Home-grown 5th wheel project--wheel lacings

[tom sparks]

As your sensor gets closer to the hub though the spoke spacings get less
regular--that is, the spokes are not spaced exactly 10 degrees apart, half
of the intervals will be more than 10 degrees and half will be less. 

If this won't cause any problems, great, but if it does you may have to lace
up the wheels in a radial pattern.
This requires shorter spokes and a bit of skill to get right.

The 2X, 3X, and 4X patterns are used to transmit torque better and to bear
more load.  Those are not great concerns here so I'd give radials a go.
Besides, a radial pattern just looks slightly more exotic.

Better yet,  why not use a rear wheel hub with threads for the freewheel
already built in.  Then you can fabricate a circular plate to mount your
magnets that will screw onto to those threads--you can even use off the
shelf locking rings to lock it in place. It would be much more secure than
trying to get a reliable mount to a 14 gauge spoke.  Unless of course you
use aero bladed spokes.

Or why use magnets at all if you have a stable plate.  drill small holes in
the plate at regular intervals and use an optical system.  Any machine shop
that cuts gears should be able to keep the intervals regular.

Or, here's another approach:  Use an aero disc (flat not lenticular) and
mount anything anywhere. You might be able to get a used one for not much
money, many cyclists are going to DuPont or Spinergy 3 and 4 spoke style
wheels anyway so a nice flat disc could be found on the used market.

Best regards,
Thomas Sparks



At 21:20 6/18/96 -0400, you wrote:
>Thanks Bruce, Orin, Dan and Peter for the wonderful input.  I'll zip over
to the
>bicycle shop and get an idea of what the mag pickup looks like.  I might be
able
>to do just as you suggested and mount a small magnet onto every other spoke.  
>There seem to be approx. 36 spokes on a typical wheel so that would be 18
>positions
>which is one every twenty degrees.  Based on my initial calculations using
>36 spokes
>on a 26 inch O.D. tire/rim combo, I would get a 1000 Hz signal at approx.
>129 MPH.
>Thus, with only 18 spokes, I should get a 500 Hz signal. 
>
>I did a quick check on how much time a .100" thick spoke would break my
>light beam
>if I was monitoring near the edge of the rim. (20.5" dia.)  I found that the
>spoke
>would obstruct the beam for only 60 microseconds at 129 MPH!! I'd have to
>widen that pulse width by either using a 1 shot timer, or by moving the
>sensor closer to the 
>hub.
>
>        The research continues.
>
>        BTW, I like the idea of correlating the data via integration of
>the accelerometer data.  I'll probably load it all
>into MATLAB and crunch it in just that fashion.
>
>Cheers!
>        --Dan.
>
>
>
>