[sdiy] Looking for a mini rotary encoder with very low torque (servo type)

Thu Dec 12 17:47:42 CET 2024

> Is it more important to measure the surface of the paper itself due to torque/slippage reasons like on a tape machine, 

Yes.

> or will measuring the speed of the take up spool get you the same info?

No.

>  If the latter is an option, what about a magnet and a hall sensor on the take up spool, 
> disk the same diameter as the take up reel in the drive mechanism with some other sort of sensor on it like cheater mentioned, 
> or even a small notch in the take up spool (or equivalent disk in the drive mechanism) that has a limit switch with roller against it.
Measuring the take up spool rotation speed will hide the actual problem I have
which is paper thickness accumulation on the take up spool (with fixed speed)
that speeds up the overall moving paper speed !

So far my software only put 25 fixed parameters (by means of a potentiometer) to control
the PLAY stepup motor steps and would not check for any speedup in a song.
That’s what I discovered some days ago and am trying to fix.

The solution is to read the paper moving surface (regardless of the take up spool speed )
But in a very small space to do it.
So no place for any encoder disc (it would need to be smaller than 18mm in diameter.. see why below), 
nor any ‘normal’ size Opto-Interrupter..

Because of the very small and limited space I could mount this thing,

I will use a model car wheel with rubber tire (overall outside diameter 18mm),

mounted on a small 1/16in. shaft that will turn a small glued piece of opaque plastic
in the slot of a very small SMD opto-interupter like this one :

The below picture shows the actual tiny wheel with rubber tire I will use (to put against the moving paper)
and part of the setup I used in a past project with a small rotating piece of plastic
moving inside a Opto-Interrupter.
Mine will be much smaller. 

I’m now waiting my Digikey order for the Opto-Interrupters + nylon hardware.

And thanks Gerry for your nice suggestions !

De : Synth-diy <synth-diy-bounces at synth-diy.org> De la part de Nathan Trites
Envoyé : 12 décembre 2024 10:17
À : Gerry Murray <synthimuse at gmail.com>
Cc : synth-diy at synth-diy.org
Objet : Re: [sdiy] Looking for a mini rotary encoder with very low torque (servo type)

This is the direction I was just thinking, and was also on the Adafruit site looking at plug and play sensor options. 

Jean-Pierre - I'm assuming this is to make the speed on your piano roll player programmable/repeatable? Is it more important to measure the surface of the paper itself due to torque/slippage reasons like on a tape machine, or will measuring the speed of the take up spool get you the same info? If the latter is an option, what about a magnet and a hall sensor on the take up spool, disk the same diameter as the take up reel in the drive mechanism with some other sort of sensor on it like cheater mentioned, or even a small notch in the take up spool (or equivalent disk in the drive mechanism) that has a limit switch with roller against it.

If it must be against the paper, opto-interruptors and disks are available on their own, and then you could rig something up so that assembly rests lightly against the paper:

https://bc-robotics.com/shop/opto-interrupter-with-mounting-tabs/

https://bc-robotics.com/shop/encoder-disc/

Nathan

On Thu, Dec 12, 2024 at 9:22 AM Gerry Murray via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org> > wrote:

Hi JP

You could maybe try a resolver. The resolution of them can be very high 
: up to 16 bit.
https://www.mouser.co.uk/applications/resolver-encoder-motor-control/
https://www.instructables.com/Arduino-Resolver-Module/

I always like it when you put an inquiry on the list because, usually 6 
months later on, a really cool project emerges. :-)

Best wishes

Gerry

On 11/12/2024 15:09, Jean-Pierre Desrochers via Synth-diy wrote:
> I'm looking for a very small (20mm or less body diameter)
> rotary encoder with very low torque (servo type).
> The low torque shaft is needed because it will turn by means
> of a small wheel with rubber sides that will be put against a moving surface, turn and 'follow'
> the moving surface.. no slipping allowed !
>
> The precision of steps/turn is not important.
> But the higher will be best..
>
> I was thinking of using a dismantled PC mouse (rubber ball type)
> and use one of the two  X/Y optical rotary encoders, but these PC mice
> nowadays are hard to find.. So.
>
> I checked Digikey and Mouser but they have encoder too big
> for my uses..
> The smaller I found has 20mm in diameter..
> https://www.digikey.ca/en/products/detail/nidec-components-corporation/RES20D-50-201-1/6469509
>
> Any suggestions ?
>
>
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