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'[EE] Clutch for motorising a potentiometer'
2010\11\10@171308 by ivp

face picon face
Hi all

could I have suggestions please for a long-lasting material that
can act as a clutch between a motor and a pot shaft

Or suggestions for a different construction method perhaps

I've found (a) a range of inexpensive pots with access to the back
end of the shaft and (b) that other types aren't very difficult to dis-
assemble anyway to make access. There is a variety of cheap 3V
to 12V motors I can use

I'm DIY-ing because pots aren't available in either the value or
configuration (eg stacked) I want, or are infrequently available
or are tres expensive

The material would have to be grippy enough to transfer motor
drive to the shaft but not so grippy as to make the shaft hard to
turn by hand against the gearbox. And also not wear down of
course, although the clutch would be (lightly) spring-loaded

I used to have a cheap motorised pot around here somewhere
and have a sneaky suspicion it used some sort of direct drive
that dis-engaged when the shaft was turned by hand or when
the shaft reached the end of its travel

TIA

Joe

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2010\11\10@171726 by KEITH E ELLIOTT

picon face

go to mouser and look for position indicator.  basically a pot with a keyway where the shaft should be.  then you dont ha
ve to worry about marrying shafts together
 
{Quote hidden}

> -

2010\11\10@172249 by Olin Lathrop

face picon face
ivp wrote:
> could I have suggestions please for a long-lasting material that
> can act as a clutch between a motor and a pot shaft

Since pots have a wiper that drags accross some resistive material, they are
not that long lasting themselves.  If you really want long lasting, you
probably need to use a shaft encoder that works magnetically or optically.

A cute trick I've seen is to use just a stepper motor.  When the user turns
it you get pulses out the windings, and it can act like a shaft encoder
without the zero reference.  Of course it's a motor, so you can make the
shaft move electronically too.  It can be done, but it's not trivial and
will take some development.

How long does it really have to last, and how many operations before it's
allowed to break?


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(978) 742-9014.  Gold level PIC consultants since 2000

2010\11\10@172556 by KEITH E ELLIOTT

picon face

you can also use the encoder from a disk drive motor,  very cjeap

{Quote hidden}

> -

2010\11\10@175414 by ivp

face picon face
> A cute trick I've seen is to use just a stepper motor.  When the user
> turns it you get pulses out the windings, and it can act like a shaft
> encoder without the zero reference.  Of course it's a motor, so you
> can make the shaft move electronically too.  It can be done, but it's
> not trivial and will take some development

That would work. I wrote it up for PIClist last year

http://www.piclist.com/techref/io/sensor/pos/enc/stepper_as_encoder.htm

That particular implementation was incorporated into a reasonably
low-tech tracking device and worked well

I do have enough steppers, and have seriously considered it. Also
magnetic or optical encoders. But you'll appreciate when you have
a cheap pot and a cheap motor, it is tempting to put them together
to make a new useful component

> How long does it really have to last, and how many operations
> before it's allowed to break?

Well, I'm thinking perhaps more about the durability of the clutch
material itself, and its natural degradation over time. eg rubber
breaking down, plastic hardening etc. Number of shaft turns is a
little hard to estimate but I'd say generally infrequent (at least for
one application I have right now). Maybe I should look around
here and see how various materials I know the approximate age
of have fared over the years

Joe

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>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
> -

2010\11\10@175428 by jim

flavicon
face

Joe,

I too have a few (3-4) motorized pots around that were used in DELCO
radios for GM cars.
I'll look at them tonight to see if I can tell how it's done for sure,
but IIRC, there are two disks.   One is attached to the pot shaft.  The other is a slip fit over the
shaft, and has a rubbery substance
coating the inside surface. This one also has a gear tooth wheel
attached to it.  These two disks are  contacting each other by a slight spring pressure.  The motor is
mounted above the pot and engages with  the toothed wheel.  As the toothed wheel turns, it being in spring
loaded contact against the disk attached
to the shaft, therefore turns the pot.  At the end of the travel, the
pot stops, but the disks now slip so
no damage occurs.  Reversing the voltage source to the motor turns the
pot the other way, and at the end of
the travel there, it slips again like at the other end.  If you want to
manually adjust the pot, you turn
the knob and the disks slip by each other allowing the pot to turn, but
the motor doesn't turn, therefore
it doesn't offer any resistance to movement.  I hope you can follow
what I'm trying to say here.  
Basically, it is similar to a manual transmission car clutch, except
instead of it disengaging by pressing
the clutch pedal, this one doesn't really disengage.  It just slips
like the clutch was only partially
engaged.  The teeth on the flywheel is engaged with the motor to drive
the shaft CW or CCW, and the pot
shaft is like the transmission input shaft.

