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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: jackssmirkingrevenge » Tue Jul 17, 2018 6:02 am

mrfoo wrote:When I worked for a certain airline, I won't give names but it was one of the ones who had a fleet of Concordes and wasn't french


Oh come on man, why do you have to be so vague? Was it Ethiopian Airlines?
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: Short question topic

Unread postAuthor: hectmarr » Tue Jul 17, 2018 9:59 am

I bought a Chinese 12vol compressor, and it is a TRASH! I was thinking about trying to build a small electric compressor with this old glow motor .21. Has anyone tried it? works?
In the glow plug it is replaced by a small check valve, and the shaft is driven by a powerful electric motor, of the brushless type, by a reduction, and powered by a pack of lithium polymer batteries. It would work like a small high-rev pump. The electric motor has 40,000 rpm and about 700 W,
The carburetor would be necessary only to vacuum the necessary lubricant.
The complicated part is already done. Maybe with a bigger glow engine ... I do not know.
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Re: Short question topic

Unread postAuthor: mrfoo » Tue Jul 17, 2018 10:33 am

Has anyone tried it? works?

Yep, it works as a dirty hack, but you'll only get low pressure from it. The absolute maximum pressure you can theoretically achieve will be ambient atmospheric x motor compression ratio once the ports are closed. Generally, for a 2 stroke model engine that's gonna be around 7:1 max, so you'll maybe get something approaching 7 bar "stock", perhaps more if you resleeve to eliminate the exhaust port and work hard to minimise dead volume in the cylinder.

If you're machining, why not machine something better...
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Re: Short question topic

Unread postAuthor: hectmarr » Tue Jul 17, 2018 11:17 am

mrfoo wrote:
Has anyone tried it? works?

Yep, it works as a dirty hack, but you'll only get low pressure from it. The absolute maximum pressure you can theoretically achieve will be ambient atmospheric x motor compression ratio once the ports are closed. Generally, for a 2 stroke model engine that's gonna be around 7:1 max, so you'll maybe get something approaching 7 bar "stock", perhaps more if you resleeve to eliminate the exhaust port and work hard to minimise dead volume in the cylinder.

If you're machining, why not machine something better...

Good data what you tell me. Actually it is not for high pressure. With 5 bar that is what I need, it would be fine. The question is to use all this that I have thrown in my workshop. The important thing is that it is as small as possible. The Chinese garbage I bought, I'm stupid, :oops: makes the pressure rise only at 3 bar and it gets very hot. I've already burned the engine alone in an afternoon of playing with it to test it. Luckily it is very little price.
Machining is not in my possibilities. Maybe I'll go for one of better quality directly.
I leave a picture of the compressor garbage. I have disarmed it to see the problem, and the problem is EVERYTHING. The engine smells like burning.
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Re: Short question topic

Unread postAuthor: farcticox1 » Tue Jul 17, 2018 1:35 pm

I had the same one, got it up to 120 psi once and it cooked it

These are good for at least 100 psi

s-l500.jpg
s-l500.jpg (25.63 KiB) Viewed 273 times


https://www.ebay.ca/itm/Viair-92C-Chrom ... c&_ipg=200
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Re: Short question topic

Unread postAuthor: hectmarr » Tue Jul 17, 2018 3:16 pm

You were lucky ... mine only reached 60 psi and from there it never happened ... It would be enough in terms of pressure, but it seems great to put in the weapon.
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Re: Short question topic

Unread postAuthor: hectmarr » Wed Jul 18, 2018 5:47 pm

Recycling motor compressor refrigerator, works perfectly :) to compress some air in an old steel MAPP can. Luck that Jack followed him ami, because it solves the fact of trying some small hybrid without manual pump.
I use a push button to avoid forgetting on the compressor ... It takes 35 seconds to achieve 100 psi in this can. I'm waiting for the pressure gauge to reach me from 0 -20 bar to reach about 14 or 15 bar.
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Re: Short question topic

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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Thu Jul 19, 2018 2:21 am

See, it was easy! Welcome to the fridge compressor master race :D
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Re: Short question topic

Unread postAuthor: farcticox1 » Thu Jul 19, 2018 6:27 am

I do find that a precharge helps a lot, my aircon compressor is like 4x faster to build up with 20psi input. Can help to achieve higher pressures as well.
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Re: Short question topic

Unread postAuthor: hectmarr » Thu Jul 19, 2018 8:29 am

farcticox1 wrote:I do find that a precharge helps a lot, my aircon compressor is like 4x faster to build up with 20psi input. Can help to achieve higher pressures as well.

Do you speak of using two stages? Two refrigerator compressors in series?
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Re: Short question topic

Unread postAuthor: mrfoo » Thu Jul 19, 2018 9:09 am

Yes, stage 1 low(ish) pressure high volume stage 2 high pressure low volume (fridge compressor).

It's a shame you're so far away, I have a 2 cylinder 2hp compressor head and motor I'd happily give you.
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Re: Short question topic

Unread postAuthor: hectmarr » Thu Jul 19, 2018 9:57 am

mrfoo wrote:Yes, stage 1 low(ish) pressure high volume stage 2 high pressure low volume (fridge compressor).

It's a shame you're so far away, I have a 2 cylinder 2hp compressor head and motor I'd happily give you.

Thank you very much for the intention although we are half a planet away! :shock:
I have a 2hp compressor, and 25 liters of tank capacity. It is for a "normal" use. The red pressure scale starts at 100 psi. I can not ask for more because it could be dangerous ....
I'm going to see what I find to use in the first stage, although I have to do some numbers so that they fit correctly in terms of volumetric flow especially. 8)
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Re: Short question topic

Unread postAuthor: farcticox1 » Thu Jul 19, 2018 1:31 pm

I use a regular compressor for the first stage

1.jpg


...........20psi.........................................................180psi
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Re: Short question topic

Unread postAuthor: hectmarr » Thu Jul 19, 2018 4:19 pm

I'm going to try, when the new pressure gauge reaches me, as my first stage, my big compressor and the refrigerator compressor motor as the second one, to see what happens. Thank you farcticox1 for the clarification. :)
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Re: Short question topic

Unread postAuthor: farcticox1 » Sun Jul 22, 2018 8:50 am

Has anyone got any 0.177 pellets they could get a measurement off. I am looking for an accurate measurement of the skirt, probably need a digital gauge. Something like 4.600mm

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