Science Fair and first Combustion Launcher

[RabidDuck]

Wow. How do install a fan? Also making a chorny looks a little to complicated/confusing for me. I have never made anything electronic from scratch. So you suggest adding a fan, researching fuel %, and making a chorny? I can't thank you guys enough!
~RabidDuck

[jimmy101]

1. Do you have a laptop (or an old computer) you can setup in the garage?
2. Do you have a microphone for the computer?
If yes two both questions then you have everything you need for a simple, but accurate, shooting chrony.

Take a look at Burnt Latke's pages for one way to install a fan. You don't need the timer circuit.

I prefer a small brushless CPU fan, which can be run from a 9V battery. You need something like an L-bracket and a couple nuts and bolts. The fan is bolted to the bracket, the bracket to the inside of the chamber. Connect the fan wires to the bolts that go through the chamber wall. Connect tha battery to the bolts on the outside of the chamber. Latke shows two fans, I prefer the smaller type. See latke's pages for details.

You can just connect the wires to a 9V battery clip (RadioShack). Clip and unclip the battery to turn the fan on and off.

A super cheapo fan like these will also work;
http://www.personalfans.com/Merchant2/m ... ry_Code=BF
http://www.personalfans.com/Merchant2/m ... ry_Code=BF
http://www.personalfans.com/Merchant2/m ... ry_Code=BF

Wander around in the local junk stores (Kmart, Target, Meijer etc.) and you'll probably find something like the above fans.

[RabidDuck]

Yes i have a Lap top and microphone. Is there a tutorial on how to set that up? TUTORIALS ARE GREAT! Lol So for those little cheap fans, i would load my projectile, put in my propane, blow the fan in there for 1 or 2 seconds put on the end cap and fire? Also i did the calculations. My chambers volume is 64 ounces. It converts to 1892.71 milliliters. So i took that and times it by .04 or 4% 75.71 milliliters. That sounds like too much propane to put in. Am i doing this right? Also for your propane meter starman how did you connect the ball valve to your chamber?
~RabidDuck

[starman]

You should leave the fan running while you fire...makes a difference. If you meter propane you won't really have the need to have the cleanout. You can just install a ball valve that will allow air in when refueling. Just be sure to close it before fueling and firing.

[jimmy101]

Read the spudwiki on chronometers; http://www.spudfiles.com/spud_wiki/inde ... hronometer

Just set the MIC equi-distant from the muzzle and target. Use Audacity (google and download it) to record the firing. In audacity measure the time between the round exiting the barrel and the round hitting the target. The average velocity over that distance is just the time divided by the distance from the muzzle to the target.

Read the files associated with SoftChrono. (http://talonairgun.com/forum/viewforum.php?f=16)

The fan should be permanently (and rigidly) mounted inside the chamber. Inject your fuel with the chamber closed up via a syringe or fuel meter. Turn the fan on and let it run for a couple seconds. Fire the gun with the fan still running.

Yes, your numbers are correct, 76ml is 4% of 1900ml. This assumes the 76ml is at the same pressure as the 1900ml.

[RabidDuck]

Ok i am getting there. So i have the injection part of the meter done i just need to set the cannon up for it. So instead of a clean out cap what do i put on there? if i have threads there it it ok? After the other cap is on how do i put the ball valve on? This is going to be awesome And about the fan, so once i mount it inside i run the wires out from where? and what should i use to turn the fan on and off? I saw someone had said just a 9 volt battery but i just wan2 see if there is a better or easier way.
Thanks
~RabidDuck

[jimmy101]

Keep the threaded cleanout as the breech of the gun. I wouldn't use a ball valve since you still need to get into the chamber for servicing (replacing fan, examining the spark gap etc.).

You could use threaded fitting to attach the ball valve to the gun but that is probably more work, and $$$, than it is worth. The main advantage of the ball valve is the somewhat faster cycling time. In your case, that isn't important.

Meters are usually plumbed to the chamber either with a 1/4" brass fitting or with a schrader type valve.

No more answers concerning the fan from me. Read Latke's fan page, it explains everything.

[jimmy101]

waffles (duplicate post deleted)

[RabidDuck]

OK everything is done except for the fan! i attached a quick connect to the clean out cap so i can now inject the propane. So i don't understand on how much propane to inject? What PSI is 76 ml? Or how do i measure with the propane meter? The only question about the fan is where do i have the wires coming out from and what to use as a on/off switch? Thank you all! I will be making a new thread for the pictures, data, and videos.
~RabidDuck

[psycix]

An on/off switch can be just any sort of switch, or if you cant find such a thing, just connect the wires.
Most people connect the wiring this way:
Holes are drilled through pvc, bolts or screws are tapped in (airtight!), just like most sparkgaps are made.
Then wire the fan to the two bolts on the inside, and wire the battery to the same bolts, but then on the outside.
That way you have a secure and airtight way of getting those wires to your fan.

Have you already read the spud wiki?
You should definitely check out the chamber fan and fuel meter pages, they will answer most of your questions.

Another way of mounting the fan into the chamber instead of bolting it down with brackets is by simply sanding down the fan to the right size and then squeezing it in. This is also described on the chamber fan page in the spudwiki.

[RabidDuck]

Ok sorry i've been working on other things and haven't been able to get on for a while. I have everything done now. But i just need to know which way to put the fan in? Do i make it so it blows air towards the front or backwards? I have a good set up with alligator clips for the battery but i just need which the fan faces.
Thanks

[roboman]

It doesn't really matter, since you can just reverse the polarity, and the fan will reverse. If I were you, I would hook up a DPDT toggle switch so that it will act as a direction control for the motor. Also, don't use alligator clips. Instead, use the proper battery holder/snap for your battery. Also, solder all of your electrical connections. It's really worthwhile, since you don't have to worry about loose or incomplete connections.

[starman]

It doesn't really matter, since you can just reverse the polarity, and the fan will reverse.

It does matter...computer fans are not bi-directional. Reversing voltage polarity simply results in no fan blade movement at all.

[jimmy101]

Usually people point the fan towards the front of the gun. With a small fan it probably doesn't really matter all that much.

[RabidDuck]

Ok thanks for all the help! I have a radar gun and am testing it tomorrow morning. I will put up pictures when i get a chance. You guys have been a big help. Thanks again
~Rabbid