Rotary Encoder Knobs

[krapht]

I had the opportunity today to use somebody else's very nice hi-fi system, and there were some large aluminum rotary encoders/knobs used for control. These were honestly the best knobs I've felt. 

I really want one on my next project. My question is, how do I get the same turning feel? These knobs are incredible. The resistance to turning decreased as the rotary speed of the knob increased, and was very smooth. It almost felt like I was turning a shaft in a motor. Anyway, I quite liked this, as large adjustments were easy to make, while still allowing for small precision turns.

How is this done?

Edit:

http://www.mp3car.com/input-devices/95509-new-product-force-feedback-haptic-encoder.html

So it looks like one of the ways this is done is to actually hang a motor off the encoder shaft to provide feedback. I need one. Although I wonder how expensive to would be to wire a large inductor around the pot shaft to get the same resistance profile.

[mazurov]

Stepper motor can be used for that. Google 'stepper rotary encoder' for the schematic, it's quite trivial. To get a feeling or resistance energize coils a little. I used to have a stereo (many years ago) that also rotated the knob when I changed volume via remote. The knob was made out of plastic BTW, the heaviness comes from the current.

[Paul Price]

The precious "turning feel" is actually created by having a small but weighty flywheel on the pot shaft.

An object at rest tends to stay at rest, an object in motion tends to stay in motion. Momentum feels good.
In any mechanical system, the coefficient of static friction is usually much greater than the coefficient of sliding friction. Sliding feels good.

[HAL-42b]

The expensive ones are usually machined from solid aluminium and mounted on ballbearings.




Source: http://www.esoteric.jp/products/esoteric/c02x/indexe.html

[Alex Eisenhut]

[pmbrunelle]

The expensive ones are usually machined from solid aluminium and mounted on ballbearings.




Source: http://www.esoteric.jp/products/esoteric/c02x/indexe.html

Looks like a tolerance stack nightmare.

So there's a through-hole encoder, which is soldered to a PCB, which is somehow screwed onto the chassis (with a plastic intermediary maybe?).

From the other end, you have a female encoder shaft receptacle, which is attached to a purple piece, which is on a steel shaft, which is supported by bearings, which are in some flange, which is apparently screwed onto the chassis via the four mounting holes.

Somehow, by some act of God, the female encoder shaft receptacle is supposed to be concentric with the encoder shaft...

The blue female encoder shaft receptacle looks like some flexible rubbery thing; an attempt to accommodate some misalignment. Maybe it works, but I wouldn't showcase this as an example of good design.

Now that they mention 100 000 uF of power supply capacitance for a preamplifier, this screams of audiophoolery. Also the large transformers powering... I don't know what?

As stated, you need inertia for the feel. If you need inertia, steel would be better than aluminium, because it's heavier. However, aluminium is cheaper to machine.

For best feel, you need to reduce friction. To reduce friction, you must not have an overdefined shaft. A rotation axis is defined by two supports. In the previous bad example, there are the two bearings which are conflicting with the bushing in the encoder.

I would prefer to have the encoder all the way at the rear of the chassis, with a long shaft to the knob in the front. On the front panel there should be a self-aligning bearing. Possibly a cardan joint or something at the encoder end.

[HAL-42b]

The aim here is to convey the feel of quality and justify the price tag.

If it's stupid and it sells it ain't stupid, no?

[krapht]

Ah. The stepper motor encoder idea sounds neat, but wouldn't you get disjoint resistance as you passed each step? So it would be as if the motion was quantized. I can see how that might be useful in some applications, and of course, once you have the stepper motor, you can do all sorts of haptic feedback.

The flywheel sounds about right. That's the mechanical rotary equivalent of an inductor which is what I was thinking. Are rotary dashpots also used for this purpose? Although I don't know what the turning feel of that would be like. Anyone know good sources for these sorts of things? Aliexpress/Ebay, I suppose?

Yes, I realize a nice feeling knob is a luxury and so is "stupid" from a technical point of view. However, I enjoy making and using items which are beautiful as well as functional.

[CaveMannDave]

Hi:
Older high-end stereo amps and tuning controls on Ham rigs and test equipment frequently had large diameter knobs backed with big Zinc or brass gyroscope wheels in low-torque shaft bearings.

NICE feel, fine adjustment, quick seeking.

Cheers,

Dave

[Richard Crowley]

Another method of achieving that feel is judicious use of grease (silicone, etc.)