vary speed of synchronous motor

[rneale]

I want to vary the speed of a 16mm projector by approximately plus or
minus fifteen percent. The object is to implement a home-brew transfer
of film to video. Of course there are commercial services that do this,
but they are very expensive, I have a lot of film, and experimenting
with my Sony camera shows that if the speed of my projector could be
changed just a little, it would work well enough for my purposes.

Naturally, I would separate the projector's motor power from the lamp
power, and use a separate variable-frequency drive to operate the motor.
Open-loop control would be fine. The motor draws about an amp all by itself.

All the variable-frequency drive information on the Internet seems to
involve multi-phase supplies and special motors. I found a couple of
specialized variable-frequency lab power supplies that operate from
standard household power, but they cost thousands of dollars and are way
overkill.

I don't want to alter the projector, other than breaking out the motor
power leads separately. Anyone have any suggestions?

Reg Neale

 

[John Larkin]

I want to vary the speed of a 16mm projector by approximately plus or
minus fifteen percent. The object is to implement a home-brew transfer
of film to video. Of course there are commercial services that do this,
but they are very expensive, I have a lot of film, and experimenting
with my Sony camera shows that if the speed of my projector could be
changed just a little, it would work well enough for my purposes.

Naturally, I would separate the projector's motor power from the lamp
power, and use a separate variable-frequency drive to operate the motor.
Open-loop control would be fine. The motor draws about an amp all by itself.

All the variable-frequency drive information on the Internet seems to
involve multi-phase supplies and special motors. I found a couple of
specialized variable-frequency lab power supplies that operate from
standard household power, but they cost thousands of dollars and are way
overkill.

I don't want to alter the projector, other than breaking out the motor
power leads separately. Anyone have any suggestions?

Reg Neale

Function generator or whatever, driving a medium-big stereo amp and a
step-up transformer. I like the Peavey PA amps. I have a 400-watts
RMS/channel stereo beast that we use for generating super-accurate 60
Hz at up to 480 VAC, for testing electronic energy meters. We've used
it for years and it seems bulletproof. For a dinky-ish motor, a
smaller amp should work, maybe a flea-market stereo receiver. Adding a
cap across the secondary of the stepup tranny will null the power
factor and make the amp work less.

John

 

[Roy J. Tellason]

I want to vary the speed of a 16mm projector by approximately plus or
minus fifteen percent. The object is to implement a home-brew transfer
of film to video. Of course there are commercial services that do this,
but they are very expensive, I have a lot of film, and experimenting
with my Sony camera shows that if the speed of my projector could be
changed just a little, it would work well enough for my purposes.

Naturally, I would separate the projector's motor power from the lamp
power, and use a separate variable-frequency drive to operate the motor.
Open-loop control would be fine. The motor draws about an amp all by itself.

All the variable-frequency drive information on the Internet seems to
involve multi-phase supplies and special motors. I found a couple of
specialized variable-frequency lab power supplies that operate from
standard household power, but they cost thousands of dollars and are way
overkill.

I don't want to alter the projector, other than breaking out the motor
power leads separately. Anyone have any suggestions?

Reg Neale

I can't remember exactly where or when, but one of the hobby-type magazines
(Popular Electronics maybe?) had a project to do just this in it some time
back. Fairly low-power, and I don't remember what the intended application
was, but maybe if you have access to a library with this stuff on hand it'd
prove useful to look at.

 

[Kalman Rubinson]

I can't remember exactly where or when, but one of the hobby-type magazines
(Popular Electronics maybe?) had a project to do just this in it some time
back. Fairly low-power, and I don't remember what the intended application
was, but maybe if you have access to a library with this stuff on hand it'd
prove useful to look at.

I have several articles for such devices depending on how much
power/variability is needed. Most of these were hobbyist designs for
the control of phonograph turntables or tape decks.

As an aside, VPI (a NJ manufacturer of turntables) makes a devise
called the SDS which will do the job, as will their earlier model, the
PLC. There are a few other similar devices on the market.

