CYGN-B

[laserist]

Laser Images’ scan through actuator technique worked. The Hermit commented that its rotation into the beam path was a questionable feature, but that didn’t bother me. The scan glass comes up on a musical cue – the rotation is to the cue – the cue is over and so is the rotation – but the scan glass remains. The design problem for me - it wasn’t balanced. Gravity was an issue. Sliding the scan glasses into place would have been a problem for Laser Images unless you did it vertically. And there’s gravity again. Why was it a problem? Sliding horizontally (sort of) - say the scan glass is two inches wide - you’d need 4 inches per scan pair minimum, and the original head was built in a 19” rack. It wouldn’t fit. One of the early design criteria was projector foot print. They wanted to keep it as small as possible. Planetariums back then cared about every seat. They still do. Even though they rarely fill them. Laser Images’ first projectors were designed with the Spectra Physics 164 lasers mounted as close to vertical as the warrantee restriction allowed. The tube was installed backward to make it less likely that bore material would fall onto the rear Brewster window. The Mark IV had a scan glass tray that a big old rotary solenoid slammed into place for Tank in Laserium I. The Mark VI had 3 scan glasses per scanner activated by linear solenoids behind the scan panel using coaxial brass tubing to connect to the scan glasses. When business slowed down to the point that we wanted to run multiple shows in the same week on even day – the scan glass mounting design was modified to allow the scan glasses to be swapped quickly. So anyone designing a scan glass system for today – be it linear or rotational - consider designing in a quick change capability – from the start.

[Greg]

That cleared things up a bit. Now we can see that we have the essentials of a full 6b scan glass system. Brian again, for preserving so many unique and important specimens of an otherwise lost medium. What is missing is the rolled steel pins, the steel rods, the knurled screws for the clamps, and then the DIYable stuff including the solenoid interface bar, the brass tubing, and a mountable chassis. Perhaps these missing materials are not difficult to obtain if one knows what to ask for.

I see how to assemble the scan glass quick swap mechanism. Very clever. I would never have thought of the pull the screw to release latch.

Also, that discussion about the rotation of the scan glass being the cue gave me a flashback. I remember that used very prominently in the Zeppelin number coming up soon for analysis. So the point of a scan glass system yet to be built is to play these cues as close to the original as possible. Anyone remember, was there any regularity to the 3 effects used across the channels such as diffraction, fuzz, and something else?

I was really into Hitchhikers for a while back in the 1980s, especially the Infocom text adventure with InvisiClues.

[laserist]

There's some confusion evidenced in your post. There were no knurled clamping screws just ordinary cap screws. And the scan glasses were driven by the diode logic board.

The solenoid driver circuit for the scan glass solenoids was clever. It used +/- 20 volts or so to activate the solenoid and then switched one of the voltages to ground to reduce the current to just hold the scan glass in place.

I did have the scan glasses individually addressable as well as having manual control of the Lumia actuators in 2013, but I have it on very good authority that I'm odd...

[Greg]

The solenoid driver circuit for the scan glass solenoids was clever. It used +/- 20 volts or so to activate the solenoid and then switched one of the voltages to ground to reduce the current to just hold the scan glass in place.

There seem to be solenoid driver boards available for pinball games. I wonder how easy it would be to adapt a board such as this to drive a scan glass actuation system.

https://allteksystems.com/products/u...d-driver-board

[laserist]

Solenoids of pinball machines are low duty cycle high voltage operation. Laser Images' wanted the start force of a high voltage with the hold of a lower voltage.

[ronhip]

Anyone remember, was there any regularity to the 3 effects used across the channels such as diffraction, fuzz, and something else?

Greg,

In my memory, the three glasses closest to the scanners had cross-star filters, the middle set were 2-axis diffraction gratings - high dispersion on yellow and green, and low dispersion on red and blue, and the front 4 scan-glasses were "other" various things depending on the show. So really, at least in San Francisco, we only changed the top (outer) row of scan-glasses. We also settled on a pretty much standard set of lumia effects and never switched them out unless absolutely necessary. Pulling on the lumia mounts, even with the later and gentler 1/4" audio plug mounts, tended to affect alignment, and there was always the potential of hitting other things when the plugs suddenly released. My preference was to stay away from the laser head as much as possible once things were working to my satisfaction. It also made turn-over between shows quicker. We most often did two or three different shows every evening!

