About year a half-ago I cleaned the dust from my ED80 on EQ5 with dual-axis drive and started using it again for astrophotography. The mount sat in the study for about 6 years while life took other priorities. After my restart the limitations of the dual-axis drive became obvious again, just like I concluded years ago. With extremely careful polar alignment and LOTS of luck I could manage 1min exposure with my ED80 and a DSLR. So I needed to upgrade. I really wanted to have guiding working and also GOTO.
One of the options was to modify the dual-axis controller to connect it to a computer using some sort of shoe-string device. I gave up on that idea once I figured out that it would be too slow. The dual-axis drive motors have very high gearing and it would take 20min to move from one part of the sky to another. Also backlash was very bad.
So, the decision was made to get new motors and to reduce backlash with a belt-driven system. Of course it needed to be computer controlled so I decided to use
OnStep for this. It is open source, comes with ASCOM drivers, allows the mount control from mobile phones etc.
I finished the work about the year ago and have been using the mount for imaging since then. To summarise the main outcomes:
- Guiding works well with PHD2 and I was usually doing 3min exposures on ED80 with a DSLR from my backyard. 3min was actually sky-limited due to the light pollution but I don't think much longer would work well due to the DEC backlash (see below).
- GOTO is fast with similar speeds as my newly acquired NEQ6. It can be programmed and the motors can go faster but I felt uneasy seeing my telescope moving too fast (OnStep does support acceleration and deceleration of motors).
- It definitely sounds better than the grinding noises coming from my NEQ6
- The backlash in DEC is still there. I could not get rid of it. I think that the belt drive is backlash free and that the backlash I can observe comes from the worm drive in the EQ5. I tried adjusting the worm drive but I don't think I did a great job. Actually the backlash seems to be similar to that of the NEQ6 which I recently bought. I ended up guiding DEC on one side only. That seems to be commonly done with NEQ6 as well. Cheap mounts... what else can be said.
- As expected guiding in RA works perfectly.
The information about the build will follow below. I'll break up the info in several sections, otherwise the post would be too long. I hope this info will help someone else who decides to embark on a similar journey.