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Old 27-04-2019, 07:39 PM
Averton (P and C)
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DIY Equatorial Platform

We have a small 130mm F5 Newtonian table top scope. It is mounted on a simple Az-Alt base. We wish to provide tracking and had seen the Poncet, Gee, D'Autume etc platforms. Whilst these look good their design was to be low height to keep large scopes from being too high to get to the eyepiece. We actually wish to raise our scope (ie place on a table) to use comfortably while seated. So we have come up with a design with similarities to a barn door tracker.



We are hoping that this will be successful for our needs.
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Old 27-04-2019, 07:42 PM
Averton (P and C)
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With pictures this time
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Old 27-04-2019, 08:45 PM
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Interesting....
I wonder why you did not use the slanted plane as RA circle, this way you could have longer tracking time (this design seems to be limited to ~1 hour max?)
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Old 27-04-2019, 10:13 PM
Averton (P and C)
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Yes you are correct - the design is for plus and minus 7.5 degrees from horizontal. The idea was to keep it simple and maintain the scope on its original base for other use. There maybe better ways of doing this but this is our first effort.
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Old 28-04-2019, 07:37 AM
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I had something like this in mind.
BTW, you can have tracking by implementing only adequate DIY F/W electronics, like OnSTEP (still actively being developed)or Bartels system (older), without such radical mechanical modifications - and you will also get GoTo.
I am using both solutions.
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Old 28-04-2019, 10:12 AM
Averton (P and C)
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Hi,


Thanks for the links.
Very interesting ideas.
We had looked at OnStep but discounted it at this stage due to the difficulties of motorising the existing mount in a way that had any resolution and accuracy. Our first tests didn't look promising.
Definitely some future projects though.
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Old 28-04-2019, 12:52 PM
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highly recommend if you haven't already that you have a look at Reiner Vogel's website notes re EQ platforms. I built a vertical south segments (i'm in new zealand. Norther hemisphere would be vertical north segments) platform. ) platform using the design concept. For drive I use a packaged celestron basic drive (for their very basic non tracking GEM mounts) costing about $50 on ali express. For rollers I use 8mm hard steel shaft and bearing blocks also from aliexpress. Total parts cost is under $100.
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Old 28-04-2019, 07:52 PM
Averton (P and C)
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Hi Hamish,


We have definitely seen and studied Reiner Vogel's website. Also we have seen a number of Poncet style platforms. If we were going to go down this road we would still need to build a table to put the platform on to make viewing comfortable. So the idea is to combine the table and the platform into one item. We certainly like your budget and we should stay reasonably close to that as we already have quite a lot of the components from other projects in the past.



Clare & Peter
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Old 28-04-2019, 07:57 PM
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We have completed the foot assembly. The black feet are 3D printed in PLA Flex which is horrible to print (note the rough surface). The feet are largely hollow hopefully to conform to irregularities on the ground. The yellow parts, including the ball for the foot joint, are printed in PLA+ which is much nicer to print.



C & P
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Old 01-05-2019, 08:19 PM
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We have made some progress with our EQ platform construction.
See pictures.
The micro switch, which wasn't on the original drawings, is a down limit switch to stop the stepping motor at the completion of the one hour tracking.

Now it's onto the electronics.


P&C
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Old 08-05-2019, 09:41 AM
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Design for the electronics for the platform.
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File Type: pdf Motor driver.pdf (10.5 KB, 4 views)
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Old 08-05-2019, 10:26 AM
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Why don't you just buy Arduino MEGA board and load it with OnStep f/w?
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Old 08-05-2019, 12:18 PM
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+1 with Bojan. You've got stepper motors running it and onstep is excellent.

Several hardware options. You can go with the mega. Or if you don't mind a bit of soldering get the latest min/maxPCBs made and shipped to you - cost me $25 (incl postage) to get 5x miniPCBs and smart handcontroller PCB from easyEDA.
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Old 08-05-2019, 08:32 PM
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Hi Bojan & Chris,


