The MountOne is an astronomical platform with integrated GOTO tracking capabilities, designed to mount Telescopes and Astrographs. I have developed four astrographs in parallel with the MountOne.

The MountOne GOTO Telescope Mount uses two high performance 0.9° stepper motors coupled to two 5-stage 405:1 belt-driven reduction-drives. This configuration effectively removes all backlash in the motion system. The MountOne is able to track with a computed  resolution of 0.25 arcseconds per-step while still being able to slew at 3° a second.

Thirty six bearings across the DEC & RA axes provide smooth and jitter free movement. Genuine Gates 3GT belts are used for each compound stage and are individually tensioned for optimal performance.

Integrated Slip-Rings pass power and signal data between the MountOne and one of four attached astrographs. No unsightly wires or cables to worry about.

OnStep firmware controls the mount and provides a data-link to a huge range of astronomy software packages via one of the four attached astrographs.

The Printed Equatorial Tripod (PET) provides polar alignment between latitudes of 30-90°.

The MountOne GOTO Telescope Mount, Printed Equatorial Tripod, and Four Astrographs can all be printed on machines with a build volume of 180x180x180 or greater.

The MountOne & The Four Astrographs have taken over 18 months to design, test & develop.

This is not my first 3D printable GOTO mount, these are not my first 3D printable astrographs. If we are counting the tangible only, I think this is mount three (technically four), and the second astrograph (technically third), but if you count each scope separately it's six (technically seven). Anyway, it doesn't really matter. The point is perhaps that there is a chain of development which has landed us here, with The MountOne & The Four Astrographs.

There is more information about the development of The MountOne & The Four Astrographs further down the page.

GOTO Mount Specification.

• 0.25 Arcseconds-per-step.
• 0.9° Stepper Motors for both RA & DEC.
• 405:1 Gearless Reduction Drive.
• ~4kg carry capacity.
• 3°/s Slew Rate.
• Genuine Gates belts.
• 36 Ball Bearings.
• OnStep Telescope Control Software & Electronics.
• 30-90° equatorial tripod.
• Four developed astrographs to choose from, or design your own.
• Prints in build volumes of 180x180x180 or larger.

The Astrograph Specifications.

• Raspberry Pi 4/5.
• Raspberry Pi HQ Camera (Except DSLR Astrograph).
• GPS (Optional).
• INDI Library.

100MM Astrograph.

• 100mm F/3.5 Apochromatic Lens.
• Integrate Focus using OnStep.

Pinefeat Astrograph.

• Pinefeat's Canon EF / EF-S Lens Controller for Focus & Aperture.
• Accepts Canon EF & EF-S Lenses.

DSLR Astrograph.

• Use gphoto2 compatible DSLR Cameras & Lenses.
• Full camera control.

Sky-Watcher SKYMAX 102 OTA Astrograph.

• Focus control using OnStep.
• Optional SV165 Guider Scope.

The MountOne & The Four Astrographs are available now.

Sample Images.

The Moon.

Captured with The 100MM Astrograph.

M45 - The Pleiades.

Captured with the Pinefeat Astrograph & Canon EF 75-300 III Lens. A short session of approximately 20 minutes. Click for the full sized image.

M 51 - The Whirlpool Galaxy.

Just 25 minutes of imaged sky captured with the 100MM Astrograph. Click for full-sized images, you can see much greater detail, and, unfortunately, light pollution from aircraft and satellites.

IC 1805 - The Heart Nebula.

This is a very busy part of the sky, and with only 50 minutes of exposure with the 100MM Astrograph, only the stars can be seen. There is still a mass of detail, which can be viewed in the full-sized image, click to open.

Why?

The MountOne is the result of my desire to fix the problems that were a feature of The Micro Scope.

This was primarily backlash in the system. The Scope's drive system used two NEMA 11 90:1 planetary gearboxes coupled to belts for the final drive. The gearboxes had a lot of backlash.

Second to that was finding a method to autofocus the lens. It was particularly difficult to get a sharp image with the manual focus lenses that I had to use for the Micro Scope. There was no easy way to implement autofocus, although I did play around with the idea, I ultimately abandoned it due to the complexity it would have added, and the additional space required.

Taking those two bug-points, we now have two features to integrate into the new design that will become the MountOne. The first part of the new design would be the mount, the part that houses the motors and enables the GOTO functions.

How.

Problem One.

How do we eliminate backlash from the system?

Removing the gearboxes is the quickest way to remove backlash, no gears = no backlash. But, that then leaves the small problem of accurately tracking the sky.

Typically, the Earth rotates once per day. We need to be able to accurately track the movement of the sky at that same rate, and slew the astrographs around the sky at a sensible speed. Doing so without gears will be difficult.

I did some poking around on the internet, more commonly known as research, to see what the internet says. My research highlighted worm gears as being widely used in GOTO mounts. 

Worm Drive.

The first design for the mount incorporated a 60:1 worm gear. The design at this time was also intended for manufacturing primarily using CNCd metal, with the choice of 3D Printing the parts instead.

