Moving a dome and EM relays

I have a domed observatory. Presently, it has two a/c motors that operate the rotation of the dome, and the shutter. The latter opens to the sky as the shutter is raised. I must move either manually with a lever.

I'm about to replace the manual operation with two circuit boards (not yet purchased) that will be attached to the dome and the circular support holding it up, sometimes called a skirt. The dome moves on wheels. The two boards communicate wirelessly. Solar cells will provide power to the boards. The electric motors used for manual operation, I think, will no longer be of use. It looks like they will have to be replaced by DC batteries. I'm kind of guessing here. However, according to the manual for the two boards, relays will be provided. I'm guessing they will somehow be needed to go between them and each of the circuit boards.

Does this latter part make any sense? Comments welcome. I'm just trying to get a feel for what I may need beyond the two circuit boards, and a few minor accessories provided with it. No batteries included!

The following materials are included in the kit (rotation and shutter control version): ? Two controller boards ? One motor sensor board ? One motor sensor cable ? One magnetic sensor with magnet ? One serial (RS-232) cable assembly ? Mounting hardware for optical sensor ? Computer CD-ROM ? Induction wire ? Mounting hardware for induction wire

Reply to
W. eWatson
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Relays have an output much like an ordinary switch, it quite likely that the relays on the controller boards can be connected in place of the motor-control levers you now have, and the rest of your existing hardware be retained.

--
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Reply to
Jasen Betts

You seem to be saying you will use DC batteries to operate the observatory, rather than AC power you use now. Am I correct? If that is true, you will need DC motors to move your dome and shutter, and you don't mention whether you have DC motors picked out to replace your AC ones.

I built an observatory controller recently, and some of what you say sounds familiar, but some does not sound right.

Is there a website for the kit you plan to use, so we could see how it works?

Unless the 'circuit boards' have motors to control, they're not going to move anything.

according

Relays turn power on and off, much as your manual lever does for your AC motors. Are the relays capable of switching power for your AC motors?

I think one of the sensors will sense when the shutter is fully open or fully closed, so the control board can use relays to turn the motor on and off.

Reply to
aioe

I believe that's true, but I really do not know yet.

I haven't any idea what DC battery I would need.

I'm not sure it will be helpful, but here . There's a 66 page or so pdf for it somewhere on their site that is just a copy of the other sources on that page. They get more specific than the Intro.

I have no idea. I do understand the basics of how they work. The ref above will likely tell.

Don't know. See ref.

Reply to
W. eWatson

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eed DC motors to

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If you've got AC power why do you want to switch to DC? You can get AC relays too.

George H.

Reply to
George Herold

This may not apply in the OP's case, but some pretty elaborate 'scopes get hauled out to a field for a 'star party'. They get run off of car batteries in series.

That was part of the spec for the one I built.

Reply to
Randy Day
[snip]

Before you decide to buy that control package, you need to decide:

- what kinds of DC motors can replace your AC motors, in terms of physical size (will they fit?), torque (can they move the dome and shutter?) and speed (can they move them fast enough?)

Your website specifies that it runs 12v motors up to 5 amps. 12v car batteries or marine batteries should do fine. It also says you can use external relays to control AC motors. That might be the simplest way for you.

If you still want DC, you might find some power window motors at an auto scrapyard, or even a car starter motor, though that might be overkill...

Reply to
Randy Day

Believe me this scope is going nowhere. It's big.

Reply to
W. eWatson

If you could give us a picture and tell us how big the AC motors are would help. This sounds like a bigger job than you imagine. Changeing the motors will take a significant amount of mechanical engineering.

--
John G.
Reply to
John G
[snip]

Then I'd venture to say you're better off using relays to switch the AC to your existing motors. That way you don't have to re-engineer a setup that already works. Buy 12v relays with switch contacts rated to handle your motors; you can hook the coils up to the motor outputs of your controller.

You can still use solar to operate the controllers if you like, too...

Reply to
Randy Day

Assuming that the existing a/c motors move the dome & shutter with whatever degree of accuracy/speed/precision you need, there is no need to change them. Literature for the new controller says: "It is possible to connect other types of motors, such as AC motors, using external relays."

Assuming that the lever you use now operates a switch, you will replace that switch with relay contacts. In fact, you may be able to retain the lever setup as is, and just wire the relay contacts in parallel with the existing switch. Retaining the lever setup will allow you to manually operate just as you do now, if you need to.

If you do operate the dome manually with the new controller powered off or not functioning, you need a means of letting the controller "know" the position of things. Since it didn't control the movement and couldn't "see" the movement, it won't know the position. You would have to tell the PC where the thing is currently aimed so that it can move the proper distance & direction to the new aiming point.

