MountOne | 102OTA Assembly.

Don't Panic!

This guide is 99% images.

Index.

If you would like to develop MountOne yourself or wish to help support my further development of the MountOne, detailed drawings, datasheets and STEP files are available by downloading the MountOne CAD Packs.

Printed Parts.

The MountOne & Astrographs were developed with Bambu Lab PLA-CF. Final testing and checks were performed with Bambu Lab PETG-CF. Parts were printed using E3D's A1 Series High Flow ObXidian 0.4mm Nozzle. I recommend PETG-CF for the MountOne and Astrographs. For best results, dry your filament before use.

Full details on how to print these parts are in The 102OTA Printed Parts Documentation.

Electronics & Fixings.

The 102OTA Hardware KIT includes the following required fixings.

  • 1 x LDO 0.9° Stepper Motor & Cable.
  • 1 x GPIO Highjacker.
  • 2 x 6811-2RS Bearings.
  • 1 x Gates 2GT 132T Loop-Belt.
  • 1 x 16T 2GT Pulley.
  • 1 x 36T 2GT Pulley.
  • 15 x M5 20mm Screws for Plastic.
  • 4 x M2.5 8mm Screws for Plastic.
  • 4 x M3 8mm Countersunk Bolts.
  • 4 x M2.5 15mm Standoffs.
  • 4 x M2.5 4mm Socket Cap Screws.
  • 5 x M2 6mm Socket Cap Screws.

Parts you will need to source yourself.

  • Sky-Watcher SKYMAX 102 OTA.
  • Raspberry Pi 4/5.
  • 5V DC/DC Converter.
  • Raspberry Pi 5 Active Cooler (Optional).
  • Raspberry Pi M.2 HAT (Optional).
  • Adafruit Ultimate GPS (Optional).
  • Raspberry Pi HQ Camera.
  • Raspberry Pi HQ Camera 30mm FFC.
  • Dovetail Baseplate.
  • Various Cables & Wires. 

If you have downloaded the MountOne 102OTA CAD Pack, there is a full BOM inside.

The 102OTA Astrograph will more than likely work fine with the Raspberry Pi 4. All the imaging is performed on the Canon camera, including storing the photos (you'll need a card in the camera).

We go through the software setup in the MountOne 102OTA Software Documentation. This guide is solely for the purpose of the hardware assembly.

Focus Cup.

Insert a bearing into the two openings.

Ensure they sit flush against the case.

You'll need a single 8mm rod for the Cup.

Insert the rod into the cup as far as it will go.

Slide on a spacer.

Feed the rod through the bearings as shown.

Fit another spacer.

Install the 36 Tooth GT2 Pulley.

The Motor.

Orientate the motor with the cable plug pointing as shown. Secure with four M8 Countersunk screws. Do not tighten them at this time.

Slide on the smaller pulley and the belt, hook the belt over the larger pulley.

Rotate the Cup to slip the belt into place.

Tighten the grubscrews, making sure one of the grubscrews aligns against the motor flat. Also, check the pulleys align.

While pulling the belt taught, tighten the screws.

GPS.

The GPS is an optional extra. I am using Adafruit's Ultimate GPS.

It is held on with two M2 6mm Screws.

DC/DC Converter.

The DC/DC Converter is similarly attached using two M2 6mm screws.

Raspberry Pi 5.

The Pi is affixed at three points, with three M2.5 15mm standoffs.

I have preinstalled the official active cooler.

Check you have it in the right orientation.

GPIO Highjacker.

The GPIO Highjacker was developed specifically for use with the MountOne Astrographs with the aim of making the GPIO more accessible and improving the wiring. Full story on the Blog Post. 

The GPIO Highjacker breaks out power (5v & 3.3v), i2c, five UARTS and provides headers to input 5V from DC/DC converters while still allowing the use of HATs. 

Full details | GPIO Highjacker.

M.2 HAT.

This is an optional extra and replaces the need for an SD Card.

Secure with three M2.5 5mm screws.

Raspberry Pi HQ Camera.

We're using the HQ camera as our sensor for this astrograph.

Remove the cap. Take extra care to keep the CCD clean.

Place it face-down in the back of the housing.

Install all four M2.5 8mm Screws For Plastic before tightening them down.

The Wiring.

I'm not going to provide a wiring schematic as there are too many different combinations of the DC/DC converters and GPS Modules to do so effectively. Check the datasheets for each module you are using and confirm the connections and wiring aligns with the input on the GPIO Highjacker, or GPIO. It is pretty straight forward. Note that for UARTS Tx on one module, it connects with Rx on the other, etc.

There are predefined connections for the wiring harness from the MountOne and we need to conform with those. We'll be using eight wires, UART Tx/Rx, +5v/GND and a motor connector. Check the motor phases match the MaxPCB4. Refer to the MountOne Electronics documentation for additional information.

You will need a longer 300mm Camera Cable.

Note: The Raspberry Pi can draw more than 1.5A from the DC/DC Converter. Make sure you use higher-rated (~5A) wire for the power from the DC/DC Converter to the Raspberry Pi. Using the incorrect cable can result in low voltage warnings.

I have secured the cables to the spare hole in the RPi with a cable tie.

Dovetail Clamp.

There is a dovetail on the base of the Sky-Watcher 102, I have designed this astrograph to take advantage of this system. The hole spacing is 38mm x 38mm. If you need something different, download The 102OTA CAD Pack.

Loosely install the clamp using four M5 20mm Screws For Plastic.

To ensure the clamp is square, lay the bracket down as shown on a flat surface and tighten the screws.

There is a path through the Bracket Arm for the cables.

I have included the STL for a version with an 8-way Microfit 3 socket.

Assembly.

Before we can begin, the 102 OTA needs to be aligned as shown below.

Slide the assembly down over the OTA.

Align the Focus Cup with the knob, it may take a bit of wiggling to get it to seat correctly.

It should sit all the way down.

Tighten the thumb screw.

Covers.

The side is affixed with a single screw.

The cables need encouraging to play nicely.

There's a slot at the front for them to exit the case.

The other side is held on with four M5 20mm Screws For Plastic.

Mounting The Astrograph.

Plug the wires together.

Attach the Bracket with six M5 20mm Screws For Plastic.

For easy access I am attaching the MountOne to a desk tripod. You can just as easily use a standard tripod, or the Printed Equatorial Tripod (PET).

Mount the 102OTA on the Bracket, and connect the cable.

I have taken off one cover to access the cables and to check the wiring.

Check the wiring. The 102OTA requires a third Stepper Driver be installed in the FOC position on the MaxPCB4.

Make sure the motor wiring is correct!

The additional FOC motor should copy the wiring for the other stepper motors (this passes through the DEC Slip Ring).

When you are certain all is well, connect the power.

If all has gone well, there should be no magic smoke.

I am using the Smart Hand Controller (SHC) to control the MountOne to move the astrograph to a more accessible position. We will also use it to check the focus functions as expected.

There is also an OnStep App available if you wish to use your phone instead.

Check both the RA & DEC.

Check the Focus.

If everything is working correctly, power down the Raspberry Pi, disconnect the power and refit the covers.

Next, we will install the software.

Glamour Shots.

Continue to the 102OTA Software Documentation.

Back to Main Documentation.