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Old 15-05-2017, 11:20 PM
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Belt-modding and computerisation of EQ5

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.
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Old 15-05-2017, 11:30 PM
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Part 1, the upgrade of the mount:

Parts used:
2x NEMA 17 stepper motors (400 steps/rev)
2x DRV8825 Stepper motor drivers
2x 60 teeth GT2 pulleys from ebay
2x 15 teeth GT2 pulleys from ebay
2x GT2 belt from smallparts.com.au

GT2 belts are timing belts designed for minimal backlash and are used in 3D printers. I believe that they are the best choice for reducing backlash.

My choice was to use 60 and 15 teeth pulleys to get a gearing ratio of 4. I would have liked a higher gearing but the size of the pulleys was the limiting factor. 4x gearing with 400 stepper-motor steps per revolution and 32x microstepping on EQ5 gives a final resolution of 0.17 arc-sec per step. I tested the performance of the motors with 32x microstepping and did not detect any missed steps.

After my build was finished SilentStepStick TMC2100 stepper motor controllers came out which allow up to 256x microstepping. I was considering upgrading to them but did not see any need to do so with my ED80. There is no guarantee that my stepper motors would work with such a high microstepping anyway.

The motors were mounted on custom designed mounts which were 3D printed in ABS. Red because I only had red filament at the time


edit: Added a CAD image of the DEC mounting that was 3D printed.
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Last edited by luka; 16-05-2017 at 11:37 AM.
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Old 16-05-2017, 06:43 AM
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Looks great!
I was planning to do the similar thing to my LXD75 (also controlled by OnStep... or anything else as I intend to integrate Step/Dir drivers with motors in the same housing).
It is quite OK as it is now (originally it had gear coupling, resulting in too high PE) but sometimes I need GoTo, so...
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Old 16-05-2017, 11:44 AM
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Thank you Bojan. Part 2 is coming soon.

I should also mention the advantage of having a 3D printer. I mistakenly ordered belts what were few mm too long. 5 minutes later I increased the thickness of one wall in the model and few hours later a new part was printed which moved the motors further away from the worm axis. Problem solved


Also as the motor mounts are plastic (which can bend easier than metal), they were designed with 3 walls for extra strength. Also the walls of the motor mounts are touching the motor walls so no flexing is possible.
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Old 16-05-2017, 11:58 AM
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3D printer is a must!
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Old 20-05-2017, 10:50 PM
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Part 2: Electronics to control the mount

As mentioned before, I decided to build a controller based on OnStep project. OnStep is an open source project with all details freely available. OnStep controller connects to PC via USB and comes with ASCOM driver so the usual astro Windows software works out of the box. A mobile phone can be used as a hand controller via Bluetooth. OnStep also supports WiFi and can be connected to this way. I never used this option as there was no need for it.

One of the features that I am missing in my NEQ6 is that you can connect to it from multiple devices at the same time. I could just pause guiding in PHD (connected via USB) and move to a different object via SkySafari on my phone, connected by Bluetooth. Both devices (PC and mobile phone) can be connected at the same time... actually a 3rd device can be also used via WiFi.

To build electronics, I decided not to go the "Arduino way". I am not a big fan of Arduino, I think it is too expensive and way underpowered compared to alternatives. I already had a Tiva (Stellaris) Launchpad TM4C board which runs Arduino IDE clone (Energia) so I modified the OnStep code to run on it. My modifications have been accepted by the OnStep maintainer and OnStep now officially supports Launchpad TM4C boards. That is the beauty of open source

The Launchpad connects to PC via USB. For Bluetooth I used an industrial Bluetooth module Parani ESD200. This gives 100% reliable connection with a long range of 30m - I actually tested it to be much, much more (around 100m with direct line of sight).

The electronics has been placed in a plastic box. I have used IP67 rated (waterproof) connectors for everything.
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Old 20-05-2017, 11:00 PM
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Part 3: Software

The ASCOM driver on the PC allows full control of the mount with any ASCOM compatible software. Furthermore, the OnStep controller also supports LX200 command set. For example, the guiding works really well with PHD2 and GOTO works with CDC. I did not try other PC software but I am expecting everything to work as it should.

From a mobile phone SkySafari can fully control the mount once it is setup as LX200 compatible.

OnStep controller is receiving regular updates and can be easily updated via USB.

Also, I should correct my comment from my first post, when slewing at full speed the mount is slower than NEQ6 but not by much. I tested them side-by-side and the speed difference is clearly noticeable. Another thing to note is that OnStep goes back to park position when crossing the meridian. This slows down the movement. However, the project is continuously updated so this may change in the future... or it may already have, it looks like I need to do another update of my controller
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Old 25-08-2017, 08:16 AM
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In a Swedish forum there is a thread about belt modding an EQ5 and use this kit:
http://www.beltingonline.com/heq5-te...rive-kit-12097

But be aware, you can't use tha handterminal anymore!

/Lars
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