Boy, a picture here would have saved a lot of dialog.  I'll see if I
can get some good photos of the pots I
have at home.  That should help you out in understanding my description
above.

Regards,

Jim

> ---{Original Message removed}

2010\11\10@180500 by ivp

face picon face
> go to mouser and look for position indicator.  basically a pot with
> a keyway where the shaft should be.  then you dont have to worry
> about marrying shafts together

Is this what you're thinking of ?

http://nz.mouser.com/Sensors/Motion-Position-Sensors/_/N-6g7q6?Keyword=potentiometer&FS=True

http://www.murata.com/catalog/r50/el0595.pdf

Looks good as a pot alternative, but there's still the resistance
of a DC motor's gearbox though, hence the clutch idea

Joe

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**********
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2010\11\10@180633 by ivp

face picon face
> I too have a few (3-4) motorized pots around that were used in
> DELCO radios for GM cars.
> I'll look at them tonight to see if I can tell how it's done for sure,
> but IIRC, there are two disks

Cheers, look forward to any more info you can provide

Joe

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Quality PIC programmers
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2010\11\10@182715 by Sean Breheny

face picon face
If you limit the current you feed to the motor why do you need a
clutch? There shouldn't normally be much friction in the pot shaft so
you don't need much torque to move it unless you are fighting
someone's hand.

Sean


On Wed, Nov 10, 2010 at 5:13 PM, ivp <EraseMEjoecolquittspam_OUTspamTakeThisOuTclear.net.nz> wrote:
{Quote hidden}

>

2010\11\10@235242 by Mohit (Lists)

picon face
Thick walled silicone tube from the motor to the pot shaft. Tube ID slightly lesser than the shaft OD. It allows a bit of mismatch between centres. And it has friction yet will slip too. If shaft ODs aren't equal, you could use tubes with different IDs, and the thinner one could slip into the broader one.

In fixed width font:
                  \    --------------------    /
Pot |========       [[[[[[[[[[ Motor
  /    --------------------    \
              Tube

Regards,
Mohit.

ivp wrote:
{Quote hidden}

> http://www.embedinc.com/products/index.htm

2010\11\11@003256 by Dr Skip

picon face
Get some HDPE cutting board type material (cheap and available in many
thicknesses at many places - also from industrial suppliers) in a
suitable thickness for what follows. Cut 2 disks of a reasonable size.
Drill one to tightly fit the pot shaft. Drill the other for the motor
shaft. Position the disks against each other with some spring loading as
you suggest. Long wearing and tolerant of slight alignment problems
and/or drilling off center. Larger disks = more friction, but it is a
bit slippery to begin with. If too slippery, use an alternate material
for one disk with more 'grip'. The 'self lubricating' qualities of HDPE
will prevent wear even with a lot of slippage.

Can even be machined for a set screw if thick enough and using flatted
shafts.

-Skip


{Quote hidden}

>

2010\11\11@042424 by alan.b.pearce

face picon face
>  I too have a few (3-4) motorized pots around that were used in DELCO
> radios for GM cars.
>  I'll look at them tonight to see if I can tell how it's done for
sure,
> but IIRC, there are two disks.
>  One is attached to the pot shaft.  The other is a slip fit over the
> shaft, and has a rubbery substance
>  coating the inside surface. This one also has a gear tooth wheel
> attached to it.  These two disks are
>  contacting each other by a slight spring pressure.  
The easiest way to mock up an arrangement like this would be to use a
phosphor bronze ripple washer between a couple of flat surfaces. The
surfaces could be the faces of ordinary gears that fit the relevant
shafts.
-- Scanned by iCritical.

2010\11\11@073706 by Olin Lathrop

face picon face
jim@jpes.com wrote:
> If you want
> to manually adjust the pot, you turn
> the knob and the disks slip by each other allowing the pot to turn,
> but the motor doesn't turn, therefore
> it doesn't offer any resistance to movement.

Therefore it *does* offer resistance to movement.


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(978) 742-9014.  Gold level PIC consultants since 2000

2010\11\11@094153 by jim

flavicon
face

Excuse me for living.  "Therefore, it offer little resistance to
movement".

Regards,

Jim

> ---{Original Message removed}

2010\11\11@101025 by Olin Lathrop

face picon face
jim@jpes.com wrote:
> Excuse me for living.

Living is OK, making incorrect statements however is not.

