EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Infraviolet on May 30, 2022, 09:31:28 pm
-
I was wondering if this sort of thing exists at all. I'm familiar with potentiometers which make multiple turns to run through their resistance range, but they still have two limits to them. Is there such a thing as a potentiometer without the limits, one which when going below the low end resets to the high end and vice versa, so if you made say 1.5 turns it would go from say 0 ohms to the maximum resistance, reset to zero ohms, then to half way through the log or linear scale. Perhaps with some deadband of all zero or all maximum resistance for a fraction of a rotation around the "reset" point. Does this sort of thing exist for sale? I know there have been some DIY projects to make them using conductive paint and handmade wiper brushes, but are there any manufactured devices which can cope with being turned an arbitrary number of times?
Thanks
-
There are precision single-turn (360-degree rotation) pots with continuous rotation.
This one has only 340 deg of "electrical rotation" due to dead-band, but continuous mechanical rotation. https://www.potentiometers.com/SP22G.cfm (https://www.potentiometers.com/SP22G.cfm)
What you want is topologically possible, I guess, on a generalized Möbius strip.
Another possibility is a "sine-cosine" pot, with two wiper points rotating (continuously) on a rectangular resistive surface, which also repeats after 360 degrees just as the two functions do.
https://www.megatron.de/en/category/sin-cos-potentiometer-nonlinear.html?dv_t3_referrer=https%3A%2F%2Fwww.google.com%2F (https://www.megatron.de/en/category/sin-cos-potentiometer-nonlinear.html?dv_t3_referrer=https%3A%2F%2Fwww.google.com%2F)
Probably what you need is a single-turn continuous pot driven by a planetary reducing drive, such as used on tuning controls.
-
What you want is topologically possible, I guess, on a generalized Möbius strip.
It could also be done with just gears or a belt. If you wanted the shaft inline with the pot, planetary gears could be used.
-
Maybe Vishay Spectrol type 601-1045 would do, albeit no classic potentiometer:
- Full continuous 360° Smart Position Sensor
- Ratiometric output over 360° range with no dead band
-
I bought a WDD35 from Ali some time back. Not very cheap for a potentiometer, but worth it's price.
It's a continuous rotation potentiometer, and if you want more then one turn, then adding some gears or timingbelt is the simplest solution.
I bought it mostly out of curiosity but also for a project for measuring oscillations and step accuracy of stepper motors but I never got around to doing that.
Another option is to use one of those HALL sensor things with a rotating magnet and do the rest in software.
It all depends on your application.
-
See https://www.orenelliottproducts.com/product-category/planetary-reduction-drives/ (https://www.orenelliottproducts.com/product-category/planetary-reduction-drives/)
For your application, use with a single turn continuous rotation pot.
N.B. They are ball bearing friction drives so, although they don't slip in normal movement, it is possible (and likely if the pot has end stops) for the input shaft position to slip relative to the pot shaft position
-
Planetary drive with balls.
That orenelliot site states:
Constant input/output relative position?: NO
I interpret that as they will slip or creep over time.
-
I was wondering if this sort of thing exists at all. I'm familiar with potentiometers which make multiple turns to run through their resistance range, but they still have two limits to them. Is there such a thing as a potentiometer without the limits, one which when going below the low end resets to the high end and vice versa, so if you made say 1.5 turns it would go from say 0 ohms to the maximum resistance, reset to zero ohms, then to half way through the log or linear scale. Perhaps with some deadband of all zero or all maximum resistance for a fraction of a rotation around the "reset" point. Does this sort of thing exist for sale? I know there have been some DIY projects to make them using conductive paint and handmade wiper brushes, but are there any manufactured devices which can cope with being turned an arbitrary number of times?
Thanks
Never seen one in the wild.
I've seen resistive rotary encoders with a continuous resistive ring with connections to the 0, 120 and 240 degrees points, letting you decode the wiper position. But they are very rare and exotic.