Thanks for your comments & suggestions as they are greatly appreciated. We have learnt a great deal researching the items that you have suggested. "Why not use OnStep?" is an excellent question. There are a few reasons at this time.
  1. When we started this project we did not know as much about the various other options. Even at this time we have now only seen the online documentation of some of them and certainly not seen them in action so we are basically learning as we go along.
  2. We actually enjoy the making of things as well as astronomy. In fact, we enjoy the designing, making and programming of hardware. Also it is much easier to understand and modify code that you have written yourself than to work from other people's code. All a bit like exercise for the brain.
  3. We guess that if we are honest, like all engineers, there is a bit of the thought that you can design a better widget. This is probably not the case in this situation but there is still the fact that the design is for our own particular circumstance and constraints.
  4. This is the biggest reason. As you can see from the pictures, the hardware is completed and we are just tidying up the electronics. We have actually had the opportunity of using the mount with breadboarded electronics on a couple of occasions. It has certainly delivered on our original expectations, that being it is totally successful for observing over the one hour period without losing the subject from the FOV. However, as you pointed out from the very start, the design does have limitations and since using it we have had a small taste of the potential that tracking has for imaging. Testing thus far has shown that our current unit is good for low magnification and exposures up to 15 seconds, however, at magnifications greater than 200, the limit of reliable exposures is around 2 seconds. Basically all this means that we have already started to think about a better tracking design as a next project.
So the current plan is to accept this platform for what it is and enjoy using it and start thinking of an improved mount design. Our research thus far on OnStep has raised a couple of questions. As we use only Linux as our OS and Stellarium, the OnStep documentation is vague in this area. It talks about INDI drivers but then gives examples of its instruction set being Meade LX200 codes. This would seem to invalidate the need for an INDI driver when using Stellarium as Stellarium happily outputs LX200 codes to the /dev/ttyUSB0 port. We have put a serial port analyser on the codes and confirmed their validity and written a small amount of code to make Stellarium think it has a scope attached and this works. Another initial question is that the instructions for OnStep say that you should boot with the scope pointing to the SCP, which would seem to be less accurate than starting with the OTA level (which can be quite accurate) & facing north (not so accurate) but easier than the SCP.

Early stages of thinking for this next project so plenty of time to change things this time around.


P&C
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Old 09-05-2019, 07:32 AM
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Yep – someone on this forum said the best telescope is the one that is used…

After power up OnSTEP starts assuming the scope is in home position (it was conceived for EQ mount first). However, you do not have to worry about that too much - I switch on my version of OnSTEP system connected to laptop running CdC, then I point the scope to bright object and sync - and that is giving me enough precision for GoTo and so I have a full control of my EQ6 from my laptop screen.
LX200 is supported on both serial ports, in my case USB is used by CdC for positioning, the other serial port on MEGA board I am using for guiding (normally it is used for wireless communication). ST4 port I use for fine manual control (buttons on housing).

The best thing about OnSTEP is that you can use this firmware (or, I should say "sketch" as I was warned by someone on Arduino discussion forum that I will not get very far with term "firmware" ?? No idea why is that ) on variety of platforms, some of them are really cheap ($5max on ebay)

Have a look at OnSTEP group .. you can ask questions there, Howard (and other contributors) is very helpful.
.
I am also using Bartels system on my 10” Dobson.
It is sort of considered "obsolete" these days (because it runs on DOS platform), but many people still use it because of its flexibility and because it works. And it is still better (with more features) compared to any other freeware available.
I am running Bartels software on Fujitsu ST 1000 pen computer (100MHz 486, with CF card as HD - the whole thing cost me about $50).
Upon power up, I can either sync on SCP or on any other bright object, and encoders (taken from old mechanical serial mouse) take care of manual pointing (or I can GoTo if/when needed.

You can see some details here about my mechanical solution (it is not ideal either - I need to add rubber rollers on the rim to minimise vibrations).
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Old 09-05-2019, 10:26 AM
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Hi Bojan,
Thanks again for clarification regarding OnStep start up and calibration. We'll continue to research the things you have mentioned. We had a quick look at your encoder setup. Great work. There are many good ideas for us to consider for our next project. We also noticed that you use one of our favourite suppliers, Banggood.



Peter & Clare
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Old 09-05-2019, 11:05 AM
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Yes, bangGood is good.. and so is ebay - very often you will find something on one but not on another - so check both of them.
Also, IMO ebay's search engine is a tad better, it is easier to locate wanted items.
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Old 10-05-2019, 08:45 PM
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The electronics is now cleaned up and off the breadboard. Also we have changed from the test set up with an A4988 stepping motor driver to a TMC2100 running in stealthChop mode. Wow, what a difference. It is totally quiet and we need to add a buzzer to the circuit to warn when the run has completed.
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Old 21-05-2019, 08:01 PM
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Our Equatorial Platform is now completed and we have used it several times. The experience compared to untracked is the proverbial chalk and cheese. Our speed calculations must have been very close to correct as with only average polar alignment objects stay in the FOV for a considerable length of time. We are very happy.


However, there is a weakness in the design which should have been obvious from the onset. The objects stay in the FOV but actually move around (literally round) within the FOV. This is caused by actually rotating the threaded rod whereas other designs have the rod fixed and rotate a gear that either lifts or lowers the rod. The rod run out in the lathe is within a few thou, however, no matter what coupling (we are now on the third iteration) there is far more run out at the end of the 200mm of rod when connected to the stepping motor. The last coupling as pictured is machined from mild steel and clamps rather than having a set screw on the flat of the stepping motor shaft. This is the best so far but still not perfect. The run out of the rod highlights the fact that the hinges will allow side to side movement. The periodic movement limits the length of exposure time considerably so we are presently re-engineering the stepping motor mount to include a threaded gear and fixing the threaded rod at the top end. Hopefully this will be a great improvement.
Peter & Clare
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