[chbot] Shaft Encoder

[Charles Manning]

There are different kinds of hall effect sensors. Some need to have
alternate poles to turn on/off and some do not.

With the HE sensor I am using I only need one magnet.

The HE sensors are a bit more expensive than optical forks, but they are so
much simpler to use and don't need any supporting electronics.

I bought the tiny magnets from a place in USA by mail order, but might end
up using something I bought from Natures Discovery.

Interestingly, that flexible fridge magnet stuff is made up of alternate
bands of north and south magnet and  would make an effective linear encoder.

Quite a few DC motor encoders use HE sensors because they are far more
robust against dust etc than optical sensors.


On Thu, Sep 4, 2008 at 8:34 AM, Richard Jones <rjtp at ihug.co.nz> wrote:

> Thanks Charles,
>
> The UGN3141 Hall effect sensor from South Island Components does look
> interesting, a little more expensive than optical.
>
> To ensure that the hall effect sensors get low enough gauss to release do
> magnets need to be alternated N S N S? That would mean an even number so to
> detect direction of rotation you need 90 degree separation between hall
> effect devices rather than 180 degree that works with an odd number. Where
> do you get your tiny magnets?
>
> I wonder if you might be able to place the hall effect sensor somewhere
> inside a brushed DC motor?
>
> Richard
>
> On Thu, 4 Sep 2008 07:38:10 +1200, "Charles Manning" <cdhmanning at gmail.com
> >
> wrote:
> > Hi Richard
> > There's an alternative that we are dabbling with using a Hall Effect
> > sensor
> > that is probably a lot easier to do than shaft encoders.
> > The Hall Effect sensor is just a 3-pin transistor like device that
> detects
> > a
> > magnetic field (eg. UGN3141 from South Island Components). The magnet can
> > be
> > one of those tiny 2.5mm Neodymium magnets embedded in a gear (Drill a
> hole
> > and glue it in). Since some of gears inside the gearbox rotate quite fast
> > you can get pretty good resolution.
> >
> >
> > On Wed, Sep 3, 2008 at 10:06 PM, Richard Jones <rjtp at ihug.co.nz> wrote:
> >
> >> I came across this shaft encoder arrangement for the Tamiya Twin-Motor
> >> Gearbox: http://www.noplabs.com/twinmotor/twinmotor.html
> >> This came via the HBRC mailing list. Andrew showed something along these
> >> lines at one of our robotics meetings several years back.
> >>
> >> Richard
> >>
> >>
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>
>
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