This page created 05-08-2001 01:57:37

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gAss Rammer

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I came up with an idea for a combat robot weapon. I could build a light, powerful weapon that was also quite simple. (At least the idea was to have it be powerful.) I wanted to use air cylinders and power them with an air/fuel combustion, just like a gasoline engine. A gas powered ramming device.

I got the idea after helping my nephew build a tennis ball cannon out of pop cans. You squirt some lighter fluid in the stack of cans. Then cram a tennis ball in the end. Next you hold a lit match next to the igniter hole and it fires. It goes 20 or 30 feet straight up. Pretty good considering the compression ratio is 1:1.

So I thought I could do the same thing with an air cylinder and use it to drive a spike on a combat type robot.

After some thought I decided to use two cylinders. A small one to suck in the air/fuel mxiture and then compress it into the larger cylinder. Then a sparkplug would fire the mixture which will ram out the rod on the big cylinder. Then I would open the exhaust valve to let the cylinder return to starting position.

Seemed like it might work. But would it have enough power? Would it blow up in my face? Would it get hot and melt some of my parts? Only way to find out was to build it...

Bryan Anderson suggested that I drill some holes in the big cylinder at the far end of travel. These would work like exhaust ports on a 2-cycle gas engine. This solved one fear that I had. I didn't know what to do with extra pressure that would be developed. This will let it out at full travel. I'm sure this will give me the pleasant BANG!!! that I'm looking for.

I couldn't find anything that would match the threads of a sparkplug. So I made one from a 1/4" to 1/8" reducer, a steel screw and some epoxy plumber's putty.

If I can find some way to make a spark I can run my first test.

First Attempt

Initial concept. Two valves
and a model airplane
Next concept with single
Collection of cylinders.
Brian's idea to drill exhaust
ports at the end of travel.
Homemade sparkplug next to
lawnmower sparkplug.
Ready for initial test. Top
Ready for initial test. Side

Fire in the hole!!!

I went out to my garage in the middle of the night to find my "transformer" box. I think it has an ignition coil off a car. I didn't find it. But I found lots of other neat stuff that I forgot I had. Plus I found the weed-whacker size engine that I bought about 15 years ago.

So at about 4AM I went ot Walmart and bought a barbque grill igniter. It seemed to be firing my homemade sparkplug okay. So I found my can of lighter fluid and hooked the igniter to the sparkplug.

I squirted some lighter fluid into the exhaust port and pushed the piston back to about 1/2" of the bottom. I held the cylinder in one hand (Actually it was lying on my leg and I held it down with my hand) and held the ignitor in the other hand.

I clicked the ignitor. Nothing...

So I clicked it a bunch more times. Nothing...

So, did I just expect this to do something? What a let down... Maybe the fuel didn't get back up to the sparkplug? I opened the valve and slid the piston back and forth. Clicked it again. Nothing...

Maybe the sparkplug isn't working? I opened the valve and clicked the ignitor. Nothing, which is what I expected. So I turned it so I could see through the valve with the sparkplug at the bottom. Not right in front of my face, mind you. I clicked it and I could see the spark. I did it a couple more times just in case there was a chance of singeing all the hair off my head.

So I squirted a little lighter fluid right at the valve opening. Click... Nothing... I played with the valve and the piston and still nothing.

So then I tilted it up and squirted lighter fluid right down the tube past the valve so it had plenty and was probably right on the spark plug. I positioned (balanced) it on my leg again and...

Click - WHAMO!!!!!!

There was no hesitation about it. Slammed right down against the far stop and I may have detected a WHOOSH!! as the mixture exhausted. Maybe more of a PFFFT!! It was hard to tell since my ears seemed to be ringing. But I didn't get the BANG!!! that I was looking for. Maybe gasoline would make it sound more threating. But that sounds like an outdoor experiment. ;-) Also once I get some springs on it I will have a higher compression ratio. (Higher than 1:1)

Hey that was pretty cool! So, I think I repositioned it and clicked it again and nothing happened. So I opened the valve and squirted lighter fluid down the tube again. I rebalanced it and...

Click - WHAMO!!!! Just like before.

I guess I need a richer mixture than I thought. Seems like I need a good squeeze as opposed to a few drops. I guess we were running the tennis ball cannon pretty rich too.

So you are probably asking "Are you crazy?!?!". Well, yes.

Did anything break? Nope... My homemade sparkplug didn't even come apart.

Did it get amazingly hot? No, it is slightly warm after the second "firing", though.

Did it fly out of my hand? It didn't seem to have as much of a kick as I expected it to. But it did happen pretty quickly. I'm sure if it were pushing something then it will have more recoil. Could it be that the piston slamming against the far end counteracted the recoil so I didn't feel as much. As I say, it all seemed to happen instantaneously...

Did I lose any fingers? Not yet...

It does smell a little funny in here now...

The gAss Rammer lives!!!!

Now I have to add the small cylinder and see if I can get it to draw in the fuel mixture and then fire. Eventually I plan to add a screw drive to the small cylinder to cycle the piston out and in. And so the piston can't move once it completes it's compression cycle.

PS. If this was done at RSOH, we probably wouldn't have tested it in the living room. ;-)

Second Attempt

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