real time dyno

[John Faubion]

> I have been trying to work out how to mount some sort of speed sensor on
the
> front wheel. It is difficult as it uses spoked motorcycle front wheels in
an
> open wheel format. So there is no front brake and hence no backing plate
to
> mount things on, just a rear hand brake and a parachute!
> 
> One other thing, which we don't have a problem with at the moment but is
kept
> in mind, is that the front wheels can be prone to lifting off the ground
and
> hence losing the rotational information.

The only other way I know of is to use a fifth wheel. RacePak has a system
that uses a small aluminum hub with a solid rubber tire of about 5-6 inches
in diameter. This is designed to be mounted off the rear axle housing and
it has a spring load mechanism to keep it in constant contact with the
ground. I remember a while back there were several people saying that a
wheel this small wouldn't work due to the high frequency required to
monitor it but I know this system is designed for professional drag racers
and is used on Kenny Bernsteins top fueler running over 300 MPH! 

Let see at 300 MPH, that's  300/3600x5280 = 440 feet/sec. A 6 inch wheel
covers 6xPI/12 = 1.57 feet. So our input frequency from a single magnet or
even an optical sensor mounted to it, would be 440/1.57 = 280 Hz. I'm not
sure but I think if we tripled the number of magnets we could still handle
the frequency without problems and you would get a resolution of about a
half foot on the track for about 2500 samples per quarter mile. No this
wouldn't work on public roads but it should work on a drag strip.

John Faubion
jfaubion at beaches.net