OT: ABS - or is it Pure BS/wheel sensors

From: Stan Perkins <stan_at_netcom.com>
Date: Tue Apr 6 16:58:38 1999

Jason Willgruber wrote:
>
> I'm not sure if anyone else knows about what I'm talking about, but in my
> Jeep (pre-ABS), there's a little panel on the dashboard (not original).
> There's 4 LED's on the panel (one corresponding to each wheel). When the
> wheel corresponding to a particular LED is completely stopped, the LED
> lights steadily red. When the wheel is turning, the LED flashes green (one
> flash for each revolution).
>
> Anyone know how this would work (with out me pulling it out of my Jeep)? It
> would be probably a good accessory for non-ABS cars.
> --
> -Jason Willgruber
> (roblwill_at_usaor.net)
> ICQ#: 1730318
> <http://members.tripod.com/general_1>

It's probably a similar system to the one used by Etak with their early
car navigation systems. Basically, they used a special adhesive tape
that contained a small bar magnet every inch along its length. This was
applied to the circumference of the inside of each front wheel rim, and
a Hall effect sensor was attached to a point on the front axle (usually
to a part of the brake caliper assembly) where it was within an inch of
this tape as it passed by. Each magnet passage would produce a countable
pulse, and the Etak computer could determine the wheel speed and
direction of rotation for each front wheel. *Supposedly* it could also
detect a turn by the differential speed of the front wheels, but it also
had a flux gate compass to help determine direction and turns.

A pretty clever system that worked quite well, considering it was all
done without reference to external navigation data sources like GPS,
LORAN, etc!

Since your system apparently produces only a single pulse per
revolution, I would guess there's one magnet somewhere on each wheel
rim. The speed resolution with only a single pulse per revolution is
probably not good enough for ABS use.

Hope this helps,
Stan
Received on Tue Apr 06 1999 - 16:58:38 BST

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