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Mad strobe?

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vtsteam:
Hi to old friends! Sorry I've been away so long -- one of my periodic lapses! I've been building bows, so only woodwork this winter.

Lately I was thinking I'd really like to see what a bow and arrow was doing when it releases. I'd like to know what changes in design do to arrow speed at multiple moments during release. There are high speed consumer grade video cameras out there made by Casio that can shoot 1000 fps -- but the quality of the video isn't too great, and the price for a used one imported from japan is $120 -- on up. Unsure of quality and out of my price range at present.

I don't know what's available super cheap for multiple flash stop-action strobes either, but I suspect they aren't cheap. They'd have to charge a pretty big capacitor (I assume) to flash like 10 frames in maybe a 50th of a second. And some kind of programmable sophisticated interval timer circuit.

So then I was thinking of good old Muybridge with his multiple cameras fired by strings across a race track way back in photo history. Only could I do something similar with say, a bunch of old fashioned hot shoe camera flash units from ebay triggered by an Arduino board. I was thinking I could program in the intervals wanted, that way.

Does this seem feasible? I don't remember exactly how the flash shoe triggering worked, but I think it was just a switch -- is that right? Or was there a signal from the camera? "Hot" shoe does seem to imply a voltage. Anybody know specs if so?

I figure the time interval of interest -- might not be totally accurate, but here it is.... A very fast arrow from a wooden bow might reach 200 feet per second terminal velocity, and is about 28" long. Since it starts from zero, it averages about 100 ft/sec through the bow, and is about 2 feet long -- so as a guess roughly 1/50 second in the bow. Let's say 1/60th to be more conservative -- I don't know actually.

It would be nice to have an image every tenth of that -- ten images total -- so the intervals between flashes might be about 1/600 second. The flash duration itself should be as short as possible. I don't know how short a used flash unit can flash for, but a tenth of the interval would be nice. That's a duration of say 1/6000th second. No idea if that is possible -- anybody know?

That would mean the arrow traveled about 1/4" (if I'm figuring right) during the duration of the flash. At that rate the phot will be a little blurry, but maybe good enough to get a measurement of the distance from release, which is the main thing I'm interested in. Faster would obviously be better -- if you think that's possible....?

I think most of the automatic thyristor flashes for SLRs of the past adjusted the flash length -- which isn't something I want. Ideally it would just flash for one set duration, and flash as short as possible to still register on my digital camera set to a time exposure. The bow would be set against a black background and the distance to subject would be quite short. The arrow would have an automatic release.

I'm thinking an Arduino Uno R3 board (I have a few) and an interface digital switching board like this 8 channel job (well I guess that's 8 frames per photo, but acceptable). But I don't know if it would be fast enough:

http://www.ebay.com/itm/New-8-Channel-5V-Solid-State-Relay-Module-Board-OMRON-SSR-4-for-Arduino-/321866921038?hash=item

It seems possible to get older flash units in the $5 range on ebay:

http://www.ebay.com/sch/Flashes-/48515/i.html?_sop=15&Compatible%2520Brand=Universal

To me this whole idea seemed like a total maddmodder approach, so I just had to come back and ask you guys if  this seemed feasible to you, and if you had any suggestions or recommendations.

It is nice for me to tie bowmaking with this, my old favorite forum. I've felt kind of out of touch with you.

Steve

awemawson:
Steve, good to see you back from hibernation  :thumbup:

Tucked away in a cupboard somewhere I have a stand alone strobe unit that can be varied from several  seconds between flashes, up to freezing rotation of a part spinning at several thousand RPM. Uses a triggered neon tube iirc. They turn up on eBay for peanuts. The spectrum of the flash might be an issue, I presume that it's at the red end. Not sure if it would match the response of a digital camera too well?

Imagineering:
Most of the work in this field has been done and can be found on the Web. Basically the 2D sinusoidal path of the Arrow is complicated by changes in; Weight, Weight distribution, Length, Fletching length, Fletching height, Young's Modulus relating to the Shaft just for starters. Then there is the Resonant Frequency of the Bow & BowString to consider ... When we were playing around with all of this, we just gave up, (as it was doing our Heads in),   :doh:  and concentrated on what happened at the Target ...

vtsteam:
Hey Andrew! Do you have a mfr and type for something like that -- looking for something roughly $50 range. Not sure what to look for. Red is okay if it isn't infra-red out of the digital camera's usable spectrum. I'm not looking for fidelity, just position.

imagineering, not interested in the arrow flight or its physical nature, other than mass. An unfletched lumberyard dowel is fine. Only what the arrow and limbs are doing during the power cycle is of interest, as I said above. I'm building bows, not arrows. And what is of interest is seeing what an incremental change I make on a bow yields in actual photographed effects, not following predictions from somebody else's mathematical model. And yes the latter may be all over the net, but they change every few years and are the subject of continuing arguments.

I don't want a formula for someone else's bows built to their ideas of efficiency, I want time lapse photos of my own bows built to what I want out of a bow. Turns out my old eyes aren't good enough to record and memorize 8 images in a 60th of a second...  :lol:

awemawson:
Steve, mine was made yonks ago - probably in the 1950's from the black crackle paint finish - by Ferranti who I worked for for many years. I've seen the same design made by several of the defence companies so I suspect that it was an NPL design (National Physical Laboratory)

It used a tube like this one currently featuring on eBay, and is just a relaxation oscillator. Capacitor charges via a variable resistor, until the tube fires and discharges it.

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