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Short question topic

A place to ask general spud cannon related questions.
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Re: Short question topic

Unread postAuthor: wyz2285 » Fri Jul 10, 2015 8:38 pm

Question:
How to remove anodizing from aluminium with house hold items? (Resources is not very good where I live, not even car battery acid is sold).
Also, how to remove heavy duty paint/powder baked paint from aluminium, also with basic resources.
Thanks.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Short question topic

Unread postAuthor: mark.f » Fri Jul 10, 2015 8:51 pm

Sanding drum, hand sander, needlegun, files... the list goes on. :D

How pretty does it have to look?
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Re: Short question topic

Unread postAuthor: equusvenustas » Fri Jul 10, 2015 9:41 pm

This occurred me but i don't know if it works i'm gonna test this right now. If the anodizing isn't too thick, you could prepare a weak NaCl solution and do some electrolysis, just connect the aluminium to be de-anodized to the anode, and a stainless steel electrode to the cathode and use 12 to 30v dc but be careful as this can etch too much or cause pitting also you can get shocked if you use 12 or more volts and you touch the electrodes with your hands soaked in electrolyte.

Edit: Nope, i just tried it it does remove the anodizing but if you connect the aluminium to the CATHODE as it produces sodium hydroxide but you will need a carbon anode and it will produce a lot of chlorine, to avoid that you could use sodium bicarbonate instead of NaCl still is an slow process.
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Re: Short question topic

Unread postAuthor: wyz2285 » Sat Jul 11, 2015 9:51 am

@mark.f I'm planning to re-anodize it with a different color so the surface need to be neat.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Short question topic

Unread postAuthor: Juggernaut12121 » Mon Jul 13, 2015 4:20 pm

I've seen people use degreaser cleaner and oven cleaner, either making a bath of it and constantly brushing off the anodizing for a few minutes or just spraying it on, letting it set for a while, and then wiping it off.


I was also wondering whether or not there was a limit to how far you could screw in threads. I have some Iron fittings and pipe and while threading it together one or two sections of the pipe seems to have been screwed into the fittings slightly farther than the female threads of the fitting reach.
I was just somewhat paranoid and wanted to know if there was any risk in having threads that do this, if they put any extra stress or strain on the pipe or fittings.
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Re: Short question topic

Unread postAuthor: vng21092 » Mon Jul 13, 2015 6:03 pm

hey guys, quick question. How will I know when I've broken the sound barrier? When I aim my gun at a tree far away and fire, I get a very distinct uh.. crack? It's pretty loud, it echoes. But I'm putting in my data into GGDT and I'm coming up with 887 FPS, and speed of sound is around 1000? I threw up a little video of it in my basement, not sure if you can tell from the video, but it's actually pretty loud http://www.spudfiles.com/pneumatic-cannon-database/topic26230.html#p379648
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Last edited by vng21092 on Mon Jul 13, 2015 6:10 pm, edited 1 time in total.

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Re: Short question topic

Unread postAuthor: Juggernaut12121 » Mon Jul 13, 2015 6:09 pm

You can try and find out how fast it's going, set up some sort of backdrop that allows you to both see the projectile and track how far it's going (set up sections on the back drop with known distances). Take a video of a shot and look at it frame by frame. I'm sure you can do the math from there so I'll shut up. By the way awesome job on at least coming close to breaking the sound barrier!
(Also, speed of sound varies with a few variables such as temperature and I think air pressure, but it's usually around 1100 fps)

Edit: I hadn't realized it was a 4.5mm, it may be hard to figure out the speed that way considering the projectile is a little small. Otherwise I would recommend setting up a microphone and figuring the speed using the sound of the muzzle blast and the sound of the projectile hitting the target but if it's supersonic then it will probably complicate that process, either one's worth a try I guess
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Re: Short question topic

