Tag Archives: OnStep

It’s Not Rust! It’s Just Grease!

19 Sunday Dec 2021

Posted by in astronomy, Hopewell Observatorry, Optics, Telescope Making, Uncategorized

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Here is a photo of the inside of the declination axis of the Ealing mount at Hopewell Observatory.

The gears you see were made about 50 years ago by the Ed Byers company, who continue to produce some of the finest gears anywhere. The periodic error on this mount is very, very low, which is a Good Thing, and why we want to keep it and just upgrade the old drive. As you can see in a previous post, the old system had a finicky clutch drive that had caused a lot of problems, but worked very well indeed when it worked properly.

I am working to replace it with a more modern, reliable and user-friendly, namely an OnStep ‘build’.

The friendly and helpful folks at the OnStep project were asking for a picture showing how the existing Byers drive was put together. I hope these four photos help.

In the first photo, notice the greasy worm gear at the bottom left. It was removed from the mount, along with the old motors, and is sitting on my desk (with the old grease cleaned off), directly coupled to the stepper motor, which connects to one of the OnStep boards (in the wood-and-black aluminum box). In the second photo,

The black anodized bracket in the second photo holds the motor and the worm gear rigidly together. The bracket bolts into a place in the mount (not shown). It took a bit of work to get the stepper motor and the worm gear lined up within a couple of thousandths of an inch, but it’s done. Prasad turned me onto those cool little universal joints that permit one to connect items that don’t match perfectly.

20 turns of the worm gear, times 359 teeth on the big gear, means that it takes 7,180 turns of the stepper motor to make one full revolution of this declination axis or of the right ascension axis, which is identically mounted. (Not that you would want to go about spinning your telescope very far on either axis!)

So 19.97 turns of either motor make the scope travel 1 degree (7180 divided by 360).

And since our stepper motors make 200 steps in one revolution of the worm gear, it takes about 3994 motor steps to make the scope turn by that one degree (the last result, times 200).

Or if you are micro-stepping by, say, the rate of one sixteenth of a step, then by my calculations it will take 63,911 microsteps to turn by that degree (the last result, times 16). And that seems to be outside the range of permissible microsteps for these stepper motors, perhaps causing them to scream in protest. (I swear, that’s what it sounds like!)

From left to right: A spare OnStep board inside its wood-and-aluminum project box; the NEMA23 stepper motor on its bracket; a universal joint; a big bearing; the first worm gear (now cleaned off)

It appears that Khaled and Prasad might be correct: I might need to add a toothed gears and a belt to this arrangement to reduce that last number (63,911) by some factor. For very little money I just ordered a pair of such things, designed for 3-D printers and other computer-controlled machines. It will have 60 teeth on the motor and 20 teeth on the worm gear, and then the above would instead have only 21,304 microsteps to turn one degree. (No wonder they protest!) Once again I’ll have to disassemble the motor and drive bracket and do a bit of machining. A drill press and a punch will be fine.

The last two photos give some more detail on how the old drive system worked.

Close up of worm gear driving a toothed gear wheel that drives another worm gear that drives the right ascension axis
One of the original drive motor and clutch assemblies in place, inside the mount. All those gears have now been removed.

Mysterious Noises from Stepper Motors for the Ealing Telescope Mount

18 Saturday Dec 2021

Posted by in astronomy, Hopewell Observatorry, Telescope Making

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A few blog entries ago, I thought I had made great progress in getting the old telescope drives for Hopewell Observatory’s venerable Ealing Mount to work again. Unfortunately, it became clear that one had to adjust the amount of friction in the clutches very, very accurately, and I saw no way to fine tune it.

So I bit the bullet and decided to convert the mount over to an inexpensive system, at least partly DIY, that uses very inexpensive solid-state printed circuit boards and Android phones to control stepper motors that make the telescope point in the directions desired. (Instead of spending many thousands on a Sidereal Technologies rebuild.)

This system is called OnStep and is spearheaded by a number of very generous volunteers: Howard Dutton, who basically invented the system and wrote all the original code, along with Ken Hunter, George Cushing, and Khaled Bahayeldin, and a number of others whose names I don’t recall. It uses off-the-shelf components, chips and sub-boards, that cost very, very little; these are put on one of a slew of different possible 3D-printed circuit boards. There is even a Wiki that could use a bit of editing. It’s got a ton of information but when I was starting out, I found it extremely confusing, and I am not alone. I promised to try to improve it when I get the Ealing telescope working properly.

After getting the software to work, then you arrange the connections to your telescope’s gears, power supply, and communications inside your own mount.

I am immeasurably aided in this conversion effort by Alan Tarica, who is the co-leader of the Washington, DC-area’s Telescope Making, Maintenance, and Modification Workshop (which has been going on for about 80 years) and by Prasad Agrahar, who made a remarkable telescope in our TMMMW several years ago and went on to build his own OnStep conversion of an existing commercial telescope. Prasad’s example showed me that if our old Ealing drive died, we should try OnStep.

Well, the Ealing drive did finally die. (It had presented problems ever since it was first delivered to the University of Maryland Observatory nearly 50 years ago.)

Michael Chesnes and Bill Rohrer of Hopewell helped materially with removing the old components of the scope and with then trying to debug the electrical problem that has now sprang up with our roll-off roof.

