Here are some pix of the progress Alan Tarica, Michael Chesnes, Bill Rohrer and I have made so far on our conversion project for the university-grade Ealing telescope mount’s motor drive at The Hopewell Observatory, with moral support from other Hopewell members.
The project has gone through quite a few different very-low-budget but very-labor-intensive phases.
(We are a low budget organization, and being a retired school teacher, I for one have more time than I have money.)
The first phase involved me trying to re-install the clutches on the original gear and synchronous motor system from the 1970s.
This required careful disassembly and re-assembly of a very complex gear train, which I did accomplish, but I was unable to fine-tune the exact amount of friction needed, so I gave up on that approach and decided to try an electronic conversion that many other folks had been using on their own telescopes.
Namely, an Arduino-based system called OnStep that grew out of the modern CNC industry that powers modern 3-D printers and most modern fabricating machinery of all types.
Our version has MaXESP3 boards made and sold or generously given to us by Ken Hunter and George Cushing. We have also had considerable help from OnStep’s Howard Dutton, Robert Benward, and NCA’s own Prasad Agrahar.
The MaxEsp board (about the size of my hand) powered two little stepper motors (roughly cubical, 5 cm on a side) donated by Prasad. We were given by Ken, and also purchased, some tiny LVL and TMC stepper drivers about the size of a postage stamp that fit into rails on the MaxEsp board. The motors were connected to the wonderful original Byers gears inside the mount by ingenious little direct-drive couplings donated by Prasad.
This rebuild required me to remove all the original motors and gears and clutches in the scope mount’s motor box and carefully line up the new motors with the telescope shaft, which required some careful machining and filing.
We discovered that those stepper motors didn’t have enough torque to drive the mount, even with all of the optical tubes removed.
(Btw, connecting all these electrical components was a huge learning curve for me! There are SOOOO MANY different types of connectors, and we have now discarded several types as unsuitable. Wiring up and soldering some of those connectors require the skills and steady hands of a seasoned watchmaker or Heathkit veteran — which I am not. My hands shake terribly!! One small slip of one of my hands, one time, was enough to fry two of those tiny drivers and blow a tiny fuse… I had to adjust a tiny potentiometer screw while the circuit was live… I didn’t realize there was a better place to connect my grounding lead to… fortunately those drivers only cost a few dollars…)
It was suggested to add a belt and put pulleys of different sizes onto the stepper motor and the mount shaft. That required moving the stepper motors and hence a bit more machining.
But that didn’t work either.
So I ordered bigger stepper motors.
But the first ones I ordered also didn’t have enough torque either! I found I could stop their rotation with my bare hand!
So I ordered some more powerful stepper motors. And got rid of the belts and pulleys. (We have extras if anybody’s interested!)
But they needed more current (amperes) and voltage than the Tiny postage-stamp sized stepper drivers could produce.
Larger stepper drivers won’t fit directly on the MaxEsp board, and also need more voltage than the board can tolerate.
So Ken Hunter figured out a way to bypass that: he changed (for free!) some of the wiring on the back of two of our MaxEsp boards, and suggested some much larger stepper drivers about the size of a small deck of cards, and a regulated switching power supply that puts out a steady, adjustable direct voltage from 0 to 42 volts that is the size of a medium-length hardback novel.
But the MaxEsp board can’t take that many volts, so we needed something called a buck step-down power supply to reduce the 0-42vdc power down to a steady 10 or 12 volts – just for the MaxEsp board.
We wired all that up and re-adjusted the stepper motors and got the worm gear from the stepper motors to mate properly with the Byers gears on the scope mount — not an easy task! Physically screwing in the gearbox was insanely difficult until We figured out an easier way. We only fried two of the buck power supplies via short-circuits, but this was no great loss since five of them had cost about $15.
Everything worked great when we had all the components wired up **outside** the cavities built into the mount itself. But when we carefully slid the five separate components into those cavities, some of the many, many tiny little colored and numbered and labeled leads broke off that connected all those components, broke off.
Yes, we made wiring diagrams — I think we are on version eight or nine now! (Mine are done in pencil on large sheets of thick art paper. Bob Benward has generously made electronic versions for us; I’ll have to send him the revisions.)
We took it all back out, and did some trouble shooting. I tried using an old Heathkit oscilloscope made by the late Bob Bolster (one of the principal founders of Hopewell) but made little progress until Ken explained **where** to connect the o-scope leads (hint: at the output from the MaxEsp board and not at the output from the drivers), and Alan brought in a brand-new solid-state o-scope.
Using that info, and using Alan’s new, more sensitive and easier-to-use o-scope, and taking careful notes, and examining those outputs on the o-scope screen when we try to slew or track with the scope controls, I finally figured out that one of our OnStep boards had some defects, but the other two were ok.
It also became obvious that trying to shoehorn all these components inside the original compartments inside the Ealing mount wouldn’t work. We needed a nice sturdy electrical project box. I didn’t see any at local hardware stores that were large enough, so I ordered a sturdy steel one online. It ended up still being too small, so I exchanged it, and with Alan’s assistance, built standoffs to isolate and secure all the components, and I was able to mount and wire them all up correctly onto a removable steel plate that fits inside the box. It’s all modular, and swapping out components is pretty straightforward. (See the photos below.)
Michael, Alan and I decided to place the box against the north side of the masonry pier supporting the telescope. (Drilling the mounting holes into the concrete ended up being harder than I expected, but we got it done.) We also had to drill holes for the “Liquidtight” flexible electrical conduit that connects the OnStep/Arduino circuitry inside the box to the mount where the motors and gears reside. And holes for the fan and vent. And for the Wi-Fi / Bluetooth antenna. And the USB port.
When I finished wiring up everything, I turned on the power… and…
It turned out that I had done something to the 0-42VDC power supply so that it received 110VAC but put out nothing at all. I was too hot and tired to figure out and fix whatever I did on-site that Memorial Day, so I ordered another one, which should arrive this afternoon.
I’ll connect the new power supply on Sunday.
Here are some pix.
The fan and USB jack are on the left. Some of those dangly wires need shortening.
I had to stop up a number of the holes I had previously drilled in those panel covers on the mount, to keep insects out. If you don’t, marmorated stink bugs and lady bugs enter in droves and many die.