Automate turning of manual rotary switch?

[markp]

Got a little problem. I've been asked to come up with something that turns a
manual 3 way rotary switch from one position to another and back again under
software control. The switch is one of those bulky things with a pointer
style knob. They basically want to control a piece of equipment without
modifying it in any way.

Does anyone know of a switch actuator manufacturer? I'm looking for
something I can place over the switch with a motor or solenoid to turn the
switch (about 45 degrees per switch position).

Thanks!

Mark.

 

[markp]

A Ledex switch perhaps, like
http://www.surplussales.com/switches/SWLedex-1.html

Chris

Thanks for that. That's something like what I'm looking for, except I don't
need the wafers. However, the switch has mechanical stop positions on it
that the motor would have to overcome, so may need a bit more gearing.

Mark.

 

[Jon Kirwan]

Got a little problem. I've been asked to come up with something that turns a
manual 3 way rotary switch from one position to another and back again under
software control. The switch is one of those bulky things with a pointer
style knob. They basically want to control a piece of equipment without
modifying it in any way.

Does anyone know of a switch actuator manufacturer? I'm looking for
something I can place over the switch with a motor or solenoid to turn the
switch (about 45 degrees per switch position).

I don't.

But you reminded me of a remove control TV I used to have. It
used a few metal bars that were "hammered" when you pushed a
mechanical button. (Basically, tuning forks.) These emitted
a precise audible tone which was decoded and used by the TV
set to cause the tuner to move left or right (you had one
control for each.) The TV could be set while sitting in a
rocking chair from across the room! The knob was _also_
designed as a standard manual tuner so the remote wasn't
required, at all. You could, of course, use the TV as a
"normal" TV of the time where you had to get up and switch
channels by hand.

Of course, manufacturers soon got rid of the manual tuner
assemblies and digitized these and then began using buttons
and remote controls which, today, seem more necessary than
mere convenience, anymore.

Interesting question.

Jon

 

[markp]

I'll bet that you're doomed to rolling your own, but I'd sure do those
suggested web searches.

Indeed, but this is a one-off so a ahnd crafted solution would be OK (as
long as it's reliable!)

Motor -> gear -> adapter on the mechanical side, position feedback ->
processor -> software -> drive -> motor on the electro-software side.

Can you remove the knob and attach directly to the shaft, or do 'they'
want you to leave the knob on?

Ideally leave the knob on, but could remove it and replace it. I'm not sure
whether the knob is press-fitted or screwed.

Does it have to work under manual control when the software isn't diddling
with it?

No, there will be a little control box with a manual override so all done in
software.

How much individual adjustment are you allowed? How can you anchor this
gizmo to the equipment?

Good question. There are some existing fixings I could attach to, I'm sure
they could accept a few holes drilled in the panel that has the switch.

In principle this is a snap, but in reality there's some effort to make it
all work.

This might be quite a tough mechanical challenge, as you say it sounds easy
but the devil is in the details. The switch has click positions, I may need
a way to sense it has seated properly in a particular position. Also I don't
want this to ever sit just off centre of a position in case the switch
contacts arc.

Mark.

 

[markp]

I don't.

But you reminded me of a remove control TV I used to have. It
used a few metal bars that were "hammered" when you pushed a
mechanical button. (Basically, tuning forks.) These emitted
a precise audible tone which was decoded and used by the TV
set to cause the tuner to move left or right (you had one
control for each.) The TV could be set while sitting in a
rocking chair from across the room! The knob was _also_
designed as a standard manual tuner so the remote wasn't
required, at all. You could, of course, use the TV as a
"normal" TV of the time where you had to get up and switch
channels by hand.

Of course, manufacturers soon got rid of the manual tuner
assemblies and digitized these and then began using buttons
and remote controls which, today, seem more necessary than
mere convenience, anymore.

Interesting question.

Jon

Tuning forks to control tellies! Nice. I shan't be using that method though

 

[markp]

Your basic requirement is a torque-limited (so it doesn't break the
shaft)
reversible motor that senses the clickstops of the switch (or that
has some springy coupling and can relax between changes). Simply
attaching a motor will not work, because it might park the switch
between positions.

