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DC motor as fan

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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DC motor as fan

Unread postAuthor: strangers » Sat Oct 27, 2007 9:45 pm

I had heard that dc motors used for chamber fans could cause sparks and prematurely ignite the fuel in a potato gun, and I was wondering is this statement is true for small DC motors from things like R/C cars?
See I have this DC motor with the shaft ducttaped to a set of little fan blades from a Legos set and was wondering if I could safely mount it in a 4" cleanout cap.
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Unread postAuthor: cwazy1 » Sat Oct 27, 2007 10:02 pm

why not just get a 80mm case fan? all new models are brushless and will not spark
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Unread postAuthor: hi » Sat Oct 27, 2007 10:03 pm

yes. the reson it could ignite is because a brushed motor creates sparks while its running. This is why I personally use brushless motors in my cannons, though i have seen cannons with brushed motors. chances are it wont ignite, but it is possible.

motors in an RC car is garenteed to be a brushed motor unless you puchesed it sepratly and it specificly says "brushless".

you can get a DC brushless computer fan for about $5, which is $5 well spent in my opinion.
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Unread postAuthor: strangers » Sat Oct 27, 2007 10:20 pm

The only place I can get PC fans around here is a crappy, third-rate computer repair shop and the fans I get there crap out after the first few shots and start smoking and making crackling sounds so that out the question, any alternatives?
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Unread postAuthor: hi » Sat Oct 27, 2007 10:33 pm

your car fan has some slits on the side to help cool it off. if you can seal those off it should be fine.

i know DR takes apart though personal fans that you get at wal-mart. they use DC fans, but they have a plastic outer caseing, which makes it safe.

again, the chance is small, but possible.

you dont have a radio shack or frys?
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 10:44 pm

Like hi said, silicone or similar over the slits in the motor.
Unless there is a place for the gas to get in it won't ignite the fuel.
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Unread postAuthor: strangers » Sat Oct 27, 2007 11:11 pm

Yeah, I have an expensive Radioshack and a nonexistant budget :).
Well, what if the motor is wrapped in duct tape, that should work shouldn't it? Thanks for the help guys :thumbright: .
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 11:18 pm

strangers wrote:Yeah, I have an expensive Radioshack and a nonexistant budget :).
Well, what if the motor is wrapped in duct tape, that should work shouldn't it? Thanks for the help guys :thumbright: .


Yes that should work, make sure it is wrapped tightly.
Oh and just in case make sure not to aim at anything of value when you switch the fan on for the first time :wink:

Edit: Maybe one could use a sparking motor for an ignition source?
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Last edited by Novacastrian on Sat Oct 27, 2007 11:41 pm, edited 1 time in total.
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Unread postAuthor: ammosmoke » Sat Oct 27, 2007 11:31 pm

UMMMM.... you may want to also cover the rear and front of the motor, because those usually have slots next to where the brushes go in, and the front has mounting holes for screws. You are better off getting one of those cheap little motors from a crappy airsoft gun (preferably broken) or one of those cheap cardboard solar car kits that are in the "science" toy section of target.

EDIT: I just tested one of those motors in pure darkness, (mabuchi motor) and there were no visible sparks whatsoever. So yeah, if you cannabalize pretty much any moving toy, you will find one of these motors. And they will probably be mabuchi too lol..
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Unread postAuthor: mark.f » Sun Oct 28, 2007 9:11 am

It really depends on what type of motor it is and what type of current is hooked up to it.

A small DC motor running in standard alkaline batteries usually doesn't create sparks. But, my friends battery drill lights up like a Christmas tree whenever you drill into anything. It all depends on the design and current.

I'd just seal the motor with a piece of PVC, with a hole for the fan shaft to come out of, if you're worried. I think some silicone over the vents in the fan should work. Just don't run it too long, as I think those slits are made to do something. :wink:

EDIT - removed inadvertent middle english from post. :P
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Unread postAuthor: ammosmoke » Sun Oct 28, 2007 4:32 pm

I hooked it up to a 9v battery, and it was spinning at crazy rpms, so I think it would be fine. The power rating for the motor is actually 4v, so that's pretty good. I don't see why you would even want to use more than a 9v anyways.
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Unread postAuthor: strangers » Sun Oct 28, 2007 9:27 pm

Well, I managed to test it today and it worked like a charm. Ran it on 4AA batteries, I could feel the air coming out of the end of the barrel, that thing can really move some air. I just hope this one lasts longer.
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Unread postAuthor: miskaman » Sun Oct 28, 2007 10:03 pm

Try newegg.com. The cheapest fan there is $3 and the cheapest brushless I believe is about $6. Shipping to me is about $4.
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Unread postAuthor: strangers » Sun Oct 28, 2007 10:13 pm

I can't order anything online, period.
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Unread postAuthor: Hailfire753 » Sun Oct 28, 2007 10:15 pm

Hmm... This may have been sugested before, but mayby instead of avoiding the problem, it could be used to your advantage.

You could probably use the fan as your ignition. I have my doubts on how reliably this would work, and it might need some moddification to allow fuel into the spark area. It might take a while for it to spark as well.

You would just point the gun in the right direction, flip the fan switch, and it would mix the air a bit before sparking and igniting. Getto? Nahhhh....
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