Chief Delphi - chronograph

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I've been reading about some fast flying balls and was just thinking that we shoulda at least been supplied a schematic for a chronograph, so we don't have a bunch of overclocked robots end up at regionals.

Anybody already beat me to this and have a chono design they'd like to share?

Quote:

Originally Posted by Chuck Merja

Quiz: How long does it take for a ball to move its own diameter at the maximum muzzle velocity?

My calculation shows about 14msec, any others?

Closer to 15.

12 meters per second.
1000 milliseconds per second.
39.37 inches per meter.
7 inches per ball diameter.

Code:

1 sec   1000 ms     1 m      7 in   14.82 ms

----- x ------- x -------- x ---- = --------

 12 m    1 sec    39.37 in   diam   diameter

Your best bet would be to locate a local paintball shop. At the very least, you could bring your robot to their location, and use their chrono to measure ball speed (in feet per second). One of my friends happens to be a referee for paintball, so we're actually going to bring one of their chronos to the match. The chronos are highly accurate (seeing 1cm diameter balls at 180fps is no easy task), and work from a good distance, too. We're bringing him with us to stand on the sidelines and track opponent ball speed... so that we can notify the referees of any violations that we notice (not that it'll have any official bearing, but they may take the robot to the side to do tests, and tell the team to throttle it back).

Quote:

Originally Posted by zachriggle

I hope that will not be necessary, I am confident that FIRST will have some sort of testing system in place at the regionals. I'm not sure that the refs will respond positively to a team coming up to them with a radar gun saying that an opposing robot was shooting the ball too fast.

The only problem is that paintball chronos only read down to about 100 fps. I have one of my own and tried to use it and it just gives me an error. I think teams are going to have a hard time finding a chrono that will go that slow.

Kirk

Well, I was actually thinking of an emitter/detector pair close to muzzle, that would capture velocity info. The gun chronos I'm familiar with use leading edge (of bullet) detection and known distance between detectors to calc velocity. But maybe we could use one e/d pair and assume a constant (length) of our poofs. May be OK - depending upon the poof deformation/deformation variation.

You might adapt one of the many low-cost pinewood derby timing circuits to measure ball speed. Some display time and you could use a two lane timer and use the differential time to calculate velocity. Some of these circuits are very simple, and use a PC parallel port & a program to do the hard work.