The design incorporates two belt stages, firstly a 3:1 from the motor to the worm gear, and a final 6.666:1 on the worm gear's output. This setup would have given a total reduction of 1199.88:1.

I built a test stage to see how well it performed, and more importantly to check the backlash.

It was not good. There was significant backlash in the system. I am going to have to use a fully belt-driven design.

100% Belt Drive.

Before we dig deeper into things, we need to know what reduction we actually need for good tracking.

Referencing OnStep's Configuration Calculator Spreadsheet there is a recommendation of 1.25 steps per arcsecond or less. That will be our minimum target. Obviously we want to do better.

Time for a spreadsheet.

The above should be fairly self-explanatory. I am using 0.9° stepper motors and 32x micro-stepping to achieve the highest resolution from the motors. Stage 1 is from the motor to the first compound pulley, and the final drive goes from the last compound pulley to the output to move the telescope. This gives a computed resolution of 0.25 arcseconds per step. Well below the 1.25 maximum. We will also be able to hit a respectable 3° a second for slewing.

It is at this point that I dumped the idea of CNC parts and commit fully to 3D Printing. My reason for this choice is to do with the need for compound pulleys and that fact that they are almost impossible to find at sensible prices.

The design below uses off-the-shelf separate pulleys mounted to shafts with bearings at the end to assemble the compound pulleys. There is also a mechanism for tensioning the belts.

This design was scrapped for quite a few, hopefully obvious, reasons, and it was at this point that the decision was made to print the needed compound pulleys. Along with that decision was the choice to use 3GT instead of 2GT. The rationale being that the 3mm pitch can be more precisely printed with the ubiquitous 0.4mm nozzle.

The final design (it's upside down in the image above), tightly packs a 5-stage, belt-driven 405:1 reducer, complete with springless tensioning mechanisms for each belt, into a frame less than 180x180 (so anyone one with a printer with a build volume of 180x180x180 can make one). 

The drive system needs to be doubled to drive both the Declination (DEC) and Right Ascension (RA).

The end result is the MountOne GOTO Telescope Mount.

There is no backlash in the system*. Problem One solved.

A Short Note About Teeth.

Slight imperfections in the teeth profiles can have a detrimental effect on the performance of the drive system. It is very important to keep the profiles clear of print artifacts.

Enabling features like Avoid crossing walls and Arachne can help mitigate those risks. However, the one artifact that is impossible to remove in any practical way, is the seam.

While it is impossible to remove the seam,  we can compensate for it and position it somewhere where it will not impact the teeth profiles.

Modelling in geometry specifically for the placement of the seam, solves this problem.

This geometry can also be extended to contact surfaces, and bearing pockets. Throughout the MountOne & The Four Astrographs, geometry has been included with the specific intention of minimising artifacts in performance critical areas.

The Printed Parts Documentation provided for The MountOne & The Four Astrographs highlights these features and includes illustrated instructions for the placement of critical seams. 

Problem Two.

Focus & Autofocus.

100MM.

I began this project with the intention of designing more than one astrograph to go onto the MountOne. The first astrograph, the 100MM, I had already worked on before in another project which didn't get published (hence all the 'technically' parentheses above).

OnStep's MaxPCB4 has the capacity to drive two additional stepper motors, both of which could, if one chooses, be used to control the focus on two lenses. We will, of course, only be using one. Both the 100MM and 102OTA astrographs use an additional stepper motor for autofocus.

There is no need for multi-stage reduction drives for the focus. A single belt is plenty. The 100MM astrograph uses two 6811-2RS bearings with the lens in the middle. The motor driving a focus ring. The 100mm lens was specifically chosen as the focus ring does not move axially when adjusting the focus. This means the design can be simple. The lens only moves 7mm across the full range of focus.

The Sky-Watch SKYMAX 102 OTA has a focus knob to the side of the OTA. A few minutes with a set of callipers and some test prints can align all the parts together in CAD.

Off Axis.

My original 102OTA design used two Arducam IMX462 Starvis modules mounted shoulder to shoulder. The Arducam design has the sensors very close to the edge of the PCB allowing them to be mounted this way.

Why do I want two sensors together like this? Well, one can be used for imaging and the other can be used for guiding. Normally one would use a separate guide scope, or even an off axis guider. However, after watching The Space Koala's review of ZWO's 585MC Air Smart Camera I was inspired to try and do something similar.

The design worked exactly as expected and each camera could be assigned different roles in KStars. However, I ran into problems with the Arducam modules themselves. Specifically with the function for long exposures.

The issue being, as I understand it, that when taking a long exposure image the camera does some additional processing to do with white balancing. This process takes a long time (more than the exposure itself). This essentially makes any imaging effectively impossible as a single exposure can take upwards of 60 seconds (three times the exposure I was trying).

I contacted Arducam support about the problem and they said yes they know and said they will fix it, maybe one day, eventually, probably.

I have had to shelve that idea for the time being in the hope that in the future the long exposure problem can be rectified. It is a shame as the IMX462 is a very good low light sensor and I would have used it in all the compatible astrographs.

DSLR.