Ken Hunter made for us, and debugged, an entire OnStep board and refused to take any money for it. Prasad Agrahar gave us some NEMA17 stepper motors and some wires and likewise refused to let us pay. Prasad drove all the way from Philadelphia to help Alan and me figure this stuff out in person, both at the workshop and out at the observatory. Ken has spent hours, remotely from Yuma AZ, walking me through the various steps in managing the many settings that need to be uploaded and adjusted in order to get things to work. Ken told me he used to run the ATMFREE list-serve, but retired from that after an injury, and he remembered meeting me once at Stellafane. He also very kindly sent us an antenna for the system so that it can run WiFi or BlueTooth more efficiently from inside our massive metal mount.

Alan and I are fairly far along in the conversion, thanks to all this help. I had to learn some of the basics of the Arduino operating environment, which one uses to set all the many, many parameters needed to get the system running. And had to improve my soldering techniques! Fortunately, all the heavy lifting of getting all of the many lines of code working together has been done by Howard, Ken, and the others, so all I had to do was set things up to fit our particular set of choices for the board, the stepper driver, the sub-boards, the gears, and the motors.

Here is our current setup: we have two (now three) MaxESP boards running OnStep version 2.04 (iirc). (Multiple boards because they are cheap and in case one gets fried by a lightning strike or stupidity. It happens!)

They have TMC5160 stepper drivers, connected to two rather beefy NEMA23 stepper motors (200 steps per turn), which I arranged to fit exactly in-line with the worm gear that we will later put back into the mount. We have tweaked the ‘CONFIG.H’ file settings the best we could, and with an enormous amount of help, I think I’ve set the speeds of the stepper motors correctly. The worm gear turns another gear with 20 teeth, which turns another one with 359 teeth. (All made by Byers, and made very, very well.)

(We had NEMA17’s run by the TMC2130 stepper drivers, but we didn’t think they were beefy enough to rotate the very large mount we have, even if we balance it perfectly.)

It’s been a very interesting learning expedition. It’s taken quite a bit of time, but not really very much money. With mass production, the components (screws, capacitors, diodes, resistors, and so on) if purchased in medium quantities, are really very inexpensive.

However, the stepper motors are still not behaving properly. They scream instead of moving, as you can see in this video. I will post the current parameters on the OnStep wiki, where I said. You can see and hear the action in this little video. When I try to slew to any random, dummy target, the steppers will start rotating and also start making a deafening squeal that gets higher in pitch and volume. However, after a little while, both rotors stop turning either completely or almost completely. The smart hand controller pretends that the mount is moving in both axes, but it’s not true.

Right now, I don’t know what is causing this problem.

Anybody have suggestions?

Satisfying Fixes Made to 50-year-old Electro-mechanical Telescope Drive at Hopewell Observatory

29 Wednesday Sep 2021

Posted by in astronomy, Hopewell Observatorry, Optics, Telescope Making

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About a week week ago, the right ascension (or RA) drive on a vintage mount at the Hopewell Observatory stopped working. Instead of its usual hum, it began making scraping noises, and then ground to a halt. (This drive is the one that allows one to track the stars perfectly as the earth slowly rotates.)

Another member and I carefully removed the drive mechanism, and I took it home. At first, I thought it was the motor itself, but after examining it carefully, I noticed that some clutch pads inside the gearbox had come unglued, causing the clutch plates to be cockeyed. The motor itself worked just fine when disconnected from the gear box.

I recalled that the pads and the clutch had been very problematic, and that our resident but now-deceased electro-mechanical-optical wizard Bob Bolster had had to modify the gearbox quite a bit. I carefully disassembled the gearbox and used acetone to remove all the old glue that he had used to glue the pads on. After doing some research to find some equivalent pad material, I yesterday ordered some new gasket material with adhesive backing from McMaster-Carr. Lo and behold, I received it TODAY! Wow!

I cut out new pads, re-assembled everything, and the gears and worm drive work just fine. Not only that: there were no screws or nuts left over!

In addition, I now see how we can replace the extremely complicated partially-analog clutch-and-drive mechanism, in both RA and in Declination with a much simpler stepper-motor system using something called OnStep.

Here is a photo of the some of the innards of the scope:

A bit complicated, no?

In the next photo, my pencil is pointing to the clutch pads inside the gear box that had come loose, causing the clutch plates to become cockeyed, jamming the gears. The clutch is so that the observer can ever-so-slightly tweak the telescope forward or backwards in RA, in order to center the target. There is another gearbox for the declination, but it’s still working OK, so we left it alone.

The synchronous gear-motor in the background. My pencil is pointing to the problem.

Of course, we still have to re-install the gearbox back in the scope.

Bob Bolster, mentioned above, was one of the founding members of the Hopewell Observatory. He was an absolute wizard at fixing things and keeping this telescope mount going, but he is no longer alive. I was afraid that I would not be able to fix this problem, but it looks like I’ve been successful.

I append an image of a very beautifully-refurbished Ealing telescope and mount – similar to the one owned by Hopewell – that belongs to the Austin Astronomical Society. Ours is so much more beat up than this one that it’s embarrassing! Plus, both we and the University of Maryland were unable to get the telescope itself, which is a Ritchey-Chretien design, ever to work properly. So we sold the mirror and cell to a collector in Italy for a pittance, and installed four other, smaller scopes on the mount instead.