I had an ET-8 equatorial mount with a 6" F5 Newtonian reflector more than 10 years. Using Arduino and stepper motors, I have been modifying the mount up until I found OnStep (http://www.stellarjo...uipment_onstep) on the internet. Immediately jumping into OnStep I was able to come up with an WORKING GOTO system. I mean really working GOTO equatorial mount even with an android controller. I would like to share my journey with the Stellar Journey (The Website of Howard Dutton) here. I believe there are many owners of ET-8 mount who can be benefited by this thread. The main idea is not limited to ET-8. Anyone who has manual equatorial mount can easily modify to a fine functioning GOTO mount.
As you see in the photos, I have been playing with many motor-gear combinations evidenced by several holes on the mounting plates. I have been keeping the mounting scheme as simple and flexible as possible for trying many different combinations. Soon the perforated mounting plates will be replaced with dedicated good looking (?) ones.
Mechanical information of the ET-8 mount is as follows: RA worm 144:1, DEC worm 90:1, no ball bearings, cast aluminum body with steel shafts, and so on. I have added 60:15 pullies and belt (GT2) for RA, and 90:15 for DEC. Those ratios are working fine with stepping motors (200 steps/rev, http://www.omc-stepp...1206s-p-20.html). Currently this combination provides me ~2 deg/sec of slewing rate which is satisfactory to me.
The electronics is very simple: A Teensy 3.1 controller (or Arduino MEGA 2560 R3) and two DRV8825 stepstick drivers. An HC-05 bluetooth interface was used to control the mount with my android smartphone. All the works were done by Mr. Howard Dutten, and I am deeply indebted by him to have this complete GOTO mount of my own.
I may note that the total cost is incredibly cheap if you already have an equatorial mount.
Edited by photo444, 16 December 2014 - 08:36 PM.