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Old 21st July 2015, 09:01 AM
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Monty Monty is offline
Senior Moment
Join Date: Aug 2013
Member of: Southampton Buccaneers, Basingstoke ARPC
Location: Southampton
Posts: 227

Thought I resurrect this thread. I've spent some time thinking about this challenge and researching a way to achieve it and think I've now located a design that would work. RobF's Mumford unit was great, but the delay on triggering the flash is just too long for what we needed.

My original view that the flash is the critical component has been established as the right approach, no camera can manage to take an image of a pellet in flight (unless you spend £squillions on a ultra high speed shutter) and everyone that I've found on line/spoken to is using the flash gun to determine the moment of exposure, the exposure duration and light intensity. The camera is of no consequence, the result would be the same on a £5k Nikon D4 or a £20 3rd hand iPhone 3. Even the fastest shutter speed on the D4 of 1/8000th is nowhere close to what's needed. I can get my flash to fire a 1/64000th exposure and even that's not fast enough to freeze the pellet, it will still travel 1-2 cm in that time, but I should get an image albeit a bit blurred if it works. Once I've proven the design I'll be on the scrounge for some super heavy weight .177 pellets to bring down the MV.

I need to pop into Maplins and pick up what looks to be a tenners worth of electronics and dig out my soldering iron but I think I've found a design that can trigger a flash with near zero delay, or at least fast enough that between sensing an event and the flash going off the pellet will only have travelled about 7-10cm at 780fps so I may have the opposite problem to the one I had last time and get images of a pellet that's only half way down a barrel, which will look exactly the same as a rifle that's not been fired! It looks like the sensor is sensitive enough that it doesn't need to be attached to the rifle, so if I place it the length of the barrel away from the trigger block it should get quite close to firing the flash as the pellet emerges (shock waves travel at 1115fps, pellet at 780fps so the difference should be close to eliminating the 7-10cm lag). Well, it seems to make sense in theory but may require some proper mathematics.

It's now on my list of projects so watch this space!

ISP Airstream MK III No 15 which is a bit poorly at the moment and having a rest
AA Pro Sport + Ginb FT8 stock + Bushnell 4200 6-24x
EV2 MK1 + Leupold Comp 40x
Weihrauch HW100 KT laminate

SBFTC Competition Secretary

Last edited by Monty; 21st July 2015 at 09:23 AM.
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