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Simple High-Speed photography

A place to ask general spud cannon related questions.
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Unread postAuthor: rp181 » Fri Jan 09, 2009 5:11 pm

@ jimmy
I think it depends on the object that you get shocked on, whether its a smooth object or a sharp object. Sharp usually give me a stonger reaction (even if it doesn't break skin). When i got shocked from a open fuse box, i felt the "resistance" and how much
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Unread postAuthor: john bunsenburner » Fri Jan 09, 2009 5:19 pm

Great now we have a masorhistic (ok i know i mis-spelt that) how to for cameras, I am sure this will be very helpful when it comes to making high speed pics :twisted: :roll: ! We should have a thread hjacking competition with all other forums(besides certain ones which should not really be mentioned) on the net! I bet we would win!
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Unread postAuthor: Insomniac » Fri Jan 09, 2009 6:43 pm

Oi! Back on topic, NOW! :lol:

I'm still on holidays, but have managed to get my hands on a computer (now with dial-up!)

@Fishboy:
Those pics came out pretty damn well, particularly the one with the hackey sack. It's interesting how it has twisted and rippled with the stress of firing. I wonder if a barrel full of water would be enough to trip the wire (maybe attach somthing to the wire to add some drag???)

Can't wait to get home to build my sound trigger.
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I wonder how much deeper the ocean would be without sponges.
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Unread postAuthor: jimmy101 » Sat Jan 10, 2009 1:26 pm

rp181 wrote:@ jimmy
I think it depends on the object that you get shocked on, whether its a smooth object or a sharp object. Sharp usually give me a stonger reaction (even if it doesn't break skin). When i got shocked from a open fuse box, i felt the "resistance" and how much

Yes, a sharp point will tend to give a much worse shock than a dull surface since the shapr point penetrates the skin a small amount and gives much lower resistance.

I've zapped my self a couple times by picking up a photoflash board and having the sharp cut leads on the bottom of the board jab into my finger :shock:
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Unread postAuthor: rp181 » Sun Jan 11, 2009 10:23 am

Once i got shocked and there was a burn inside my skin, not on the surface, but not past the skin.
Anyway,
It might me useful to have a 2 strobe system. It will help to see what the projectile flight is like (is it flipping?) and speed with one of those black and white striped backgrounds.
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Unread postAuthor: SpudFarm » Sun Jan 11, 2009 11:15 am

any possibility that you can try to get a picture of a electric spark?
it is pretty interesting because you can see the air around it vaporize (Plasma?).
i have a video of this on youtube, but does not have enough knowlege on electric stuff to say what happends.

mabe try to get a picture of the spark that actuate the setup. or just find a clever setup from the back of your head :)
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Unread postAuthor: rp181 » Sun Jan 11, 2009 1:00 pm

I can get still frames from a video of a spark, as well as a long exposure. It doesn't look different. look at tesladownunder's site, he has alot of pictures.
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Unread postAuthor: Insomniac » Fri Jan 16, 2009 4:59 am

Got nearly everything I need for my flash trigger today, just need to wait for the MOC3020 to arrive. Gonna scrap the photo-sensitive part of the circuit for simplicity.

Now, I've just got to remember not to plug the flash's trigger into the mic port :shock: .


@jimmy101 (if you are still following this topic)

Can you explain to me how come my meter reads around 60V on the flash trigger, and not the 300V you say is present? My understanding is that putting a resistor into a circuit will drop the voltage down. If the 300V caps are behind a large resistor, wouldn't that drop the V to what it says on my meter? If this isn't correct, then wouldn't meters give very innacurate measurments on complex circuits with lots of resistors?
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Unread postAuthor: jimmy101 » Fri Jan 16, 2009 12:04 pm

Insomniac wrote:@jimmy101 (if you are still following this topic)

Can you explain to me how come my meter reads around 60V on the flash trigger, and not the 300V you say is present? My understanding is that putting a resistor into a circuit will drop the voltage down. If the 300V caps are behind a large resistor, wouldn't that drop the V to what it says on my meter? If this isn't correct, then wouldn't meters give very innacurate measurments on complex circuits with lots of resistors?

