Arduino ASCOM Focuser Pro2 DIY Files

https://sourceforge.net/p/arduinoascomfocuserpro2diy/discussion/general/thread/bc5d5f551d/

Florin Dumitrescu
2024-02-25 


Hello everyone!

I just wanted to share with you my design of a 3D printed bracket for a TS Optics 2.5" rack and pinnion focuser. My project uses a 28BYJ motor (in bipolar mode with an A4988 driver) and it's connected to the reducer shaft using a flexible coupler. I will also share the files for the PCB and schematic that I have used.

NOTE! This is the most minimal version of the focuser, with no lights, buzzers or buttons. Just the motor and the temperature probe are included with this schematic, so, if you want to build this yourself, please make sure to disable everything else in the arduino code.
ALSO! I have built this board WITHOUT the RESET pin cap/switch combo. I found that they were useless for my situation, so I chose to drop them from my board, in order to save some space. YOUR SITUATION MAY BE DIFFERENT, so proceed at your own risk or design your own PCB to fit your needs.

Prepping:

Print the box, lid and bracket. I'd advise you to use PETG if you live in a warm climate or plan to leave the setup in the sun for prolonged time. PLA has poor UV resistance and low-ish melting point, so it will warp in the sun.
Printing settings that worked for me are :

Ender 3 V2
0.25 layer height
0.5 line width (with a 0.4 nozzle)
1 mm walls and top/bottom
50% infill, cubic
235C hotend, 75C bed
95% flow rate
Fan OFF
Supports : Yes
Retraction enabled to minimise stringing.
My settings work for me, but you might need to adapt yours for your printer.

Etch and populate the PCB, then solder the wires to the board as noted on the silkscreen. Cut the RED wire, as it's not used. As we won't be using half stepping for this motor, there's no need to cut the trace between the two coils in this motor.
If you need more information about this matter, look here: https://ardufocus.com/howto/28byj-48-bipolar-hw-mod/

I have not created any holes for the 28BYJ motor in the lid, so you will need to put your motor inside the front lid and drill two holes to match where the motor brackets are. These holes will be used to mount both the motor and the box to the big bracket.

Optional step if you want a temperature sensor installed: Drill a hole for a 3.5mm stereo audio jack (or whatever 3 pin connector you want to use), mount the connector on the box and wire it to the VCC,SIG and GND pads on the PCB. Enable the temperature probe in the Arduino code to use it. Make sure the new connector is positioned in such a way that it doesn not interfere with the motor when the lid is added.

Slide the PCB in the box, drill the holes in the stand-offs in the board, then use some small screws to fix the PCB in place. The lid and the box are friction fit, so there's no need for any screws or glue.

The 28BYJ has a 5mm dia. shaft and the fine adjustment is a 4mm dia. shaft. Find a suitable flexible coupler. The lenght should be standard 25mm. If you already have a coupler with different holes, design and 3d print adapters for it.

Install an M4 nut in the slot at the top of the clamp, then insert a 35mm M4 bolt.
Install two M3 10-15 mm Hex bolts through the clamp, lid and motor brackets, then secure them with two M3 nuts on the inside. You might want to epoxy the nuts in place, so you can adjust the focuser from the outside without having to open the box.

In order to install this bracket, you will need to remove both the fine and coarse adjustment knobs (from the same side of the focuser). To remove the fine adjustment knob, it's pretty straight forward: undo the grub screw on the side and slide it out. To remove the coarse adjustment knob, there are two grub screws that you need to undo in order for the knob to come out. Look online for guides on how to remove this grub screw.

Slide the 4mm end of the flexible coupler on the motor shaft, spread the clamp with a flat head screw driver and slide it over the reducer housing, making sure to align the coupler with the fine adjustment shaft. Tighten the M4 bolt on the clamp, secure the grub screws in the flexible coupler and adjust the focuser box using the two M3 hex bolts to make sure the coupler is as straight as possible.

I've included a plastic flap in the bracket that covers the ball bearings inside the reducer mechanism, so the grease won't leak out and dust won't get in.

Enjoy!