Alan Tarica, Ealing mount, George Cushing, Hopewell Observatory, Howard Dutton, Ken Hunter, Khalid Bahayeldin, OnStep, Prasad Agrahar, stepper motor, Telescope Making, Telescope Modification
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?
Ken Hunter said:
Thanks for including the video…
Well the noises you are hearing is the motor ramping up in speed, slewing until near the target then ramping down in speed as it gets near the target. The noises are proper but quite a bit louder that I am used to hearing. Most of that could be because the motor has no load, is being operated in a quiet benchtop environment or because the Driver setup is wrong. (Remember that I am not familiar with your steppers and drivers) it could possible be a mix of all of the above situations.
I did not hear the BUZZER at the beginning and end of the GOTO. That is another issue that we can tackle later. (SHC and Config.h BUZZER set to ON?)
If you have slewed to a star (or any location) the OnStep controller is sending out the commanded co-ordinates to the SmartHandController (and Astro program) where the scope should be pointing based on the configuration and the steps issued to the motor drivers. It is an “OPEN LOOP” system so there is nothing to tell OnStep the scope isn’t moving, drivers skipping steps etc..
When you first turn OnStep ON, it assumes it’s at the North Celestial Pole so slewing to Alpheratz is just a real short slew from NCP. Try doing an Alignment (follow Wiki directions) using 3 stars and make 2 of them near the Equator on the East and West side of the meridian. That way you can hear each Axis as it goes through the process of Ramp Up, SLEW, and Ramp down.
If you are connected to an Astro program, it’s really refreshing to see the simulated scope move from one target to the next and that should be part of your testing as well as with the SHC. It is quite normal for the 2 steppers to move at different rates for different amounts of time as each axis gets near it’s destination. One may even stop while the other continues to its target location… All quite normal!
If the stopped stepper is still making noise or getting hot, the driver currents are probably set too high in Config.h.
After trying that decide if the action is as expected. (Does the OnStep controller in fact think it’s going there and the mission is completed (from OnStep’s point of view)?) If the motors are really not completing the process for each slew we can continue troubleshooting to see what is wrong (if there is something wrong).
Keep sending progress reports and by the time it gets too hot we’ll have the scope working 100%
I think you missed the problem: while the steppers were making all that racket, they weren’t actually driving the shafts.
I suspect I’m going to have to add a belt and pulley system to reduce the quantity “AXIS1_STEPS_PER_DEGREE”.
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