Question for Tom re: Ball Exit Sensors

[bjjb99]

In the Dark Angel pressure data you've posted, there is a second curve representing output from a sensor that detects a ball exiting the barrel. I noticed that there is a very small but broad bump prior to the ball exit spike, from 4350 to around 4370 on the X axis. Any thoughts on what that bump might be? Is this instrument drift, or a measurement of a real effect?

Is the exit sensor an optically based, pressure based, mechanically based, or something else entirely? I'm curious if the pre-exit bump is the static air in the barrel, pushed out ahead of the ball. Some sensors might detect this while others would ignore it completely.

BJJB

[Redkey]

I'm guessing it's a pressure sensor. An optical sensor would be a sharp spike... since it's either on or off.

[AGD]

The small bumps are noise from the pressure sensor getting vibrations from the shot cycle. In this particular case the sensor was coming loose and I didn't catch it until a few tests later. The ball exit sensor is optical.

AGD

[Redkey]

Optical? Interesting. I've build a couple chronos using IR LEDs and phototransistors as optical gates and I get square waves out of the them. Is your optical sensor off-the-shelf or something you've built. I think I saw photos of your setup somewhere around here... I'll have to check.

[BlackVCG]

This one?

http://www.automags.org/~TomAGD/gundyno03.JPG

[AGD]

Most optical sensors are pulsed to eliminate stray light. Unfortunately they can't see fast events like the ball flying by. In the pic above I was using an Omron sensor with this problem but got around it by inserting a piece of foam rubber in the end of the barrel and letting the ball shoot it out. After this pic I just used one of our ace sensor boards to see the ball go by. That is what was used in the graph.

AGD

[FreshmanBob]

for your tests do you guys use normal paintballs or the synthetic nylon/whatever material ones? Seems like for all those tests the normal paintballs would get messy.

[AGD]

We only use nylon for these types of tests.

AGD