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Custom Builds for the EQ5


Drawbacks of the Dual-Axis Kit

When AstroEQ was first designed, I like many had the dual axis kit for my EQ5. Naturally I designed AstroEQ to work with those motors. However what quickly became apparent is that they are simply not build for use with a Go-To system. They work fine for tracking, and occasional small corrections in position, but for Go-To they are simply too slow.


It all comes down to the gear box. The motors come with a 120:1 gear box attached which means that the motor has to spin 120 times, or 5760 steps for one revolution of the work gear. To get high speed movements like the 800x speeds that you can get from the Synscan systems would require the motors to spin far faster than they are capable and so they just stall out. The gearboxes are not exactly precision either which only adds to the problem. All in all you can get around 50x speeds out of them, put that in perspective, it would take 14 minutes for the telescope to move from one side of the sky to the other - that's 14 minutes of precious astronomy time wasted!


Of course then if you are interested in Astrophotography you ask even more out of the motors, you want them to be able to guide the scope using PHD or an autoguider. Then the motors seem even more hellish. For the RA motor it isn't that bad, people have guided quite happily with that axis for over 10 minutes with a 200p newt. But the DEC motor, that is a different story as that one needs to keep changing direction. The aforementioned gearboxes have so much backlash in them that you need to run them at 0.9x speed for almost a second before the mount starts moving the other direction.


What are the Alternatives?

So you are now wondering, well then, what is the point in AstroEQ if you can't guide with it and the Go-To movements take forever. Lets get something straight, those aren't shortcomings of AstroEQ, they are shortcomings of the dual-axis kit. AstroEQ can guide, it can guide well, and it can happily achieve 1200x Go-To movements with the right motors - theoretically the software could do 40000x speeds, but I doubt anyone would want there telescope moving across the sky in 1 second flat, something would surely break 8-O!


Next question then, where do I get these amazing motors from? Well truth be told, there are many different stepper motors in all sorts of shapes and sizes which will all work well, and many places which sell timing pulleys and belts at reasonable cost. The main hurdle to overcome is mounting the motors to your telescope mount, and for that you need to get creative one cloudy evening. See the section below for more info.


Final question, why don't you sell these if they are so much better? Well that one is simple, I don't have the same purchasing/manufacturing power of Skywatcher or other large companies, I'm just a student sat in his room soldering together these controllers. I've tried looking several times for someone who would manufacture the metal brackets for mounting the motors, but the quotes I have had for anything less than thousands of these things has simply been ridiculous.

EDIT: An AstroEQ user with contacts in the CNC industry had a small number of the NEMA14 brackets (designs below) fabricated. He is currently selling 3 pairs on eBay for a reasonable price. You can find the brackets on eBay here.


Of course there are other alternatives to DIY. It is possible to get stepper motors/motor brackets from companies which were designed to fit onto EQ mounts as after market parts if you look hard enough. It is also possible to get things 3D printed nowadays which may make some decent brackets. You may also know someone locally that could fabricate something for you.


Making Your Own

Early on I ditched my dual axis motors and spent a weekend fabricating some motor brackets from a bit of angle Aluminium that I got off eBay. So I figure you might like a parts list (in fact two people has already made a pair!). I designed the brackets using Google Sketchup and have included dimensions. There are two sizes of brackets, one for the smaller NEMA11 motors, and one for the more standard NEMA14 motors:

Here's an idea of what you need for an EQ5 mount using the bracket design:

  • 2 x Bipolar Stepper Motors, with the following spec:
    • Rated Current: <1.2A per Phase
    • Rated Voltage: lower is better, look for around 3V to 4V. Lower voltage = Higher current though.
    • Inductance: again, lower is better. Look for something <10mH per phase
    • Step Angle: typically 1.8 degrees.
    • Examples:
      • NEMA 14 like these
      • NEMA 11 like these
      • There are many others and from many different shops, the above are just examples.
  • 2 x RJ11 6P4C Sockets
    • These are for connecting the motors to the same cables as the Dual-Axis kit.
    • Here is one example, though you can find them easily on eBay.
    • Connections are simple, one motor coil to contacts 2 & 5, the other to contacts 3 & 4.
  • 2 x 40 Tooth Timing Pulleys with 6mm Bore
    • This is what I got.
    • Ask for a 6mm bore and an M3 Grub Screw
  • 2 x 15 Tooth Timing Pulleys with 5mm Bore (or whatever diameter motor shaft you have)
    • This is what I got.
    • Those already have grub screws, so you don't need to ask for one.
  • 2 x Timing Belts (1x 61 Tooth, 1 x 63Tooth) with a 6.35mm width (or to match your pulleys if different from above)
  • Some Metal, Angle and Bar
    • Stuff to make the motor brackets with. You could use plastic I suppose.
    • In the designs, you will notice the pieces look like an Angle piece with a flat bar attached.
    • You can get 60mmx60mm Aluminium Angle which is 2mm thick of eBay quite cheaply.
    • You can also get 20mmx6mm Aluminium Flat Bar of eBay cheaply as well.

That should be about everything you need. Depending on where you source the parts, the costs are probably similar to the dual axis kit, but what you end up with is something much more reliable and higher quality, not to mention far superior performance in both guiding and Go-To speeds.