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Member Since 26 Sep 2008
Offline Last Active Nov 18 2013 06:09 PM

Posts I've Made

In Topic: Bob long says

31 October 2013 - 02:13 PM

"we're not causing no friction"


Does that mean they are causing friction?

In Topic: Chronograph calibration / precision experiment suggestion.

26 September 2013 - 02:57 PM

I'm not sure I followed what you were trying to say, but I concede that there's no reason to use a paintball marker to test velocity.  If you know the distance a projectile crosses between two switch points, you can use output relays from each switch to start and stop a timer.  Then you can calculate velocity by the distance divided by the time.  Did you mean error induced by the accuracy of the switch response?  That's a point I'd potentially concede with a photoelectric switch.


The timing chips on Doppler devices are, at least, suspected to drift over time (which, if that suspicion is true, could cause them to be less accurate). Can we guarantee that the photoelectric method of measuring distance traveled over time doesn't have the same problems?


The problem is that you are using one device (like the photo electric based shooting chrony that both punkworks and I use) with a % of uncertainty to calibrate a device that has it's own, much higher, % of uncertainty measuring the speed of an object that has an speed with an unknown % of certainty.


Where are your controls? We can conduct the above experiment, then feed all the results (assuming we have enough data) into an ANNOVA and figure out what's going on... BUT, I prefer to run experiments as cleanly as possible.


I don't think that we should rely on anything that uses a timing chip as a control... if we can help it. I suggested dropping a ball from a known height, so we can calculate it's speed at any position on it's fall path given it's distance and rate of acceleration. We can compare the accuracy of a photoelectric device with our, estimated, speed projections and eliminate the possibility of timing chip drift effecting the measured speed (or we could adjust accordingly). This method will, also, give us the added benefit of being repeatable all over the country. Anyone with an object of sufficient density and low surface area could give us data. I could test my shooting chrony in my garage, you could test your handheld Doppler, someone could use a radar gun, etc.

In Topic: Chronograph calibration / precision experiment suggestion.

25 September 2013 - 11:37 AM



high speed camera against a back drop of black and white lines to determine distance over time, similar to what you see on myth busters could calculate an exact velocity.

i already said why this wont work.


Yeah, I think you're going to be better off with an instrument that will switch on/off a relay when the paintball passes or makes contact with an object.  It would seem like two photo eyes switching a timer across a known distance apart could work if you can measure the distance in a range where the paintball is not dropping significantly.  Either that, or the sensitivity of the eye would need to cover a broad vertical range without generating false positives.  That's the cheapest solution I can come up with, though I don't think it's going to be as accurate as a pressure plate switch.



The object's speed being measured needs to be calibrated, using a marker to shoot a projectile introduces another, unnecessary, variable.

In Topic: Chronograph calibration / precision experiment suggestion.

17 September 2013 - 04:26 PM

I think the best way to do this is to calibrate the object that you are taking the speed of. I suggest dropping a steel ball from a fixed height.


Btw, after noticing a 20 fps deviation at the last field I played on between chronos, I'm very interested in the results. It's my understanding that the timing chips can "wander," unpredictably, over time in these devices... so readings between a new device and an old one may not be similar, even if they are the same model.

In Topic: LPR Question for Spool Valves

18 June 2013 - 09:49 AM

For the record, I'm not looking at either gun to buy, it was more just a thought that popped into my head and due to noe being incredibly familiar with any of the Dye designs I figured asking the crowd would help.
I'm perfectly happy with my shockers as well, and as far as i can tell, it is simply that the LPR in the design of the DM helps more than the it would in the shocker.
If I'm correct in my napkin engineer thinking, it is the same basic function as the solenoid inserts that drop the pressure on the shocker, just slightly more refined and tuneable. and that is why it would help more, the solenoid inserts already drop the pressure that functions the bolt and therefore the LPR already has its job done, and cant drop it much more.

You'll have to excuse me, because I haven't owned a shocker before... the closest I've gotten is a quest (which does have an LPR). How do the solenoid inserts drop the pressure?