Android, Arduino, DM524, ealing, electronics, MaxESP, motherboards, OnStep, signal, stepper drivers, Stepper Motors, TB6600, Telescope, Telescope drive
Guy BrandenburgJul 6
At long last, we have finally got the venerable, massive Ealing telescope mount at Hopewell Observatory working again, after nearly 9 months, with a totally different, modern, electronic stepper motor drive based on Arduino.
My first post to the OnStep group ( https://onstep.groups.io/g/main/message/37699 ) was on October 21, 2021, over eight months ago. In it, I wrote that I had decided to give up trying to fix the electro-mechanical synchronous drive and clutches on our Ealing-Byers mount at Hopewell Observatory, and asked the folks on the OnStep message boards for help in choosing the best OnStep combination to drive such a mount.
Since then, it’s been a very long and steep learning curve. We only fried a couple of little slip-stick drivers and maybe one MaxESP board. We got LOTS of help from the OnStep list (not that the posters all agreed with each other on everything)! We ran into a lot of mysteries, especially when we found, repeatedly, that configurations that worked just fine on our workbench wouldn’t work at all when the components were put into the mount!
But now it works.
Let me thank again in particular:
* Prasad Agrahar for giving me the OnStep idea in the first place by showing me a conversion he had done;
* Alan Tarica, a fellow ATMer, for cheerfully partnering and persevering with me in working on this project for the past 8 months in many, many ways;
* Ken Hunter for providing tons of basic and advanced advice and a lot of hardware, all for free;
* Robert Benward for extremely helpful advice and drawings;
* George Cushing for providing some of the original boards we used;
* Khalid Bahayeldin for lots and lots of OnStep design features;
* Howard Dutton for designing, implementing, and supporting this whole project in the first place; and
* Arlen Raasch for bringing his wealth of trouble-shooting experience and a lot of nice equipment up to Hopewell, spending full days up there, and saving our asses in figuring out the final mysteries. Among other things, he kluged (by the way, “kluge” is German for “clever”, not clumsy) a level shifter to make it so that the 3.3 volt signals from our MaxESP3 board would actually and reliably communicate with the higher-voltage external DM542T stepper drivers that controlled the very-high-torque NEMA23 steppers, rewiring some of the jumpers on our already-modified MaxESP boards, and making the wiring look professional, and other stuff as well, thus essentially pushing us over the finish line.
* All of the Hopewell members for supporting this project
* Bill Rohrer and Michael Chesnes who physically helped out with soldering and wiring work at the observatory.
I plan to write up a coherent narrative with a list of lessons learned, and perhaps I can help make some of the step-by-step directions in the OnStep wiki a bit clearer to the uninitiated. Obviously I’ll need to write a user guide for this mount for the other Hopewell members.
If Alan and I had gone straight to our final configuration, this project would have been quite a bit cheaper. In addition to what’s inside the mount and control box at the observatory, we now have on hand something like this list of surplus items:
* four MaxESP boards in various stages of construction and functionality;
* a dozen or more different slip stick stepper drivers we aren’t using;
* four or more external stepper drivers, mostly TB6600;
* five or more stepper motors of different sizes;
* a hand-held digital oscilloscope;
* lots and lots of wires of many types;
* lots of metal and plastic project boxes of various sizes;
* lots of tiny motherboards; and
* lots and lots of sets of various mechanical electrical connectors (many were used, later cut off, and then ended up in the trash).
Yes, one does need spares, and yes, lots of this stuff has multiple uses, but this has not been a ‘green’ project. On the third hand, it has been extremely interesting and fun to learn all these new skills.
The final substantive changes that got the Ealing mount up and running were made during the Fourth of July fireworks down in the valleys on each side of the ridge that our observatory sits on. What were the changes? (1) switching the black and white leads from the mains power leads (they original, scavenged, cord had the white lead as Hot!) and (2) reversing the Declination motor direction. It also helped that I was not zoned-out and punchy from lack of sleep, as we had been when Arlen and I had last worked on it.
On July 4th, it at long last worked properly!
This Ealing mount’s original, labeled, built-in manual RA and DEC setting circles make it quite easy to put the scope into Home position before you turn on the power. One just loosens the clutches and moves the axes to 6:00 hours exactly in Right Ascension and 90 degrees exactly in Declination. From there, I found the OnStep system behaves very nicely. It accurately slewed to a number of bright, obvious targets of various sorts on both sides of the meridian. However, when I tried to get it to aim that night at M13, it refused, sending an error message that it was too close to the zenith for safety. And it was (altitude 87 degrees)! Very impressive – a safety feature I hadn’t even known about!
None of the objects that I slewed to was far from the center of the field of view, even when the scope slewed across the meridian. I was using an old, 2-inch diameter 50 mm Kellner eyepiece on an f/12 six-inch aperture D&G refractor.
I found that the Android app to be **much** better for initial setup than the SHC. Arlen, Alan and I all found that setting the correct latitude, longitude, UTC offset and so on from the SHC was a real brain-twister because of its unfortunately not-very-friendly user interface. Using the OnStep app on a cheap, old Android tablet made the whole initialization process very much easier and faster, especially after I let the tablet discover what time it really was from my iPhone’s wireless HotSpot.
However, I found that the hand paddle is much better for fine-tuning of pointing and so on, because the bright display on an Android, no matter how dim one makes it, will destroy one’s night vision, and one cannot reliably feel where the directional buttons are on a flat screen while staring through an eyepiece. Obviously, one can feel the buttons on the SHC quite well, maybe even with gloves. A joy stick would be even better…
Alan and I and the other Hopewell members still have many more OnStep features to learn.
However: if I had known this project would take over eight months of hard work, I think I might have tried fiddling with the original Ealing clutches some more.
Oh well, we have a mount that has much more capabilities than it ever had, and Alan and I have learned quite a bit of electronics! I’m proud of what we did!