My motorised focuser for Astromaster 130 (saved in case of site error)

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by , 11-07-2019 at 06:14 PM (1246 Views)
Quote Originally Posted by MarcinM View Post
Hi there,

After almost 10 years gap returned to hobby. I bought Celestron Astromaster 130, but after couple uses I decided it needs motorised focuser. It was really annoying when I tried to set focus and everything was shaking, vibrating etc from the slightest touch. So here it is, few words about it first.
Initially I though about using two servos connected together, without batteries, but then stepper motor idea shown up. Had to design few parts using tinkercad (my first ever try at 3d designing). Controller can be unplugged from focuser (uses 9 pin connectors), so optical tube can be disconnected from tripod with no wires hanging around. Power is provided through the same long cable which connects controller and focuser, almost at the end with 9 pin connector cable splits for +5V and GND from my 4s 8Ah lipo (that supplies power for NexStar, dew heaters and motorised focuser, using 12V and 5V stabilisation). It's slow, but this type of stepper motor can go up to 15rpm only using 5v, could be modified to bipolar and then use 12V, 30rpm could be achieved. But it's very accurate and can go really slow. Speed is controlled using potentiometer, direction using 2 pushbuttons. Speed can be adjusted either when one of the buttons is pressed, motor works as long as button is pressed and stops when button is released. Only 5 wires of 8 are used for remote, 5V, GND, Pot middle pin, Switch1 and Switch2. 5V common for Switch1, Switch2 and Pot.
Helps alot with imaging, I've modified microsoft webcam so it sits in focuser instead of eyepiece.

Parts used:
28BYJ-48 stepper motor
ULN2003 stepper driver
Arduino Nano
2x 10k resistors (have to be soldered between digital pins (one for each pin, no.2 and no.3) and GND
10k potentiometer
2x 9pin connectors (male and female)
4 meters of 8 wire ethernet cable
2x pushbutton switches
plastic enclosure
3d printed parts
6mm belt, type GT2, 202mm lenght
drive pulley 16T, GT2
couple bolts, screws and nuts

Here's the code for arduino:
#include <Stepper.h>

int forward = 2;
int reverse = 3;

Stepper motor(512, 8,10,9,11);            

void setup() {

void loop() {
  int Speed = analogRead(A0);
  int RPM = map(Speed, 0, 1023, 0, 100);
  int f = digitalRead(forward);
  int r = digitalRead(reverse);
  if(f == 1 && r == 0 && RPM > 1){
  if(r == 1 && f== 0  && RPM > 1){
And couple photos
Attachment 170561blogs/gabby76/attachments/191665-my-motorised-focuser-astromaster-130-saved-case-site-error-screenshot.pngblogs/gabby76/attachments/191657-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_004002.jpgblogs/gabby76/attachments/191658-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_003925.jpgblogs/gabby76/attachments/191653-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_031003.jpgblogs/gabby76/attachments/191656-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_030807.jpgblogs/gabby76/attachments/191654-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_030935.jpgblogs/gabby76/attachments/191655-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_030915.jpgblogs/gabby76/attachments/191659-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_140046.jpgblogs/gabby76/attachments/191660-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_140113.jpgblogs/gabby76/attachments/191663-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_185717.jpgblogs/gabby76/attachments/191662-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_185712.jpgblogs/gabby76/attachments/191661-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_185708.jpgblogs/gabby76/attachments/191664-my-motorised-focuser-astromaster-130-saved-case-site-error-20180107_185735.jpg
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