The main 300V cap (C2 in the diagram below) is not "behind a resistor" but the small 0.022uF trigger cap(C3) is behind a 1 megaohm resistor (R3). Both caps get charged to >300V. The big-ass resistor (R3) in series with the small cap is to keep the big cap from discharging through the trigger circuit. If the big cap did discharge through the trigger circuit the HV transformer (the one that takes 300V to ~10KV) would probably explode.

Image
(Image from Sixmhz's pages)

The trigger switch is in series with the small cap and the trigger transformer. When you connect a DVM to the switch contacts you discharge the trigger cap through the trigger coil (T2) and the DVM very quickly, RC=(0.022uF)(10Meg)=0.22 seconds (assuming the DVM's internal resistance is 10Meg). Once the trigger cap is discharged you now have the big-ass cap discharging through the 1Meg resistor and the 1 to 10 Meg internal resistance of the DVM. That forms a voltage divider and what the DVM reads is the 300V times the DVM's resistance divided by the sum of the two resistances. That drops the apparent voltage down into the 60V range.

In circuits in general you have to be very careful of any readings with a volt meter. Usually, the internal resistance of the meter is much grater than the circuits so the circuit doesn't even notice the meter. In some cases however, the circuits resistance (actually, more precisely it's impedance) is large enough, and close enough to the meter's, that you will get inaccurate readings. Usually though the 1 to 10 megaohm resistance of the meter is high enough that the readings are OK since megaohm resistors aren't all that common in circuits.
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Unread postAuthor: Insomniac » Fri Jan 16, 2009 4:31 pm

So basicly, the tiny trigger cap can't supply the 300V for long enough for the meter to get a reading, so you end up reading the voltage present (supplied by the main cap) between the camera's big resistor, and the one in the meter. Once you take the meter away there is no longer the second resistor present, so the voltage dividor dissapears and you are left with the regular 300v. Correct?
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Unread postAuthor: rp181 » Fri Jan 16, 2009 6:53 pm

Yes. Multimeter's are passive in voltage mode. That means they pull current (a very small amount) to measure it. When there is a small capacitor, it drains the capacitor. Multimeter's will also drain bigger capacistors (try it with the photoflash) and you will see the voltage go down slowly.
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Unread postAuthor: Hotwired » Fri Jan 16, 2009 7:11 pm

Indeedy.

I have a tiny flash camera charging circuit which consists of the original transformer, the transistor, an original diode, two bought resistors plus an LED and it can overcharge a 300V flash capacitor to around 450V as long as you're not trying to follow it with a meter attached.

With a meter attached it can only make it to around 320V or so as well as charging a little more slowly.

[quote=SpudFarm]mabe try to get a picture of the spark that actuate the setup[/quote]

It's not that impressive. Looks exactly like the tiny spark you'd get from a 9V battery.
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Unread postAuthor: Insomniac » Sat Jan 17, 2009 11:11 pm

While I wait for the parts I figured I would mess around with the camera anyway. Here are the results (0.5 sec explosures of mini spudgun minus the barrel)

Image
Image
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This one had a tea-light candle on top.
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This one didn't.
Image
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I wonder how much deeper the ocean would be without sponges.
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Unread postAuthor: starman » Sat Jan 17, 2009 11:23 pm

WOww, those are beautiful!! A couple of those trimmed right would make awesome computer desktop wallpaper.

How again are you synchro-triggering your camera/spudder? What is the black you are using for your background?

EDIT: OK sorry I just reread your original post on the synchro-trigger. I would like to figure a way to trigger my digital camera to do this.
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Last edited by starman on Sat Jan 17, 2009 11:27 pm, edited 1 time in total.
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Unread postAuthor: FishBoy » Sat Jan 17, 2009 11:27 pm

very cool. how much did the sound trigger setup cost?
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