They will work as well as they do now if you use the external relays with the new controller.

You need a battery, and the external relays. According to the list you posted below, the relays are not included.

It might be a good idea to discuss the installation with someone who has already done it. To me, it looks like setting up their optical rotation sensor may be a somewhat finicky operation. I would not purchase the thing unless I first determined that I could install the sensor properly. The heart of their equipment depends entirely on the sensor. It counts every revolution of the motor, and it relies on the sensor to detect that revolution. You have to paint the motor shaft 1/2 white and 1/2 black, and mount the sensor a specific distance from the shaft at a specific height above the mounting plate. For the system to work properly, *every* complete revolution of the motor shaft has to be detected. Miss one, and your aim will be off by the amount of movement each complete motor revolution produces. Also, there can't be any accumulation of error or you'll continually have to recalibrate.

Ed

Reply to
ehsjr

I'm back after a trip. Azimuth AC motor is (see Grainger) Dayton 1LPN9, and the shutter AC motor is 6K974. The DC equivalent of the latter is

1z831.
Reply to
W. eWatson

You can get a feel for the size of matters by going to my web site at , click on Observatory.

Reply to
W. eWatson

Doubtful. The dome weighs 1500 pounds and the shutter about 400 pounds. The dome rotates on rollers though.

A clerk at an auto show mentioned the window motors, but then thought differently about them.

Reply to
W. eWatson

Good find. I guess you found that in the pdf manual. Yes, I see it. Interestingly though, the president of the company suggested DC on their Yahoo Group, but gave no explanation why.

I understand the concept of a relay, but how does it work in the case of motors here?

Pages 12-15 of the manual talk about optical rotation sensor. I think I'd better read that. I see they provide one sensor.

"new controller"? A circuit card.

If I go DC, then I'll need two 12v batteries, and two solar cells.

Despite the popularity of the dome, I have found no one on the MaxDomeII Yahoo Group that has ever done it. Ash Dome is the mfger. They don't even know of anyone who has done it. Well, one older post on the YG had the poster talking about several people who have installed the device on their domes. However, I responded to him for details, and as of yet haven't heard back.

I would not

Something that may save me on this whole matter is a friend who lives 45 miles from here who I think used the cards for a different type dome. I plan to see him Tuesday, so maybe he can provide me with details. He built the domed obs himself.

Thanks for the tips. I think I need to dig into the manual more. I've only done a quick read to see what's there, and have relied on the YG for some other issues. I'll probably aim to get the AZ part working first. The shutter is much harder, since the motor is mounted in an assembly near the top of the dome.

Reply to
W. eWatson
[snip]

A 12v electric winch motor might work, but you'd have to check the current required.

Sounds like relays running your present motors are still your best bet, though...

Reply to
Randy Day

As it turns out, I will need at least one DC motor. The one that operates the shutter. Right now a power cable runs from it to the power outlet on the apron. I need to remove the cord to prevent entanglement with me or the telescope.

Reply to
W. eWatson

A 12v electric winch for mounting on trucks/ATVs should do the trick.

HTH

Reply to
Randy Day

Well, I'll take a guess at that. It may be that the new controller was designed to provide more precise rotation increments to a DC motor than it can to an AC motor via a relay. The controller can time *exactly* how long current is applied to a DC motor. With an AC motor, the controller must operate a relay, and the controller cannot control how long the relay takes to transfer. When the controller tells the directly connected DC motor to move, current through the motor starts immediately. When it tells a relay connected AC motor to move, there is a delay while the relay contacts transfer. The controller can't "see" that delay so it can't be as precise in controlling how much rotation you get at the motor shaft.

We are not talking about a large amount of error. In fact, a relay's transfer time is likely to be much faster than the time it takes you to operate your existing lever switch. Therefore, it should be more precise in controlling motor rotation than your manual lever switch. The fact that the error the relay introduces is likely much less than the error the manual lever switch causes is one reason to go with your existing AC motor setup (assuming it meets your needs at present) and relays when you install the new controller. The other is cost: you'll be able to buy relays for way less than it would cost to replace your motors.

Ok, here's a schematic representation of your present setup showing your lever operated switch and the motor it controls:

-------- / | AC |-----o o-----[Motor]---+ | Source | | | |-----------------------+ --------

Here it is again, except this time it shows the addition of the relay that your new circuit will control:

/ +--o o--+

And some form of battery monitoring/charge control, unless that is already built into the new controller.

Ed

< snip >
Reply to
ehsjr
[snip]

Another possibility occurs to me; if the controller uses an H-bridge configuration to provide DC forward-reverse direction control, AC control would be a bit different.

Reply to
Randy Day

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