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Unread postAuthor: JDP12 » Mon Sep 20, 2010 3:34 pm

That's crazy impressive! looking forward to seeing it completed
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Unread postAuthor: Ragnarok » Tue Sep 21, 2010 12:16 pm

Hmm. Investigation today shows that I'm going to need a better method of stopping the piston - it's absolutely destroyed the current system.
I'm a bit surprised, as the piston would have had no more than about 20 joules of energy at the bumper (about 25 m/s), but I guess it could well be as a result of the astronomic forces on the piston even after it's stopped.

Either way, it's a lesson in why you should test in increments. A full power test could have been quite dangerous.

Fortunately, I've got an idea for a upgraded system, a friction based dohickey that should easily do the job and at the same time, cut piston bounce. (Because spring-like bumpers, such as rubber or foam, store energy, which can potentially turn back into kinetic energy. A friction system will burn it off in a one way energy transfer).
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Unread postAuthor: Ragnarok » Wed Sep 22, 2010 5:03 pm

More musings from me, I'm afraid.

Currently, I'm using a 120cm barrel on HEAL 1.5, taken from HEAL 1. This works (obviously), but as I've taken quite extensive lengths to cut the lengths of HEAL 2's action by 5 cm (versus that of its predecessor), I think it's time to revert to a 100cm barrel length, like HEAL originally started with.

Some simulations show that fitting HEAL 1.5 with this length of barrel would retain ~95% of the velocity of the 120cm barrel, but it would have a friendlier overall length of 124cm.
Ultimately, the barrels are interchangeable (so longer barrels could be used as wanted) - but as a "standard" length, I think it would be better. It's not giving up much as far as velocity, but I'd be less likely to smash it into doorways as I move it around the house*.

*Yes, this has happened, although mostly with the 1.9m long Behemoth.
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Unread postAuthor: Ragnarok » Wed Nov 24, 2010 4:46 pm

Well, I've been an idiot.

The pull through string broke on me, and now I have to work out how to get a polishing tool out of HEAL 2's chamber.
(Suffice to say that, as the hefty string snapped through load, it's wedged in rather solidly.)
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Unread postAuthor: jrrdw » Wed Nov 24, 2010 6:46 pm

Piece of razor blade on a stick and piece it out??? What is your polishing tool made of? If it can be cut up, hey...
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Unread postAuthor: Ragnarok » Wed Nov 24, 2010 7:33 pm

It's mostly wire wool. So cutting it to pieces isn't really feasible - this particular grade is fairly tough, and even if I did cut it apart, then it'd just knot back together.

The other problem is, that like HEAL's chamber, HEAL 2's chamber has a kink in it, which is where this stuff is jammed - so there's no straight line path at it, else I'd've grabbed a long rod and poked at it.
(Did try with a length of garden hose, but to no avail - not strong enough.)

I think I've found a solution though. It should be possible to replace the pilot fitting with an attachment so that I can couple HEAL up to it.
Some generous pneumatic encouragement should move it. If it doesn't... well, I'll have to resign myself to disassembling it and redoing all the work.
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Unread postAuthor: Selador » Wed Nov 24, 2010 7:49 pm

Instead of garden hose, try PEX.
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Unread postAuthor: saefroch » Wed Nov 24, 2010 9:03 pm

Ragnarok wrote:Some generous pneumatic encouragement should move it.
:D I've moved all sorts of stuck objects in my cannons with "pneumatic encouragement." It works wonders... if you're ready for it to release :roll:
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Unread postAuthor: Ragnarok » Wed Nov 24, 2010 10:03 pm

Oxbreath wrote:Instead of garden hose, try PEX.

Not sure there's a point - it wasn't that the hose wasn't strong enough, it's my grip that isn't strong enough. The hose just slips through my hands (no innuendo intended), so I can't actually put the kind of forces needed into play.

Not even sure if I've got any PEX around, but I do know that I have the required pipe fittings to do it pneumatically.

The other upside to doing it pneumatically is that the even application of force is less likely to cause it to dig into the chamber walls.
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Unread postAuthor: Zeus » Wed Nov 24, 2010 10:14 pm

Pnuematic encouragement will certainly do the job, I had a nerf dart slip into the chamber, about 1cm square, hooked it up with the burst disc in front of the launcher, took it to ~60 PSI, worked great.

Good luck with it.
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Unread postAuthor: jrrdw » Thu Nov 25, 2010 8:18 am

Lube the exiting side of the chamber before applying the air, that should help once you get the cleaning tool moving. Will also help against gouging, possibly.
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Unread postAuthor: ramses » Thu Nov 25, 2010 10:49 am

Since I doubt the wool is air tight, put it together, pressurize very slowly, and then fire a blank.

Then remove the place where it is now stuck :roll:
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Unread postAuthor: Ragnarok » Thu Nov 25, 2010 3:07 pm

ramses wrote:Then remove the place where it is now stuck

That'd be the valve. If you try and force something that's firmly stuck in 26mm ID pipe into a 20mm valve... yeah, that's epic fail waiting to happen.
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Unread postAuthor: ramses » Thu Nov 25, 2010 10:03 pm

You could put a large washer in the chamber port to stop it from wrapping it around the inside of your valve. 8)
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Unread postAuthor: mark.f » Sun Feb 27, 2011 11:22 pm

Dead topic. Oh well.

ITWOST, I finished playing around with a prototype piston, and have settled in until I can get the materials for the final revisions and my pump.
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