Star Sailor Mount Build Guide

In this free build guide you’ll learn how to build a sophisticated GoTo mount with luxury features such as WiFi accessibility and ST4 port guide capabilities. High quality parts such as TMC 2130 stepper motor drivers paired with custom 3D printed parts powered by the capable, open-source, software OnStep results in a robust mount for only $310 (similar mounts regularly sell for over a thousand). Don’t worry, the build isn’t too hard 😃 See the price breakdown below:

Mount name – $120
OnStep powered “Brains” – $145
2x NEMA 17 stepper motors – $20
Misc. hardware – $20
PLA filament – $5
Tools – $0 (Hex wrenches and screwdrivers – I assume most have these already, if not you can get both for under $10)
Grand total excluding shipping – $310

Before we start– if you’re worried about not having a 3D printer there are a few options: 1. Contact me and we can work something out 2. Order the prints from a company online 3. Buy a cheap 3D printer and build the mount and still have a 3D printer left over at the end to sell or to use for your own entertainment

The build is basically as follows: Take a manual german equatorial mount and strap some NEMA 17 stepper motors to it to belt drive both axises using 3D printed motor mounts. The guide will be broken down into four parts: Preparation, RA Axis, DEC Axis, and Finishing Up. Enjoy!


First thing’s first, you’re going to need to buy the Explore Scientific FirstLight EXOS Nano Equatorial Mount. The hardware you need includes six M3-.50 x 10 Machine Bolts and eight M3-.50 x 6 Machine Bolts. You’ll also need eight M4x4mm grub screws. Get two 4 wire 200 step NEMA 17 stepper motors. You’ll need two 2GT belts, one 158mm long and one 250mm long. Grab some PLA filament in whichever color you’d like (I got red). You’ll also need a barrel jack 5.5×2.1mm input (I have 4 left so the first 4 people to contact me I’ll mail a free one) and separate from this build, and any other mount, you’ll need a portable battery (I got one that outputs 12V through a car jack, remember to also get an adaptor wire that goes from male car jack to male barrel jack). To control everything you’ll need to get some sort of OnStep (software) powered controller. The one I got, highly recommend, and the one I have housing modeled for is the JTW OnStep SMT edition. It is worth noting that if you can solder and you’re patient enough to source cheap parts you can build your own for less but for the ease of use and setup for the price I highly recommend JWT’s. Here’s a list of everything you need to print: 3 20T 2GT pulleys with 5mm bores and one 20T 2GT pulley with a 6.35mm bore. One 80T 2GT pulley with a 6.35mm bore. One RA axis motor mount. one DEC axis motor mount. One brain housing and lid. Below are interactive files and a picture or two of what they make (sorry about some models looking glitchy, it won’t be a problem when they’re sliced and printed). As far as slicing goes I just did standard accuracy (0.18mm) for everything and 20% infill works in most cases but just to be extra I did 50% for the housing of the brain to fill in the walls a bit more as they’re sort of thin. Make sure you use supports for every part exept for the lid.

RA Axis

The RA axis is the easier axis to install. First remove the manual adjustment knob if you put that on when setting up the mount. The area you removed the adjustment knob from is the place you’re going to attach the 80T 2GT pulley. Just do this by screwing in both grub screws and make sure it is very firmly tightened onto the metal shaft. Now do the same by attaching a 20T 5mm bore to a stepper motor. Place the stepper motor in the appropriate mount and screw it in using the M3-.50 x 6 Machine Bolts. Now unscrew the big screw you see on the flat bit of the body of the mount. Place the motor mount where it will be screwed on later and put a 250mm 2GT belt on both pulleys, pull back slowly until the belt tension is taught. Then to keep this tension just tighten the big screw.

DEC Axis

The DEC Axis is a tinsy bit tricker but still not too bad. Start with removing the manual control knob and replacing it with a 5mm 20T pulley. Screw the motor into the mount. Now for the tricky bit. You’ll see three screws that keep a worm gear in place, the tightness of these screws control how easily the DEC axis moves. You’ll need to remove them to slot the motor mount in. Make sure you don’t drop the bit the houses the worm gear. Then you can simply screw them back in (make sure to add the belt before screwing everything in), the motor mount by default should be very close to the perfect tightness when the screw head hits the plastic. You might need to use quarter rotations to get the perfect tightness, you can test it by hand spinning the DEC axis and feeling for any extra (detrimental) resistance. The motor mount should already be spaced perfectly for belt tension so there’s no need to worry about that. Now you’re pretty much done with the build! All that’s left is to put the “brain” into it’s housing and do some software stuff!

Finishing Up

To connect the stepper motors into the brain you’ll need to strip the ends of the connection wire so you can screw them on. Preferably you do this with wire strippers but a pair of scissors will do the trick if you’re careful. To make them easier to screw in I soldered tiny pieces of thicker gauge wire to the end but you don’t have to do that. Once you’re done with all that simply slot the brain into the housing, and screw it in(M3-.50 x 10 Machine Bolts)! Also make sure to screw in the antenna and barrel jack power input. Then you can simply screw on your lid (M3-.50 x 10 Machine Bolts) and viola! You’re all done with the build! To set the software up, you can do everything wirelessly without much hassle! Plug it in and connect your WiFi to “OnStep”, the default password is “password”. Go to the smart web server and from there you can edit the appropriate values! If you need custom values you can read the OnStep documentation but luckily enough, you’re following this guide and all your variables are the same as mine! So here’s the information you’ll need to enter: Your own location in longitude and latitude, the RA axis will have 128 microsteps and 39253 steps per degree, the DEC axis will have 256 microsteps and 12516 steps per degree. When you need to polar align the mount you can use an app called PS Align Pro and a phone mount, which I’ll add a download link to below. I modeled mine for an iPhone 12 as that’s what I have but you should be able to easily edit it for any phone. If you can’t contact me and I’ll do it for you 😁 You can control OnStep with a plethora of applications from capturing software, iOS and android apps, the smart web server, a hand controller, and more.

Please, tell me what you think about this guide below:

PS: Sorry about the profile picture being blank, I’m working on it

4 responses to “Star Sailor Mount Build Guide”

  1. Gabriel Kirmani Avatar
    Gabriel Kirmani

    This is a test of the comment system, it’s pretty cool, you should try it out 🙌

  2. Nora Hall Avatar
    Nora Hall

    Very impressive. It looks exactly like my Sky Watcher EQM 35 but more affordable, wish I saw this before I wasted a few hundred bucks…

  3. AstroAlex Avatar

    Big ups mate
    I might try this soon do you reckon glow in the dark plastic filament would be alright

    1. Gabriel Kirmani Avatar
      Gabriel Kirmani

      Thanks 😁 I don’t see why not 🤷‍♂️

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