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'What is the estimated torque ?'
2002\08\06@035314 by Pang

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Hi all,

Just received a sample for a low torque potentiometer. As i checked it, I
found that it is not suitable for my application. The torque is not low
enough eventhough the potentiometer is classified as low torque. As such I
would like to enquire, what is the estimated torque such that I can turn the
shaft of a potentiometer using only one finger? Or maybe in another way...
what is the torque for a normal desktop fan? Is such a potentiometer (with
that level of torque) available?

Thanks..

Best rgds,
Pang

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2002\08\06@035959 by Wouter van Ooijen

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> what is the torque for a normal desktop fan? Is such a
> potentiometer (with
> that level of torque) available?

Are you sure you want to use a potmeter? If you want to detect/measure
the turning of a fan a optical or magnetical sensor might be better
(think of the speed/distance etc gimmics for a bike, or the rotation
sensor of a floppy).

Wouter van Ooijen

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2002\08\06@042055 by CK Chan

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maybe you can consider digital potentiometer instead ?


-----Original Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of Pang
Sent: Tuesday, August 06, 2002 10:43 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: What is the estimated torque ?


Hi all,

Just received a sample for a low torque potentiometer. As i checked it, I
found that it is not suitable for my application. The torque is not low
enough eventhough the potentiometer is classified as low torque. As such I
would like to enquire, what is the estimated torque such that I can turn the
shaft of a potentiometer using only one finger? Or maybe in another way...
what is the torque for a normal desktop fan? Is such a potentiometer (with
that level of torque) available?

Thanks..

Best rgds,
Pang

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2002\08\06@110130 by M. Adam Davis

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Your questions don't add up.

I can turn a high torque anything with my finger if the knob is big and
light enough.  In other words, the force you apply with your finger
translates to torque through a lever.  If you have a small diameter
shaft on your low torque pot, then your finger may have to apply a great
deal of force to turn it, if you attach a 1 foot stick to it then your
finger will have to apply very little force to the end of the stick.

The fan blade is the same way.  You'll apply less force at the ends of
the blades then you'll apply at or near the center.

The trade off is distance moved.  At the center you only need to move it
a little to get a large degree of rotation, whereas at the outside you
need to move it further.  Force * Distance = Work, the work is the same
whether you turn it a the center or the end, but the distance and force
changes.

If you knew the torque you needed (ie, .01 foot pound or some other
absolute torque measurement) then we could help you more easily.

Since, however, you seem to be asking for a relative measurement (fans
have widely varying torques) then you need to give a little more
information:

What will be turning the pot?
Will it turn the pot directly, or is there a
knob/attachment/lever/belt/pulley/etc on the pot?
How much force is going to be applied to the point at which they (the
pot and the other object) meet?
Are you also going to be dealing with friction/slipping?

By the way, a normal desktop fan requires a lot more torque to turn than
any small pot I've ever dealt with.  Take the fan blades off the shaft
for a better torqure comparison.  Better yet, put the fan blades on the pot.

I hope this helps!

-Adam

Pang wrote:

{Quote hidden}

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2002\08\06@111818 by Paul Hutchinson

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If this is a cost sensitive application then get an optical, hall-effect or,
other position sensing device that does not have wiping contacts (as others
have already suggested). You will probably also need a unit with ball
bearings instead of bushings.

If you must use a potentiometer, you will most likely need a custom
manufactured unit. These can cost hundreds of dollars, may take many months
to obtain and, may have many thousands of dollars in engineering charges.

The New England Instrument division of Invensys can definitely make you
exactly what you need http://www.speed-position.invensys.com/default.asp. If
this is for a panel mounted user activated pot then the Invensys Clarostat
division may have a suitable product.

Paul

> {Original Message removed}

2002\08\06@161740 by Peter L. Peres

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On Tue, 6 Aug 2002, Pang wrote:

>Hi all,
>
>Just received a sample for a low torque potentiometer. As i checked it, I
>found that it is not suitable for my application. The torque is not low
>enough eventhough the potentiometer is classified as low torque. As such I
>would like to enquire, what is the estimated torque such that I can turn the
>shaft of a potentiometer using only one finger? Or maybe in another way...
>what is the torque for a normal desktop fan? Is such a potentiometer (with
>that level of torque) available?

To measure torque wind a few turns of twine on the axle, measure its
diameter (of the axle) and turn while adding weights on the twine (I use
coins put in a small plastic bag hung on the twine - our 10 Ag.  coins
weigh exactly 4 grams each). Use thin twine or the thinnest monofilament
fishing line you can find.

Peter

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