🚀 go-pugleaf

In article <1992Nov22.203815.9006@hemlock.cray.com>, kilian@cray.com (Alan Kilian) writes:
> Well here's another project for you.
>  
> A friend of mine (Who shall remain nameless) always makes his hobbies
> complicated and scientific.
> He's into archery now. Well (you say to yourself) how complicated can you
> make archery? Pretty complicated as it turns out. He has measured the draw
> force/draw length relationship and made a graph. Then integrated the thing
> to get energy and used the weight of an arrow to get acceleration and
> velocity (He even knows the Horsepower of the bow). Now he wants to actually
> measure the acceleration of the arrow as it goes from rest to about 
> 200 Feet per second. This is where I cone into the picture.
 
Why not do this instead?  Get a light (styrofoam) spool of light thread, and
glue two large cardboard disks to each end.  Punch a hole in each disk near
the midway point of the annular region formed between the spool and disks.
These holes should line up so that light passing through one passes through
the other.  Forgot to say that the center of each cardboard disk should be
punched out so that the spool ends and disks are concentric.  Mount the spool
on a spindle, and have a light source on one side, and a light detector on
the other, opposing one another at the aligned holes in the disks.
 
Tie the end of the thread to the arrow.  When the arrow is shot, the thread
will unwind spinning the spool.  Each revolution of the spool will cause an
interrupt level when the light on one side is detected at the other.  During
each interrupt, record the time.
 
If you want, you can set up a counter based on the light detection pulses
that causes an interrupt and reset of the counter at some state.
 
Maybe a better way would be to just punch the hole in one disk, and have the
light source and detector positioned on either side of it.  
  
 
        |               |
        |               |
        |\_____________/|
        |   spool       |
    ------------------------ spindle
        | _____________ |
        |/             \|
     O---->O            |
  source|detector       |
  
  
Of course, rewinding the thread for a second attempt would be a pain.
 
Jeff White     jhwhit01@ulkyvx.louisville.edu