-
Reduction gearing still doesn't let you turn an arbitrary number of rotations in to less than 1 rotation. It lets you get more rotations than 1, but only by some fixed ratio.
The term"continuous mechanical rotation potentiometer" seemed to help with searching, seems some potentiometers are designed like ordinary ones but simply with end stops omitted.
-
The sine/cosine pots have four excitation points on the resistive surface, to be connected to balanced drives, and have truly continuous rotation of the two wipers.
Normal "continuous rotation" pots have a dead zone between the ends of the resistance element (20 deg in my example above).
The only other way that could work would be to have the "endpoints" diametrically opposed (180 deg apart) to allow continuous rotation with no dead zone.
"Helipots" (trademark) use a helical winding, which can have 3, 10, 20, 40, or so turns from end to end.
Years ago, when analog servos were more common, surplus houses had stock of "servo" pots that used a gland mount (with screws) instead of a bushing mount (with nut).
-
I have a weather vane that works like this, it is a potentiometer with continuous rotation, it has by necessity a small dead spot directly North which needs to be dealt with in software. I haven't seen a standalone pot like this but that doesn't mean they don't exist.
-
The continuous rotation sine/cosine pots are still available. They have no deadband. We used them extensively in radar to create the sweep signals for PPI displays. I have some here on the shelf. If you only want one output signal just use the sine or cosine by itself. The resistive element is a continuous 360 degree surface with four connections spaced 90 degrees apart. In radar we fed a sawtooth wave to the 0 degree tap, an inverted sawtooth wave to the 180 degree tap and grounded the 90 degree and 270 degree taps. The vertical and horizontal deflection signals were taken from the sine and cosine wiper connections. The same 360 degree continuous rotation pots are also available in a simpler format called a resolver potentiometer. They are designed to survive at least a half million full rotations before degrading and becoming electrically noisy. Radar spins at generally 27 rpm or less so you can calculate a life cycle.
-
... so if you made say 1.5 turns it would go from say 0 ohms to the maximum resistance, reset to zero ohms, then to half way through the log or linear scale. Perhaps with some deadband of all zero or all maximum resistance for a fraction of a rotation around the "reset" point. Does this sort of thing exist for sale?
Yes, Potentiometers without end stops do exits and two variants have already been mentioned: SP22G and WDD35. And these do have a small dead-band during which the wiper is open. (Typically between 5 and 20 degrees)
there are also HALL based IC's which can generate an analog output and these can also be bought in a housing resembling a potentiometer with an magnet on the axle. These have a very small dead band, or no at all, or can even have a programmable hysteresis.
Forget the gearing if this is not what you want. This has only been mentioned because you mentioned multiturn pots (old fashioned with end stops) and the potentiometers without endstops always go though their whole range in a single rotation, unless maybe you have a Möbius strip potentiometer as TimFox mentioned.
So why did you yesterday still post:
Reduction gearing still doesn't let you turn an arbitrary number of rotations in to less than 1 rotation. It lets you get more rotations than 1, but only by some fixed ratio.
The term"continuous mechanical rotation potentiometer" seemed to help with searching, seems some potentiometers are designed like ordinary ones but simply with end stops omitted.
You either did not state your question clearly enough, or you mis-interpreted the answers.
-
Look for instrumentation pots
-
What you want is mechanically impossible, but you can easily use a digital pot and a rotary encoder to get the same effect.
-
Look for "servo mount potentiometers", Vishay and Bourns make them.
www.mouser.co.uk/c/passive-components/potentiometers-trimmers-rheostats/precision-potentiometers/?mounting%20style=Servo%20Mount (http://www.mouser.co.uk/c/passive-components/potentiometers-trimmers-rheostats/precision-potentiometers/?mounting%20style=Servo%20Mount)
-
Those are generally cyclical that is you can keep turning them in one direction but they are only for 340 degrees or so. They do have a dead band and not multiturn.