Automate turning of manual rotary switch?
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From: markp on 31 Mar 2010 17:22 "Jon Kirwan" <jonk(a)infinitefactors.org> wrote in message news:pp87r5laes2vrg5at1g6mcsj9v8kl8juqp(a)4ax.com... > On Wed, 31 Mar 2010 15:54:50 +0100, "markp" > <map.nospam(a)f2s.com> wrote: > >>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 Tuning forks to control tellies! Nice. I shan't be using that method though :)
From: Chris on 31 Mar 2010 17:22 On 31 Mar, 19:28, John Fields <jfie...(a)austininstruments.com> wrote: > On Wed, 31 Mar 2010 08:29:08 -0700 (PDT), Chris > > > > > > <christof...(a)talktalk.net> wrote: > >On 31 Mar, 15:54, "markp" <map.nos...(a)f2s.com> wrote: > >> 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. > > >A Ledex switch perhaps, likehttp://www.surplussales.com/switches/SWLedex-1.html > > --- > "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- Hide quoted text - > > - Show quoted text - 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
From: markp on 31 Mar 2010 17:38 >> 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. >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.
From: Phil Hobbs on 31 Mar 2010 17:37 On 3/31/2010 5:18 PM, markp wrote: > "Tim Wescott"<tim(a)seemywebsite.now> wrote in message > news:5qednQCgAZgvCC7WnZ2dnUVZ_rGdnZ2d(a)web-ster.com... >> markp wrote: >>> 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'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. >> >> -- >> Tim Wescott >> Control system and signal processing consulting >> www.wescottdesign.com > > 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. > > 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
From: Spehro Pefhany on 31 Mar 2010 17:59
On Wed, 31 Mar 2010 15:54:50 +0100, "markp" <map.nospam(a)f2s.com> wrote: >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. |