Ron

[ronhip]

[QUOTE=Greg;362226]There seem to be solenoid driver boards available for pinball games. I wonder how easy it would be to adapt a board such as this to drive a scan glass actuation system.

Greg,

Here is the driver circuit we used in the CSX system. I only captured one of the driver schematics on the card. All were identical.

Ron

[lasermaster1977]

Thanks for sharing, Ron.
I find myself on a similar quest as Greg, except using a Teensy, instead of Bela MCUs. But, I'm far from being an EE, so I have a stupid, but serious question, if I may quickly interrupt.
In the article mentioned in my previous post, it describes lowering power usage while holding an engaged solenoid in place by using a device to kick in PWM, after a short full power delay, with an optimum pulse width TTL signal switching a MOSFET, that's providing the maximum p-p voltage, which doesn't decrease with that design.
Q: Both the Bela and Teensy GPIO pins can already provide programmable PWM signals, then why not simply use those with a MOSFET driver, at the current and voltage limits of the solenoids' specs?
Thanks in advanced to whomever answers this OT question, before it disappears.

Roj

What Ron provided does what essentially is the same thing, it is just more simple...yet elegant.

Edit: It may be worth mentioning that linear and/or rotary solenoids have a specified working voltage range along with a given actuating current and holding current within its voltage range. I seem to recall it being mentioned somewhere on PLF that Laserium used Ledex linear solenoids but don't recall if it used other types like rotary or other brands. Maybe Ron or Brian could clarify this again.

[ronhip]

What Ron provided does what essentially is the same thing, it is just more simple...yet elegant.

Edit: It may be worth mentioning that linear and/or rotary solenoids have a specified working voltage range along with a given actuating current and holding current within its voltage range. I seem to recall it being mentioned somewhere on PLF that Laserium used Ledex linear solenoids but don't recall if it used other types like rotary or other brands. Maybe Ron or Brian could clarify this again.

I'm absolutely sure we used linear, NOT rotary solenoids for the scan-glass actuators. In the original Mark4 (and maybe the Mark6?) projector we used rotary solenoids to bring up the lumia 50% and 100% mirrors for the effect rows and the individual effects. THAT was a HUGE mistake. Those solenoids were amazingly loud and could easily distract those close-b,y especially during a subtle number. I used to cringe when those noises came from the projector. The later projectors switched to GM-20's which were completely silent (albeit at a substantial increase in expense!)

I'm not an electrical engineer, but is it even possible to use PWM on solenoids, which are essentially an inductors? Would that work?

I found the 6B projector scan-glass driver. It's essentially the same. I include it below for completeness.



Ron

[lasermaster1977]

I'm absolutely sure we used linear, NOT rotary solenoids for the scan-glass actuators. In the original Mark4 (and maybe the Mark6?) projector we used rotary solenoids to bring up the lumia 50% and 100% mirrors for the effect rows and the individual effects. THAT was a HUGE mistake. Those solenoids were amazingly loud and could easily distract those close-b,y especially during a subtle number. I used to cringe when those noises came from the projector. The later projectors switched to GM-20's which were completely silent (albeit at a substantial increase in expense!)

I'm not an electrical engineer, but is it even possible to use PWM on solenoids, which are essentially an inductors? Would that work?

Ron

My recollection was that linear had been mentioned. My personal recollection from my 1st Laserium show in '77 at the Gates Planetarium was rotary...from their sheer noise as you mentioned.

I too, first used Ledex rotary solenoids, still got them in a box, for rotating fixed diffraction gratings into scanner outputs, but I didn't use them for long because they were so f---ing loud! When I first heard them lock in, the noise sounded exactly like the occasional noises "clucks" I heard out of the Laserium projector several years earlier that was only a few feet away from my seat in the planetarium. I did find a way to lessen their noise but my method was not recommended by Ledex.

I don't think PWM is a good solution for these type of inductive solenoids, but could be made to work.