SpudFiles

hey guys, this post isnt about spud guns but i read somewhere else on here about pneumatics and you guys seem to know enough about them

just to let you know, i do have a potato cannon, shot a tennis ball 125m in the air, up for 10 seconds, and fires the ball at just under 200kph,


ok,
im going to be trying to make a pneumatic air ram, for stunts. im getting graded later this year and want it for practise,

the idea being, someone runs, steps on it, it flings them across the room

i understand how to do it all but am having trouble with the pneumatic side

i need to make a system that, when i flick the switch, forces the flipper out, any idea's??

Any picture of what a typical one looks like and how much force it's meant to produce?

If it can get away with say 150psi operating pressure an electric solenoid valve could be used and a contact switch that makes contact with someone stepping on the flipper.

(thus opening the valve, dumping air into the ram and so swinging the flipper up)

The How-To database is not for 'help me' posts.

Sounds like you'll be wanting a solenoid valve connected to a pneumatic acuator and an air source.
But I really doubt you'll get enough energy to 'fling' them across the room.

Or if you're feeling daring you could use a co2 flipper, not unlike the ones used in Robot Wars

heres a basic design i wanted to follow and one that works http://precisionstunts.com/airram/default.html

i didnt know where i was ment to post im new to this forum.

i was thinking more heading towards air compressor, to one way valve and air tank, then on the tank have a pressure guage, have a line going to probably 2 pneumatic rams, in that line having a switch and a blow off, but i have no idea what parts to use for any of this

These seem to be pretty simple devices, they look like they only need:
1. A pressure source
2. Pneumatic cylinders or rams
3. A "flipper"
4. A trigger mechanism

If I were you, I would go with regulated CO2 as your pressure source, since it is portable and more compact than an air compressor, but if you have a tight budget, you might want to go with an air compressor.

For the pneumatic cylinders, try McMaster (catalog page 976). You will probably need rams with a medium diameter (1.5" or 2") as they will have more lifting power at a lower pressure.

For a flipper, you could probably get away with constructing one out of wood.

For a trigger mechanism, you are probably going to need to use a solenoid valve connected to a switch of some sort (I'm not good with electronics, so I don't know what type of switch you will need). Solenoid valves can be purchased at McMaster.

I hope this helped.

If it were trigered as soon as someone stepped on it wouldnt it fire while the user only had 1 leg on it? That could really screw someones leg up. Unless they're jumping with both feet on it. Would it work if the cylinders were precharged and there was a latch holding them down? Just latch it down and have a spring pull back on the latch, when the platform drops slightlty the latch can be pulled back by the spring. If it were activated by a button the solenoid would only be on for a very short time.

How about having a burst disc that wont burst with the pressure from the ram, but when enough pressure is put on the flipper (from the person standing on it) the ram pushed through the burst disc firing it.

I have played around with ggdt (for a similar project) and I found that 4" pipe is the most effective without getting ridiculously pricey.

A 4" ram at only 150 psi would have almost one ton of lift force. You want it to be able to fire someone across the room from stepping on it, but don't want to kill them in the process, so being able to accelerate them to about 5-10 feet per second should be acceptable. From there, you can play around with GGDT and see what exactly you need.

The cheapest option for something like this would be unregged, liquified bottled gas, probably CO₂.

With a few more specs on exactly what you want, I can probably come up with something. How much travel do you want the flipper to have, how fast do you want the person to be going, etc...

I do know that 4" of surface area at 150psi will easily send an adult human flying when the pressure is applied. Have you ever tried to hold the end of a 2" pipe closed as pressure is increased inside it?

DYI: Do you have or know of any programs that are similar to ggdt but meant specifically for rams? If not I have been making the barrel length the length of travel the ram will have and the chamber however big it will be when the ram is compressed, is this right or is there a better way of doing it?

I am working on a similar project, but I want to check my calculations are right before I commit to buying materials.

A pneumatic cannon and a pneumatic ram are essentially the same thing, except the projectile is captured at the end of its travel in the latter. GGDT should work fine for it. Make sure to take into account the mass of the piston, the flipper, and the person standing on it when you're modeling it. Do you have any idea how fast you want the person to be propelled?

Also not too good a thing to have pressure increased too rapidly, if the platform slams upwards too sharply you could get a broken leg or so.

The shown flipper uses two rams at low pressure - says not more than 60psi and as low as 10 apparently. Fed by a distant air reservoir through tubing by the controls.

High flow valves such as pistons and burst disks shouldn't be necessary as dumping a large volume of gas is secondary to doing it safely.

Also not too good a thing to have pressure increased too rapidly, if the platform slams upwards too sharply you could get a broken leg or so.

Come to think of it, a 20x hybrid pushing a 4" ram attached to a section of floor wouldn't be bad as a booby trap, assuming that you could actually capture the piston at the end of the stroke - almost noiseless, apart from whatever sound a guy being fired at a concrete block on the celing at about a 200fps makes...

In the case of a flipper to throw someone across a room, a 2" solenoid valve might even be sufficient. As Hotwired said, you don't want to break their legs with sudden acceleration.

the person wont get of the ground..

the legs (knees) will colapse and bend. try to lay a two by four on a rock and stand on one end and get a FAT guy to jump on the other side.. you can't remain upright.

But if you don't absorb the energy by bending your knees your body will take that energy and take off.

Otherwise springboards, trampolines and the like wouldn't work.