Newtonian telescope mounted on equatorial mount
Skywatcher 200 PDS, mounted on equatorial mount EQ5.

I own the setup shown in the picture above: Skywatcher 200PDS, a 200 mm f/5 Newtonian reflector, mounted on a EQ5 equatorial mount. I also have bought and installed the optional dual axis stepper motors:

EQ5 manual control
EQ5 manual control for stepper motors

Without being top-notch everything works as expected and the scope and mount live up to its intended basic purpose (and price). This setup enabled me to take a few decent pictures (see for example M57). But it soon revealed its limitations for astrophotography: it is prone to vibrations and guiding is very primitive. I still use this scope a lot, although I have since moved away from astrophotography.

Using this setup as a purely visual one is nevertheless challenging. The most annoying factor is that the motor control allows a maximum slew speed of only 8 times the sidereal rate. This is extremely slow for anything except doing small corrections. On the other hand, if one for example needs to reorient the telescope to the opposite side of the sky, one must first disengage the clutches, move manually, engage again, and then make final adjustments with the slow motion controls. This process is bothersome and cumbersome for a number of reasons.

First, the clutches are located on the mount body away from any possible comfortable position. It is often the case that after manually finding the approximate area of interest the “freely floating” scope will move substantially before one succeeds in engaging the clutches again. Secondly, after reorienting the scope to the approximate area of the sky, one needs to needs to use the manual slow controls to center the object. The motors are rarely useful to do this because of the maximum 8x slew rate is so slow. One can use the manual controls, of course, but the knobs are also located in the mount body, away from any remotely comfortable position. This results in the observer having to take strange “yoga” positions to move the knobs and center the object while at the same time looking through the finder scope or eyepiece.

Solutions? I first though of building a dobsonian base. This is an interesting project and certainly have it in mind. However, I was hooked by the idea of replacing the motors and controls with a DIY system that I can control from the eyepiece, or whatever relatively comfortable observing position an EQ mounted Newtonian has to offer.

After some thinking I came up with the following requirements for a modification. I need a control system which:

  • is capable of a maximum slew rate not less than 360x, that is 180° in 2 minutes
  • is able to make small corrections of the order 8x – 20x the sidereal rate
  • is able to control with a joystick from a distance
  • is relatively robust against cold, vibrations, humidity
  • takes low power
  • is relatively silent
  • is inexpensive

I am not interested in guiding or GoTo at this moment, so those do not go into the requirements. After a lot of searching and internet exploring I decided to start experimenting with an Arduino based control of two geared DC motors, both of which I can get relatively cheaply.

Now the fingers start getting itchy. I am not completely foreign to electronics, but have no previous experience with Arduino or motor control. The whole thing is tasting like a DIY adventure. Stay in tune!

Thanks for reading and clear skies!