"In the world of spuds today"

[ramses]

ITWOST, my 4" toolie valve is mostly done. Except the piston likes to fall out of orientation in the tee, the guide is too short, and I still need a bumper.

Making the new guide requires me fitting my quick change tool post to my lathe and adapting the boring bar holder to hold my boring bars.

[jackssmirkingrevenge]

The shot was successfully ignited using 1psi of propane and 24psi of propane. The piston was held shut with 45psi and had a 50psi pop-off valve.

A fuel/fuel mix



Pretty is as pretty does, if it works let's see it!

4" toolie valve

4" diameter or seat? What's it destined for?

[ramses]

diameter. Designed originally for a physics assignment. Now it's going to be mounted on a robot to throw the first pitch at a little league game. I estimate 550 FPS with a baseball.

[Technician1002]

When you double the speed, energy goes up 4X. A 120 mph pitch is 4X the power of a 60 mph pitch. A 500+ FPS baseball is lethal.

Accidentally hitting the pitcher or catcher could result in death.

[MrCrowley]

I faced tennis balls at about 250fps in the cricket nets and if you got hit at that speed it seriously hurt. A tennis ball that speed had more energy than a 150g cricket ball at 160kph if I recall correctly. Energy like that has killed cricketers (and at least one umpire) in the past if they were hit in the head.

Though I assume no one will be facing the pitch or you're turning the pressure right down.

[Gun Freak]

LNL Yes I want to see it!

[ramses]

Nice protective gear in that video.

For the actual shot with people in the area, it will probably be turned down to perhaps 150 MPH, or approximately 30 PSI. I'll have to go regulator shopping.

Perhaps they'll lend us a watermelon or something for before/after.
Do you think it would be necessary to have some kind of countdown to the launch, to compensate for the lack of visible windup?

Anyway, I'll give specs:
4" chamber, 24" long (plus fittings)
3" porting barrel sealing compact tee valve
3" barrel 60" long
70 (!) cubic inches of dead space

piloted by a 3/4" porting piston valve.

working fluid will be CO2 for this, up to 220 PSI.


I just weighed the piston. Or rather estimated, since my scale doesn't go that high. 1200g, abouts ! I really need to bring this down, and/or find an amazing bumper. Those 3" endcaps are starting to look really friendly.

I wasn't sure how much the pressure difference was, but I basically applied the full pressure to the inside of the spool, with no pressure on the "outside". This told me that 1/8" lousy steel plate wasn't strong enough, but my friend had some 1/4" plate laying around, which he cut with oxyacetylene, so any heat treatment/work hardening is gone.

Any suggestions for a bumper, and do I need to start facing off the plates? I'd take it off the outside more, since it will hold less force.

[MrCrowley]

Do you think it would be necessary to have some kind of countdown to the launch, to compensate for the lack of visible windup?

I found that a countdown was crucial and figuring out whether the ball is fired on "one" or after the person has said "one" when counting down from three.

[ramses]

I figured as much. Do you think a servo working waving a flag would work, timed such that when the flag hit some object, the main valve was starting to open.

I guess this alludes to another question: how to deal with recoil? Should the cannon be braced, or should it be free to fly back a foot or so?

I still need bumper advice.

[jackssmirkingrevenge]

Any suggestions for a bumper

Air bumper

[ramses]

The valve is piloted. I wasn't allowed to make it a hybrid, which is probably a good thing. Piston is not close to airtight (4" PVC not exactly round, so I had to turn it undersize until it fit.

I estimate there will only be 35 psi in the pilot when the piston starts to move, and a significant amount of dead volume in the pilot.

[Zeus]

ITWOST, I scored a 25mm sprinkler valve for $5 and $35 worth of threaded poly pipe for $1. Loath as I am to admit I have a sprinkler valve based launcher, I now have one.

It's mainly for showing others who I wouldn't show the (nearly) hybrid to, that's my excuse anyway.

[qwerty]

ITWOST, My Micro 15mm chamber hybrid is curing... Should have some action tomorrow. To give you an idea of how small it is i need 0.67ml of butane for a 1X mix.

[Zeus]

Good to see you decided to go down the hybrid route. You'll be quite happy with the power.

[irisher]

ITWOST I got my 3.25" aluminum for my next hybrid and a 6ft barrel.