> "Therefore, it offer little resistance to movement".

No, you're still not getting it.  You said the motor offers little
resistance to movement because it doesn't turn.  The point is that it offers
more resistance to movement precisely because it doesn't turn.  If it were
turned by turning the pot, it would offer less resistance.

Not turning is offering infinite resistance to moving, guaranteeing the
clutch opens and the resistance you get at the shaft is the clutch
resistance.  The clutch in this case provides a upper limit to the
resistance seen when turning the shaft.  If the motor were turned by turning
the shaft, then its resistance would be less than the clutch's, thereby
offering a lower total resistance to turning the shaft.  Think of the
limiting case where the motor turns without any resistance at all.  That
would cause the least resistance to turning the shaft, and the clutch would
stay locked.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2010\11\11@103321 by jim

flavicon
face

Whatever.  It was meant to give an idea of how the clutch mechanism
worked.
Maybe I stated it incorrectly, but the person the post was addressed to
apparently  has grasped my intended meaning.  That is what is important.

You can argue semantics all day if you wish, but I'm done discussing
that matter with you.

Regards,

Jim

> ---{Original Message removed}

2010\11\11@115741 by Olin Lathrop

face picon face
jim@jpes.com wrote:
> Whatever.  It was meant to give an idea of how the clutch mechanism
> worked.

Unfortunately though, your explanation was incorrect.

> Maybe I stated it incorrectly, but the person the post was addressed
> to apparently has grasped my intended meaning.

Maybe, or maybe he just decided to skip over your error.

> That is what is important.

Leaving correct information in the archives and not misleading bystanders
are also important.  That is why incorrect statements need to be stomped on
quickly and decisively when they occur.

> You can argue semantics all day if you wish,

It wasn't semantics.  You made a flat out incorrect assertion.

> but I'm done discussing that matter with you.

Thank you.  I'm glad I don't have to spend more time on this.

I'm not sure whether you just said what you meant backwards or really
intended it the way it came out.  It's not a big deal to make a mistake.  It
only turns into a big deal when you then try to defend the mistake.  Trying
to save face is completely the wrong thing to do because it actually has the
opposite effect.  A simple "Oops I said that backwards" or the like would
have ended this, and I doubt anyone would have thought much of it.  By
trying to defend the indefensible, you dig yourself in deeper and call
attention to what could have been a minor oops and turn it into a public
stupidity.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2010\11\12@121009 by Michael Rigby-Jones

flavicon
face


> -----Original Message-----
> From: piclist-bouncesspamspam_OUTmit.edu [@spam@piclist-bouncesKILLspamspammit.edu] On
Behalf
{Quote hidden}

were
> turned by turning the pot, it would offer less resistance.

No, he didn't say that at all, I think you are being deliberately obtuse
here.  I suspect everyone but you realised that the OP means that the
action of the clutch slipping prevents the motor from offering (too
much) resistance to turning the knob.  
It required absolutely complex analysis of the OP's post for me to
understand this; I have to wonder why you had so much trouble?

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2010\11\12@130102 by Olin Lathrop

face picon face
Michael Rigby-Jones wrote:
> No, he didn't say that at all, I think you are being deliberately
> obtuse here.

Actually he did.  His exact sentence was:

 "If you want to manually adjust the pot, you turn the knob and
 the disks slip by each other allowing the pot to turn, but the
 motor doesn't turn, therefore it doesn't offer any resistance
 to movement."

It is quite clear that he thinks the motor offers less resistance because it
doesn't turn, when in fact if offers maximum resistance in that case.

> I suspect everyone but you realised that the OP means
> that the action of the clutch slipping prevents the motor from
> offering (too much) resistance to turning the knob.

Read what he said, not what you'd like to explain it away as.  I thought at
first it might have been unfortunate wording too, but then he tried defend
his statement instead of just saying "oops".

> It required absolutely complex analysis of the OP's post for me to
> understand this; I have to wonder why you had so much trouble?

It shouldn't take "analysis" at all to figure out what someone really meant..
In any case, we're not obligated to do that, and neither is it a good idea.
If you don't want to be misunderstood, write more undestandably.

You also have conveniently forgotten what actually happened here.  Jim made
the statement I quoted above as part of a larger post.  I thought it a minor
accidental error at the time, but just wanted to make sure the record was
straight.  My only response to his statement above was:

 "Therefore it *does* offer resistance to movement."

It was a simple correction, not a indictment.  Then Jim decided to get all
pissy with:

 "Excuse me for living."

