Wednesday, January 26, 2011

onward, mischief soldiers...

The mill is still down. The Variable Frequency Drive (VFD) -- which synthesized clean(ish) 3-phase power from the 240V 1-phase power available in my shop -- has died. It seems likely I brought about its death. I bricked the motherboard with an incautious press of a button in Eurotherm's software, enabling me to write user data over the firmware memory space. I'd like to ask my readers a question:


Seriously, if you helped design the Eurotherm 605 series of inverter drives, I'd like to hear from you. Just send me your street address, where you work now, your daily habits, and a photograph, and one of my... associates will be in touch.

Where was I?

Goddamned mill is down. See? Now I'm swearing. I'm swearing mad. That's why we're called "mad scientists", at least part of the time. I've got a search going on eBay and am checking a few drives a day. Something will turn up. I'll try to be patient with this, because I prefer to use an inverter drive and not a DIY (nor commercial) "phase converter". But I'll go that rout if I lose my patience. We'll see.

Since I scored the firing valve for the railgun pre-accelerator, I have been busily figuring out the plumbing necessary to connect it to the breach block of the gun, the plenum chamber, and the gas supply. All of this must safely work at 1,000 PSI. I did a lot of homework, read a lot of ANSI and ASME standards, and the corresponding pipe schedule tables, and determined that Sch. 80 seamless steel (not iron) pipe will give me a safety factor of two in working pressures(burst limits are far higher). In reality, I have a safety factor to failure of at least 4X for some components, and 6X - 8X on others.

Yasee, I frequently work with high pressure gas flowing through tiny metal tubes. That doesn't worry me much, because the amount of energy stored by compressed gas depends on both the actual mass and the pressure. The bigger the enclosed volume, the more mass. It goes up fast, and so does the potential danger. The stored energy in compressed gas is incredible.

It may be difficult to get the pre-accelerator valve to fire reliably at low pressures but to be honest, that may not be necessary. I have a hard time imagining any live (electrical) shot that won't have huge friction between the rails. A lot of contact force is required between the armature and the rails to have any hope of getting that armature the length of the gun without being vaporized. The maximum contact force will be determined by what can be pushed down the barrel by 1,000 PSI or less. That was an arbitrary number, but about the biggest I'm willing to try to work with using hardware of my own construction. The breach block assembly is going to be, um, "interesting" to design. If it doesn't leak on the first version, I'll have a heart attack.

For a while there, it looks like I'd lost my CAD files for the railgun project, but thankfully I was mistaken. Found the backup too.
So I'll be looking at that breach block assembly soon.

I also need to revisit how the bus connections are made to the gun rails, and I need to think about how to keep this beast quiet - a muzzle blast suppressor at worst or a complete containment tank for the entire range at worst. Ugh. I'd really rather not. But I've no desire to have the local constabulary knocking on my door (okay, okay, this is the new millennium so busting down my door). Even though I'm fairly certain I'm not breaking any laws (though it's so hard to be sure these days) it is better not to frighten the horses.

1 comment:

Billll said...

Did you check for the presence of Stuxnet in your controller?