Kal

 

[Alan]

I want to vary the speed of a 16mm projector by approximately plus or
minus fifteen percent. The object is to implement a home-brew transfer
of film to video. Of course there are commercial services that do this,
but they are very expensive, I have a lot of film, and experimenting

First, think about it and realize that this will likely still not
work. Even if you get them exactly matched, they will not be
synchronized. You will have part of one frame, and part of another
with black bars in between. Even if you get them correct at the
start, they will slowly drift no matter how close you are. The camera
makes it's own sync, difficult to track that down and get it out to
sync the motor, and it will still likely suffer from the below
problem..

It takes a camera that can use an external sync signal, far easier
than making the motor run to the camera's sync. Even then, you still
have to have a setup where the camera will take it's picture after the
light in the projector is on, and finish before the light goes off.
Otherwise you will only get part of the picture.

This is why it costs and there are businesses around it, because for
just a few it's way too involved to get the equipment setup to do it
yourself. If you have a lot it may be worth while though, or at least
to rent the needed items.

First look for a camera that can take external sync. Then get a
signal from inside the projector to run the synch, one side of the
bulb with interfacing circuit may be ok for this. While it's other
than hooking up to the motor, note that it's actually less, the camera
runs from the projector's rate. It may even work with just this, the
film frame could be up longer than it takes the camera to scan. I
wouldn't want to bet on it though..

These are just ideas to start, you really need to ask in the correct
forum on http://www.dvdrhelp.com/ since there are lots of people there
who've done this already. You'll get much more targeted help there on
the best way to proceed.

Alan

 

[John Larkin]

I want to vary the speed of a 16mm projector by approximately plus or
minus fifteen percent. The object is to implement a home-brew transfer
of film to video. Of course there are commercial services that do this,
but they are very expensive, I have a lot of film, and experimenting
with my Sony camera shows that if the speed of my projector could be
changed just a little, it would work well enough for my purposes.

Naturally, I would separate the projector's motor power from the lamp
power, and use a separate variable-frequency drive to operate the motor.
Open-loop control would be fine. The motor draws about an amp all by itself.

All the variable-frequency drive information on the Internet seems to
involve multi-phase supplies and special motors. I found a couple of
specialized variable-frequency lab power supplies that operate from
standard household power, but they cost thousands of dollars and are way
overkill.

I don't want to alter the projector, other than breaking out the motor
power leads separately. Anyone have any suggestions?

Reg Neale

What about a cheap UPS? You'd have to mess with the frequency controls
somehow.

John

 

[GPG]

If you feed amps in antiphase and wire transformer between them, you
will need abt 60W/CH @ 8 ohms (assuming 120 V) Jaycar catalogue has
dual powered sub amp with phase switch on one CH @. Step up abt 2:1,
120 to 240 xfmr?

 

[John Larkin]

If you feed amps in antiphase and wire transformer between them, you
will need abt 60W/CH @ 8 ohms (assuming 120 V) Jaycar catalogue has
dual powered sub amp with phase switch on one CH @. Step up abt 2:1,
120 to 240 xfmr?

That sounds good. Consumer audio stuff is incredibly cheap.

John

 

[rneale]

This seems like an excellent idea. It's already designed to handle
inductive loads and drive them at the right voltage. Might require some
tweaking though. Not sure whether the circuit syncs the output frequency
to the line when line power is available. Also the frequency adjustment
range (if any) when on battery may need to be increased.

 

[GPG]

First, think about it and realize that this will likely still not

work. Even if you get them exactly matched, they will not be
synchronized. You will have part of one frame, and part of another
with black bars in between. Even if you get them correct at the
start, they will slowly drift no matter how close you are. The camera
makes it's own sync, difficult to track that down and get it out to
sync the motor, and it will still likely suffer from the below
problem..

Use a sync separator on the camera video out to control motor. There
are a few ICs that will do this.

 

[GPG]

Use a sync separator on the camera video out to control motor. There
are a few ICs that will do this.

Had a look. LM1881. This will give you V sync.

camvideo--syncsepV--mono--div2--pd--vco--motordrive--out to projector
l
l
projector signal----------------l

pd = phase detector. Projector signal from phototransistor. Monostable to adjust
delay, max time 1 frame.