Automate turning of manual rotary switch?
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From: John Nagle on 2 Apr 2010 15:58 Phil Hobbs wrote: > 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
From: markp on 2 Apr 2010 16:18 "John Nagle" <nagle(a)animats.com> wrote in message news:4bb647af$0$1635$742ec2ed(a)news.sonic.net... > Phil Hobbs wrote: > >> 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 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.
From: JosephKK on 2 Apr 2010 16:39 On Wed, 31 Mar 2010 22:38:15 +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. > >>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. > Sure, but what you measure is torque reaction on the motor housing. 8-)
From: John Fields on 2 Apr 2010 17:03 On Fri, 02 Apr 2010 13:39:24 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Wed, 31 Mar 2010 22:38:15 +0100, "markp" <map.nospam(a)f2s.com> wrote: >>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. >8-) --- Nope. Wrap a strain gage around the shaft and measure its resistance change as the shaft twists, differentially, under it. Also, I'm pretty sure there are torque sensors which are mounted in shaft couplings ($$$) which'll do the trick. JF
From: John Fields on 2 Apr 2010 17:04
On Fri, 2 Apr 2010 21:18:52 +0100, "markp" <map.nospam(a)f2s.com> wrote: >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. --- This is starting to get interesting. :-) How ugly can the rig be? JF |