Moving a dome and EM relays

[W. eWatson]

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

 

[Jasen Betts]

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)

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.

 

[aioe]

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.

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?

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

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

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.

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.

 

[W. eWatson]

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

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

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

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?

I'm not sure it will be helpful, but here
<http://www.cyanogen.com/help/maxdome/MaxDome.htm>. 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.

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


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

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.

Don't know. See ref.

 

[Randy Day]

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

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.

 

[Randy Day]

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

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...

 

[W. eWatson]

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.

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

 

[Randy Day]

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

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...

 

[ehsjr]

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.

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.

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.

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

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!

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

 

[W. eWatson]

W. eWatson used his keyboard to write :

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.

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.

 

[W. eWatson]

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...

You can get a feel for the size of matters by going to my web site at
<www.speckledwithstars.net/>, click on Observatory.

 

[W. eWatson]

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...

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.

 

[W. eWatson]

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."

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.

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.

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

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.

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

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

"new controller"? A circuit card.

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

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

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.

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

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.

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.

 

[Randy Day]

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.

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...

 

[W. eWatson]

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.

 

[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.

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

HTH

 

[ehsjr]

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.

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.

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

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--+ <== added relay contact; new controller
| | controls the relay, opening or closing
| | the contacts as needed.
-------- | / |
| AC |--+--o o--+--[Motor]---+
| Source | |
| |-----------------------+
--------

By wiring the relay contacts in parallel with the lever switch
contacts, the motor can be controlled by either the relay or
the lever switch. You need to check that the relay contacts are
rated to carry *AND* switch the power to the motor - which means
you need to know the amperage and horsepower rating of the motor.

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.

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

Ed

< snip >

 

[Randy Day]

[snip]

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

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.

 

[W. eWatson]

I'm going to call the mfger of the boards this morning, and ask if
modeling the use of the boards is safe. That is, start with hobby DC
motors to learn the ropes, then graduate to maybe a motor that would
raise a garage door or window.