Ged ,some other questions

gedfinn · February 27th, 2012, 10:37 am #2 2012-02-27T10:37

Hiya mate,

In 12 Fpe format it should take the same effort as cocking any 12 Fpe gun ?
The reason for the question mark is, It wouldn,t have 2 " Full Power springs " In the 12 Fpe version, IE 2 cut down to equal 1 full power one,

I am hoping that it will prove more efficient ! Hence less cocking effort for its equivelent ?
But until Its shooting I won,t really know,
Any power increase above this should be the same or less effort in a single piston gun of equal output.

It feels pretty light, Again until its complete I won,t know , ( I can weigh all the parts though ) This would tell us ?
I made heavyweight piston heads,( Steel, ) welded to the pistons, These are drilled & tapped to accept the PTFE ones,
These & light springs should give a good output, Especially when allied to the new O ring Piston heads I am making, These don,t swell out under compression, Slowing the piston,s

The Swept volume is far too much for a 12 Fpe gun ( But you just gotta do it Ha ha)
I can allways reduce it ( By fitting longer piston heads made in PTFE ) But I can,t increase it?

I,ll put some Pics up when I take them, Cheers Ged.

robnewyork · February 27th, 2012, 3:10 pm #3 2012-02-27T15:10

pneuguy · February 27th, 2012, 4:23 pm #4 2012-02-27T16:23

For example, at peak pressure (just before piston bounce occurs), there's about a ton of force acting on a springer piston.

So, unless Ged has his powerplant in almost perfect balance, much of that force (many times larger than the force required to cock the slave mainspring) may get transferred to the cable between the pistons.

Possible result: Short (maybe only one shot short!) cable life.

Steve

robnewyork · February 27th, 2012, 4:55 pm #5 2012-02-27T16:55

gedfinn · February 27th, 2012, 7:53 pm #6 2012-02-27T19:53

For example, at peak pressure (just before piston bounce occurs), there's about a ton of force acting on a springer piston.

So, unless Ged has his powerplant in almost perfect balance, much of that force (many times larger than the force required to cock the slave mainspring) may get transferred to the cable between the pistons.

Possible result: Short (maybe only one shot short!) cable life.

Steve

Hi,
On checking,I see that the breaking strain of the 2mm
( 3/32 )wire rope I am using, Is 950 Lbs !!!!!!
http://www.shopwiki.com/l/wire-rope-strength

When the sear holding the rear piston is released,
the pressure on the rope almost dissapears ,( They are both travelling in the same direction )
Thats in relation to the wire ?

Also when both pistons bounce back off the air cushion the load on the wire diminishes completely ?
I have some 1.6 mm wire ( Thats where I got the 500 Lbs breaking strain from )
And I might well use it ? ( Its well up to the task ) In my opinion.

In my opinion, the 2mm wire is at least 5 times over strength

Having said all of that, Lets not look for what might not work ! A larger wire or even the chain I have could replace it !

Until its up & Shooting, we will never know !!!
I also don,t think the pistons have to be balanced ( They will be ) Or even the same length ( They will be )
The pressure on compression will allways be equal on the face of both pistons, Even if one should arrive early ?

Only a shooting unit will give the answers,
All the best, Ged.

pneuguy · February 28th, 2012, 4:56 am #7 2012-02-28T04:56

...if they annoy you. But here's an example of what I'm thinking of.

If we pretend that this sketch of mine roughly represents your design, imagine what will happen if the two springs have equal force, but the left (master) piston is (even slightly) lighter than the right (slave) piston.

When the gun is fired, the master - because of its light weight - would accelerate forward faster than the slave, allowing the cable to go slack. But then, at piston bounce, that same light weight would cause it to stop sooner and then accelerate backward faster, extending the slack cable.

Under these - hypothetical but still plausible - conditions, what would happen if the cable suddenly goes (i.e., snaps violently) taut?

Steve

robnewyork · February 28th, 2012, 7:26 am #8 2012-02-28T07:26

oo7fuzz · February 28th, 2012, 2:34 pm #9 2012-02-28T14:34

...if they annoy you. But here's an example of what I'm thinking of.

If we pretend that this sketch of mine roughly represents your design, imagine what will happen if the two springs have equal force, but the left (master) piston is (even slightly) lighter than the right (slave) piston.

When the gun is fired, the master - because of its light weight - would accelerate forward faster than the slave, allowing the cable to go slack. But then, at piston bounce, that same light weight would cause it to stop sooner and then accelerate backward faster, extending the slack cable.

Under these - hypothetical but still plausible - conditions, what would happen if the cable suddenly goes (i.e., snaps violently) taut?

Steve

guarantee that his pistons were precisely the same mass and the springs were precisely the same force value. He could never guarantee that friction would ever be equal between the moving components. Where uneven friction, even from shot to shot, would be present a condition where the moving components behaved as though they were of unequal mass and force. Which, of course, would manifest the scenario which you describe.

pneuguy · February 28th, 2012, 4:43 pm #10 2012-02-28T16:43

...my sketch. The idea being that, if the pistons are roughly equal mass, but the average spring force acting on the "slave" is greater, then the cable should stay taut and thus avoid the potentially destructive "whiplash" effect.

But my intuition tells me there're likely to be other "gotcha's" that only experimentation will reveal.

Steve