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Re: Short question topic

Unread postAuthor: vng21092 » Mon Jul 13, 2015 6:17 pm

haha thanks, I plan on making a few adjustments to it in the coming weeks or so, extending the chamber and barrel, also upping the projectile diameter to 8mm. I just plugged the values into GGDT and I've gotta say, I'm very very excited to see what it could do if it does what GGDT says it will (1142 FPS :shock: ) Image
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Re: Short question topic

Unread postAuthor: Juggernaut12121 » Mon Jul 13, 2015 6:18 pm

Can't wait to see such a thing :D
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Re: Short question topic

Unread postAuthor: jimmy101 » Tue Jul 14, 2015 2:37 pm

Sound is your best, and cheapest, method of estimating the velocity. Video is way to slow, at the standard 30 frames per second a 1000 FPS projectile will move 33 feet each frame. No matter how big the round is getting an accurate measurement is going to be difficult.

Even a cheapo PC sound card samples roughly 1000 times faster than standard video. Lets see, mic (or an entire laptop) within a couple inches of muzzle, figure 10 feet from muzzle to target and round moving at 1000 FPS (slightly subsonic). The sound of the round hitting the target will get back to the mic 18 milliseconds after the muzzle blast. Sound card sampling at 40 KHz gives a data point every 0.025 milliseconds, so the measurement error is down around 1 part in 720, that's roughly 1.5 FPS at 1000 FPS. A bit'o math to back calculate when the round hit the target and you can calculate the average velocity over that 10' range.

The only thing remotely tricky about using a sound card is that echoes can confuse things. If you shoot outdoors away from large flat surfaces (like buildings) then echoes are reduced. Shooting in a small space like a garage can give echoes that make things hard to sort out.
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Re: Short question topic

Unread postAuthor: wyz2285 » Fri Jul 31, 2015 3:02 pm

I'm trying to make an ANPEQ style thingy with a IR laser and IR torch since the real thing is expensive and illegal as hell. I have an 7.4v lipo and I need to power the 5v laser and 1.5v torch with it, is it possible to make a voltage divider with just resistors? The laser is 1.3Mohm and the torch is 1.1Mohm.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Short question topic

Unread postAuthor: mark.f » Fri Jul 31, 2015 9:37 pm

wyz2285 wrote:I'm trying to make an ANPEQ style thingy with a IR laser and IR torch since the real thing is expensive and illegal as hell. I have an 7.4v lipo and I need to power the 5v laser and 1.5v torch with it, is it possible to make a voltage divider with just resistors? The laser is 1.3Mohm and the torch is 1.1Mohm.


Don't use a voltage ladder for supply. Use a voltage regulator, a 5V one for the laser and a variable one with the correct resistor values installed for the torch.

And they're expensive for a reason. :D Although 1/2 MOA is rather disappointing given their fiddliness... also, what's the power output of your laser?
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Re: Short question topic

Unread postAuthor: wyz2285 » Mon Aug 03, 2015 2:36 pm

Disassembled a 8.4v 7cell nimh into a 4cell one for the laser and torch. The laser is pretty weak, 200mW.
Why are they so expensive? I know the laser is quite high powered but for 40USD one can easily buy a paper burning laser..
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Short question topic

Unread postAuthor: mark.f » Mon Aug 03, 2015 9:07 pm

Well, putting it into a finely adjustable carriage that can withstand dings and drops is another thing. Other than that it's probably a mixture of the $800 toilet seat thing and the materials used.

I would incorporate the "low power" mode if you decide to use a higher power diode, as IR has the annoying disadvantage of being invisible to the naked eye ( mostly).
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Re: Short question topic

Unread postAuthor: vng21092 » Tue Aug 04, 2015 3:12 pm

sorry for hi-jacking the thread guys, just a quick question. I'm ordering a new tank that comes preset at 800 psi, and I have a 1/4 ball valve that has a maximum pressure rating at 400 psi, I have a 1/2 ball valve thats rated around 1000 but it's really bulky so I'd rather go with the 1/4. How safe is this? On top of that, I'm pretty sure the preset probably won't be EXACTLY 800 psi, do you think it would be under or over? Here is the tank I ordered in case anyone has it and can tell me.
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