Automatic speedometer for paper airplanes

[Ricardodavinci]

Hello every one!
I'm designing an unusual project, and need some help! I used an Arduino and a couple of IR barriers to count the time for toy drag racing cars. Now I'm about to use the same setup to calculate the average speed of an paper airplane. The problem is when you throw an paper plain, it is not so easy to hit the IR barrier to trig the timer to start. More dificult to make the plane pass the second one....

How would you design a wide, tall and narrow barrier to trig the start and stop signal? I though about IR, PIR, ultra sonic and laser. But I'm sure some out there have a nice idea! Check out the simple drawing to get an idea of my setup.

[Rufus]

It used to be done by bouncing a beam between mirrors in a zig-zag pattern. Difficult to align and to keep the mirrors clean enough. Nowadays maybe scanning laser beams is more practical.

The requirement is similar to that of safety barriers on machinery. Searching for "light curtain" may give you some ideas or clues.

[TheCommonCathode]

Oh, so your using like a Chronograph?


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[vk6zgo]

If you are using the paper plane indoors,paint two lines on the floor.
If you have a nice high ceiling,mount one TV camera facing down.

Watch the monitor,start a stopwatch when the plane crosses the first line,stop it when it passes the second,

Calculate the average speed.
If you have a low ceiling you will need two cameras,to avoid error.

This method worked well for the WA Police catching speeders in the 1970s,using a cop in a 'plane instead of the TV camera, & 0.5km spaced lines on the road.

For a while,this was popularly known as "Pigs in Space'!
(No offence intended to any Police Officers present)

Ok,this isn't automatic,but you could probably analyse the video signal & do the calculation automatically.