I'd suggest a rotary position encoder (five bit Gray code is plenty)
and a stepper motor with a forward/reverse/release control.
It's generally easier to modify the box than to mount this kind of
thing to its control cluster, though.

I think the stepper may have to be geared to get the torque needed to move
the switch into the click positions. Technically with a stepper you
shouldn't need a position ecoder as long as it is calibrated for position,
however lose a step or two and you're in trouble, so I think you're right
that an absolute position sensor would be needed.

What might work is stepping to one of the nominal click positions then
releasing (I assume this allows the shaft to freely rotate?). Assuming the
gearing isn't too large the switch may then self align, similar to your
springy coupling suggestion.

Another interesting possibility is having some kind of torque sensor on the
shaft itself. By measuring the torque as the switch clicks into place it
might be possible to reliably detect it. Can you get torque sensors like
that?

Mark.

 

[Spehro Pefhany]

Got a little problem. I've been asked to come up with something that turns a
manual 3 way rotary switch from one position to another and back again under
software control. The switch is one of those bulky things with a pointer
style knob. They basically want to control a piece of equipment without
modifying it in any way.

Does anyone know of a switch actuator manufacturer? I'm looking for
something I can place over the switch with a motor or solenoid to turn the
switch (about 45 degrees per switch position).

Thanks!

Mark.

I would use a large RC servo and couple that to the shaft or knob.

 

[Spehro Pefhany]

For a one-off, I'd be looking at an RC airplane servo and a flexible
shaft coupling. You can get servos with nice titanium gears and brass
sleeve bearings for way under $100. The good ones have real genuine torque.

Cheers

Phil Hobbs

Yup, here's one for $119 that has 250 oz-in of torque at 4.8V

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXTHR3&P=ML

 

[markp]

For a one-off, I'd be looking at an RC airplane servo and a flexible shaft
coupling. You can get servos with nice titanium gears and brass sleeve
bearings for way under $100. The good ones have real genuine torque.

Cheers

Phil Hobbs

Thanks Phil. Wasn't aware that servos like this had good torque. I'll look
into that.

Mark.

 

[markp]

Yup, here's one for $119 that has 250 oz-in of torque at 4.8V

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXTHR3&P=ML

Nice. Thanks!

 

[ehsjr]

Got a little problem. I've been asked to come up with something that turns a
manual 3 way rotary switch from one position to another and back again under
software control. The switch is one of those bulky things with a pointer
style knob. They basically want to control a piece of equipment without
modifying it in any way.

Does anyone know of a switch actuator manufacturer? I'm looking for
something I can place over the switch with a motor or solenoid to turn the
switch (about 45 degrees per switch position).

Thanks!

Mark.

Replace the knob with a gear. Drive that gear with a gear attached
to a motor's shaft. A cam on the driven gear can activate a micro
switch for the stop positions. You'll need a gear motor already
reduced in speed to keep the driven gear relatively small - maybe
something like cat # DCM-276 ($9.00) or DCM-245 ($13.75) or
DCM-110 ($3.50) at Allelectronics. http://www.allelectronics.com/
The first two mentioned might provide enough torque to turn the
switch with direct coupling and no additional gearing advantage.

It's a kludge, but a kludge is what they're asking for, whether
they are aware of it or not. The response will be slow at 5 or
6 rpm with the first two motors and 1:1 gearing or direct coupling,
in the neighborhood of 1/2 second. With the DCM-110, it depends on
the gearing you use. Without knowing the torque requirements
it's a guess whether any of the motors will work for you.

Ed

 

[hamilton]

Replace the knob with a gear. Drive that gear with a gear attached
to a motor's shaft. A cam on the driven gear can activate a micro
switch for the stop positions. You'll need a gear motor already
reduced in speed to keep the driven gear relatively small - maybe
something like cat # DCM-276 ($9.00) or DCM-245 ($13.75) or
DCM-110 ($3.50) at Allelectronics. http://www.allelectronics.com/
The first two mentioned might provide enough torque to turn the
switch with direct coupling and no additional gearing advantage.

It's a kludge, but a kludge is what they're asking for, whether
they are aware of it or not. The response will be slow at 5 or
6 rpm with the first two motors and 1:1 gearing or direct coupling,
in the neighborhood of 1/2 second. With the DCM-110, it depends on
the gearing you use. Without knowing the torque requirements
it's a guess whether any of the motors will work for you.