During my research into INDI, cameras, lenses, motors, bearings, slip rings, software, angles of dangles and materials, one thing that a lot of people seem to do is just use a normal DSLR camera for astrophotography. Obvious really. Thankfully gPhoto2 has an INDI driver. There is a list of supported cameras in their documentation in case you have an old camera and lens knocking around.

Pinefeat's Lens Controller.

If you only have a lens, or an excess of lenses, specifically Canon EF & EF-S lenses, then the Pinefeat Lens Controller will be perfect for your application. 

The PF Astrograph uses Pinefeat's Lens Controller, pairs it with the Raspberry Pi HQ Camera, a RPi5 Model B, or Compute Module 5, and lets you take control of the autofocus functions in Canon EF & EF-S lenses.

The range of lenses the Pinefeat controller can use makes this astrograph highly versatile. You can also swap and change lenses at will (KStars configuration included).

All of the astrographs have autofocus. Problem Two solved.

The Printed Equatorial Tripod.

 

The Printed Equatorial Tripod (PET) provides a bespoke and sturdy mounting option for the MountOne & The Four Astrographs.

The PET features adjustable legs, an integrated spirit level, and polar alignment for latitudes between 30-90°.

Adjusters at the top of the legs level the tripod, referencing a spirit level in the base. The upper section of the PET can be tilted back 60° and locked in place using a securing clamp.

The MountOne is powered via cables running through the PET. A standard DC Jack resides at the back of the PET, between the left & right legs, feeding 24V power into the MountOne.

The PET Can be folded back up at the end of your session, or leave the MountOne attached and move it as a single unit. 

One More Thing.

The Raspberry Pi's GPIO is great, in most cases. But, in some cases, it isn't. One such case where it isn't great, is when you want to use a HAT, the M.2 HAT for example, and also want to run power to the Raspberry Pi via the GPIO. This is the method I use most frequently when running Raspberry Pi projects, and I was tired of dirty hacks to connect cables and wires.

The GPIO Highjacker.

The GPIO Highjacker is a basic PCB designed to be soldered onto the extension pin headers commonly included with HATs.

It has breakouts for UARTs, i2c, 3.3V, 5V, GND and 5Vin. All four astrographs use the GPIO Highjacker and one is included in all MountOne Astrograph Hardware Kits.

Full details on The GPIO Highjackers Blog Post.

Future Plans For The MountOne.

I have been playing at integrating batteries and power management into the legs in the PET. I have looked at 21700 LiPo cells, using rechargeable battery packs from power tools and a few other options.

A recent feature I have seen is to have automatic Polar Alignment built into mounts. To the best of my knowledge OnStep does not currently support this, there are no electronics or firmware for it. Yet.

Currently, improvements are underway to upgrade compatibility for the CCDs to include Will Whang's OneInchEye.

Do you have some ideas too, what would you like to see happen with the MountOne?

Can I Make My Own Astrograph?

You are more than welcome to design and develop your own astrographs for personal or commercial use.

The 102OTA weighs in at ~3.5kg. It is the heaviest of the astrographs and the MountOne swings it around no problem.

The MountOne & The Four Astrographs are licensed under CC BY-NC-SA 4.0, but this does not prevent the development of third-party astrographs.

I shall explicitly say that the development and sale of third-party astrographs for the MountOne is allowed without the need for commercial licensing.

The license does not exclude the possibility of acquiring a commercial license for the MountOne & The Four Astrographs. Visit the Contact Us page if you are genuinely interested.

Documentation.

I have spent a lot of time trying to get The MountOne & The Four Astrographs Documentation as complete as possible.

Some of the documentation seems quite long on first inspection, but there is no need to panic, it is 99% images. 

By being as concise as I can and including as many photos as possible, it should make the process of building a MountOne simple and enjoyable.

I am always available if you do get stuck, the Contact page works, and so does the Chat box in the lower right corner.

Available Now!

I have put together Hardware Kits for The MountOne & The Four Astrographs. These kits contain all the screws, fixings, niche components, bearings, and connectors that you'll need.

We have partnered with GrayDigitalArts.com, an authorised OnStep dealer, who has made an electronics kit specifically for the MountOne.

The MountOne Hardware Kits.

The Hardware Kits include all the fixings, bearings, bolts, belts, pulleys and screws required to build The MountOne or an Astrograph. A CAD Pack is also included with each Hardware kit.

The MountOne CAD Packs.

The CAD Packs include all digital resources required to edit, design, develop and 3D print The MountOne & The Four Astrographs.

The MountOne STL Sets.

The STL Sets have everything you need to 3D print The MountOne & The Four Astrographs.

The MountOne Fully Assembled.

I have a limited number of fully assembled and tested MountOne  & Astrographs available. They are made to  order so please do allow 28 days before shipping.

Glamour Shots.

MountOne © 2026 by Hexaxes Ltd is licensed under CC BY-NC-SA 4.0

*Here's where we can fall down some wabbit holes about semantics, stretch, technical details and ifs & buts. Or, we can just gloss over the whole thing and get on with our lives and hope it doesn't come and bite us in the proverbial later.