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I've got a Chinese pot datasheet, and the rotational torque is listed as "20~200gf.cm".

This Bourns datasheet lists

Rotational Torque ............. 10 to 150 gf-cm

Why such a wide range? Is this a tolerance issue, or is it something like the difference between slip and stick friction?

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2 Answers

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The tolerance stackup for the torque is probably quite large, including bearing friction (2+), wiper friction, and misalignment, all of which will drift and change with age, (cycle) life, and temperature.

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Then why even bother specifying it? :/ – endolith Nov 11 '10 at 21:46
So that someone has an idea of the different torque that will be required over a lifetime without having to run their own tests. – Kortuk♦ Nov 11 '10 at 21:51
Or why not specify each individual factor separately? – endolith Nov 11 '10 at 22:03
They do not probably have factors down that reliably, there is a large cost to thorough characterization. It is relatively affordable to characterize it. – Kortuk♦ Nov 11 '10 at 22:24
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I don't know about rotary pots, but some slide pots I've seen use an oil/grease between the wiper and housing to provide a very smooth feel. There, the friction force (fluid shear?) isn't linear, and the thixotropic properties probably change drastically even from 10°C to 30°C. – Nick T Nov 12 '10 at 19:41
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Nick has it pretty much dead on. Whenever modeling a Sensor, motor etc you will find that you end up with a very broad range that often makes it difficult to fine tune things. Adding to what Nick said there is also the difference between static and dynamic friction the means you will have different frictions and oppoing forces depending on how the arm i moving or if it is stopped. The best solution is to design it for the worst problem X 2 then your covered.

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