Ed

If this is a one off project, you can get some old 8-track drives and
remove the ratchet, paw and solenoid.

Once you look it over, you'll understand how it works.

hamilton

 

[E]

Got a little problem. I've been asked to come up with something that turns
a manual 3 way rotary switch from one position to another and back again
under software control. The switch is one of those bulky things with a
pointer style knob. They basically want to control a piece of equipment
without modifying it in any way.

Does anyone know of a switch actuator manufacturer? I'm looking for
something I can place over the switch with a motor or solenoid to turn the
switch (about 45 degrees per switch position).

Thanks!

Mark.

Perhaps proportional ball valve actuator, the kind you can put on a valve
and control with 0-10V
-ek

 

[Jon Kirwan]

Tuning forks to control tellies! Nice. I shan't be using
that method though

hehe. No batteries to replace. Can get tuning forks from
the store if you need them laying about the house. Might
even be able to learn to whistle it out without one, which
means you are never looking around for the darned remote any
more. It does have its advantages.

Jon

 

[John Nagle]

For a one-off, I'd be looking at an RC airplane servo and a flexible
shaft coupling. You can get servos with nice titanium gears and brass
sleeve bearings for way under $100. The good ones have real genuine
torque.

For this application, I'd suggest an R/C servo intended for boat
rudders. Those are geared down, slow, and not too expensive.
Here's an example, for $37:

http://www.hobbypeople.net/gallery/474142.asp

There are plenty of resources on the Web on how to drive an R/C
servo from a computer, so I'll let you find that

John Nagle

 

[markp]

For this application, I'd suggest an R/C servo intended for boat
rudders. Those are geared down, slow, and not too expensive.
Here's an example, for $37:

http://www.hobbypeople.net/gallery/474142.asp

There are plenty of resources on the Web on how to drive an R/C
servo from a computer, so I'll let you find that

John Nagle

Thanks John. I actually haven't seem the real switch yet, but I know
sometimes these things can require quite a bit of torque to overcome the
click position. I think I'll need to measure it first so I can choose an
appropriate R/C servo.

Mark.

 

[JosephKK]

I think the stepper may have to be geared to get the torque needed to move
the switch into the click positions. Technically with a stepper you
shouldn't need a position ecoder as long as it is calibrated for position,
however lose a step or two and you're in trouble, so I think you're right
that an absolute position sensor would be needed.

What might work is stepping to one of the nominal click positions then
releasing (I assume this allows the shaft to freely rotate?). Assuming the
gearing isn't too large the switch may then self align, similar to your
springy coupling suggestion.

Another interesting possibility is having some kind of torque sensor on the
shaft itself. By measuring the torque as the switch clicks into place it
might be possible to reliably detect it. Can you get torque sensors like
that?

Mark.

Sure, but what you measure is torque reaction on the motor housing.

 

[markp]

---
This is starting to get interesting.

How ugly can the rig be?

JF

Just about as ugly as it needs to be, this thing is out of site in a control
room and there's plent of room as it's an open rack. What they don't want is
to modify any of the control logic or wiring as they have a maitenance
contract with a third party. I want to come up with a solution that's
completely non-intrusive that simply automates the otherwise manually
controlled on/off switch.

Mark.

 

[tm]

Just about as ugly as it needs to be, this thing is out of site in a
control room and there's plent of room as it's an open rack. What they
don't want is to modify any of the control logic or wiring as they have a
maitenance contract with a third party. I want to come up with a solution
that's completely non-intrusive that simply automates the otherwise
manually controlled on/off switch.

Mark.

If all you want to do is switch it on and off, why not just leave
it on and switch the power to it with a relay?


T

 

[hamilton]

Just about as ugly as it needs to be, this thing is out of site in a control
room and there's plent of room as it's an open rack. What they don't want is
to modify any of the control logic or wiring as they have a maitenance
contract with a third party. I want to come up with a solution that's
completely non-intrusive that simply automates the otherwise manually
controlled on/off switch.

Mark.

How far apart are the positions ?

90 Degrees, 30 Degrees, 120 Degrees

This looks like its going to be a Real Rube Goldberg type of operation.

hamilton