Then clarifying what could have been a minor error was in fact just plain
wrong:

 "Therefore, it offer little resistance to movement."

To me, and I expect to many, it's pretty obvious what really happened.  Jim
miswrote something.  But when he got called on it he got all defensive and
tried to indict the messenger to distract from his mistake.  I'm not going
to let him get away with that, especially when I'm the messenger.  What
could have been a quickly forgotten minor error became a public stupidity by
his jumping up and down and attracting attention to it.  When I responded
with more technical detail, his answer was "Whatever".  In other words "I
realize now I screwed up and can't win this, so I'm going to pretend it
doesn't matter even after I got all pissy about being corrected.".  I have
no intention of letting someone with that kind of attitude get away with
anything.


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2010\11\12@131248 by Oli Glaser

flavicon
face
On 11/11/2010 15:11, Olin Lathrop wrote:
> RemoveMEjimTakeThisOuTspamjpes.com wrote:
>> Excuse me for living.
> Living is OK, making incorrect statements however is not.
>

Both are fine...
For me there is a reasonably clear distinction between "something it is preferable not to do" and "something that is *not okay* to do.
In fact I would go as far as to suggest in some cases it is actually preferable *to* make mistakes, and should be encouraged (e.g. whilst learning)

2010\11\12@131519 by Oli Glaser

flavicon
face
On 11/11/2010 15:11, Olin Lathrop wrote:
> spamBeGonejimspamBeGonespamjpes.com wrote:
>> Excuse me for living.
> Living is OK, making incorrect statements however is not.
>

Both are fine...
For me there is a reasonably clear distinction between "something it is preferable not to do" and "something that is *not okay* to do.
In fact I would go as far as to suggest in some cases it is actually preferable *to* make mistakes, and should be encouraged (e.g. whilst learning)

2010\11\12@134219 by Oli Glaser

flavicon
face
On 12/11/2010 18:01, Olin Lathrop wrote:
> I have
> no intention of letting someone with that kind of attitude get away with
> anything.

Of course not - they must all be brought swiftly to justice...  :-)

2010\11\15@121301 by Michael Rigby-Jones

flavicon
face


> -----Original Message-----
> From: TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu [RemoveMEpiclist-bouncesspamTakeThisOuTmit.edu] On
Behalf
{Quote hidden}

because
> it
> doesn't turn, when in fact if offers maximum resistance in that case.
>
> > I suspect everyone but you realised that the OP means
> > that the action of the clutch slipping prevents the motor from
> > offering (too much) resistance to turning the knob.
>
> Read what he said, not what you'd like to explain it away as.  I
thought
> at
> first it might have been unfortunate wording too, but then he tried
defend
> his statement instead of just saying "oops".

I did read what he said, and whilst it may not be described accurately,
in the context of the topic it's blindingly obvious to me what the OP
was trying to describe.  
When you read something, do you simply take the literal meaning of all
the words, or do you apply a bit of thought and apply context to them?

Regards

Mike

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2010\11\15@125604 by Olin Lathrop

face picon face
Michael Rigby-Jones wrote:
> I did read what he said, and whilst it may not be described
> accurately,

Exactly.

> in the context of the topic it's blindingly obvious to me
> what the OP was trying to describe.

I don't see how you can tell the difference between a accidental misuse of
words and a true stupidity when the misused words also result in clear
meaning.  From a subsequent statement he made, and you conveniently ignored,
he clarified that the latter was the case, not the former.

> When you read something, do you simply take the literal meaning of all
> the words, or do you apply a bit of thought and apply context to them?

I don't feel like apologizing for other people's bad writing.

I actually thought at first it was a innocent misuse of words and his
response would be something like "oops, of course I meant ...".  Instead Jim
decided act like a child and have a hissy fit about getting caught,
presumably to deflect attention from the actual error.  That's what actually
led to this discussion.

If you really want to do Jim a favor, bringing this up again and again isn't
the way to do it.


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(978) 742-9014.  Gold level PIC consultants since 2000

2010\11\15@135630 by Bob Blick

face
flavicon
face

On Mon, 15 Nov 2010 12:56:48 -0500, "Olin Lathrop" said:
> Michael Rigby-Jones wrote:
> > I did read what he said, and whilst it may not be described
> > accurately,
>
> Exactly.
>
> > in the context of the topic it's blindingly obvious to me
> > what the OP was trying to describe.
>
> I don't see how you can tell the difference between a accidental misuse

Gentlemen, I think we all know where everyone's coming from, it's time
to apply some damping fluid and just stop hitting "reply".

Thanks,

Bob

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