Automate turning of manual rotary switch?

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Google "rotary switch actuator" without the quotes?

JF

Google "reversible rotary actuator" without the quotes.

JF

A Ledex switch perhaps, like

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.

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"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."

I don't think a LEDEX switch can do "and back again". 

JF

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

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? Does it have to work under manual control when the software isn't diddling with it? How much individual adjustment are you allowed? How can you anchor this gizmo to the equipment?

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

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

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

s a

der

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.

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

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

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

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.

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.

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

like

Too true. Boot-mount Pye radios used them for 6-way channel selection and turning the knob on the remote control one step anticlockwise sent the Ledex 5 steps clockwise. There were no end stops.

As the OP says '... the switch has mechanical stop positions on it that the motor would have to overcome ...'. A very powerful Ledex perhaps! But that would modify the equipment.

Chris

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

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

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.

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

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

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

Mark.

Nice. Thanks!

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.

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