Project
by Ralph Lorenz
The Amazing Frisbee
Black Box or BASIC
Stamp Frisbee
Instrument Your Favorite Sporting Goods!
Is it a bird? Is it a plane? No,
it's a computerized Frisbee
with a BASIC Stamp! In this
simple project, I will show you
how to make an ultralight, but
easy-to-assemble, acceleration
recorder that you can use to
measure the dynamics of small
vehicles, much like the "black
box" aircraft flight recorders.
Frisbee
Background
I wanted to understand the aerodynamics of a Frisbee
by taking in-flight measurements of lift and drag.
Although Frisbees (the name — a corruption of that of
William Frisbie, a Connecticut baker whose pie tins
formed the inspiration for flying disks — is a trademark of
Wham-O, Inc.) are very familiar objects, their impressive
flight performance is only documented with a handful of
published studies and wind-tunnel measurements. Some
background can be found at
www.discwing.com and at
http://mae.engr.ucdavis.edu
/~biosport/frisbee/frisbee.
html. By taking in-flight measurements, I would understand
the changing aerodynamic
forces throughout a free flight.
The challenge was to make
a super-lightweight and compact instrument package. The
accelerometer and the micro-controller were tiny enough, but the power supply presented a problem. Two lithium button cells (CR2032) in
series can provide 6 V, but only about 10 mA of current.
This is, however, just enough to run a BASIC Stamp II
(although not enough to run other, faster microcontrollers
like the BS2-SX or a BasicX- 24.) The accelerometer draws
just a few milliamps at most.
The circuit itself is very simple, as the accelerometer
interfaces very easily with the microcontroller. Given 5 V,
it spits out two square wave signals, which are pulse-width
Charted Data
Figure 1. Circuit diagram for the ADXL202 (A) and MEMSIC 2125 (B) accelerometer options.
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NUTS & VOLTS
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(A)
(B)
52
FEBRUARY 2004
