range to test, ie  .1 sec, .2 sec, .3 sec, .4 sec and .5 sec.  And maybe I should log the corrections to a .txt file.

When (or if) the sky clears I'll try those.

As another point does anyone have any ideas for adjusting the relative direction of the guide scope?  Eg if you want to image the Horse-Head nebula and you plan to guide on Zeta Orionis (Alnitak).  You steer the OTA remotely via your handset to the HH Neb, but then you have to run outside and fiddle with the alignment screws to direct your guide scope.  Wouldn't  a couple of stepper motors and some extra pins on your Arduino would do the job equally well?  What do people think?

Regards

Steve.

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1 hour ago, SteveBz said:

I assume that your measurements are in msecs of RA

Lin_guider's settings are in time duration (msec). This determines the period during which the relay contacts are active in my setup. PHD may be different. Correction time for your setup may be quite different from mine - only testing will tell. The text file corrections could be useful in drawing a graph.

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  • 4 years later...

Hey there! 

 

 

I know this is a long dead thread, but here goes nothing.

Let me start by saying thank you! I, too, was struggling with inconsistent tracking when using the EQ2 motor and this autoguiding project was a true life saver. 

I managed to adapt your project and make it work with an Arduino and PHD2 (through some custom ASCOM drivers written by someone) with the RA motor only. It works really well, even for exposures of 2 minutes, but the DEC drift starts to show up... I can't really do a very good polar alignment, given the EQ2s' lack of fine AZ control and lack of a polar scope. PHD2 polar drift is somewhat successful, but it's still not perfect. So... I went ahead and ordered a second Motor for the DEC axis as well and I am in the process of mounting it on the scope, but I'm wondering how you have attached the motor to the mount.. The bracket that comes with the motor doesn't really go anywhere on the mount. Also, did you have any trouble with the fact that the DEC adjustment screws in and out? I know the adjustment will be very fine, but I was wondering if at some point it gets too far in/out and starts bending the motor. 

 

Any help will be greatly appreciated! 

 

 

Thank you!

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Hi @Flo94218,

Good to see someone else having fun with getting an EQ2 to guide. Following on from using LinGuider, I went down the same path as yourself, using an Arduino and PHD2 for guiding - worked well as you have found.

The lack of fine AZ adjustment does make polar alignment trickier. I used Sharpcap for this, and still do with my EQ5.

Fitting the DEC motor was straightforward using a simple L bracket and flexible coupling - see attached image. There is plenty of adjustment on DEC, so it's just a case of setting the screw somewhere around the middle of its range. Guiding only moves the screw a small amount one way or the other, so there's no worry about reaching the screw's limit. In fact, the tangent arm DEC arrangement makes for very good DEC guiding as the backlash found with a worm and grub arrangement doesn't exist. I wish my EQ5 guided as well in DEC!

To drive the motor either no voltage, +5V or -5V was supplied, depending on the guiding requirement from PHD2. The circuit board from the motor housing wasn't used for DEC.

Looking forward to hearing how your dual axis guiding goes!

DEC Motor.jpg

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Thank you for the tip!

 

I ended up making a hole straight into that metal piece and taping a screw there. Holds fine, no movement whatsoever. I also thought that the elastic coupler would work fine against the in/out issue, but hearing someone that has been using it for a while puts my mind at ease.

I will try looking into sharpcap for polar alignment, the one in PHD2 is kinda unintuitive for me... never used that software before. I used the same 9V for the DEC motor as well, I hope it won't be too powerful and send it over shooting, but I think phd2 knows how to deal with that.

I am currently using a camera lens stuck at 50mm and a generic Webcam 1/2.7". It sees the stars pretty well, but I might need to get a longer focal length guide scope.. I am imaging with a 130/920 omegon reflector and a Canon 1100D and that 50mm is waaaaay too small, I think it's best that the guide scope is 1 third of the main scope's focal length..  I am not sure if the crop factor applies in the equation as well or not.

I managed to get a pretty good shot of M42, 8x30sec 1600ISO using RA guiding only with really crappy polar alignment, but I think it came out really great for a 300 euro setup lol.

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Edited by Flo94218
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That's a pretty good image for a 920mm FL reflector on an EQ2! Nice colours.

Looks as though guiding is working well as it's difficult to get the simple RA motor to track accurately for 30 seconds. A longer FL guide scope will likely have a higher F# than the lens you are currently using, which means less light getting through to the guide camera, possibly making it difficult to detect stars. I initially used a  Microsoft Cinema webcam so chose an Orion Mini 50mm guidescope as it has a relatively low F# of 3.2, which helped with detecting stars.

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Thanks! 

 

Last night, I've moved the tracker's circuit to the Arduino box and attached a much bigger 10k potentiometer with a chicken-head knob, so it's much easier to finely adjust the tracking speed... my thought was that, if I can get the tracking speed as close as I can to the right one, fewer guiding pulses will be needed, which, I guess, it's a good thing. 

By doing that, I've also removed the big plastic box, so that I get a larger sweep of the telescope before something hits the tracker. I guess there might be a way to flip the whole assembly 180 degrees, so that it points downward, but I can't be bothered to make another bracket for just a few more degrees of movement. 

Really looking forward to testing it. Sadly, I've only had cloudy nights ever since last Saturday (when I actually took the photo above). More time for diy-ing I guess :D 

It would've been really cool if a slewing mod could be implemented, although, with the stock tracking motors, it would have been a veeery slow slew. Also, the DEC screw is stopping anyone from doing a real slew mode on both axes. 

I will assume that you have removed the big gear for the same reason, correct? I might hack that off as well. 

 

As for the photo, thank you! It's not as good as I would've wanted it to be, but I have just discovered that the main mirror was completely coated by a layer of dust and everything was really hazy when looking at it, so I gave it a good cleaning and now I hope it's gonna make a difference. The colours have been tweaked quite alot.. it was more towards a red-ish  hue (probably because of the astromod on the camera).

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You can see in the attached image that I too added a larger knob to the RA motor speed control. When guiding as the battery voltage reducing slightly, I would adjust the speed knob to provide a roughly equal number of slow/fast guiding pulses as they varied as the battery voltage dropped. Not critical though.

Although it would be really useful, I don't think accurate slewing is really possible with this setup due to the DEC arrangement and the lack of precise stepper motors.

The large gear was cut off in a bid to provide more space for the motor, though it wasn't really necessary as it turned out.

Another mod I did was to lengthen the counterweight shaft to allow the weight to be moved slightly further out and achieve a balance. It pushed the EQ2 beyond its design limit, but it did cope. 

If you haven't already imaged the Pleiades, they are a lovely target that are easy to find.

 

 

DSC_0014.JPG

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  • 4 weeks later...

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