Single Optical Gate Chrono...

[Redkey]

I know this was kind-of talked about before... But, I wanted to revisit the issue.

A 0.68 diameter ball travelling 300 ft per second would block the beam of an optical gate for roughly 0.000189 seconds. If the output of the gate is used to trigger a 20 MHz timer it would collect something like 3778 samples, with each sample representing around 0.08 ft/sec.

What else needs to be considered? The width of the gate beam, the speed of the gate, is the beam blocked at max ball diameter, true diameter of the ball... I would guess that the ball diameter would be the biggest issue. If one ball is 0.005" inches larger than another the velocity calculation would be off by about 2 fps.

Does anyone know if the ball retains it's shape as it travels down the barrel? If the balls were to have different amounts of squish as they scooted down the barrel it would cause even more troubles with the calculations.

Anything else? I might start with two gates and see how the numbers compare... depends on the amount of free time I have.

Thanks for any suggestions.

[AGD]

The ball does retain its shape but balls are not round to begin with either. Nice idea and probably doable, might have problems with noise like the ball shape though.

AGD

[athomas]

Ball noise would definately be a problem. Everytime you shot an "egg" shaped ball it would be very inaccurate. I would go with the leading or trailing edge method if I was using optical sensors.

How about sonic sensors? I'm not sure how fast they can be polled but they can be very accurate if you get the right ones. This allows you to measure the speed of the ball as it moves away from you much like a radar sensor. It would measure a difference in ball position vs time and calculate the velocity of the ball.