[chbot] Shaft Encoder

[Charles Manning]

I just checked data sheets and other info...

The UGN3141 turns on at 100Gauss and off at 45Gauss. The Earth's magnetic 
field is less than one Gauss. Therefore there is no need for a "turn-off" 
magnet with these parts.

On Thursday 04 September 2008 08:44:40 Charles Manning wrote:
> 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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