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Old 28th October 2015, 11:06 AM
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Brian.Samson Brian.Samson is offline
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Join Date: Jun 2009
Member of: Pontefract, Doncaster Airgun Range
Location: Doncaster
Posts: 2,336

Originally Posted by DEAN C. View Post
Hi Brian,

Great idea and you should be applauded for doing this, and I think it will set the standards for years to come, worldwide.

Just a thought but rather than involving momentum in calibrating, would simple pressure calcs not work ie P = Force over area? Would that not equate to a known Ft/lb energy or metric equivalent in KPa? You might be able to capture a max pressure reading on a gauge that way using some kind of small pneumatic linear actuator (sealed ram) for calibrating.

This would take frontal area and mass x gravity into account or is there more to it? Maybe its my simplistic engineers head that might have missed something out, but well done anyway and I'll be interested in the results.

Yeah possibly Dean.

The important thing (I think) is not to set the device up to deliver 5fpe of kinetic energy and assume that 5fpe of kinetic energy with a steel probe hitting a paddle will be exactly the same as 5fpe of kinetic energy of a pellet hitting a paddle. When a pellet hits the paddle it squashes flat - squashing a pellet flat uses energy, so the amount of kinetic energy transferred to the paddle will be quite different between the two types of collision.

What I'm going to try to do is calibrate the device based on effect.. so calibrate it so that it has exactly the same effect as a pellet hitting the paddle, but not calibrate it so that it has the same Kinetic energy.

Once I have that calibrated, then all I need to do is come up with a method of making sure other devices are delivering the same energy/momentum/force.. whatever it is we want to use as a benchmark really, I don't think it matters too much.

There are two types of calibration I need to do though...

Firstly, for the devices used at the Worlds I need those to be set up fairly accurately, so yeah, I could make sure the plunger/piston has the same mass and use a combro to make sure they have the same velocity and have reasonable confidence that all the devices would be about the same.

But... for people just making them for use at their own local club, I probably need a far simpler, less expensive and possibly less accurate way of make sure they're putting out the same sort of momentum as the calibrated devices used at the Worlds.

Cheap, Simple, Globally accessible, doesn't matter if it's not too accurate. (are Combro's a global thing or they mainly UK only?)
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